90 Antiope's Dual Asteroid Occultation - The Results

After occulting each other (and the star LQ Aquarii), 90 Antiope made a memorable day this past July 19. That dual-asteroid occultation was a treat for those on the Pacific coast, becasue these events are the events you don't see everyday. After waiting almost two months, we have finally got the report in from Sky & Telescope concerning what actually happened that commemorated day. Although asteroid occultations are not very impressive as grand-scale total solar and lunar eclipses, asteroid occultations "can be just as rewarding — and sometimes have far more scientific value," Kelly Beatty writes in his post, Antiope Occultation Yields Double Bonanza.

4 Days before occultation. Photo Credit giant Keck Telescope: W. Merline & others

Considering carefully the last remark, 'far more scientific value' (from the quote above), astronomers have realized the complexity and scientific values of this occultation. To describe this event in detail, from our earlier post entitled 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.

Sky & Telescope points out three advances in why this occultation was so beneficial, despite the low magnitude of the binary pair and bright condition of the moon.*

1) Despite the fact that 90 Antiope is just at magnitude 8.27 together (9.02 each separate), the star occulted was rather bright (magnitude 6.7) and could be viewed easily by small, personal telescopes.
2) Visible, 90 Antiope is comprised of two bodies, each approximately 90 kilometers across, which when viewed in a stellar occultation, is very impressive. (90 kilometers = 55 miles).
3)The predicted track of occultation visibility crossed a well-populated region of the United States and portions of Canada.

"I'm happy to report that Antiope did not disappoint," Beatty writes. Fifty plus observers plotted their estimations concerning the occultation, as the plot below demonstrates. If you can note, the southern object has a rather well pronounced missing side, perhaps a crater, but astronomers are not entirely sure. Since 90 Antiope was discovered in 1888 by German astronomer Robert Luther, many observers have watched these objects in their celestial course; a myriad have noted that irregularity in perfect proportion.

Each multicolored line shows an approximate estimate on the path of occultation. Credit: IOTA, David Dunham

Concerning the actual occultation of LQ Aquarii, astronomer William Merline (leader of a team from the Southwest Research Institute; giant Keck Telescope in Hawaii) had predicted that each component of 90 Antiope would "clip" the edges of the star. Because of this, a 'partial' occultation is granted, but no-one expected that the gap would be that wide. "A few observers in the middle had no occultation by either component," explains David Dunham, IOTA's president. "We're debating whether to call these central miss observations 'Moses chords' or 'Hercules chords', for threading the Pillars of Hercules to gain new knowledge."


In a grandiose conclusion, this occultation has provide a significant amount of scientific information. Sky&Telescope ranks it to be "among the most remarkable and scientifically valuable in recent years." Although pure irony, in the era of the 1970s, when astronomical understanding was nothing compared to today**, astronomers argued that there was no such thing of dual asteroids (See our other article, under title 'The History...Binary-Asteroids'). David Dunham was one that actually supported this 'outlandish' idea, and he finally did succeed in his efforts. This was resolved due to the fact of Galileo and Ida & Dactyl (lower portion of article). Today more than 200 multiple asteroids are known. (I recommend that link immensely for study).

Ida and Dactyl, thanks to Galileo spacecraft.

Sky&Telescope: "You can click here to learn more about IOTA and here for predictions of upcoming occultations that you might be able to observe. And you'll find several articles right here on SkyandTelescope.com about how to view and record occultations."

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*Sky&Telescope takes credit for the formation of the ideas, I take credit for the embellishment of them - and they are embellished.  
**This is a eloquent simile, yes, there was astronomical understanding in the 1970s, but becasue of today's astronomy knowledge and equipment, we know much more. 

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.