VANTA black is apparently the blackest material in the world – so far. Made out of vertically-oriented arrays of carbon nanotubes grown in situ, reflects only something like 0.035% of the light that hits it. Imagine that coating the inside of a telescope tube! No more stray reflections!

https://en.wikipedia.org/wiki/Vantablack

NCA-business-card

If you have ever cleared a sidewalk after a snowstorm (like I did this morning), you’ve probably noticed that shoveling snow is a lot of hard work.

I wondered just how hard I was working to shovel our porch and sidewalk, so I did some rough calculations. 

Not knowing the weights or masses of snow or water in American customary units I did it all in metric units because it’s so much easier.

Using a construction tool, I measured the snow as being about 13″ deep, or about 33 cm (1/3 of a meter). I shoveled a path that was roughly a meter or so wide, and a grand total of about 21 long paces (roughly a meter each) in length.

Which means I had shoveled a volume of 1/3 *21*1 or 7 cubic meters. If that was all liquid or solid water, that would be exactly 7 metric tons. But snow is about 90%air, so if we divide that by 10, we get 700 kilograms instead, or about 1500 pounds of fluff.

 Huff, huff, puff indeed.

By the way, my son Josef Brandenburg, a DC-area fitness expert and personal trainer, has a nice interview with Bruce Depuyt on the right way to shovel so that you don’t throw your back out and end up in the emergency room along with many thousands of other folks. (I didn’t.)

Got another puzzle for you: an f/3 8″ mirror that appears to have been made by laying a plastic layer on an unfinished thin mirror blank! I’ve never seen anything like it!

Anybody got any ideas?

Some background: Some weeks ago, Al P brought in to the DC-area ATM workshop the optics for a telescope that someone gave him a decade or so earlier. The telescope originally had some sort of thin, full-sized window that we determined was almost perfectly flat, so it had no corrective power that we could determine. He thought that the diagonal mirror had been attached to the window, but the rest of the telescope had long since disappeared. The aluminum layer on the mirror was in fairly decent shape considering how old the mirror was.

The mirror was very thin: 8″ across (20 cm) and only about 1 cm thick, so about 20:1 instead of the 6:1 diameter-to-thickness ration that used to be recommended in the 1930s through 1990s. The back of the mirror blank had circular grooves impressed into it, so many that at first glance it looked like an old-time glass LP record (rather than a vinyl one).

It was also very ‘fast’, with an focal ratio of almost exactly three (3)!

Unfortunately, the mirror was seriously undercorrected, and thus unusable if put into a telescope as is, even though a Ronchi test showed no signs of turned-down edge or of unwanted roughness or weird zones. A numerical Foucault test with Couder-style zones, repeated several times, revealed the lack of correction.

Eventually Al decided to try to refigure the mirror with an ordinary pitch lap, so he removed the aluminum layer with muriatic acid (HCl), and we remade a burgundy pitch lap and tried to get the lap into contact. It seemed to Al that the original bevel had pretty much vanished, so he used a fairly coarse sharpening stone to bring it back. We noticed a funny texture around the end of his bevel but weren’t sure what it was.

When we pressed the mirror against the lap, we immediately discovered that there was a huge amount of bumpiness and jerkiness – something was catching the lap, much like riding a Big Wheel trike on a cobblestone street. Plus, the pitch tended to stick to the mirror and had to be repeatedly removed with fingernails, turpentine, and paint thinner.

We tried rewarming and re-pressing the lap, with no improvement. When we ran our fingers around the edge of the glass, near the bevel, it seemed like there was a raised rim, almost like on a saucer. So Al got out a finer sharpening stone and increased the bevel all the way around, to about 3 or 4 mm wide. Still no improvement in the bumpiness, and the weird texture around the edge of the glass got even worse.

Then we tried removing all traces of upward-facing lip around the edge of the glass by taking a large sort-of-flat piece of 1/4″ glass, sprinkling some 220 grit and water on it, and stroking the mirror, face down, against the grit and piece of glass.

That also did not do anything to improve the bumpiness. Plus, it began to look to us more and more like this mirror had been made in a totally weird manner: a fairly rough piece of glass was hogged out to the correct curvature, then somehow coated with a smooth layer of plastic, then aluminized. If they did any figuring on it, they clearly did not use a pitch lap!

I attach a few photos that are badly out of focus because iphones don’t like to take close ups. The bright bars are LED fluorescent lights in the ceiling; the concentric rings or grooves are on the back of the mirror. Pay attention to the irregularly-shaped non-shiny areas, where we think the original plastic coating came off.

I am also going to link to a youtube video that I took through a cheap 60X – 100X LED microscope.

A few more clues: the plastic layer (if that’s what it is) does not seem to be removed with either HCl or turpentine or mineral spirits.

If anybody has any thoughts on this mysterious mirror, Al and I will be all ears.

Meanwhile he plans to create a new tool from dental plaster and porcelain tiles and regrind it to f/5.

A wonderful astronomical weekend near Spruce Knob WV, at the Almost Heaven Star Party.

The fields at The Mountain Institute where it’s held remind me of the farm I grew up on, near Clarksburg MD, and the farm I lived in with Susan Greenthal Hurd in East Ryegate VT about 44 years ago.

The altitude here in WV does mimic the climate in VT. I have never gotten bitten here at TMI or AHSP or anywhere else I’ve hiked or canoed in West Virginia by any ticks or chiggers – which bedeviled me and my siblings 50-60 years ago in Clarksburg MD and continue to bite me at the Hopewell Observatory in Northern VA near Haymarket.

I brought my 12.5″ truss-tube dob, which you can see in one picture. I had just re-made the secondary cage and spider and secondary adjustment mechanism. I had to perform emergency surgery to cut off the truss tubes by exactly one inch so that all of the eypieces would actually come to a focus.

Part of the road up to TMI and AHSP

Baling hay in fields right next to TMI / AHSP

Learning how to use a sextant; if you know the exact time, you can use this to calculate your location to within 100 meters or so.

Beautiful but slightly threatening clouds the first night ended up dissipating. We had three beautiful nights of observing!

Me and my 12.5″ truss-tube dob that I built,

This is the Durbin Rocket railroad – a small and slow coal-burning locomotive designed to carry heavy loads of lumber. If you sit behind the engine, you WILL be coated with coal dust and cinders.

A friend’s minimalist, ultra-light dobsonian telescope, either 18 or 20 inch diameter. Note the lack of mirror box! It also tracks and has both Argo Navis and a go-to capability.

One of the many excellent talks. In this one, Jan Wisniewski (Vish – NYEV-ski) is showing how to make an IR on-axis autoguider.

Here I demonstrate how light and insubstantial are the famous Seneca Rocks that I passed on the way back from the star party.