Roma occults Delta Ophiuchi on 8 July 2010 at 21:56 - 22:17 UT

by Paul Schlyter (

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Experienced sky observers can go directly to the links.

Asteroid no 472, Roma, was discovered by Luigi Carnera on 11 July 1901. Roma is 47 km in diameter and rotates ones every 9.8 hours. Roma's orbit is nearly a circle 2.55 times more distant from the Sun than the Earth's orbit. It resides in the main asteroid belt and one revolution in its orbit takes 4.06 years.

Delta Ophiuchi (δ Ophiuchi), with the proper name Yed Prior, is a red giant star in the constellation of Ophiuchus. δ Ophiuchi is a bright star with magnitude 2.7 which resides 170 light years away from us.

Shortly to the left (east) of δ Ophiuchi we find ε Ophiuchi, a yellow giant star 108 light years away from us. ε Ophiuchi has the proper name Yed Posterior. The name Yed is from the arabic word "The Hand" and the two stars δ och ε Ophiuchi were considered a mark of Ophiuchus' (the Snake Carrier's) hand when he carried the head of the Snake (Serpens Caput). The battle between the two must have been violent since the Snake was torn into two pieces: we also have the Snake's tail (Serpens Cauda) at the other side of Ophiuchus.

The night between 8 and 9 july, at 21:56 - 22:17 UT, (472) Roma passes in front of Delta Ophiuchi and hides that star for up to 5 seconds. The zone where this can be observed is as wide as the diameter of the asteroid, i.e. about 50 km.

Since Delta Ophiuchi is a red giant star with a very large diameter the disappearance and reappearance will probably not be instantaneous; instead we can expect to see the star fade away for perhaps one or two seconds, and then reappear at the same pace.

The map below shows the occultation zone over Europe:

and this is a global map also showing the zone over South America:

If you try to observe this occultation, please share your observations with me here afterwards and tell me what you saw. Please also give me your geographical position, preferably from a GPS (many modern cell phones have a GPS built-in). Negative observations (i.e. if you didn't see any occultation at all) are also interesting.

Keep a continuous watch on the star during about one minute at the expected time of occultation at your position: (check that your watch shows the correct time!!). It's good if you also note the time of any disappearance and reappearence you observe, preferably to the second if you can:

21:56 UT: Finland (bright twilight)
21:57 UT: Scandinavia (bright twilight), Northern Germany (twilight)
21:58 UT: Germany, France
21:59 UT: Spain
22:00 UT: Portugal
22:02 UT: Canary Islands
22:10-13 UT: Brazil (bright dusk in westernmost parts)
22:14 UT: Bolivia (bright dusk to daylight)
22:15 UT: Peru (daylight)

Good luck! Below are star charts to help you locate and identify Delta Ophiuchi - do practice finding it a few days in advance if you haven't located it before.

The northern sky from Scandinavia at the moment of the occultation:

This star chart is in black-and-white and more suitable for printing on paper:

More detailed star chart over Ophiuchus:

Photograph of Ophiuchus:

Old star map over the constellations around Ophiuchus:


An occultation is when one celestial body passes in front of and temporarily hides another celestial body. The most common type of occultation is when our Moon passes in front of and hides a star for up to one hour. The Moon can also pass in front of the planets, and the planets can pass in front of one another (extremely rare, won't happen again within our lifetime) or in front of stars (happens perhaps once every few years for reasonably bright stars). Our Moon can also pass in front of and occult our Sun, which happens between 2 and 5 times each year, and this we call a solar eclipse.

Asteroids are tiny "planets" which reside more or less everywhere in our solar system, although most of them reside in the main asteroid belt between Mars and Jupiter, and many also reside outside Neptune. The asteroids are very small but also very numerous (we know several hundred thousand asteroids), thus it's not at all uncommon that an asteroid passes in front of a star and hides it for a few seconds. But it is uncommon that an asteroid occults a star bright enough to be visible to the naked eye.


The visibility of the occultation to observatories and observers

IOTA: summary
IOTA: global map
IOTA: global map in larger scale
IOTA: map over Europe

EAON: global overview map and star charts and data

Detailed info about the zone: Latest From 30 June From 25 June From 27 May