Thursday, July 5, 2012

Jupiter Occultation

An occultation is an event in which a celestial body covers another, farther away object.  Usually, the term is used to describe an event when the moon covers a star or a planet or when a planet or an asteroid covers a far away star. On July 15th there will be a marvelous Jupiter occultation. The moon will cover Jupiter for about an hour (the exact time and durtaion of the occultation is  dependent on the observer's location).

Occultations can also contribute to science. During the 80s Uranos occulated a distant star. Photos of the events showed that just before and after the occultation the star blinked several times. The theory was that Uranus has a set of rings (like Saturn). When Voyager 2 reached Uranus it detected and photographed the predicted rings.

Seeing Jupiter's occultation is possible with the naked eye, but the look through a telescope, even using a small magnification, is marvelous. At first, two of Jupiter's large moons (Io and Europa) will disappear behind the moon, then Jupiter will disappear and then the other two moons (Ganymede and Callisto). It is best to check your local almanch for the exact times. The times given here are appropriate for Israel. Unfortunately the event will not be seen in the United States at all, but US observers will have a Venus occultation in August!

Here are some tips for occultation observations:

  1. Start early - Even the view of Jupiter so close to the moon is great so start watching it as soon as possible (Which will be when the moon and Jupiter rise in the morning)
  2. Check the weather - If weather is bad its worthwhile to drive off to somewhere else. Check with other astronomers in different cities nearby
  3. The occultation itself is very very short - a few seconds only, so make sure you know exactly when it happens.
  4. If you have two telescope use both. If you want to try and photograph as well you might need help. It is difficult to handle both at the same time and you might need to choose between visual observation or astrophotography
  5. Check out when the end of the occultation occurs. You will need to be very accurate for this, and you can divide your attention between visual and photography to the start and end of the occultation
  6. Do not forget the moons! Watch carefully until all moons are occulted.

Jupiter occultation times for Israel (GMT+3)
Date: July 15th (The night between Saturday and Sunday)
Occultation start: 4:03
Occultation end: 5:06
Jupiter Occultation - Illustration
Jupiter Occultation - Illustration