See A Potentially Hazardous Asteroid Zip By Earth Wednesday

2014 JO25’s orbit extends to from well beyond Mars to within the orbit of Mercury. Discovered in 2014, the potentially hazardous asteroid will swing just about four times the distance of the moon from Earth on April 19.  Credit: Gianluca Masi

Astronomers are constantly on the lookout for slippery asteroids and comets passing through Earth’s neighborhood. Thanks to their efforts, we know of at least 16,000 NEOs or Near-Earth Objects, the majority of which are asteroids. Of that number about 1,800 are potentially hazardous. One of them, 2014 JO25, will be speeding by our planet Wednesday.

Not to worry. The giant speeding boulder will miss us by a safe distance of about 1.1 million miles (1.8 million km). But before it’s on its way out, we have a marvelous opportunity to see it with our own eyes. 2014 JO25 is big — about 2,000 feet (650 meters) across — and twice as reflective as the moon, making it bright enough to spot in telescopes as small as 3-inches. Most NEOs are much smaller and consequently fainter.

As it approaches and then recedes from Earth, 2014 JO25 really boogies, moving from Cepheus on April 18 all the way to Coma Berenices in just one night. Positions are marked every 5 hours. The asteroid will be faint and low on the 18th and will fade after the 19th. Created with Chris Marriott’s SkyMap

I bet a lot of you have never tracked a fast-moving asteroid before. It’s a blast because you can watch it creep across the telescope’s field of view in real time like a slothful satellite. The last time an asteroid this size or larger whizzed by was in September 2004, when 4179 Toutatis came within about four lunar distances of Earth.

Closest approach occurs around 12 UT (7 a.m. CDT) on Wednesday April 19th. That evening, North American observers can catch it cruising south-southwest across Coma Berenices, a dim constellation behind (east of) the tail of Leo the Lion. At that time, the asteroid will be traveling at the rate of about 1 arc minute for every minute’s worth of time. An arc minute is equal to 1/30th the apparent width of the full moon. It may not sound like much, but that’s fast enough to see movement right before your eyes when using a magnification of 50-75x.

In this closer view, tick marks show the asteroid’s position every 15 minutes (with labels every hour) as it tracks across Coma Berenices on the night of April 19–20 CDT for observers in the Americas. Stars are shown to magnitude +11.5 and north is up. Mel 111 is the naked eye Coma Berenices star cluster. Credit: Bob King; Source: Chris Marriott’s SkyMap

2014 JO25 was discovered in May 2014 by astronomers at the Catalina Sky Survey (CSS) near Tucson, Arizona. Once its orbit was calculated and a size estimated based on its brightness, the asteroid was classified as a PHA or potentially hazardous asteroid, defined as having a diameter of at least 330-490 feet (100-150 meters) and a miss distance from our planet of 4.6 million miles (7.5 million km) or less. Astronomers estimate that a PHA strikes Earth once every 10,000 years with the impact causing regional devastation, if it strikes land, or a major tsunami if ocean.

This map (the first of three close-up maps) shows the asteroid headed south-southwest across the constellation Coma Berenices between 9 and 11:30 p.m. CDT. Tick marks show its position every 15 minutes and stars are plotted to magnitude +11.5. Start time is 9 p.m. CDT (2 UT April 20). Click for a larger version you can print out and use at the telescope.
Bob King; Source: Chris Marriott’s SkyMap

When closest, 2014 JO25 will shine at about magnitude 10.7, well within the limit of a 3-inch telescope, and look like a moving star. Just a pinpoint. By Wednesday night over the Americas, it will have faded to about magnitude +10.9, still bright as these things go. I’ve included several charts to help you find and track the fast-moving object.

Asteroid watchers and astrophotographers can watch 2014 JO25 pass 15′ east of M64, the Black-Eye Galaxy, about 12:45 a.m. CDT on April 20th. For more maps including one for European observers, please visit Sky & Telescope.  Credit: Bob King; Source: Chris Marriott’s SkyMap

As it scoots through Coma, it will pass just ¼° east of the bright galaxy, M64 (a.k.a. The Black Eye Galaxy) around 12:45 a.m. CDT, April 20. The key to spotting a somewhat faint stellar object is to allow time to identify and get familiar with the star field the asteroid will pass through 10 to 15 minutes in advance — then lay in wait for the moving object. Don’t be surprised if 2014 JO25 deviates a little from the predicted path depending on where you live. Cast your gaze around the path in search of the asteroid. For more maps, check out my write-up at Sky & Telescope.

While the charts will work for most observers, you can always prepare your own. Here are two easy ways:

1. Download the free home planetarium software Stellarium for Windows or Mac. Once you’ve chosen your city, click on the configuration icon (lower left side of screen), select Plugins, scroll, and select Solar System Editor. Click Configure and select the Solar System tab. Select Import orbital elements in MPC format, then Asteroids. Under Select bookmark, choose the PHA option and click Get orbital elements. Scroll through the list and find 2014 JO25, then click Add to list. Next, close the dialog boxes, choose a time you want to view the asteroid, and click Search window (magnifying glass in lower-left corner of screen). Type in the name 2015 JO25 and the program will take you straight to it. I know — sounds like a lot of steps, but it’s painless. And accurate.

2. If you already have a program like Starry Night, Megastar, etc. that can plot an asteroid path, just go to the Minor Planet and Comet Ephemeris Service, type 2014 JO25 in the open box, scroll to the end of the page, select your software. and click on the Generate ephemerides/HTML button. Save the file that pops up on your screen into your program, open the program, select the asteroid, and create a custom map with time intervals and a magnitude range to your liking.

If you have bad weather, Gianluca Masi, an Italian astrophysicist who loves sharing sky events on his Virtual Telescope Project site, will host a live show and real-time photos starting at 19:30 UT (2:30 p.m. CDT) April 19.