Rare Eclipse of a Star Visible with Binoculars by the Double Asteroid 90 Antiope

n. Calif. to w. Montana Mon. night/Tues. am, July 18/19

The eclipse of the star LQ Aquarii will last up to 30 seconds in a 125-mile-wide path from the San Francisco Bay area to Boise and w. Montana

A few who happen to be in the right place might see two eclipses, one by each component of the Antiope pair

ANYONE in the path can help accurately measure the size and shape of the objects by making simple observations of the eclipse

The International Occultation Timing Association (IOTA) seeks as many observations of the eclipse as possible

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. 

You don't have to be an amateur astronomer to contribute; the charts on this Web site will allow anyone with binoculars and only a 
rudimentary knowledge of the sky to find the star, LQ Aquarii.  Binoculars should be steadily held, such as against a fence post or 
a car's roof, to give a good view.  Those with small telescopes and camcorders could make an especially accurate record by finding the 
star, then recording it by aiming the camcorder into a wide-field eyepiece. Time accurate enough for this event can be obtained from 
this time Web site. Basically, try to time the eclipse with whatever resources you have, even if that's just your eyes and ability to 

The sections below give more information about this unusual event.  The first section explains what will happen.  The second section 
about the path tells when the eclipse will occur, depending on your location, and gives maps showing the location of the predicted path, 
and the wider uncertainty zone where it may occur.  The third section tells how to find LQ Aquarii, the star that will be 
eclipsed, including a simple full-sky chart and binoculars-view chart to find the target, which will be rather close to the Moon.  
The fourth section tells how you might be able to time the eclipse, either by counting, with a watch, or with a camcorder, and then how 
to report your observation.  If you observe the star, we want to know, whether or not you actually had an eclipse, since the closest 
"miss" observations will constrain the shape of Antiope that we determine.  Also, many asteroids are known to have small moons, and 
Antiope could have one that could eclipse LQ Aquarii briefly for some lucky observers outside the actual main eclipse path.  Other 
short sections describe coordinated plans to observe the eclipse, report observations, and describe a meeting of IOTA at Sierra 
College in Rocklin, north of Sacramento, that will occur this weekend before the occultation - all are welcome at the meeting.
The sections below give more information about this unusual event. 


The asteroid Antiope consists of two nearly equal objects, each about 55 miles (90 km) in diameter, so each will produce an eclipse 
(astronomers call the event an "occultation") with a duration of up to about 30 seconds.  The predicted orientation of the objects, 
and projection of the shadows on the Earth's surface, indicates that an occultation by one of the objects should be visible in a path 
about 125 miles (200 km) wide, with the disappearance of the second object occurring about a minute after the disappearance by the first 
object.  Since there could be other small objects in the Antiope system, observation from at least 3 minutes before to 3 minutes 
after the central time for your area is recommended.  Most observers within the path will have an occultation by just one component, with 
the leading component occulting the star for observers in the southern part of the path, and the following component occulting in 
the northern part.  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.  In addition, a large crater is predicted to be on the leading edge of the leading component.  A 
diagram showing the predicted orientation of the objects (north up), and an arrow showing the direction of motion relative to LQ Aquarii, 
is shown below.

When LQ Aquarii is occulted, the event should be a sudden spectacular disappearance to the very faint level of light of Antiope.  With 
binoculars, you won't see Antiope, but those with 8-inch and larger telescopes might see the asteroid, which is magnitude 12 on the 
logarithmic "magnitude" scale used by astronomers.  You don't need to see Antiope, you just need to see LQ Aquarii to see the 
occultation and make a useful observation.  The drop in brightness will not be instantaneous because the star is a red giant with an 
estimated angular size of 0.002 arc seconds that subtends 2.7 km at Antiope.  The disappearance and reappearance for a central 
occultation should last 0.9 second, enough to notice even with visual observations, and this will be prolonged for grazing events; 
an observer near the edges of the path for a component could have a grazing or even partial occultation of the star that might last even 
ten seconds.  The geometrical occultation (occultation of the center of the star) will occur at the 50% level of the light of the star, 
so you should try to estimate when that occurs, as well as the start and end of the disappearance (and reappearance).  Visual observers 
can just try to call out or note the time of the 50% level, or of the complete disappearance, and try to estimate the observed 
duration; if you use a tape recorder (or a camcorder, using its audio recording capability for the observation), you can call out 
the events with sharp calls like "start", "mid" (if you can estimate the 50% middle), and "end", then say whether it was a "D" 
(disappearance) or "R" (reappearance).

Observers using telescopes with video equipment should slightly defocus the light of the bright star to prevent saturation; more 
about this is discussed in IOTA's more technical account here.

To get an idea of what to expect, you might look at some YouTube videos of past occultations; here is a Web page with links to them.  
Look in the asteroidal occultation videos section. A good one is the occultation by Iduna, a grazing event with three 
occultations of the star, like what might happen with the Antiope occultation, but with longer event durations.

It is important to realize that these predictions have errors; the path for an occultation of an 8th-mag. star by the asteroid (217) 
Eudora ended up about 60 miles north of the prediction, causing nearly all, of about two dozen stations deployed for that May 29th 
event, to have no occultation, and there are similar issues with Antiope's star, LQ Aquarii.  Also, the orientation of the Antiope 
pair predicted for the time of the occultation may be in error; it's possible that the Antiope components will be more widely separated 
such that observers close to the actual central line, wherever it may be, might thread between the components with no occultation by 
either.  Observations are planned to try to improve both aspects of the prediction, and if they are successful, we may be able to update 
the path prediction a few days before the event.  But any update will have its own errors, so observations from an area much wider 
than the predicted path are needed to have a reasonable chance to accurately map the profiles of both Antiope components, which is our 


 The eclipse (or occultation) path is shown in a small-scale map of North America below.
Working backwards in time, the path is over northern California, with the southern limit passing through San 
Jose and Stockton at 3:25 am PDT (10:25 Universal Time, or UT).  With errors as large as 60 miles, the actual s. limit for the 
southern component could be much farther north or south, we think anywhere from Vallejo and Sacramento to Soledad and Merced.  The 
path passes over the northern Sierra region of n.e. Calif. and the Reno (near the predicted s. limit) region of Nevada at 3:24 am PDT; 
s. cen. Oregon & n.w. corner of Nevada at 3:23 am PDT; eastern Oregon and west-central Idaho (Boise region) at 4:22 am MDT (10:22 
UT); Challis Nat'l Forest, Idaho at 4:21 am MDT; n.w. Montana at 4:20 am MDT (some morning twilight, Sun alt. -10 to -12 deg.); s. 
Alberta (Lethbridge & Medicine Hat) & n.cen. Montana (Cut Bank) at 4:19 am MDT (dawn with Sun alt. -7 to -10 deg.); and s.e. Alberta 
and s.w. Saskatchewan (n.w. of Saskatoon, which could have an occ'n) at 4:18 am CST (10:18 UT).  The Sun altitude of only about -6 deg. 
at Saskatoon will hinder observation with binoculars, but not with telescopes, where the star can be found 20 minutes or more before 
the occultation, when the sky will be dark enough to see the fainter stars near it, and follow the target in the brightening sky.     

A map showing the shadows of both components as they are predicted to cross northern California is below.
Other maps like this, showing the predicted zone between two dark gray lines, and others showing the wider range where an occultation 
by at least one of the Antiope components could occur, is on IOTA's more detailed Web site.


The target star, LQ Aquarii, will be in the southern sky about ten deg. south of, and a little to the right of, the bright gibbous 
Moon.  First, determine the diameter of the field of view of your binoculars, or of the finder scope of your telescope.  Binoculars 
typically have fields of view five to ten degrees across, while those of telescopic finder scopes usually are three to six degrees 
wide.  Binoculars usually have a statement near one of the eyepieces stating either the size in degrees, or the distance across that can 
be seen at a distance of 1000 yards.  If the distance across is 260 ft., the view is 5 deg. across; if it's 525 ft., the view is 10 deg. 
wide.  If there is no statement, you can estimate the field of view by looking at the Big Dipper.  The two "Pointer" stars at the front 
of the bowl of the Big Dipper are 5 deg. apart, while the two stars at the top of the bowl are 10 deg. apart.  At the time of the 
occultation, the Big Dipper will be low in the north opposite the direction to the Moon, but you can use the Big Dipper to measure the 
size of your field of view anytime before, when the Big Dipper will be higher in the northwestern sky.

The star charts below show how to find LQ Aquarii.  There are two versions of each chart, a labeled and unlabeled version.  The 
unlabeled version doesn't have any lines connecting the stars and no labels, to give the appearance you'll see; only the target star 
is underlined to point it out.  The labeled charts have the target star prominently labeled "LQ", the names of stars around it, and 
the names of the constellations in the area in all caps.  You can use the labeled charts to follow the descriptions below.

For this event, so close to the Moon, you don't really need the full-sky chart, but it is included to give the overall context, to 
show the Big Dipper for finding the field of view, and possibly to use at about the same time some night before the event when the Moon 
won't be near the target star (but the Moon will be closer to full and brighter before the night of July 18/19).  The full-sky charts 
have N, W, S, and E on the horizon circle to mark the directions north, west, south, and east, respectively.  All of these charts, 
to save ink if you print them, show the stars as black dots on a white background; if you import the chart file into the Windows 
Paint program, you could reverse this to show the stars as white on a black background).  The names of the brighter stars of Aquarius 
are shown, but they are a little fainter than the stars of constellations like Pegasus above it, and nearly overhead.  The 
names of just a few other prominent constellations, and of the two major planets and of the brightest stars, are also given.

The full sky charts are here, labeled......

and unlabeled.....
On the night of the occultation, you can just point your binoculars at the Moon, then move south (down) to find the star Hydor about 6 
deg. below and to the left of it, then tau (actually, tau Aquarii) another 6 deg. below and to the left of it, and then LQ is just 2.5 
deg. (generally, half or quarter of a binoculars field of view) above tau.  Hydor at magnitude (mag.) 3.7 is about five times 
fainter than the Pole Star while tau Aquarii is about six times fainter (mag. 4.0); LQ is fainter than either of them, at mag. 6.7, 
it's about ten times fainter than tau Aquarii.  Another way to find tau Aquarii is to find the bright star Fomalhaut about 15 deg. above 
the southern horizon, and move north to find Skat (at mag. 3.3, about four times fainter than the Pole Star but a little brighter 
than Hydor) and then tau.  This has the advantage of avoiding looking at the bright Moon with your binoculars or finder scope, 
since that will make you lose any dark adaptation and it may take several seconds to see the fainter stars with the binoculars after 
moving away from the Moon's glare.  Look at the more detailed charts below to see how to use your binoculars to find LQ.

The labeled full sky chart has a rectangle showing the area of the intermediate chart, which are given below.

The intermediate charts are here, labeled......
and unlabeled......

These charts have "up", the direction to overhead, at the top of the chart, that is, the view is oriented as you should see it at the 
time of the occultation.  LQ (short for "LQ Aquarii") is shown at the center of a circle with a diameter of 5 deg., the view of some 
binoculars.  But some binoculars have a 10 deg. field of view, twice the size of that circle.  As you can see, with the 5 deg. field of 
view, if tau is placed at the bottom of the field, then LQ will be near the center.  The Moon is actually only a half-degree across, 
not nearly as large as shown on the chart, but it will be very bright.  The faintest stars on this chart are 6th mag., the faintest 
that can be seen with the naked eye on a dark night.  But with glare from the bright Moon, you won't see the fainter stars by naked eye, 
but they will be easily seen with binoculars.  You can use this chart to move your binoculars field of view (that is, to "star hop") 
from the Moon to Hydor, then to tau.  Or you can use it to star hop from Fomalhaut to 88, then up to Skat and tau.  Another approach 
might be to locate the relatively bright star Sadalmelik, and the distinctive Y-shaped "Water Jug" to its left, then work your way 
down to tau, but that will not be easy with the bright Moon on the night of the occultation.  You should use the more detailed 
binoculars view below to find and positively identify LQ. 

Another approach, useful for telescopes or binoculars firmly mounted on a tripod, is to pre-point to a brighter star that will be in the 
same direction relative to your local horizon sometime before the occultation.  Since the Earth is rotating, the view with a fixed 
instrument constantly changed, and you can take advantage of that with this "pre-point" technique.  The pre-point line, called the 
"pre-point line of declination", is shown on the labeled chart, with tick-marks at one-minute intervals and the pre-point time labeled at 
5-min. intervals.  The times are labeled in UT; subtract 7 hours for PDT.  For example, if you point your binoculars or finder scope (or 
a wide-angle, low-powered view in a small telescope) to the star "nu" (nu Aquarii) shown near the right side of the intermediate 
chart at 1:49 am PDT (8:49 UT), then clamp the tripod or telescope mount so it doesn't move, then LQ will be near the center of the 
field of view at the time of the occultation.  For this event, there's some value in pre-pointing because you can do it at a 
greater distance from the glare of the Moon so you can see the fainter stars more easily.  It's a good idea to visually check one 
of the pre-point opportunities just to see if a tree or building doesn't block the view; if it does, you need to find another place 
to see the occultation (but this shouldn't be too difficult a problem since the event's altitude is almost 40 deg., not quite 
halfway from the horizon to overhead.

The large rectangle on the labeled version of the intermediate chart shows the area of the binoculars charts that are given below. 

The binoculars charts are here, labeled.....
and unlabeled....

They are similar to the intermediate charts, direct views with "up" at the top of the page.  If your finder scope has a right-angle 
prism, it may give a reversed view; in that case, turn the printed page with the chart over so you're looking at the back side, and 
shine a flashlight from underneath so you can see the reversed view.It shows that when you locate tau and put that star near the bottom 
of your field of view, LQ will be near the center (of course, if the field of view is 5 deg.), then you should see the star 70 a little 
above and to the left of LQ, and about the same brightness, and the star 74 in the lower left, and some of the other stars.  You should 
be able to see most of these stars with binoculars, but the faintest ones might be washed out, or hard to see, with glare from the Moon.  
To reduce that, you might try to block the Moon with a high tree limb, but you don't have much leeway, with LQ only ten deg. below.  
Note that the brighter star tau has another star, "69", a little brighter than LQ, below and to its right; that will help you confirm 
that you've located tau, and don't confuse it, for example, with Hydor.  Skat also has a star near it, "77", but that star is almost 
directly below Skat, while 69 is more to the side of tau.  The pre-point line of declination shows that the star 54 provides a good 
pre-point opportunity at 3:06 am (10:06 UT), but I think that LQ will be easier to find directly.  Many more pre-point opportunities 
and extensive charts are given on the more technical Web page.

Note that the pre-pointing information described above is for California's Central Valley; the times will be almost a minute later 
in San Francisco, and will be earlier at locations farther northwest in the path.  The charts were also prepared for the Sacramento area, 
but they will not differ significantly for other locations.  For Idaho, Montana, and central Canada, the Moon, Aquarius, and 
Fomalhaut will all be lower in the southern sky, but the Big Dipper will be higher above the northern horizon.


We are most interested in knowing the length of the eclipse (or occultation) at your location; measure this as well as you can.  The 
simplest way is to just start counting when the star disappears, and stopping when it reappears, remembering the number you were at when 
it reappeared.  Count out loud, but softly, not so loud that you will wake the neighbors.

STOPWATCH (or digital watch with stopwatch function):A better way to time the length (or duration) of the eclipse is with 
a stopwatch.  Most digital wrist watches have a stopwatch function; check your watch for this and use it for the occultation.  Even 
better is to use two stopwatches, starting them both at the disappearance, and stopping only one of them when the star 
reappears.  Go to your computer with the other (still running) stopwatch and watch the display of the seconds at the time web site 
at http://www.time.gov/ (bring up this Web site before the occultation, and click on your time zone shown on the map to start 
the time display, which will take several seconds before it starts).  Stop the running stopwatch when the seconds change from 59 to 00 at 
the change to the next minute, and write down that time.  Then read the stopwatches (or digital watch with stopwatch function) and write 
down their elapsed times. 

Another way, if you have a tape recorder or small digital audio recorder (or a camcorder that records sound as well as video, can 
be used like an audio recorder), is to start a recording (it must be continuous, not voice-activated) and call out the time three or four 
minutes before the occultation (such as, at 3:21:00 am for those in California's Central Valley), go outside to your observation spot 
with the recorder, call out "D" when the star disappears and "R" when it reappears (or, thinking it like a light, "off" and "on"), 
then go back inside and call out the time you see on the time web site display.  Then later (can be the next evening, just soon enough 
so that you have a good recollection of what happened), play the recording back, using a stopwatch, to measure the duration of the 
occultation, and the durations from the time calls before and after the occultation to your disappearance call. 

An audio recording is useful to have a record of what happened; we would also be interested in knowing the times that you started 
watching, and stopped watching, the star (just say to the recording when those occur).  We recommend watching the star starting three 
minute before the predicted time (starting at 3:22 am PDT in California's Central Valley) and stop watching three minutes after 
the predicted time (3:28 am PDT in the Central Valley).

If you have an astronomical CCD, the best way to use it to time occultations is by taking a long exposure while letting the stars 
trail; for information about this technique, click here.

Even better than an audio recording would be a video recording showing the star.  In the third paragraph, it was described how a 
camcorder might be aimed into a low-power eyepiece of a telescope to record the star.  More information about timing occultations is here.
We are trying to coordinate observations of the occultation, to cover the predicted path, and its wider uncertainty zone where an 
event could occur, as densely as possible with approximately equally-spaced stations.  If you plan observations from an 
observatory, or can record the occultation either with telescopic visual, video, or drift-scan CCD observations, please let us know so 
that we can include you in our plans, and don't just duplicate your effort with one of our mobile stations.  If you are mobile, let us 
know and we will suggest a band about a mile wide, specified on a Google map Web site, where you can select an observing site to most 
effectively increase our coverage of the occultation.  Details are on our more detailed Web site about the occultation.


We don't care if clouds covered the star, or you slept through the alarm, or didn't watch LQ Aquarii at the right time for any other 
reason.  But if you did watch, or record, this star at the right time, we want to know, whether or not you had an occultation.  
If you had no eclipse of the star, just let us know that fact and send your location in an e-mail message to 
reports@asteroidoccultation.com .  We prefer that you use a GPS receiver, Google Earth, or the interactive google map at this site,
to determine your longitude, latitude, and elevation above sea level.  If you have any trouble doing this, just send the address of 
your observation point, including the approximate distance (just by pacing; we only need to know with an accuracy of 50 feet or 20 
meters) the distance from the center of the nearest road, and from the nearest cross street.  Also, if possible, tell us the times that 
you started and stopped watching (or recording) LQ Aquarii.

If you had an occultation, we also want to know your timings of the disappearance and reappearance, their durations if you timed them, 
and your estimate of the accuracy of those times (visual timings are typically accurate to about 0.3s, but give a different value if you 
think your accuracy was a little better or worse than this).  If you just timed the duration, provide that.  If you only counted for the 
duration, repeat your counting a few times, using a stopwatch (or digital watch with stopwatch feature) to measure the durations, and 
report those.  If you don't have access to a stopwatch or digital watch to do this, you might try it watching the time display at the 
time Web site given above, or send us your telephone number in an e-mail message, and we'll call you and ask you to repeat the count 
over the phone so we can time it. 

If you were able to measure the local time of the disappearance from the time Web site (or by other means as described above), report 
that (but give the Universal Time hour, which will be 10 for all of North America, rather than the local time hour), and also the time 
of the reappearance by adding the duration time to the disappearance time, and the estimated accuracy. 
Reports of observations of the occultation, whether an occultation happened (positive) or not (negative), should be sent to 
reports@asteroidoccultation.com .  You should use this Excel report form.  When you save the file to your computer, change the name of 
the file, replacing "LastName" to your last name.  If you can't open or otherwise use the Excel file, write to the above reporting e-mail 
address; if necessary, a plain text version of the report form can be used.  Attach the completed form to the message that you send to 
reports@asteroidoccultation.com .  Note that LQ Aquarii is called HIP 112420 (number 112420 in the Hipparcos star catalog) on the Excel 
report form, and also on the prediction Web sites. 

If you video record the star, we'll want to analyze your recording to determine accurate event times.  Send us a message specifying your 
location (as described above) and saying that you have a video recording; you might play it back to report preliminary event times.  
We'll arrange to obtain a copy of your recording.  You might capture about a 30-second part of your recording to an .avi file on your 
computer using Windows MovieMaker as described here, and arranging with us to upload that file to an .ftp site so you 
don't need to physically send us your video tape. 


Results from observations that we receive will be posted on IOTA's asteroidal occultation results Web site.  A good example of results 
of another occultation, of the star HIP 13021 by the asteroid 135 Hertha that was observed on December 11, 2008, by observers in the 
path from Oklahoma to southern California, are shown in this figure.  The figure projects the observed occultation timings onto the plane 
of the sky at the asteroid, thus revealing the dimensions and peanut-shape of 135 Hertha.  Small telescopes were needed to see HIP 
13021 since it was about five times fainter than LQ Aquarii. 

We look forward to adding your observation to the outlines of the components of Antiope that we hope to obtain following the July 19th 


You are invited to attend the 29th meeting of the International Occultation Timing Association that will be held at the planetarium 
of Sierra College in Rocklin, Calif., northeast of Sacramento, on July 16 and 17, the weekend before the Antiope occultation. 
Astronomers from as far away as France and Germany will be attending the free meeting, open to all who might be interested in 
occultations.  We'll be discussing results from other asteroidal occultations, lunar events, and observing techniques, including a 
workshop on making observations from unattended video stations.  For more about the meeting, click here.

David Dunham, July 12, 2011
President, International Occultation Timing Association (IOTA)
Greenbelt, Maryland (but will be in n. Calif. for the occultation)
Phones home 301-220-0415; cell 301-526-5590 
office e-mail david.dunham@kinetx.com
home e-mail:  dunham@starpower.net .