If each person living in the US, Canada, and Mexico were to travel to the zone of totality on April 8, 2024, it would clearly be an impossible transportation nightmare.
However, if we were somehow able to spread ourselves out evenly, the end result wouldn’t be so bad: only about 4 people per acre! (Or 8 per hectare.)
The eclipse will traverse around 3,000 miles from Mazatlan to Newfoundland, and the zone is on average about 110 miles across. Multiplying those two numbers gives the total area: about 330,000 square miles.
The USA has about 330 million people, Mexico about 120 million, and Canada has a bit under 40 million. Adding those numbers gives about 490,000,000 people. If we divide the total number of people by the total number of square miles, you get about 1500 per square mile.
Now a square mile is defined as 640 acres, so if we divide that 1500 people per square mile by 640 acres per square mile, you get around two and a half people per acre — or roughly five people per hectare…
But of course having everyone spread out evenly like that would be impossible!
Happy New Year! Scientists have proved that folks who celebrate more New Years tend to live longer! If you made it this far, then congratulations! What are your astronomical plans for this new year?
Vera Rubin in the News: You do realize that January 1 is a pretty arbitrary point on our helical journey around the G-class star we call the Sun, as it travels around the super-massive black hole at Sagittarius A*. You may have seen a nifty (but not 100% accurate) animation (e.g. https://www.universetoday.com/107322/is-the-solar-system-really-a-vortex/ ) that shows how the Earth and all the other planets travel on a corkscrew path around the Sun as we all orbit the center of the Milky Way.
Vera Rubin, an early member of NCA, and a long-time DC resident, was featured in the December 2023 issue of Astronomy ( https://www.astronomy.com/science/vera-rubin-found-a-lifetime-of-wonder-in-the-dark-skies/ ) magazine because (as you probably know) she found through careful research that the speeds of stars like ours, as they orbit around their galaxies, don’t make sense if you add up all the known mass and crank out the Newtonian formulas for gravity and their speeds. The stars near the edges of galaxies go just as fast as the ones near the middle, which is NOT true in, say, our solar system, where Mercury travels at 48 km/s, Earth goes 30 km/s, and Neptune’s speed is 5 km/s. So far, nobody has found the missing ‘dark matter’ that would make these speeds work on galactic scales, and no astrophysicist has (to my knowledge) come up with modifications to Newtonian dynamics that both satisfy all the other laws of physics and also solve the problem. We have a profoundly open question, thanks to this pioneering astronomer’s work!
While it is a shame that Vera was never awarded a Nobel prize for her work, NASA and others did rename the Large Synoptic Survey observatory in Chile after her in 2019, and it should be in full operation after we make one more turn around the Sun. (See https://rubinobservatory.org/ and also the December 2023 monthly talk for Northern Virginia Astronomy Club https://www.novac.com/wp/ ).
If you are not a member of the NCA email list-serve, and would like to join it, just send an email to capitalastronomers+subscribe@groups.io . It makes no difference what you put in the subject line or body of the email.
Reminder thatJanuary’s meeting will be strictly virtual. The URL to log in can be found elsewhere in this month’s issue.
You already know that on April 8, a total solar eclipse will make its way across the Pacific Ocean to Mexico, a highly-populated area of the central USA, and eastern Canada.
If you have never seen a total eclipse, then I highly recommend you make plans to do so at least once it your lifetime. It’s the only time you can see the sun’s chromosphere and corona with your naked eyes. It inspires awe in me every time I see it, and I have seen no photo or video that does it justice. Partial eclipses are nice, but nothing beats totality for making you realize that we are only 8 light-minutes away from the incredibly massive thermonuclear reactor that is responsible for our very existence.
If you are planning to go, but don’t already have lodging along the path of totality, a very brief online search suggests that hotels and motels in the zone of totality (e.g. Dallas) seem to have doubled or tripled their rates for the event (understandably). However, there are plenty of other motels that are located within 100 miles of that strip, at much lower prices. Given the great US interstate highway system, it should not be too hard to drive from such a motel to somewhere inside the zone of totality on the morning of the event, even if traffic is heavy.
The lowest probability of clouds along the entire path is at Mazatlàn, but the crime situation today in Mexico is just too scary for me.
My wife and I have arranged for an Airbnb somewhere in Austin and are probably driving from DC to that address, and probably staying put for the event unless a forecast for clouds impels us to drive somewhere else.
I think I’ll bring my own Coronado PST and the 6” scope that I re-made as a travel scope for the 2017 eclipse.
We are putting in an order for hundreds of NCA-branded, safe, solar eyeglasses for NCA members to give away at this and other events. The board has discussed the issue, and my decision as president is that these should be given away, not sold. Why?
Jeff Norman, our assistant secretary-treasurer investigated, and found that while NCA is a non-profit, we would still be required to calculate and collect sales tax and give receipts for each one that we sold; we would need to then pay those funds to the District of Columbia. This is way too much trouble and work for Jim Simpson (our secretary-treasurer) and Jeff, for a relatively small amount of money.
Fewer and fewer people even carry dollar bills or quarters in their pockets or purses, and we definitely don’t want to go through the hassle of doing electronic payments for a dollar or less.
Cash donations from the public might need documentation.
I think the best thing is to use any interaction with the public to recruit any interested person to sign up as a new NCA member at our website and to help out at similar events.
No other astronomy club that I know of is charging the public for these, and we would appear to be less than generous.
If a current NCA member would like to reimburse the club, at roughly the final cost ends up being, for a large quantity of them that you would like to give out at some event, that would be great, but not required.
If you decide to stay in the DMV area for the event, you can help the public enjoy the partial eclipse at the National Air and Space Museum on April 8 with a variety of optical aids, including live feeds from totality. The NCA Hydrogen-alpha double-stack Solar Max telescope will be available for use.
If you are interested, there are several different designs for inexpensive, safe DIY solar viewers. Here is a fairly original one: https://richardsont.people.cofc.edu/safe_solar_folder/the_2-lens_SSV.html . I have made one of these with leftover floorboards, and I have purchased some extra lens sets from Surplus Shed so you can make your own out of wood or cardboard, either at the Chevy Chase Community Center or anywhere you like.
However, it appears that the safe solar viewer in 8a works much better with an achromatic doublet than with the singlet lens in the original design, because the sunspots are not obscured by bluish tinges. I will try that soon.
Please warn people not to look through any scope at the sun without proper solar filters at the front end of the scope!
The sun is putting on quite a show so far this cycle; who knows what will happen in 2024?
John Hornstein reminds us that we still need an NCA member (that is, one of you reading this) to volunteer to be our next vice-president starting in June. This person will be in charge of finding speakers for our monthly meetings, introducing those speakers, and finding candidates for our elected board for the next year. We have a wealth of top-notch astronomical entities in the area (Goddard, Carnegie, STSI, and the Naval Research Lab, to name just four), and many of their staff are more than happy to share their research with us, if we ask them nicely. Plus, we can have remote speakers from all over the world!
Annual dues for regular members are increasing to $15 as of September 2024.
Student dues will stay put for now at $5/year.
In 2025, regular dues will go up again, to $20/year, and student dues will rise to $10/year.
If you want to sign up for a three-year membership, that will also increase next year, to $35, but life memberships will stay at $200.
Exploring the Sky will start up again on April 6, but with a new contact person and planetarium operator, since Ranger Renée Maher is moving to a new position in the NPS .
Renée will be sorely missed. She was the person who came up with the idea of holding planetarium shows and telescope observing on the same evening, which worked out extremely well. She is a great planetarium operator and story teller, and has been great fun to work with as well. She emailed me that she has done many of the steps needed to make sure the joint NCA-NPS-EtS program continues as we did last year, but she doesn’t know who the new contact person will be will be, or even the new supervisor. Her last day at the Rock Creek Nature Center is January 13.
Here is the tentative schedule for these events, as proposed by Jay Miller and me. All dates are on Saturdays, and all times are PM, local time for the DMV region. They are designed so as to not interfere with monthly NCA meetings or national holidays, and to begin somewhere between the end of civil and nautical twilights.
Anybody bringing a telescope is advised to begin setting up earlier than the official starting times, if at all possible.
Month
Day
Sunset
Civil Twilight
Nautical Twilight
Astro- nomical Twilight
Planetarium Show Starts
Exploring the Sky Starts
April
6
7:37
8:04
8:36
9:09
7:30
8:30
May
4
8:15
8:44
9:20
9:58
8:00
9:00
June
1
8:28
8:59
9:38
10:23
8:00
9:00
July
13
8:33
9:04
9:43
10:27
8:00
9:00
August
10
8:08
8:37
9:12
9:49
7:30
8:30
September
7
7:28
7:55
8:27
8:59
7:00
8:00
October
5
6:43
7:10
7:41
8:12
6:30
7:30
November
2
6:05
6:33
7:05
7:36
6:00
7:00
We always need folks who either have scopes or who have information they can share with the public. While Rock Creek Park no longer has the dark skies it did two centuries ago, this event may be the only chance that members of the public will have of seeing the Moon, the planets, and other bright objects with their own eyes, in real time, rather than in a photo.
The planetarium shows occur rain or shine in the Nature Center. Obviously, the telescope observing part of the event will depend on the weather.
I want to thank all of the folks who have brought their scopes to these events this year and during past years. I especially want to thank Jay Miller for organizing the NCA side of this for many years no2.
In the next few months, local counties and cities in the DMV area will host science/STEM fairs. We appear to have sufficient NCA volunteers (thanks!) but we could aways use some more.
When I show people things in the sky with a telescope, I want to help them to realize how lucky we are to live on a nice, warm, wet little planet in a relatively safe part of a medium-large galaxy.
I also want them to realize that if we aren’t careful, we could turn this planet into one of those many varieties of deadly hell that they are viewing in the eyepiece.
We should be very thankful that this planet got formed in a solar system that had sufficient oxygen, silicon, iron, nitrogen, and carbon for life as we know it. We are fortunate that all of those ‘metals’ I just listed (as astronomers call them) got cooked up in cycle after cycle of stars that went boom or whooshed their outer layers into the Milky Way. We are lucky to be alive at the far multicellular side of the timeline of life on Earth*, and that no star has gone supernova in our neighborhood recently or aimed a gamma-ray burst directly at us.
We are exceedingly lucky that a meteorite wiped out the dinosaurs 65 million years and allowed our ancestors, the mammals, to take over. We can rejoice that most of us in the USA can have our physical needs (food, shelter, clean water, clean air, and communication) taken care of by just turning a knob or a key, or pushing a button, instead of hauling the water or firewood on our backs. (There are, obviously, many folks here and abroad who live in tents and who have essentially none of those nice things. We could do something about that, as a society, if we really wanted to.)
I am often asked whether there is life elsewhere. My answer is that I am almost positive that there are lots of planets with some form of life in every single galaxy visible in an amateur telescope. But there is no possible way for us humans to ever visit such a planet. Nor can aliens from any exoplanet ever visit us, whether they be single-celled organisms or something you would see in a Sci-Fi movie.
Yes, it is possible to send a handful of people to Mars, if we are willing to spend enormous sums of money doing so, and if the voyagers are willing to face loss of bone and muscle mass, and the dangers of lethal radiation, meteorites, accidental explosions, and freezing to death. If they do survive the voyage, then by all means, let them pick up some rocks and bring them back for analysis before they die.
But wait: we already have robots that can do that! Plus, robots won’t leave nearly as many germs behind as would a group of human beings. And we already know a lot about how Mars looks, because of all the great photos sent back by ESA, JAXA, NASA and others for some decades now. You can see photos taken by NASA at JMARS, which I highly recommend. (https://jmars.asu.edu/ )
While one can justify sending a few brave folks to Mars for a little while, it is completely insane to think that we can avoid our terrestrial problems by sending large populations there. Mars is often colder than Antarctica, is close to waterless, has poisonous perchlorates in its soil, no vegetation whatsoever, and no atmosphere to speak of. How would millions or billions of exiles from Earth possibly live there? Do you seriously think they can gather enough solar energy to find and melt sufficient water to drink and cook and bathe and grow plants and livestock in the huge, pressurized, aluminum cans they would need to live in? No way.
I wish there was some way to get around the laws of physics, and that we could actually visit other exoplanets. But there isn’t, and we can’t. I’ve seen estimates that accelerating a medium-sized spaceship to a mere 1% of the speed of light would require the entire energy budget of the entire human population of the planet for quite some time. (For example, see https://physics.stackexchange.com/questions/447246/energy-requirements-for-relativistic-acceleration )
Let us assume, for the sake of argument, that you could actually generate enough energy to accelerate that spaceship with nuclear fusion or something else that doesn’t violate the laws of physics as far as we know.
The next problem is the distance. It’s a bit over 4 light years to the nearest known exoplanet in a straight line, (compared with under 2 light-seconds for the Moon or about 35 light minutes for Jupiter). The table below gives the number of planets lying each extra solar system that are thought to be terrestrial (as opposed to gas giants) and to be within their stars’ habitable zones. Nobody knows if there is any life on any of those planets right not, but it is possible that astronomers may one day figure out a very effective way to test for extra-solar life. Let us suppose that a few of the ones in this list do have breathable atmospheres and are neither too cold nor too hot, have a fair amount of liquid water, and are protected from nasty radiation by magnetic fields and belts.
Unfortunately, a one-way trip to Proxima or Alpha Centauri for any possible spaceship, at one percent of the speed of light, (3,000 km per second), in a straight line, and pretending that you don’t need years and years to both accelerate and decelerate, would take over four centuries. And that’s for the very closest one! All the other planetary systems are many multiples of that distance! See this or this table:
Our fastest spacecraft so far, the Parker Solar Probe, reaches the insanely fast speed of 190 km/sec, but that’s still fifteen times slower than my hypothetical 1% of c. At the speed of Parker, it would take around six thousand years to reach the Proxima Cen planetary system! If all goes well!
Do you seriously think that a score or so generations of humans would all agree, century after century, that they, and their descendants — born and raised in a big metal box rushing through space — for the entire 400 years, would consent to live in a large metal box with no gravity to speak of, subject to who knows how many blasts of gamma rays, x-rays, and super-high-energy cosmic particles? What are the chances that each single generation would agree to stay the course and that not a single meteorite going the other direction, over a course of four centuries, would happen to smash into the space ship and instantly disable all the life support systems and kill all the passengers, quickly or slowly?
And how do you keep alive all the animals we would need to feed us upon arrival? I guess you compost all the poop from all the cattle, chickens, and so on. But do you also bring zillions of insects and tons of plant seeds as well, knowing full well that if you do so, then you lose the vast majority of the information you could have learned about an actual, functioning, extra-solar ecosystem like nothing we can possibly imagine.
The argument is made that perhaps the travelers would be put into suspended life. If that were possible, and nothing went wrong, upon arrival, they could take a triumphant group selfie and put it into a radio message back to Earth saying, “Hi, we made it, wish you were here…” That reply will of course take four years to reach Earth. Would people back on Earth still remember the handful of people who began the trip out, made over four centuries earlier? What will the humans back on earth remember about the absolutely prodigious effort expense that their ancestors had made to build and power that rocket, 20 generations or so earlier?
Let us suppose they have the tremendous luck to find, after 4 to 10 centuries of travel, a nice warm exoplanet with water, oxygen-producing life, and air that we can breathe.
Unfortunately, there is an overwhelming chance that there would be no humanoids or any other Sci-Fi characters. The chances are that creatures that look like insects, crustaceans, fish and salamanders are the most highly-organized life forms – at best; after all, for most of the existence of life on earth, it was single-celled organisms! Our travelers would have to have to build an entire urban and agricultural infrastructure *from scratch*, with no help. They could only do that if the plants and animals they brought from Earth are able to flourish.
The return trip, if desired, would of course take another four or more centuries, if the handful of travelers can find a proper power source and if they can figure out how to create, completely from scratch, an entire agricultural and industrial instructure. They would have to figure out where the natural resources of that planet (wood? minerals? energy sources?) are located, and how they can make use of them, to build something like the incredibly precise absolutely enormous rocket-building industries we have here, on a hypothetical planet that has never even had any mammals living on it.
If these voyagers should run into any technical problem while doing trying to build a modern civilization from nothing, fat chance of getting a prompt reply from Earth, since the question would take years to reach its home base back here!
Yes, the very closest exoplanets are a mere 4 LY away, but the others are all much, much farther away, so one-way trips for ones within 10 parsecs, i.e., in our tiny corner of our galaxy, at one percent of the speed of light, would require a thousand to three thousand years to reach. Each way.
Forget it. Just send a radio message, and see if we get a reply. Oh, wait – we’ve been doing that for several decades so far. No reply so far.
Speaking of radio – it’s only 120 years since Marconi first sent a very crude radio message from a ship to a station on land, and now we routinely use enormous parts of the entire electromagnetic spectrum for all sorts of private and public purposes, including sending messages like this one. Astronomers are able to gather amazing amounts of information via the longest radio waves to the very shortest gamma rays and make all sorts of inferences about worlds we have never seen at optical wavelengths. In addition, we have begun detecting gravity waves from extremely distant and powerful events with devices whose accuracy is quite literally unbelievable.
There is no planet B. We must, absolutely must, take care of this one, lest we turn into one of those freezing or burning variations of hell that we see through our eyepieces. Think I’m being alarmist? We now know this nice little planet Earth is more fragile than we once believed. It has been discovered that life was almost completely wiped out on this planet several times. The Chixculub impact I mentioned earlier, the Permian extinction and Snowball Earth are just three such events.
More recently, folks thought it was impossible for people to cause the extinction or near-extinction of the unbelievably huge flocks and herds and schools that once roamed the earth: passenger pigeons, buffaloes, cod, salmon, redwoods, elms, chestnuts, elephants, rhinos, tropical birds, rainforests, and so on, but we did, and continue to do so. The quantities of insects measured at site after site around the world have plummeted by 30 to 70% and more, over just a few decades, and so have the numbers of migratory birds observed on radar feeds. Light pollution, the bane of us amateur and professional astronomers, seems to be partly responsible for both the insect and bird population declines. The rise in the levels of atmospheric carbon dioxide and global temperatures are very scary.
In addition, we are dumping incredible amounts of plastic into the oceans, and rising water temperatures are causing coral reefs around the world to bleach themselves and die, while melting glaciers are causing average sea levels rise and threaten more and more low-lying cities.
What’s more, only a very tiny fraction of our planet’s mass is even habitable by humans: the deepest mine only goes down a few miles, and people die of altitude sickness when they climb just a few miles above sea level. Most of the planet is covered by ocean, deserts, and ice cap. By volume, the livable part of this planet is infinitesimal, and the temperatures on it are rising at an alarming rate.
Will we be able to curb the burning and leaking of fossil fuels sufficiently so as to turn around the parts of global warming caused by increases in carbon dioxide and methane? I am not optimistic, given that the main emitters have kept essentially none of the promises that they have been making to those various international gatherings on climate, and graphs like this one, taken from: https://ourworldindata.org/fossil-fuels
I have been wondering whether we may need to reduce temperatures more directly, by putting enough sulfur compounds into the stratosphere. We have excellent evidence that very violent volcanic eruptions have the power to lower global temperatures with the sulfates they put into the stratosphere. It would not be great for ground-based astronomy if such compounds were artificially lofted high into the atmosphere to lower global temperatures, and we won’t know for sure exactly which areas of the planet would benefit and which would be harmed, but at least it’s an experiment that can be stopped pretty easily, since the high-altitude sulfates would dissipate in a few years. High-altitude sulfur compounds do not seem to cause the obvious harm that SO2 does at the typical altitude of a terrestrial coal-burning power plant.
Adding iron to the oceans to increase the growth of phytoplankton, which then consumes CO2, dies, and settles to the bottom of the ocean, has been tried a number of times, but doesn’t seem to have a very large effect.
I agree that large-scale injection of sulfates into the stratosphere is scary. I also agree that there is a whole lot of unknown unknowns out there and inside of us, and we are being very short-sighted, as usual.
We have mapped the far side of the moon better than we have mapped the floors of Earth’s oceans – yet permits are being filed right now to begin deep-ocean dredging for manganese nodules, which will enrich some folks greatly. Unfortunately, that dredging is bound to utterly destroy those slow-growing ecosystems, before we even know what’s down there in the first place!
We continue to dump unbelievable amounts of plain old trash, fish nets, fishing lines, live ammunition, modern warships and hazardous chemicals into the oceans.
While the waters and atmosphere of the USA are much, much cleaner now than they were when I was a kid in the 50s and 60s, places like Delhi or Beijing are so polluted that folks can barely see the sun on a clear day.
If dark matter and dark energy really do exist, that means that scientists have absolutely no idea what 96% of the universe is made of!
If dark matter and dark energy don’t exist, then that means that astrophysicists don’t understand long-distance gravity and physics nearly as well as they thought. The late Vera Rubin (a past NCA member who should have won a Nobel for her careful measurements of the rotational measurements of galaxies that led to the Dark Matter hypothesis) once told me when we were co-chaperoning a field trip to the Smithsonian for the Carnegie Institution for Science’s Saturday program for middle-schoolers, that she thought that the entire question is perfectly open. I think she’s still correct.
If the Big Bang is real, then how come the Webb is seeing fully-formed galaxies as far back in time as it can see?
Do the alternative theories to the Big Bang (eg, Burbridge’s hypothesis that matter is being created in the centers of active galactic nuclei) make any sense?
But — does anybody have better solutions?
Can we engineer our way out of the mess we are making on this planet – the only home that humans will ever have?
There is cause for optimism:
Our NCA speaker this month, Deborah Shapley, will tell how, almost exactly a century ago, astronomers finally figured out that the Milky Way was just one of many billions of other galaxies. Since that time, the amount of astronomical information gathered has been staggering, as has the efficacy of the instruments!
After scientists figured out what was causing the ozone hole, every single agency and government in the entire world passed and enforced regulations that banned those chlorofluorocarbons that were used in almost everything from air conditioners to hair spray. Since that time, there has been almost complete compliance and agreement, and the ozone hole continues to shrink, as you can see here.
I have vivid memories about how smoggy and stinky the air used to be on a typical summer day in almost any American city of my youth. A fat-rendering plant right here in Georgetown (DC) stank worse than a hundred skunks, and is now gone. I know a paper mill in West Virginia whose fumes had long killed almost all the vegetation downwind of the factory. Nearby, acid drainage from an abandoned coal mine turned a stream so acidic that the rocks (and water) were amazing shades of orange, reds, and yellow. The rivers of this national often flowed with raw sewage, trash, and mine waste. Some, like the Cuyahoga, even caught fire, repeatedly (see https://www.smithsonianmag.com/history/cuyahoga-river-caught-fire-least-dozen-times-no-one-cared-until-1969-180972444/ ). The passage and actual enforcement of the Clean Air and the Clean Water Acts have cleaned up the air and water in this country to an amazing degree in my lifetime (I’m over 70). The cleanup of the Potomac and Anacostia Rivers in that period has also been tremendous. However, my friends who grew up in India and China tell me that the air and water pollution over there is worse than I can possibly imagine and is not improving at all.
When I was young, it appeared that nearly every adult I knew chain-smoked cigarettes and drank a lot of alcohol, and the bars, restaurants, dormitories, private houses, classrooms, buses and airplanes everywhere were filled with tobacco smoke. Despite the lies and obfuscation of the tobacco industry, not only legislation but also public opinion is such that today, I seldom encounter the nasty smell of tobacco smoke anywhere, even on people’s clothing on the bus or subway, and the number of drunk-driving fatalities is way down as well.
During my youth, the various nuclear powers exploded literally hundreds of nuclear weapons in the open air and underwater, spewing Strontium-90 and other radionucleides into things like cow or human milk, and doing untold destruction to the oceans nearby. While the number of world-wide nuclear explosions per year has dropped tremendously since then, they still continue, and may start up again on a larger scale.
Some noteworthy experiments re stopping global warming are listed in this month’s National Geographic. One of them, which has promise but also obvious drawbacks, involves dumping large quantities of finely ground-up alkaline rocks and minerals like olivine counteract the increasing acidification of the seas being caused by the absorption of so much carbon dioxide. Will these experiments work? I don’t know.
But let us not turn this planet – the only home we will ever know – into one of the barren, freezing or boiling versions of hell we see in the eyepieces of a telescope.
I have raised pigs, and I noticed that they never foul their own beds, if they are given any room to move around. Let’s be better than pigs and stop trying to extract riches in the short run while destroying the lovely planet we all love in the long run!
Heaven is not somewhere else.
It’s right here, if we can keep it that way and fix the damage we have done.
* For five-sixths of the roughly 3.7-billion-year time line of life on earth, all living things were single-celled microbes (or microbes living together in colonies). We mammals have only been important for the last 1.7% of that time, (ie since the dinosaurs died out 66 million years ago), the first known writing system was invented a few millennia ago, and Marconi only sent the first ship-to-shore radio message 130 years ago, which is an infinitesimally small fraction of 3.7 billion. Home radios only became popular 100 years ago.
Assuming that planets and stars are created at random times in the history of the universe, and assuming that a certain amount of enrichment of the interstellar medium by many generations of dead stars is necessary before life can begin at all, then it looks to me like the odds are not at all good for intelligent life of any sort to exist right now on any random planet we may study. And, unfortunately, if they do exist, we will never meet them. If there is an incredibly advanced civilization somewhere within 100 light years that can actually detect those first radio signals, then they just received our first messages. If they do respond, we won’t get the answer for another century or two!
For example, take a look at this time line of life on earth at a linear scale. If a hypothetical space traveler should somehow arrive on the 3rd rock from our Sun at a random moment in time over the past 4.5 billion years, then that’s like tossing a dart at this graph while blindfolded, and seeing where it lands. Notice the kind of organisms dominating during most of the past 4 billion years! The chances that they would happen to arrive here in the past few centuries or so, when we humans began to really understand science, are vanishingly small!
My original title began with “Space Travel is Impossible” — which is obviously false, because it is an incontrovertible fact of history that a handful of American astronauts, at enormous expense, did in fact land on the Moon and return. I remember the event well; I was working in a factory in Waltham, Mass that summer as part of the SDS Summer Work-In.
I should have written, “Space Travel to Exoplanets Is Impossible”.
But you could make the case that traveling to the Moon is barely even space travel! The distance to the moon is less than the total mileage on my last two automobiles (a Subaru Forester and a Toyota Prius) added together. Or, at the speed of light, the Moon is about 1.5 light-seconds away, the Sun about 8 light-minutes, Jupiter 34 light-minutes, and Saturn is about 85 light minutes this month. But the very nearest star-planet system to us is over four YEARS away, and the distances to the vast majority of exoplanets are measured in light-decades, light-centuries, or light-millennia.
I remember the Space Race! Both the USA and the Soviets poured incredible sums of cash, labor, raw materials, and brain power into that race, while, frankly, millions of people around the world starved or were killed in proxy wars between those two powers, representing two ideological and political opposing blocks. The incredibly expensive and dangerous race to win global prestige by being the first power bloc to reach the various goals has, so far, at its apogee, carted a handful of men to the near side of our Moon, less than two light-seconds away! And some people think we can easily travel to exoplanets that are light-decades or light-centuries away!
For many years now, I have been trying and (mostly) failing at using some sort of digital camera when testing the optics of the mirrors we fabricate and evaluate at the ATM workshop at the Chevy Chase Community Center here in DC.
I can now report that there finally is some useful and non-vignetted light at the end of the testing tunnel!
Foucault, knife-edge image, raw
Same mirror, at a different longitudinal location, image flipped right to left (ie across the y-axis), and then pasted onto the original image
Same mirror, same location as the image directly above, with circles and measurements added in Geometer’s Sketchpad
I used an old Canon FD film camera lens (FL=28 mm) that I got about 40 years ago and haven’t used in several decades to get a bunch of really nice knife-edge images of a 16″ Meade mirror, located on a stage that can be moved forward and back in whatever steps I like by a smartphone app and a stepper motor setup that Alan Tarica and Pratik Tambe designed and put together.
Just now, I finally figured out how to use IrfanView to take one of the images, flip it left-to-right (that is, across the y-axis) and superimpose one onto the other with 50% transparency. A bright ring appeared, which shows the circular ring or zone where the light from our LED, located just under the camera lens, goes out to the mirror and bounces directly back to the lens and is captured by the sensor as a bright ring.
I then captured and pasted that image into Geometer’s Sketchpad, which I used to draw and measure the radii of two circles, centered at the doughnut marking the center of the mirror. This is a somewhat crude measurement of the radii, but it appears that this zone is is at 83% of the diameter (or radius) of the original disk, which is 16 inches across.
Now I just need to do the same thing for all of the other images, and then correlate the radii of the bright zones with the longitudinal (z-axis) motion of the camera and stand, and I will know how close this mirror is to a perfect paraboloid.
There is an app that supposedly does this for you, called Foucault Unmasked, but it doesn’t seem to work well at all. As you can see from these images, FU is unable to find zones that are symmetrically placed on either side of the center of the mirror. I don’t know what algorithm FU uses, but it sure is f***ed up.
Foucault Unmasked thinks that those two red marks are the zone being measured here. It’s pretty hard to be more wrong than that.
Again, FU at work, badly. Not quite as awful as the previous one, but still quite useless!
Thanks a lot to Tom Crone, Gert Gottschalk, Pratik Tambe, Alan Tarica, and Alin Tolea for their help and suggestions!
There is a pretty well-known paradox which goes something like this:
You hear that the Smith and Jones families each have two children.
You are told that the older Smith child is a girl, and that at least one of the Jones children is a girl.
Assuming that boys and girls are equally likely to be born (I know this is not quite true, but let’s pretend) in any given pregnancy, what are the chances that the Smiths have two girls? How about the Joneses?
Most people would say that those probabilities are equal: 50% in both cases.
But they are not. In fact, it is much less likely that the Joneses have two daughters!
Here is why:
In any family with two children, there is an older sibling and a younger one.
In the Smith family, you know that the older child is a girl, but you know nothing about their younger child, so the younger one is equally likely to be male or female. So the chances that the Smiths have two daughters is indeed 1/2, or 50%.
In the Jones family, all we know is that there is at least one girl. Let’s look at a diagram that shows all of the equally-likely possibilities in any family with two children:
With the Smith family, we can rule out cases 1 and 2, leaving us cases 3 and 4.
However, with the Jones family, we can only rule out case number 1. Cases 2, 3, and 4 — which are all equally likely — are all possible outcomes for the Joneses. Notice that only in case number 4 do the Jones have two daughters. So with the Joneses, the chances that there are two daughters is only 1 in 3, or 33.3%.
Several people have helped me with this applied geometry problem, but the person who actually took the time to check my steps and point out my error was an amazing 7th grade math student I know.
It involves optical testing for the making of telescope mirrors, which is something I find fascinating, as you may have guessed. Towards the end of this very long post, you can see the corrections, if you like.
Optics themselves are amazingly mysterious. Is light a wave, or a particle, or both? Why can nothing go faster than light? We forget that humans have only very recently discovered and made use of the vast majority of the electromagnetic spectrum that is invisible to our eyes.
But enough on that. At the telescope-making workshop here in DC, I want folks to be able to make the best ordinary, parabolized, and coated mirrors possible with the least amount of hassle possible and at the lowest possible cost. Purchasing high-precision, very expensive commercial interferometers to measure the surface of the mirror is out of the question, but it turns out that very inexpensive methods have been developed for doing that – at least on Newtonian telescopes.
Tom Crone, a friend of mine who is also a fellow amateur astronomer and telescope maker, wondered how on earth we can report mirror profiles as being within a few tens of nanometers of a perfect paraboloid with such simple devices as a classic Foucault knife-edge test.
He told me his computations suggested to him that the best we could do is get it to within a few tenths of a millimeter at best, which is four orders of magnitude less precise!
I assured him that there was something in the Foucault test which produced this ten-thousand-fold increase in accuracy, but allowed that I had never tried to do the complete calculation myself. I do not recall the exact words of our several short conversations on this, but I felt that I needed to accept this as a challenge.
When I did the calculations which follow, I found, to my surprise, that one of the formulas I had been taught and had read about in many telescope-making manuals, was actually not exact, and that the one I had been told was inherently less accurate, was, in fact, perfectly correct! Alan Tarica sent me an article from 1902supposedly explaining the derivation of a nice Foucault formula, but the author skipped a few bunch of important steps, and I don’t get anything like his results. it took me a lot of work, and help from this rising 8th grader, to find and fix my algebra errors. I now agree with the results of the author , T.H.Hussey.
I am embarrassed glad to say that even after several weeks of pretty hard work, an exact, correct formula for one of the commonly used methods for measuring ‘longitudinal aberration’ still eludes me. was pointed out to me by a student who took the time to Let’s see if anybody can follow my work and helped me out on the second method.
But first, a little background information.
Isaac Newton and Leon Foucault were right: a parabolic mirror is the easiest and cheapest way to make a high-quality telescope.
If you build or buy a Newtonian scope, especially on an easy-to-build Dobsonian mount, you will get the most high-quality photons for the money and effort spent, if you compare this type with any other type of optics at the same diameter. (Optical designs like 8-inch triplet apochromats or Ritchey-Chrétiens, or Maksutovs, or modern Schmidt-Cassegrains can cost many thousands of dollars, versus a few hundred at most for a decent 8″ diameter Newtonian).
With a Newtonian, you don’t need special types of optical glass whose indices of refraction and dispersion, and even chemical composition, must be known to many decimal places. The glass can even have bubbles and striations, or not even be transparent at all! Any telescope that only has mirrors, like a Newtonian, will have no chromatic aberration (ie, you don’t see rainbows around bright stars) because there is no refraction – except for inside your eyepieces and in your eyeball. All wavelengths of light reflect exactly the same –but they bend (refract) through glass or other materials at different angles depending on the wavelength.
Another advantage for Newtonians: you don’t need to grind and polish the radii of curvature of your two or three pieces of exotic glass to exceedingly strict tolerances. As long as you end up with a nice parabolic figure, it really doesn’t matter if your focal length ends up being a few centimeters or inches longer or shorter than you had originally planned. Also: there is only one curved mirror surface and one flat one, so you don’t need to make certain that the four or more optical axes of your mirrors and/or lenses are all perfectly parallel and perfectly concentric. Good collimation of the primary and secondary mirrors to the eyepiece helps with any scope, but it’s not nearly as critical in a Newtonian, and getting them to line up if they get knocked out of whack is also much easier to perform.
With a Newtonian, you only need to get one surface correct. That surface needs to be a paraboloid, not a section of a sphere. (Some telescopes require elliptical surfaces, or hyperbolic or spherical ones, or even more exotic geometries. A perfect sphere is the easiest surface to make, by the way.)
In the 1850’s, Leon Foucault showed how to ‘figure’ a curved piece of glass into a sufficiently perfect paraboloid and then to cover it with a thin, removable layer of extremely reflective silver. The methods that telescope makers use today to make sure that the surface is indeed a paraboloid are variations and improvements on Foucault’s methods, which you can read for yourself in my translation.
Jim Crowley performing a Foucault test
It turns out that the parabolic shape does need to be very, very accurate. In fact, over the entire surface of the mirror, other than scratches and particles of dust, there should be no areas that differ from each other and from the prescribed geometric shape by more than about one-tenth of a wavelength of green light (which I will call lambda for short), because otherwise, instead of a sharp image, you just receive a blur, because the high points on the sine waves of the light coming to you would tend to get canceled out by the low points.
Huh?
Let me try to explain. In my illustrations below, I draw two sine waves (one red, one green) that have the same exact frequency and wavelength (namely, two times pi) and the same amplitude, namely 3. They are almost perfectly in phase. Their sum is the dark blue wave. In diagram A, notice that the dark blue wave has an amplitude of six – twice as much as either the red or green sine wave. This means the blue and green waves added constructively.
Next, in diagram B, I draw the red and green waves being out of phase by one-tenth of a wave (0.10 lambda) , and then in diagram C they are ‘off’ by ¼ of a wave (0.25 lambda). You will notice that in the diagrams B and C, the dark blue wave (the sum of the other two) isn’t as tall as it was in diagram A, but it’s still taller than either the red or green one.
One-quarter wave ‘off’ is considered the maximum amount of offset allowed. Here is what happens if the amount of offset gets larger than 1/4:
In diagram D, the red and green curves differ by 1/3 of a wave (~0.33 lambda), and you notice that the blue wave (which is the sum of the other two) is exactly as tall as the red and green waves, which is not good.
Diagram E shows what happens is what happens when the waves are 2/5 (0.40 lambda) out of phase – the blue curve, the sum of the other two, now has a smaller amplitude than its components!
And finally, if the two curves differ by ½ of a wave (0.5 lambda) as in diagram F, then the green and red sine curves cancel out completely – the dark blue curve has become the x-axis, which means that you would only see a blur instead of a star or a planet. This is known as destructive interference, and it’s not what you want in your telescope!
But how on earth do we achieve such accuracy — one-tenth of the wavelength of visible light (λ/10) over an entire surface? And if we do, what does it mean, physically? And why one-tenth λ on the surface of the mirror, when ¼ λ looked pretty decent? For that last question, the reason is that when light bounces off a mirror, any deviations are multiplied by 2. So lambda – about 55 nanometers or 5.5×10^(-8) m- is the maximum allowable depth or height of a bump or a hollow across the entire width of the mirror. That’s really small! How small? Really insanely small.
Let’s try to visualize this by enlarging the mirror. At our mirror shop, we generally help folks work on mirrors whose diameters are anywhere from 11 cm (4 ¼ inches) to 45 cm (18 inches) across. Suppose we could magically enlarge an 8” (20 cm) mirror and blow it up so that it has the same diameter as the original 10-mile (16 km) square surveyed in 1790 by the Ellicott brothers and Benjamin Banneker for the 1790 Federal City. (If you didn’t know, the part on the eastern bank of the Potomac became the District of Columbia, and the part on the western bank was given back to Virginia back in 1847. That explains why Washington DC is no longer shaped like a nice rhombus/diamond/square.)
So imagine a whole lot of earth-moving equipment making a large parabolic dish where DC used to be, a bit like the Arecibo radio telescope, but about 50 times the diameter, and with a parabolic shape, unlike the spherical one that Arecibo was built with.
(Technical detail: since Arecibo was so big, there was no way to physically steer it around at desired targets in the sky. Since they couldn’t steer it, then a parabolic mirror would be useless except for directly overhead. However, a spherical mirror does NOT have a single focal point. So the scope has a movable antenna (or ‘horn’) which can move around to a variety of more-or-less focal points, which enabled them to aim the whole device a bit off to the side, so they can ‘track’ an object for about 40 minutes, which means that it can aim at targets around 5 degrees in any direction from directly overhead, but the resolution was probably not as good as it would have been if it had a fully steerable, parabolic dish. See the following diagrams comparing focal locations for spherical mirrors vs parabolic mirrors. Note that the spherical mirror has a wide range of focal locations, but the parabolic mirror has exactly one focal point.)
I’ll use the metric system because the math is easier. In enlarging a 20 cm (or 0.20 m) mirror all the way to 16 km (which is 16 000 m), one is multiplying 80,000. So if we take the 5.5×10-8 m accuracy and multiply it by eighty thousand you get 44 x 10-4 m, which means 4.4 millimeters. So, if our imaginary, ginormous 16-kilometer-wide dish was as accurate, to scale, as any ordinary home-made or commercial Newtonian mirror, then none of the bumps or valleys would be more than 4.4 millimeters too deep or too high. For comparison, an ordinary pencil is about 6.8 millimeters thick.
Wow!
So that’s the claim, but now let’s verify this mathematically.
I claim that such a 3-dimensional paraboloid, like the radio dish in the picture below, can be represented by the equation
where f represents the focal length. (For simplicity, I have put the vertex of the paraboloid at the origin, which I have called A. I have decided to make the x-axis (green, pointing to our right) be the optical and geometric axis of the mirror. The positive z-axis (also green) is pointed towards our lower left, and the y-axis (again, green) is the vertical one. The focal point is somewhere on the x-axis, near the detector; let’s pretend it’s at the red dot that I labeled as Focus.)
You may be wondering where that immediately previous formula came from. Here is an explanation:
Let us define a paraboloid as the set (or locus) of all points in 3-D space that are equidistant from a given plane and a given focal point, whose coordinates I will arbitrarily call (f, 0, 0). (When deciding on a mirror or radio dish or reflector on a searchlight, you can make the focal length anything you want.)
To make it simple, the plane in question will be on the opposite side of the origin; its equation is x = -f. We will pick some random point G anywhere on the surface of the parabolic dish antenna and call its coordinates (x, y, z). We will see what equation these conditions create. We then drop a perpendicular from G towards the plane with equation x = -f. Where this perpendicular hits the plane, we will call point H, whose coordinates are (-f, y, z). We need for distance GH (from the point to the plane) to equal distance from G to the Focus. Distance GH is easy: it’s just f + x. To find distance between G and Focus, I will use the 3-D distance formula:
Which, after substituting, becomes
To get rid of the radical sign, I will equate those two quantities, because FG = GH, omit the zeroes, and square both sides. I then get
Multiplying out both sides, we get
Canceling equal stuff on both sides, I get
Adding 2fx to both sides, and dividing both sides by 4f, I then get
However, 3 dimensions is harder than 2 dimensions, and two dimensions will work just fine for right now. Let us just consider a slice through this paraboloid via the x-y plane, as you see below: a 2-dimensional cross-section of the 3-dimensional paraboloid, sliced through the vertex of the paraboloid, which you recall is at the origin. We can ignore the z values, because they will all be zero, so the equation for the blue parabola is
or, if you solve it for y, you get
There is a circle with almost the same curvature as the paraboloid; its center, labeled CoC (for ‘Center of Curvature’) is exactly twice as far from the origin as the focal point. You can just barely see a green dotted curve representing that circle, towards the top of the diagram, just to the right of the blue paraboloid. center of the circle (and sphere). Its radius is 2f, which obviously depends on the location of the Focus.
D is a random point on that parabola, much like point G was earlier, and D’ being precisely on the opposite side of the optical axis. The great thing about parabolic mirrors is that every single incoming light ray coming into the paraboloid that is parallel to the axis will reflect towards the Focus, as we saw earlier. Or else, if you want to make a lamp or searchlight, and you place a light source at the focus, then all of the light that comes from it that bounces off of the mirror will be reflected out in a parallel beam that does not spread out.
In my diagram, you can see a very thin line, parallel to the x-axis, coming in from a distant star (meaning, effectively at infinity), bouncing off the parabola, and then hitting the Focus.
I also drew two red, dashed lines that are tangent to the paraboloid at point D and D’. I am calling the y-coordinate of point D as h (D has y-coordinate -h)and the x-coordinate of either one is
I used basic calculus to work out the slope of the red, dashed tangent line ID. (Quick reminder, if you forgot: in the very first part of most calculus classes, students learn that the derivative, or slope, of any function such as this:
is given by this:
So for the parabola with equation
the slope can be found for any value of x by plugging that value into the equation
Since
the exponent b is one-half. Therefore, the slope is going to be
which simplifies to
Now we need to plug in the x coordinate of point D, namely
we then get that the slope is
To find the equation of the tangent line, I used the point-slope formula y – y1=m(x – x1). ; plugging in my known values, I got the result
To find where this hits the y-axis, I substituted 0 for x, and got the result that the tangent line hits the y-axis at the point (0, h/2) — which I labeled as I — or one-half of the distance from the vertex (or origin) to the ‘height’ of the zone, or ring, being measured.
Line DW is constructed to be perpendicular to that tangent, so any beam of light coming from W that hits the parabola at point D will be reflected back upon itself. Perpendicular lines have slopes equal to the negative reciprocal of the other. Since the tangent has slope 2f/h, then line DW has slope -h/(2f).
Plugging in the known values into the point-slope formula, the equation for DW is therefore
Here, I am interested in the value of x when y = 0. Substituting, re-arranging, and solving for x, I get
Recall that point C is precisely 2f units from the origin, which means that the perpendicular line DW hits the x axis at a point that is the same distance from the center of curvature CoC as the point D is from the y-axis!
Or, in other words, CW = AT = DE. This means: if you are testing a parabolic mirror with a moving light source at point W, then a beam of light from W that is aimed at point D on the paraboloid will come right back to W, and the longitudinal readings of distance will follow the rule h2/(4f), where h is the radius of the zone, or ring, that you are measuring. Other locations on the mirror which do not lie in that ring will not have that property. This then is the derivation of the formula I was taught over 30 years ago by Jerry Schnall, and found in many books on telescope making – namely that for a moving light source, since R=2f,
where LA means ‘longitudinal aberration and the capital R is the radius of curvature of the mirror, or twice the focal length. So that’s exactly the same as what I computed.
HOWEVER, this formula [ LA=h^2/(2R) ] does not work at all if your light source is fixed at point C, the center of curvature of the green, reference sphere. In the old days, before the invention of LEDs, the light sources were fairly large and rather hot, so it was easier to make them stationary, and the user would move the knife-edge back and forth, but not the light source. The formula I was given for this arrangement by my mentor Jerry Schnall, and which is also given in numerous sources on telescope making was this:
that is, exactly twice as much as for a moving light source. I discovered to my surprise that this is not correct, but it took me a while to figure this out. I originally wrote the following:
But now I can confirm this, thanks in part to two of my very mathematically inclined 8th grade geometry students. Here goes, as corrected:
If one is using a fixed light source located at the center of curvature C, and a moving knife-edge, located at point E, the the rays of light that hit the same point D will NOT bounce straight back, because they don’t hit the tangent line at precisely 90 degrees. Instead, the angle of incidence CDW will equal the angle of reflection, namely WDE. I used Geometer’s sketchpad to construct line DE by asking the software to reflect line CD over the line DW.
However, calculating an algebraic expression for the x-coordinate of point E was surprisingly complicated. See if you can follow along!
To find the x-coordinate of E, I will employ the tangent of angle TDE.
To make the computations easier, I will draw a couple of simplified diagrams that keep the essentials.
I also tried other approaches, and also got answers that made no sense. It looks like the formula in the 1902 article is correct, but I have not been able to confirm it.
I suspect I made a very stupid and obvious algebra mistake that anybody who has made it through pre-calculus can easily find and point out to me, but I have had no luck in finding it so far. I would love for someone did to point it out to me.
People have long wondered why flying insects can be seen spiraling around light sources at night. Among other suggestions was that the critters were used to navigating by the Moon, and got confused, or that they were seeking heat.
An ingenious new study shows that the navigation idea is not completely wrong, but the insects instead use sky glow, even at night, as a major clue for how to orient themselves: by keeping their dorsal (back) to a point or diffuse light source, for millions of years, then they would keep their legs pointed down and they would fly the way they want.
However, these researchers found that if they placed a light bulb in roughly the center of an otherwise darkened, enclosed space inside a tent with flying insects, then most (but not all) species of nocturnal insects flying above or to the side of the light tended to orient their bodies so that their dorsal side was towards the light— so that they were flying sideways or upside down! Thus disoriented, they would flitter around, confused as to which way was up.
This also explains why it is so easy to catch nocturnal flying insects by shining a bright light onto a sheet or blanket laid on the ground: convinced by hundreds of millions of years that “light = up”, a large fraction of the critters fly **upside down** towards the lighted surface and careen onto it, out of control.
Caution: This study has not yet been replicated or peer-reviewed, but if it holds up, then it unveils a very simple and inexpensive fix for both ever-worsening light pollution and the collapse of our global insect populations: simply put shielding around ALL exterior light fixtures at night, so that NO light is emitted either upwards or sideways. (This is known as a Full cut-off (FCO) lighting.)
Larger animals like birds, reptiles, and mammals can simply use gravity to tell them which way is up. Insects, by contrast, are apparently so small that the air itself acts like a viscous medium, and tends to overpower the cues from gravity, much like scuba divers can get confused as to which way is up — unless they follow cues like air bubbles and where the diffused light from the surface comes from.
“The largest flying insects, such as dragonflies and butterflies, can leverage passive stability to help stay upright 30, 31. However, the small size of most insects means they travel with a lower ratio of inertial to viscous forces (Reynolds number) compared with larger fliers32. Consequently, smaller insects, such as flies, cannot glide or use passive stability, yet must still rapidly correct for undesired rotations33. Multiple visual and mechanosensory mechanisms contribute to the measurement and correction of undesired rotations, but most measure rotational rate rather than absolute attitude 26, 28, 32, 34. In environments without artificial light, the brightest portion of the visual environment offers a reliable cue to an insect’s current attitude.”
“Inversion of the insect’s attitude (either through roll or pitch) occurred when the insect flew directly over a light source (Fig. 1 c & Supp. Video 3), resulting in a steep dive to the ground. Once below the light, insects frequently righted themselves, only to climb above the light and invert once more. During these flights, the insects consistently directed their dorsal axis towards the light source, even if this prevented sustained flight and led to a crash.”
The researchers report that certain types of insects did **not** appear to get confused by lights at night: Oleander Hawkmoths (Daphnis nerii) and fruit flies (drosophila).
Because of the wet weather and clouds predicted for Saturday, April 29, 2023 we are canceling the free, public open house we had planned for tomorrow night — itself a postponement because of the clouds on the previous Saturday.
We will try again in the fall.
This is what the GFS forecast is producing for a forecast of average cloud cover for 8 pm EDT Saturday (00:00 Sunday, Universal Time, aka Zulu time) in the mid-Atlantic sector. White means ‘Overcast’.
Come to Bull Run Mountain for a free night under the stars looking at a variety of targets using the telescopes at the Hopewell Observatory on Saturday, April 27, 2024.
You are invited, but will need to RSVP and, in this litigious age, must agree to a waiver of liability for anything that might happen out there in the woods – and they do exist! Plus we don’t have running water — so, we use an outhouse.
But if you take the risk you, for free, can view Jupiter and its moons, comet 12P/Pons–Brooks, and a bunch of bright open clusters like the Pleiades, Beehive and Orion star clusters — and a gaggle of galaxies and double stars.
We have a variety of permanently-mounted and portable telescopes of different designs, some commercial and some made by us, some side-by-side, enabling several people to view the same object in the sky with different magnifications.
The date is Saturday, April 27. We suggest arriving near sundown, which will happen near 8 pm. It will get truly dark about an hour later.
There are no street lights near our observatory, other than some dimly illuminated temporary signs we put along the path, so you will probably want to bring a flashlight of some sort.
If you own a scope or binoculars, feel free to bring them!
Hopewell is about 45 minutes by car from where I-66 intersects the DC beltway. The last two miles of road are dirt and gravel, and you will need to walk about 200 meters/yards from where you park. We do have electricity, and a heated cabin, but since we have no running water, we have an outhouse and hand sanitizer instead.
We are located about 30 miles west of the Beltway on Bull Run Mountain – a ridge that overlooks Haymarket VA from an elevation of 1100 feet, near the intersection of I-66 and US-15. Detailed directions are below.
Assuming good weather, you’ll also get to see the Milky Way itself, although not as well as in years past, because of ever-increasing light pollution.
If you like, you can bring a picnic dinner and a blanket or folding chairs, and/or your own telescope binoculars, if you own one and feel like bringing them. We have outside 120VAC power, if you need it for your telescope drive, but you will need your own extension cord and plug strip. If you want to camp out or otherwise stay until dawn, feel free!
If it gets cold, our Operations Building, about 40 meters north of the Observatory itself, is heated, and we will have the makings for tea, cocoa, and coffee.
Warning: While we do have bottled drinking water and electricity and we do have hand sanitizer, we do not have running water; and, our “toilet” is an outhouse of the composting variety. At this time of year, the bothersome insects haven’t really taken off but feel free to use your favorite bug repellent, (we have some) and check yourself for ticks after you get home.
The road up here is partly paved, and partly gravel or dirt. It’s suitable for any car except those with really low clearance, so leave your fancy sports car (if any) at home. Consider car-pooling, because we don’t have huge parking lots.
Two of our telescope mounts are permanently installed in the observatory under a roll-off roof. One is a high-end Astro-Physics mount with a 14” Schmidt-Cassegrain and a 5” triplet refractor. The other was manufactured about 50 years ago by a firm called Ealing, but the motors and guidance system were recently completely re-done by us with modern electronics using a system called OnStep. We didn’t spend much cash on it, but it took us almost a year to solve a bunch of mysteries of involving integrated circuits, soldering, torque, gearing, currents, voltages, resistors, transistors, stepper drivers, and much else.
We could not have completed this build without a lot of help from Prasad Agrahar, Ken Hunter, the online “OnStep” community, and especially Arlen Raasch. Thanks again!
OnStep is an Arduino-based stepper-motor control system for astronomical telescopes. For this niche application, OnStep uses very inexpensive, off-the-shelf components such as stepper motors and their controller chips — which were developed previously for the very widespread 3-D printing and CNC machining industry.
Getting this project to completion took us nearly a full year of hard work!!! The original, highly accurate Byers gears are still in place, but now we can control the mount from a smart phone!
We also have two alt-az telescopes, both home-made (10” and 14”) that we roll out onto our lawn, and a pair of BIG binoculars on a parallelogram mount.
The drive is about an hour from DC. After parking at a cell-phone tower installation, you will need to hike south about 200 meters/yards to our observatory.
Physically handicapped people, and any telescopes, can be dropped off at the observatory itself, and then the vehicle will need to go back to park near that tower. To look through some of the various telescopes you will need to climb some stairs or ladders, so keep that in mind when making your plans.
Our location is nowhere near the inky dark of the Chilean Atacama or the Rockies, but Hopewell Observatory is mostly surrounded by nature preserves maintained by the Bull Run Mountain Conservancy and other such agencies. Also, our Prince William and Fauquier neighbors and officials have done a fair job of insisting on smart lighting in the new developments around Haymarket and Gainesville, which benefits everybody. So, while there is a bright eastern horizon because of DC and its VA suburbs, we can still see the Milky Way whenever it’s clear and moonless. “Clear Outside” says our site is Bortle 4 when looking to our west and Bortle 6 to our east.
DIRECTIONS TO HOPEWELL OBSERVATORY:
[Note: if you have a GPS navigation app, then you can simply ask it to take you to 3804 Bull Run Mountain Road, The Plains, VA. That will get you very close to step 6, below.]
(1) From the Beltway, take I-66 west about 25 miles to US 15 (Exit 40) at Haymarket. At the light at the end of the ramp, turn left (south) onto US 15.
(2) Go 0.25 mi; at the second light turn right (west) onto VA Rt. 55. There is a Sheetz gas station & convenience store at this intersection, along with a CVS and a McDonald’s. After you turn right, you will pass a Walmart-anchored shopping center on your right that includes a number of fast- and slow-food restaurants. After that you will pass a Home Depot on the right.
(3) After 0.7 mi on Va 55, turn right (north) onto Antioch Rd., Rt. 681, opposite a brand-new housing development. You will pass entrances for Boy Scouts’ Camp Snyder and the Winery at La Grange.
(4) Follow Antioch Rd. to its end (3.2 mi), then turn left (west) onto Waterfall Rd. (Rt. 601), which will become Hopewell Rd after you cross the county line.
(5) After 1.0 mi, bear right (north) onto Bull Run Mountain Rd., Rt. 629. This will be the third road on the right, after Mountain Rd. and Donna Marie Ct. (Do NOT turn onto Mountain Road, and note that some apps show a non-existent road, actually a power line, in between Donna Marie Ct. and Bull Run Mtn. Rd.) Bull Run Mtn Rd starts out paved but then becomes gravel, and rises steadily.
(6) In 0.9 mi, on BRMtn Road, you will see a locked stone gate and metal gate, labeled 3804. That is not us! Instead, note the poorly-paved driveway on the right, with the orange pipe gate swung open and a sign stating that this is an American Tower property. We use their road. Drive through both orange gates, avoiding potholes keeping at least one tire on the high spots. We’ll have some signs up. This is a very sharp right hand turn.
(7) Follow the narrow, poorly-paved road up the ridge to the cell phone tower station.
(8) Park your vehicle in any available spot near that tower or in the grassy area before the wooden sawhorse barrier. Then follow the signs and walk, on foot, the remaining 300 yards along the grassy dirt road, due south, to the observatory. Be sure NOT to block the right-of-way for any vehicles.
(9) If you are dropping off a scope or a handicapped person, move the wooden barrier out of the way temporarily, and drive along the grassy track to the right of the station, into the woods, continuing south, through (or around) a white metal bar gate. (The very few parking places among the trees near our operations cabin, are reserved for Observatory members and handicapped drivers.) If you are dropping off a handicapped person or a telescope, afterwards drive your car back and park near the cell phone tower.
Please watch out for pedestrians, especially children!
In the operations cabin we have a supply of red translucent plastic film and tape and rubber bands so that you can filter out everything but red wavelengths on your flashlight. This will help preserve everybody’s night vision.
The cabin also have holds a visitor sign-in book; a first aid kit; a supply of hot water; the makings of hot cocoa, tea, and instant coffee; hand sanitizer; as well as paper towels, plastic cups and spoons.
The location of the observatory is approximately latitude 38°52’12″N, longitude 77°41’54″W. The drive takes about 45 minutes from the Beltway. A map to the site follows. If you get lost, you can call me on my cell phone at 202 dash 262 dash 4274.
With an Amazon Fire Tablet, on which I placed SkySafari Pro ($15), we can now get the OnStep mount at Hopewell Observatory to go to any target we want, without any wire connection needed at all. The ‘Smart’ Hand Controller is no longer a necessity, which is good, because it’s always been rather a PITA.
The SkySafari Pro interface is really nice and much more user-friendly than any other planetarium software I’ve tried so far. Among other things, you can use your fingers to pan around and zoom into the sky map display, and double tap on a target of interest. Once you’ve located your target on your screen, you can then press ‘GoTo’, and the scope will begin slewing to that target. While it’s doing so, you can watch where the telescope is currently pointing to on the screen’s display, kind of like those airplane icons on maps on some airline flights – only a lot more accurate and zoomable. BTW the connection is via WiFi.
Once the scope thinks it has arrived at the proper location, you can look through the eyepiece (or at a display screen) to see if it is properly centered. If not, then in order to center it, you simply tilt the tablet in the direction you want the scope to go! And changing the speed of such movement is really easy!
I have thanked Arlen for showing me this on his cell phone. I myself could never get it to work properly with my iphone, but after some time downloading the proper software onto the tablet and making the proper wifi connections with the proper IP address and port number, in a nice warm location here in town with at least a halfway decent WiFi connection, with a spare OnStep setup on the bench in front of me, then it was easy.
I demonstrate this with the following clumsy video.
BTW, SkySafari Pro works on Android and other tablets, on MacOS, Windows, and supposedly even on iPhones. You do need to pay for the Pro version, because the free version does not have telescope control capabilities.
So, for very little money, but a whole lot of work, we have 21st-century Wi-Fi control over a very fine telescope mount!
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