APOD 4.7

This weeks picture is of Saturn's moon Rhea, which has one of the oldest surfaces known. Rhea spans 1,500 kilometers making it Saturn's second largest moon after Titan. Estimated as changing little in the past billion years, Astronomers believe Rhea has remained unchanged in a billion years! Rhea contains craters that are so old they are no longer round and have jagged edges. Rhea's rotation is locked on Saturn like our own moon and the picture shows the side of Rhea that is constantly facing Saturn. Rhea is made up of mostly water-ice (whatever that is)but it is believed to be made of 25 percent rock and metal. The robot Cassini took this picture last month from 350,000 kilometers away! It's amazing that a quality image like the one above can be taken at such a far distance.

Biography: Subramaniam Chandrashekhar

Subrah Chandrasekhar, known to the world as Chandra was born on October 19, 1910 in Lahore, India. Subrah was nephew to Nobel-prize winning physicist C.V. Raman. He received most of his school education by private tuiton and graduated from Presidency College Chennai in 1930 with a degree in physics. In July after he graduated, Chandrasekhar was awarded a Government of India scholarship to pursue graduate studies at the University of Cambridge, where he was admitted to Trinity College and became a research student of Professor R. H. Fowler. On the way to England Chandrasekhar discovered his biggest astronomical success the astrophysical Chandrasekhar limit. The limit describes the maximum mass of a white dwarf star, or the minimum mass above which a star will ultimately collapse into a neutron star or black hole. When Chandra first proposed this limit during his fellowship at Trinity college in the 1930's, it was obstinately opposed by Arthur Eddington and much to Chandra's frustration none of the established physicists in Europe came to his rescue. This episode had a bitter impact on Chandra resulting in his move to the University of Chicago in the United States and in his choice of moving to another research topic. Chandra, however, compiled all his work on the topic of stellar structures into a book for posterity. This also subsequently led to his style of working continuously in one specific area of physics for a number of years and at the end of that period compiling a book on that topic. As a result, Chandra has left us with great expositions on different topics. Chandrasekhar developed a style of working continuously in one specific area of physics for a number of years; consequently, his working life can be divided into distinct periods. He studied stellar structure, including the theory of white dwarfs, during the years 1929 to 1939, and subsequently focused on stellar dynamics from 1939 to 1943. Next, he concentrated on the theory of radiative transfer and the quantum theory of the negative ion of hydrogen from 1943 to 1950. This was followed by sustained work on hydrodynamic and hydromagnetic stability from 1950 to 1961. In the 1960s, he studied the equilibrium and the stability of ellipsoidal figures of equilibrium, but also general relativity. During the period, 1971 to 1983 he studied the mathematical theory of black holes, and, finally, during the late 80s, he worked on the theory of colliding gravitational waves. Subrahmanyan Chandrasekhar tragically died of heart failure in Chicago in 1995. In 1999, NASA named the third of its four "Great Observatories'" after Chandrasekhar. The Chandrasekhar number, an important dimensionless number of magnetohydrodynamics, is named after him, as well as the asteroid 1958 Chandra.
Works Cited
Wali, Kameshwar C. (1991). Chandra: A Biography of S. Chandrasekhar. Chicago: The University of Chicago Press.
Wali, Kameshwar C. (ed.) (1997). Chandrasekhar: The Man Behind the Legend - Chandra Remembered. London: imperial College Press.
"The Man Behind the Name." Subrahmanyan Chandrasekhar. 29 Aug. 2006. Harvard U. 8 May 2008 .

APOD 4.6

This weeks photo was taken in Chile last October and shows a faint glow which is the gegenschein. Gegenschein is a faint brightening of the night sky in the region of the ecliptic directly opposite the Sun. The gegenschein is so faint that it cannot be seen if there is any moonlight or light pollution, or if it falls in the vicinity of the Milky Way. The orientation of the ecliptic at this time of year makes it a favorable time for trying to view optical phenomena associated with dust in the plane of the planets. The zodiacal light and the gegenschein which is German for counter-glow, often easily viewed in the tropics, are seen in the morning sky for our latitude in September and October. Also visible in the background is the Andromeda galaxy in the lower left as well as the Pleiades. During the day, a phenomenon similar to the gegenschein called the glory can be seen in reflecting air or clouds opposite the Sun from an airplane.

APOD 4.5

This is a photo of specifically Messier 86 which is one of the brightest galaxies of the Virgo Cluster Galaxies, and is situated close to the cluster's center. With well over a thousand members, the Virgo Cluster is the closest large cluster of galaxies. On average the cluster galaxies are measured to be about 50 million light-years away. M86 was discovered and cataloged by Charles Messier on March 18, 1781 when he also cataloged 7 more nebulous objects in the same region of the sky. This bright giant galaxy is either an elliptical of type E3 or a lenticular galaxy of type S01. M86 is the galaxy which has the fastest approaching velocity, and thus the highest blue shift, of all Messier galaxies.

APOD 3.4

Stickney crater is the largest crater on Phobos, which is a satellite of Mars. It is located at 5°S 55°W on Phobos and is 9 km in diameter, taking up a substantial proportion of the moon's surface. It is named after Chloe Angeline Stickney Hall, wife of Phobos's discoverer, Asaph Hall. It has a smaller, unnamed crater within it, resulting from a later impact. Grooves and crater chains appear to radiate from Stickney, and had led to theories that the impact that formed it nearly destroyed the moon. It is possible that Stickney is large enough to be seen with the naked eye from the surface of Mars. It is located at the middle of the left edge of Phobos's face, on the Mars-facing side. This incredible picture of Stickney was taken by the Mars Reconnaissance Orbiter as it passed within six thousand kilometers of Phobos last month.

APOD 4.3

This week's astronomy picture is of Jules Verne European Space Agency's Automated Transfer Vehicle. It was used for the first time on April 25th to raise the orbit of the International Space Station. A 740-second burn of the Automated Transfer Vehicle's main engines successfully lifted the altitude of the 280 ton station by around 4.5 km to a height of 342 km above the Earth's surface. The ATV was named after Jules a French author who pioneered the science-fiction genre. He is best known for his novels Journey to the Center of the Earth, Twenty Thousand Leagues under the Sea, and Around the World in Eighty Days. Verne wrote about space, air, and underwater travel before navigable aircraft and practical submarines were invented, and before any means of space travel had been devised. Using a laser guided rendezvous system, the Jules Verne docked smoothly and safely with the orbiting station on Thursday, delivering 7,500 pounds of equipment, supplies, and fuel.

APOD 4.2

This weeks APOD is titled Across the Universe (aka best movie ever!) and is a picture of a cosmic explosion classified as GRB080319B and detected by the Swift satellite. The source of the flash is estimated to be over 7.5 billion light years away, an unfathomable distance, and is 2.5 million times more luminous than the brightest supernova we know of. Obviously this is incredibly important discovery, and by observing the optical emission during the gamma ray burst, which usually last less than 2 minutes, we c an begin to understand the mechanism releasing enormous amount of energy. It is commonly believed that in the case of GRB longer than 2 s the phenomenon is caused by a collape of a massive star ending with a formation of a black hole. However, the details of the process still remain uncertain.