Occultation

Here is yet another Astronomical Term - Occultation. Sounds weird but a simple term. An occultation is an event that occurs when one object is hidden by another object that passes between it and the observer. Does it sound familiar? Yes! Eclipses and Transits are also known as Occultations.

Every object in space move in a particular direction. By coincidence any two objects may come in the same line of sight from Earth which causes Occultation. The most famous occultation is the Eclipse.

Total Solar Eclipse

In case of Solar Eclipse, the Moon comes in between the Sun and the Earth. Hence the Moon and the Sun are in the same line of sight. The Moon appears to block the Sun from the view or the Moon occults the Sun.

But this is not the case in the Lunar Eclipse. In Lunar Eclipse it is the Earth that occults the Moon when observed from the Sun and not from the Earth. Hence Lunar Eclipse cannot be called the Occultation.

Position of the Earth, Sun and the Moon during the Total Solar Eclipse (left) and the Lunar Eclipse (right)

The term Transit is used when one object appears to move across the face of another object. Usually one of the object is small when compared to the other. The most famous transits are that of Mercury and Venus over the Sun.

Transit of Mercury over the Sun

Transit of Venus over the Sun

Enlarged Image of the transit of Venus

Transit of Io (Satellite of Jupiter) over Jupiter

The other types of occultation are when a star occults another star or when a satellite occults another satellite. This can only be observed through telescopes.

Dione (Satellite of Saturn) occulting Rhea (satellite of Saturn)

Another rare type of occultation is when a planet occults another planet. It is not seen very often. Here is the list of occultation by planets that occured in the past and the ones which will occur in the future.

* 19 Sep 1702 - Jupiter occults Neptune
* 20 Jul 1705 - Mercury transits Jupiter
* 14 Jul 1708 - Mercury occults Uranus
* 4 Oct 1708 - Mercury transits Jupiter
* 28 May 1737 - Venus occults Mercury
* 29 Aug 1771 - Venus transits Saturn
* 21 Jul 1793 - Mercury occults Uranus
* 9 Dec 1808 - Mercury transits Saturn
* 3 Jan 1818 - Venus transits Jupiter
* 22 Nov 2065 - Venus transits Jupiter
* 15 Jul 2067 - Mercury occults Neptune
* 11 Aug 2079 - Mercury occults Mars
* 27 Oct 2088 - Mercury transits Jupiter
* 7 Apr 2094 - Mercury transits Jupiter
* 21 Aug 2104 - Venus occults Neptune
* 14 Sep 2123 - Venus transits Jupiter
* 29 Jul 2126 - Mercury occults Mars
* 3 Dec 2133 - Venus occults Mercury

A simulation of Venus transiting Jupiter, as it did on January 3, 1818.

Occultation can also occur in other types such as Moon occulting a star, Moon occulting a planet, Planet occulting a satellite, etc.

Minutes before the Moon occulted the star Albedaran

Before Moon occults Jupiter

Jupiter occulting Europa (Satellite of Jupiter)

The most recent occultation took place on 10th May, 2008 when the Moon occulted the planet Mars at around 8pm IST. It was clearly visible even at Chennai.

Picture of the Month - March 2008

Blasting into a dark night sky, the Space Shuttle Endeavour began its latest journey to orbit in the early morning hours of March 11. In this stunning picture following the launch, the glare from Endeavour's three main rocket engines and flanking solid fuel booster rockets illuminates the orbiter's tail section and the large, orange external fuel tank. Embarking on mission STS-123, Endeavour left Kennedy Space Center's pad 39A, ferrying a crew of seven astronauts to the International Space Station (ISS). The cargo included the first section of the Japan Aerospace Exploration Agency's Kibo laboratory and the Canadian Space Agency's two-armed robotic system. Astronauts will conduct a series of space walks to install the new equipment during the 16-day mission, the longest shuttle mission to the ISS.

Planetarium Software

Interested in Astronomy? Love to look into the night sky? Being an amateur you would find it very difficult to identify stars and planets and other stuffs. But it can be made easy using certain Planetarium Softwares. These softwares show you how a night sky may look like at any time from any place. These softwares label every star so that you can identify it in the sky easily using the software. There are many such softwares available in the internet. I came across one such software which is very user-friendly.

Stellarium 0.9.1 is a free open source planetarium for your computer. It shows a realistic sky in 3D, just like what you see with the naked eye, binoculars or a telescope. It is being used in planetarium projectors. You can set your coordinates such as your location and time zone and look through the night sky. This software also shows you the planets, nebulae, galaxies, comets, meteors, etc. Every star, planet or a galaxy is labeled which makes it user-friendly. You can zoom into any stars or planets to know how it looks like in a telescope. You can also see the night sky of any time at any year. It even shows you the night sky of the year 2100.

Here are some of the Screen Shots of the software.

The full view of the constellations.

A shooting star passing near the Moon.

A zoomed in view of the Planet Jupiter.

A zoomed in view of a nebula.

You can download this software from this website.

http://www.stellarium.org/

Picture of the Month - February 2008

You must have known how Auroras look like from Earth. But how does it look like from space? This magnificient image gives you the answer. The International Space Station (ISS) pictured the above digitally sharpened image of the green aurora crawling over northern Canada. ISS reported that the auroras appears to crawl around like gaint amoebas, 300km above the surface. Still, the auroral electron and proton streams pose no direct danger to the ISS.

Picture of the Month - January 2008

This is a spectacular image of a waning crescent Moon and Jupiter, which is seen at the bottom right of the image. The four sources of light around Jupiter are its four bright satellites namely - Ganymede, Callisto, Europa and Io. These satellites are known as the Galilean satellites as it was discovered by Galileo when he looked up at Jupiter for the first time in his newly formed telescope. The satellites can be seen clearly even through a small telescope.