Saturday, May 21, 2011

Allan Sandage Biography


Allan Sandage
Allan Sandage was an American astronomer born in 1926 who died in 2010. Sandage worked with Carnegie Observatories in Pasadena, and is distinguished for approximating the Hubble constant and the age of the universe.
Sandage's influence is pervasive. After graduating from the University of Illinois, he obtained his Ph.D. from Caltech, advised by Walter Baade, a German astronomer. He actually was a grad student assistant of Edwin Hubble, perhaps influencing his work related to Hubble's constant. He continued in Hubble's footsteps, carrying on his research program after Hubble's death. Baade then discovered two populations of Cepheid variables in the Andromeda Galaxy. Since Hubble had only considered one of the populations, the estimate of the age of the universe doubled from 1.8 to 3.6 billion years. Sandage demonstrated that H II regions do not comprise stars and are inherently brighter than stars in distant galaxies, contrary to the assumption that the brightest stars in galaxies are of equal intensity. This increased the age of the universe yet again to 5.5 billion years.
From the 1950s to the 1980s, Sandage was the premier observation cosmologist (study of the universe). He used a variety of methods for measurement, from local indicators in the Milky Way to extremely distant galaxies. In 1958 Sandage started to work at the Palomar Observatory. It was from there that he published the first reasonable estimate of the Hubble constant, the ratio of the recession velocity of a distant object to its "proper distance." Sandage's value was 75 km/s/Mpc, much lower than Hubble's 250 km/s/Mpc. This is quite impressive, considering one 2011 study estimated it at 73.8 km/s/Mpc. However, he later decreased his estimate even further to 50 km/s/Mpc, corresponding to a Universe age of 20 billion years!
Sandage utilized photometry on globular clusters, coming to the conclusion that they were about 25 billion years old. Accordingly, he concluded that the Universe expanded and contracted with a period of 80 billion years. However, most estimates place the Universe as 14 billion years old. He co-wrote an extremely influential paper with Eggen and Lynden-Bell on the collapse of a proto-galactic gas cloud into the Milky Way. Sandage wrote a paper called "The Ability of the 200-inch Telescope to Discriminate Between Selected World Models" wherein he described observational cosmology as essentially a search for the Hubble constant and the deceleration parameter q0. He basically created a blueprint for how to use a large telescope to perform observational tests. He published an atlas of galaxies that employed the Hubble classification scheme in 1961 and again in 1981.
He devised a way to measure the temporal variation of extra-galactic redshift, which became known as the Sandage-Loeb test. He also discovered jets erupting from the core of the M82 galaxy, which had been occurring for 1.5 million years. He stayed at Carnegie Observatories up until his death, having published over 500 papers in his life.

Friday, May 20, 2011

APOD 4.5

18 May 2011 - The Last Launch of Space Shuttle Endeavor

On Monday, the shuttle Endeavor launched for the last time. It carried six astronauts and docked with the International Space Station. They are going to deliver an apparatus that can detect antimatter, dark matter, and strangelets called the Alpha Magnetic Spectrometer. Dark matter is any matter whose existence can be deduced based on gravitational effects on the surroundings but cannot be "seen" by usual means. Antimatter is a counterpart to normal matter (much less abundant than it) and when combined with matter, causes fulminating cataclysms. Strangelets are objects that have strange combinations of up and down quarks. The last shuttle launch will occur in mid-July, and I will endeavor to go see it.

Monday, May 16, 2011

Biography Sources

Works Cited
"Allan Sandage - Telegraph." Telegraph.co.uk - Telegraph Online, Daily Telegraph and Sunday Telegraph - Telegraph. Web. 16 May 2011. <http://www.telegraph.co.uk/news/obituaries/science-obituaries/8150004/Allan-Sandage.html>.
"Allan Sandage, 1926-2010." Astronomy Now Online. Web. 16 May 2011. <http://www.astronomynow.com/news/n1011/16Sandage/>.
"Allan Sandage." Wikipedia. Web. 16 May 2011. <http://en.wikipedia.org/wiki/Allan_Sandage>.
Overbye, Dennis. "Allan Sandage, Astronomer, Dies at 84 - Charted Cosmos’s Age and Expansion - NYTimes.com." The New York Times - Breaking News, World News & Multimedia. 17 Nov. 2010. Web. 16 May 2011. <http://www.nytimes.com/2010/11/17/science/space/17sandage.html>.

Thursday, April 21, 2011

APOD 4.4

16 April 2011 - The Tadpoles of IC 410
This false color image shows an emission nebula known eloquently as IC 410. It's so incredible how two tadpoles can randomly form out of cosmic dust and look so beautiful. A narrow band filter traces atoms and makes sulfur red, hydrogen atoms green, and oxygen blue. The cluster NGC 1983 energizes the gas of IC 410. The "tadpoles" are an enormous 10 light years in length. The trails lead away from the center, caused by cosmic "wind."

Monday, April 18, 2011

Zooniverse

I have been doing the bubble drawing experiment in Zooniverse for several weeks. It is sometimes difficult to determine where the bubbles are because they are so vaguely defined. I have found many fuzzy red objects and galaxies as well.

Friday, April 8, 2011

APOD 4.2

6 April 2011 - The Perfect Spiral
M74 is a spiral galaxy in the constellation Pisces that offers an almost perfect head-on view. It contains about 100 billion stars and is 32 million light years away. Considering that the picture is half the width of the full moon, it actually covers quite a large surface area of the sky. It's compelling to think that this majestic structure is right in front of our eyes, but we can't see it because of the long exposure times required to reveal most of the stars. M74 has multiple blue clusters and cosmic dust lanes. Some exposure in the infrared revealed a part of the hydrogen emission spectra.

APOD 4.1

1 April 2011 - It's Raining On Titan
Titan, Saturn's largest moon, has been experiencing rainstorms of methane near its equator. The rains were visible from space as a dark band around the moon. Ironically, this deluge occurred at the same time as Earth's April showers and the geographical distribution of precipitation is similar to that of Earth. Methane on Titan behaves almost like water does on Earth, with lakes evaporating to form clouds which release methane rain.