Antares Occultations for India in 2005

Scorpio and Orion are two really beautiful constellations in the sky that many people are aware of, and have seen sometime or other. Of these, it is Scorpio (seen in the South-South East late in the evening, month of June), which will be making news this year. The reason being the repeated Lunar occultations of a bright star in Scorpio - Jyestha or Antares, by the Moon.

A Lunar occultation could be the passing of the Moon in front of any other distant celestial Object - a Planet, other Solar System objects, a distant Star or a deep sky object. Of these, the passage of the Moon in front of the naked eye Planets or bright stars is an event that is most accessible to people without any serious observing equipment.

2004 May and November, we had the beautiful occultations of Venus, by the Moon. In 2005,  there are many repeated occultations of Jupiter, by the Moon. Unfortunately, not one of the Jupiter occultations is visible from India. In recent times, there has also not been any bright star occultation by the Moon, seen from India. And 2005 is the time for a bright star occultation, again.

When it is an occultation of a star by the Moon, it is more of an useful event than the occultation of a Planet by the Moon. The usefulness lies in the fact that, every bite of data related to such events – that is, the exact timing of such an event observed from an exactly located place on Earth, goes into the modeling and determination of the Lunar limb profile – the exact contour of valleys and mountains around the visible disk of the Moon.

The website of the International Occultation Timing Association

 http://www.lunar-occultations.com/iota/iotandx.htm 

gives many useful details about doing such occultation observations. Accurate timing of a Lunar occultation of a distant star from any one given location on Earth, would be one bite of useful data that any student could contribute towards obtaining this Lunar Limb profile. This is a useful contributory observation and  with brighter star occultations, the possibilities of beginning amateur astronomers with very limited equipment, also contributing to these bites of data, is increased.

The website 

http://meghnad.iucaa.ernet.in/~aaa/occultations/ 

also gives information related to predictions of occultations for locations in India.

Coming back to Antares occultations in 2005. The Star is Jyestha or Antares - the brightest star in Scorpio. It glows with a reddish hue,  that gave it the name of Antares - or a rival to Mars or Ares.

This bright star of Scorpio, will be repeatedly moving behind the Moon, on several dates, in the year 2005. On the 4^th of Febraury and 27^th of March, the occultation should have been visible from India, except that, it turned out to be a day time event and not possible to view with even modest equipment. On the 27^th of April, Antares went behind the Moon, as seen from Delhi, at 5:25:35 AM. By this time, day was already breaking. However, members of Amateur Astronomers Association, Delhi, did observe this disappearance with a 4 inch telescope and obtained the timing stated above. (The observers were Vidur Prakash, Sneh Kesari, Vikrant Narang, A. N. Siddiqui, Munish Lagad, Jagdeep and Shilpi.) The predicted timing for the event was 5:25:03 AM., while the actual observed time was 5:25:35. This small difference of 32 seconds between the predicted timing and observed timing is the data required for modelling of the Lunar Limb profile. Since the location of the Moon, the star being occulted and the location of the Observer are well determined – it becomes possible to calculate the predicted occultation time by assuming an existing limb profile for the Moon – to begin with this would have been assumed circular. With data being added from Lunar occultations and other studies this limb profile is continously updated to give a better picture of the contour of valleys and mountains around the rim of the Moon.

The reappearance on the 27^th of April, was set for 6:35 AM. But, it did not turn out to be possible to view the event then, with modest equipment, in full daylight.

A better event of the same kind is ahead on the 20^th of June 2005. Late in the night, on the 20^th, the disappearance and reappearance of Antares behind the Moon can be witnessed in dark skies, from all over India. The only drawback being that the Moon is very close to being full and is quite likely to play spoilsport towards better visibility of the occultation. As seen from Delhi, the disappearance of Jyestha behind the Moon, happens at 11:02 PM in the night and Jyestha reappears, from behind the Moon, at 22 minutes past midnight 20^th-21^st of June 2005. This event, on the 20^th of June, will be really worth watching, from all over India. The timings of disappearance and reappearance for a few cities are given in the table below.

The exact timings, within India will not vary too much from one location to another, so that, if for some reason, you are unable to obtain predictions for your location, start observing from around 10:45 PM on the night of 20^th June. Viewing the Moon through a pair of binoculars may start showing the star Antares in the field of view, in a short while, around that time. Wait for the exact moment when the star moves behind the Moon and note that as the disappearance time and also record the reappearance time.

The important thing is to know your location exactly and be able to time the event with precision. Location can be pinpointed accurately by obtaining high resolution maps of your locality from a local Archeological Survey outlet and reading off the lattitutde and longitude for you area from the map. One simple method of obtaining accurate timing may be to synchronise your watch/stop clock (to the exact second) using the time signals that are given at every one hour, in all the AIR radio channels. 

Observations of Lunar Occultations and the more exciting Asteroidal occultations are very interesting contributory projects that senior school and college students could be easily involved in, and come up with published and useful data of their own, that will be used for studying the Moon. Surely, sufficient excitement for all of us to bring out our  telescopes and put them to use immediately?

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