BAN #399: Mountain Moonset, ATLAS no longer shrugs

7 February 2022 Issue #399

February 07, 2022

Pic o’ the Letter

A cool or lovely or mind-bending astronomical image/video with a short description so you can grok it

Not long before Christmas last year I was out in the morning to feed the goats and horses — it’s funny to me how many stories of mine start this way — and saw the waning gibbous Moon, just barely past full, starting to set in the west. I went inside, grabbed my long lens camera, and took about 70 photos. Most weren’t very good, but I’m rather pleased with how this one came out:

[The Moon setting behind the Rockies on January 20, 2021. Credit: Phil Plait]

I would’ve had to walk a hundred meters west or east to get those power lines out of the way, but in honesty I kinda like the way they make a geometric pattern in the otherwise organic background. The flock of birds was just a fun coincidence, too.

If you look carefully at he Moon you’ll see the edges are wonky. Air flowing over the mountains can be turbulent, and the varying landscape around here tends to make air currents blowing every which way as well. Light passing through air of different densities gets bent the same as if it passed through a lens — this is called refraction — so that makes little wiggles in otherwise smooth shapes. Note the power lines do in fact look straight (besides the pixelation) because they’re close to me, and the light didn’t pass through much air to get to the camera.

As always, it may just look like a pretty picture, but there is always science behind them. Always.

Blog Jam

[Artwork of a black hole powering a quasar — one story of eight highlights of the year from NRAO and Tuesday’s article. I worked hard on these videos and the VO, so please take a look! Credit: NOIRLab/NSF/AURA/J. da Silva]

Tuesday 01 February, 2022: 8 highlights of radio astronomy in 2021

Wednesday 02 February, 2022: Second-ever Earth Trojan asteroid found!

Friday 04 February, 2022: Line of sight

Astro Tidbit

A brief synopsis of some interesting astronomy/science news

I see a lot of press releases and papers, and it’s a rare one where I get viscerally excited when I see one. This is one of those very happy exceptions: The ATLAS sky survey just completed construction of two new telescopes, and operations are already underway!

Why is this exciting? ATLAS is the Asteroid Terrestrial-impact Last Alert System, an early detection and warning system specifically designed to look for near-Earth asteroids. Up until recently it consisted of two telescopes located on different islands in Hawaii, but the new telescopes are located in Chile and South Africa. Not only does that mean complete coverage of the southern sky, which cannot be 100% accessed from Hawaii, but the time zone differences between the observatories means over the course of a single day they can scan the entire dark sky for incoming rocks.

To be clear, that means any part of the sky not near the Sun, but that still means exceptional coverage. The telescopes have mirrors 0.5 meters in diameter, so they can collect a decent amount of light, and have a wide field of view, so they can cover a lot of sky quickly.

ATLAS is a great system. They’ve been in operation for several years and have discovered over 700 asteroids, including 72 potentially hazardous ones (defined as being bigger than 140 meters in size and can get within 7.5 million kilometers of Earth). They’ve also discovered over 10,000 supernovae — WOW — 

Including the superluminous weirdo 2018ATcow (the AT in the name stands for ATLAS). You may also remember reading about the comet C/2019 Y4 (ATLAS) that it discovered, which got decently bright before disintegrating.

[The comet C/2019 Y4 (ATLAS) seen from the ground (top) and by Hubble (bottom). Credit: Damian Peach and NASA/ESA/Quanzhi Ye/Alyssa Pagan]

ATLAS can find asteroids as small as 20 meters — roughly the same as the one that hit over Chelyabinsk, Russia, in 2015 — as much as a day in advance, and larger ones even earlier. That’s not a huge amount of time, but it helps. Right now most objects that size are detected after they pass us.

Incidentally, a paper also recently came out looking at how to scan the sky near the Sun as seen from Earth. The solution: Don’t look from Earth. Instead, launch a pair of space-based telescopes that would stay in Earth’s orbit but be positioned ahead of it by about 10 million kilometers. They find the efficiency of such a position would approach 99% detection rates for any asteroid brighter than 24th magnitude — about 1/15 millionth as bright as the faintest object you can see by eye. That’s dim.

That would be expensive, but together with ATLAS and other surveys — ZTF, Vera Rubin, and others — it would provide complete sky coverage all the time. And if we add in the Near-Earth Object Surveillance Mission we’ll also find ones close to the Sun in sky, including ones that orbit inside Earth’s orbit, which are usually very difficult to detect.

So yeah, I’m excited. And I surprised myself with another feeling I got after reading the press release: Relief. It’s a big sky, and space is voluminous, and there are lots of places for rocks to hide in.

But soon, there won’t be.

Et alia

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