Monday, February 12, 2018

Trials and Tribulations of Near-Earth Asteroid Hunting

Last Sunday Evening, while most Americans settled back to watch the 52nd Super Bowl, the earth entertained a celestial visitor. A 2,000-feet wide asteroid named “276033 (2002 AJ129)” silently passed within 2.6 million miles of the earth briefly becoming the second nearest knows celestial body and, brightening to 12th magnitude, shone as one of the brighter asteroids in our sky. 

I had awaited this event for months. The website Spaceweather routinely lists upcoming Earth-asteroid encounters. Whenever a relatively large object is mentioned, I take note.  

Recent list of Near Earth Objects from

Clicking on the object name takes the user to one of my favorite tools, the “JPL Small-Body Database Browser.”  There, a few clicks get the user a very accurate ephemeris. The asteroid was going to be conveniently placed in our evening sky. Moreover, the predicted maximum brightness was a glaring 12.3 magnitude. Surely, this would be an easy catch.

JPL Horizons Ephemeris for Asteroid 2002 AJ129

Sadly, I was scheduled to work on the evening of the 4th. However, 276033 (2002 AJ129) follows a highly-eccentric orbit. It approached the earth from the direction of the sun. Consequently, at closest approach, its tiny crescent disk shone a full magnitude fainter than the next evening when its full disk receded from our neighborhood. Therefore, I planned my observations for the night of February 5th.
Astronomy Now view of 2002 AJ129's Orbit
Catching these objects is like a skeet shoot. They move quickly through our skies. So, I use the wonderful JPL Small-Body Database Browser to predict the position of the asteroid at various times and plan to point my telescope at the predicted star fields at those times and wait for the asteroid to pass.

The night is brutally cold. But it is February, and I have only observed once this year. Other club members actually draw their observations through mittened fingers. I certainly can get out there and create material for a new blog posting. So, I wrap myself in layers of Kevlar and Gore Tex, fill my Thermos with hot tea (Earl Grey) and set up my scope.  At least the heavy lifting momentarily warms my muscles. 

Tonight, the asteroid travels among the stars of southern Leo. At 9:30pm, the starfield finally rises above my neighbor’s’ home. I type the coordinates into the keypad of the mount and the telescope dutifully slews to a position on the Leo-Sextants border.

Surprisingly, the first images do not show the predicted starfield. In fact, the first images show no stars at all. I can see the familiar “Backwards Question Mark” of Leo and the nondescript stars of Sextants so, clouds aren’t obstructing my view. Reluctantly, I leave the warm perch of my seat to look through the finder scope. Just where is the scope pointing?  Stars look good through the finder. It takes my frozen mind a few minutes to determine the issue. Although the finder points above my neighbor’s roof, the main scope’s physical position is well below the finder. While the finder and optical tube are perfectly aligned on distant stars, they point in radically different directions in the near-field. The scope still points toward my neighbor’s house. My first image isn’t of the asteroid or anything farther than 100 feet. It is of a highly out of focus three-inch-by-five-inch portion of someone’s roofing!

First Attempt at Imaging Asteroid 2002 AJ129 - a 3X5-inch Portion of my Neighbor's Roof.

The 9:45pm attempt fails as well. I image with a solid-state laptop. This means the computer has no hard-drive-- no moving parts. Hard drives do not work well in colder weather. The lubricant needed to whirl their disk drives thickens at colder temperatures creating all kinds of disk read errors and other scary messages. Solid state computers do not suffer these issues.

Tonight, I discover that my laptop fails below 15°F. I still do not understand why the computer struggles in these cold temperatures. I thought that electricity flowed better in colder temperatures. Although the solution is simple, I burn through another 30 minutes of observing time getting a heating pad to place beneath the laptop. At least I now get a nice place to warm my numb fingers.

By 10:30PM, the starfield hangs well above the neighbor’s roof and the laptop computer, warmed by the heating pad, runs well. The telescope slews to the predicted starfield, and I watch the preview images display on the screen. The starfield appears as predicted, but no asteroid. I wait as each 20-seconds a new exposure appears on the screen. Eventually, I notice that one of the stars near the leftmost portion of the field does not appear as a point. Instead, it presents itself as a small line. Moreover, like and inchworm, it moves slowly toward the top of the screen.  I found it! Although it is not exactly where I predicted it to be, Asteroid 276033 (2002 AJ129) is in my camera’s field of view and images are being captured every 20-seconds.

Animation of Six 20- Second Exposures of Asteroid 2002 AJ129

Predicted Path of Asteroid 2002 AJ129

Predicting the progression of the asteroid, I immediately reposition the scope.  I want a series of images with the asteroid passing through the center of the field. When I see the asteroid appear in the bottom of the new star field, I begin capturing a new set of 20-second exposures. Figuring that it would take seven minutes for the asteroid to disappear from the camera’s field, I scurry indoors to warm myself by the fire.

Animation of Eleven 20-Second Exposure of Asteroid 2002 AJ129

Afterwards, I capture a few longer exposures and shiver as I break down my setup. Hastily, I adjourn to the warm of my home to download the images forgetting to acquire dark or flat frames. 

So, what can I do with this data set? I first create a little movie. I use Photoshop Elements 10 to create a stack of 15 layers. Each layer represents one 20-second exposure. Afterwards, I “Save For Web.,” I select “animate.”  This creates a “.gif” animations that may be uploaded to things like Facebook or Astrophotography Blogs. My lack of flat fields leaves the animation heavily vignetted. 

Enhanced Animation of Asteroid 2002 AJ129

I can also use Deep Sky Stacker, to stack the images.  This makes 2002 AJ129 appear to be a series of streaks running through the frame. The horrible vignetting and doughnut-like dust circles embarrassingly emphasize my lack of flat field images. 

Stack of Fifteen 20-Second Exposures of Asteroid 2002 AJ129

If you regret missing 2002 AJ129’s passage, there are other events in the near future. On 7 March 2018, a smaller asteroid 2017 VR12 passes less that one-million miles from the earth. At a predicted magnitude 11.8, it will be a fast-moving late-night object quickly threading its way between the galaxies in Virgo. I will be out there, and I promise, I will not forget to take my dark and flat frames.

Keep Looking up to Clear Skies


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