(c) Skyhound

Above is a series of images I took remotely on the morning of April 18 from Mayhill, New Mexico, using the iTelescope T11. The movie consists of sixty 12-second exposures, spanning about 20 minutes. The field of view is approximately 22' x 16'. The asteroid was magnitude14.5. 

On April 19/20 the asteroid 2014 JO25 passed near to the earth. This event was widely observed, both visually and via imaging. During the pass there were some problems with the sources of standard orbital elements, which left some looking off track, but I am happy to say that SkyTools users have reported in from around the world that the positions from SkyTools were "spot on."

As the asteroid approached, I made the series of images that make up the above movie. The exact positions were determined from the images and compared to those predicted by the orbital elements from the Minor Planet Center, the ASTORB database maintained at Lowell Observatory, and the online JPL Horizons ephemeris generator. It was clear that the JPL elements were the most accurate. Also, as the asteroid passed close to the earth/moon system, the orbit would be perturbed. In other words, the orbit would slowly change due to the gravitation effect of the earth and moon. Normal orbital elements don't take this into account, but the JPL system does, so I decided to use it to generate sets of orbital elements at 12 hour intervals throughout the pass. These were made available as part of the "Current Minor Planets" observing list download for SkyTools users. When multiple sets of elements are available for the same object, SkyTools will select the one closest to the time being used. In this way, SkyTools was able to very accurately predict the position of the asteroid even as the orbit changed during the pass.

SkyTools user David Lloyd-Jones of Sydney Australia sent the following comparison of his own images and the prediction of SkyTools. He reported that, "It was exactly spot-on and made finding the object so easy."

 

My Own Visual Observations

I invited people to join me at a local football field, where I set up my 8-inch Dob. Finding the asteroid was easy because it would pass near a naked-eye star in the early evening. As the twilight faded, I pointed the scope just to the right of the 5th magnitude star 41 Com, referring to a printed SkyTools finder chart.

In the eyepiece, the asteroid was easy to spot because it made a right-triangle with two other 11th magnitude stars. As I watched, the shape of the triangle changed obviously in just a few seconds, which was very cool! Below is the SkyTools eyepiece simulation of what I saw. 

Note that the chart above was created automatically by SkyTools, matching my view exactly, including the sky brightness, visible stars, and orientation. 

A Rare Observing Treat in Asteroid 2014 JO25

What made this asteroid interesting to observe wasn't how close it came, but how large, bright, and fast moving it was. It became brighter than 11th magnitude, which is within reach of small (4-inch and larger) telescopes. It moved through the sky so fast that it's motion could be seen in a high-power eyepiece.

Twice as Large as Previously Thought

This asteroid was discovered in 2014 via the Catalina Sky Survey in Arizona. Initial estimates put it at about 2000 ft (650 m) in diameter. It takes 3 years to orbit the sun. On April 19th, 2017, passed near the earth, about 4.6 times the distance between the earth and moon. This was the closest pass to the earth for this asteroid in 400 years, and it will not pass this close again for another 500 years.  The next known flyby of an object of this size won't be until 2027.

Beginning on April 17, the asteroid was observed via radar using the Arecibo Observatory Planetary Radar System. These images revealed a peanut-shaped object that is twice as large as recent estimates, 0.8 miles (1.3 km) at its widest. It takes about 3.5 hours to rotate once. 

Here are some of the radar images via NASA

Greg Crinklaw Amateur/Professional Astronomer and Developer of SkyTools 

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