Mercury Revealed

The data sent by the Messenger probe which passed Mercury on Monday has started to arrive at Earth. The pictures revealed some parts of the surface that were earlier missed by the Mariner 10 spacecraft (in the 70s). The probe went as close as 200 km to Mercury. It is expected to get into orbit in another 3 years time.

-Mohit Gidwani

Mission Update : Lunar Reconnaissance Orbiter

Mission Overview

The Lunar Reconnaissance Orbiter (LRO) is the first mission in NASA's Vision for Space Exploration, a plan to return to the moon and then to travel to Mars and beyond. LRO will launch in late 2008 with the objectives to finding safe landing sites, locate potential resources, characterize the radiation environment, and demonstrate new technology
Read more about it at:
http://lunar.gsfc.nasa.gov/index.html


~Mohit Gidwani

The apparent truth of the universe-gravitational lensing

“What we see is not the complete truth”, and our universe seems to follow this statement quite naturally. We already know how the presence of the gas envelope around our planet known as the atmosphere distorts and varies the brightness and size of celestial objects under observation by multiple refractions and other optical phenomena like interference. But that’s not all when we study this art of eliminating the illusive and apparent behavior of what we see up there in the sky.

We face another gravitational-optical phenomenon known as gravitational lensing which is capable of varying the brightness and size of a distant celestial object that we might be interested in observing. Gravitational lensing occurs when gravity from a massive object, like a galaxy or a star cluster, warps space time, bending everything in it including the paths followed by light rays from a bright background source. Due to this, a time lapse is observed for the light to reach the observer leading to magnification and distortion of the apparent image of the background source. It is also known as gravitational mirage in the case where there are multiple images for a single source.

In the above image we can see four images of the same distant quasar appears around a foreground galaxy due to strong gravitational lensing.

Since our universe is taken as to be a three spatial dimensional system the gravitational lens does not have a focal point but a focal line. It has also been observed that maximum bending occurs closest to the center of gravitational lens which is opposite to that for an optical lens. Also, gravitational lensing can work on all kinds of electromagnetic radiations and not just visible light.
One of the most interesting observations was made by st. Petersburg physicist Orest Chwolson, he observed that if the source which can act as a huge lensing object, and observer lie in a straight line, the source’s apparent image would be a ring behind the actual source referred to as Einstein ring.

There are three classes of lensing -
1. Strong lensing - which causes visible distortions like in case of Einstein rings and multiple images.
2. Weak lensing - which causes very minute distortions of low degree.
3. Micro lensing - which leads to only brightness variations and no distortions.
A gravitational lens acts like a huge telescope that makes faint objects appear brighter and larger. This makes the study of distant objects comparatively easy.
When someone really wants something with all his heart the entire universe conspires in favor of it…guess it is very well doing so for the researchers all this while.

-kuhu shukla

References:
1. Wikipedia.com
2. Nasa.gov