Observing Asteroids at VATT, Part 2

Last April, my post was about doing Citizen Science from the Vatican Advanced Technology Telescope (VATT). This is a follow-up article about our latest observing run in early December 2019. I would like to thank Mark Trueblood and Robert Crawford who make our observing the success that it is. I would also like to thank the staff of VATT who are on call all hours of the night to help us out when we need help with the telescope and equipment.

As I said in my previous article about observing from the VATT, our goal is to observe Near-Earth Asteroids that might, some time in the future, collide with the Earth. “These asteroids might become ‘lost’ because of the uncertainty in their orbits.” By reducing the uncertainty in the orbits of these asteroids, we hope to remove them from the list of asteroid impactors.

This five-night observing run was an experiment: Could we observe asteroids that had been discovered only weeks earlier, but might be lost because few astronomers observe within a few days of the Full Moon? The answer is YES (for at least the brighter asteroids).

Why Astronomers Avoid Observing Near Full Moon

A little bit of science background. Have you ever been on an airplane and seen the shadow of the plane surrounded by a halo? This is called glory [link to Wiki] and is due to the interaction of light with water droplets in clouds.

An image of glory as seen from an airplane. By Brocken Inaglory – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=2204135

 

There is a similar phenomenon for the airless surfaces of planets, moons, and asteroids called the opposition effect. Have you ever taken a picture of your shadow while standing on an airless body (to avoid scattered light from the atmosphere) such as the Moon? Probably not! However, the Apollo astronauts did this and the Japanese Hayabusa2 did this from above the surface of the asteroid Ryugu.

Images taken by Apollo 17 (left) and Apollo 16 (right) astronauts. Note in the right image, only the astronaut with the Sun at his back has the “halo” around him. Images from NASA
A “shadow selfie” of Hayabusa2 with the opposition “halo” around the shadow. Image of asteroid Ryugu from JAXA.

 

For any Solar System object beyond the Earth, opposition occurs when the Earth is directly between that Sun and the object. In the case of the Moon, this is when the Moon is full. The opposition effect is caused by the lack of any shadowing on the surface of the object as well what is called “coherent backscattering.” In the case of the Moon, to the eye, the Moon looks full the day before through the day after Full Moon.  However, very close to opposition, it is about 40% brighter very close to and at Full Moon than it is a day away from Full Moon! This makes observing faint objects very difficult—Nature’s own light pollution! Also, the Moon is “up” most of the night, so there is little time when there is no Moon in our sky. A bit of trivia: the December Full Moon is called the Cold Moon. Because the Moon appears to move along the ecliptic (the path of the Sun across the sky), in the winter, when the Sun is low in the sky, the Full Moon, opposite the Sun, is high in the sky: the Sun is above the horizon for it shortest time and the Moon is above the horizon for the longest time. This is not a good time for astronomers to be observing faint objects such as asteroids!

Our Observing Run

During this observing run, because of clouds, wind, and high humidity, we had two good nights and two partial nights (not too bad for the middle of winter. Here are some pictures of the snow-capped mountain taken from the basecamp and the view from the little porch next to the room where we observe. I have included pictures taken during the day and at night to show you how bright the Moon was that night.

A view of snow-capped Mount Graham. Credit: Larry Lebofsky
Submillimeter Telescope (10-meter diameter mirror) in foreground with Large Binocular Telescope in background at sunset: Credit Larry Lebofsky.
Submillimeter Telescope (10-meter diameter mirror) in foreground with Large Binocular Telescope in background hours before Full Moon: Credit Larry Lebofsky.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

On a whim, I took a handheld picture very close to the exact time of Full Moon. The time of Full Moon made the news. On the East Coast, it occurred on December 12 and 12:12 am (10:12 pm in Tucson).

Sky view on December 11, 2019 at 10:12 pm in Tucson (from Starry Night).

 

Actual sky view at on December 11, 2019 at 10:12 pm in Tucson. Credit: Larry Lebofsky.

 

How did we do? We were able to find seven near-Earth asteroids that had been discovered from early November though early December.  Four of these asteroids had been observed for only four to 11 days. We were able to extend observations to nearly three weeks. If we had not observed them around Full Moon, some of them would have been too faint (as they move away from the Earth) for anyone else to observe them days later. In one case, an amateur astronomer was able to predict where asteroid 2019 VL4 should have been prior to its discovery and was able to find the asteroid in survey images take over 5 years earlier! Our observations reduced the uncertainty of the orbits of these asteroids, enough so that they may be re-observed the next time they are bright enough to be seen again and not end up lost.

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