Rare Event: Dual Asteroid Occultation

July 19, Tuesday, brings us a rare event of an occultation of dual (binary) asteroid 90 Antiope. Between the hours of 10:18 to 10:25 Universal Time, 90 Antiope will occult one its members, so us here in America can see it. If you're on the east coast - you're out of luck, as sad as it is. Only the northeast to southwest portions across central Saskatchewan, southeastern Alberta, western Idaho and Montana, northern Nevada, and north-central California will be able to witness this rare event.

Credit: Sky&Telescope; this is a relative path in which this event can be observed.

You should know that this binary asteroid occultation should be enough to satisfy you, but a star comes into the picture as well! The occultation incorporates a rather bright star: 6.7-magnitude LQ Aquarii (variously designated as ZC 3339, SAO 165285, and HIP 112420). It's in Aquarius, about 2½° north of 4th-magnitude Tau Aquarius. The waning moon is ten degrees away, so you should easily be able to find the asteroids.

Although this event (when one asteroid blocks out another) won't last any longer than thirty seconds, David Dunham, president of the International Occultation Timing Association (IOTA) announces, "According to the current prediction, there should be a 20-mile-wide (30-km) zone at the center where both components will occult the star." So, to be most exact, Tuesday, July 19 will bring portions of the Pacific coast an occultation of a binary asteroid, and also a star; maybe occurring at the same time?

The History and Multitude of Binary-Asteroids

Amazing to note, this isn't the first time 90 Antiope has occulted. Many times, the latest in 2005, these asteroids have occulted, but this will be the first of a star as well. There are about two-hundred know binary asteroids discovered, which is quite funny because one time astronomers thought that never to be possible. 90 Antiope's members are extrememly one-of-a-kind because they are almost identical in size and complexion, orbiting each other about every 16½ hours.

Sky&Telescope caption: In 2004 astronomers used the Very Large Telescope in Chile to record the double asteroid 90 Antiope. Its nearly identical components are separated by 106 miles (171 km) and circle each other in 16.5 hours.

To read an in-depth essay on the matter, this link features everything you need to know. You can finds results here, as well as posted on our site here Tuesday afternoon. David Durham continues to close:

Seeing a star suddenly vanish, then abruptly reappear several seconds later when a faint asteroid passes in front of it, is a startling sight that will always be remembered.  Millions of people will have a chance to see such an event before sunrise early Tuesday morning, July 19th.

Anyone with binoculars who can count, lives in or near the eclipse path, and is willing to get up in the early morning before dawn and go outside for about fifteen minutes, can help us measure the size and shape of the components of the Antiope system.  We want as many as possible to try to observe the eclipse since the detail of the object's shape that we can derive is proportional to the number of places from which the eclipse is observed.  Opportunities to see eclipses of stars visible with binoculars by double asteroids are very rare; this is the brightest star to be eclipsed by the unique Antiope pair that has been predicted since predictions of eclipses by Antiope and by many other asteroids began in 1975.  Amateur and professional astronomers from as far away as France are converging in the Sacramento Valley to try to observe this eclipse.  IOTA is holding their annual meeting at Sierra College in Rocklin, north of Sacramento, so they can best plan for this event.