Deep Sky Astronomy

The stars we see at night belong to our own galaxy. Comets, which Messier studied are local to the Solar System, whose hypothesized edge where the sun’s gravitational pull weakens is called the Oort Cloud. http://en.wikipedia.org/wiki/Oort_cloud

Beyond the sun lie millions of other suns in what scientists call the Milky Way, that bright band of light so visible in the sky, and stretching from the constellation Scorpio in the south to Cassiopeia in the north.  http://www.historyoftheuniverse.com/milkyway.html

 The planets of the solar system and stars of our own galaxy are not called deep sky. Deep sky refers to non stellar objects within the Milky Way and also extra galactic objects outside it. http://en.wikipedia.org/wiki/Deep-sky_object

 We can reach the deep sky with binoculars or telescopes. Deep sky objects within our Milky Way include:

*Supernova remnants, the gasses left behind after a star explodes.

*Star clusters, used in stellar evolution theories and distance scale of the universe

*Interstellar clouds

*Dark Nebulae, birthplace of new stars

http://www.stargazing.net/david/deepsky/deepsky.html

 Charles Messier cataloged 101 deep sky curiosities, though he did not know that some lay beyond our galaxy. Recent efforts to measure the Milky Way enabled these extra galactic discoveries. First, astronomers, using light from variable stars, calculated that our sun lay off center of our galaxy. Then in 1924 Edwin Hubble, using the 100 inch Mt. Wilson telescope, finally proved that some of Messier's fuzzies lay outside our own Milky Way.

Hubble used variable star measurements to calculate the distance to the nearest extra galactic nebula, Andromeda. Its spiral shape could be resolved in the Wilson telescope, but individual stars could not. He assigned the Andromeda galaxy’s distance as one million light years. Later calculations proved it was a million and a half light years distant. Soon it became clear Andromeda is a neighboring galaxy like our own, and belongs to a larger group of galaxies called the Local Cluster.  http://www.astr.ua.edu/keel/galaxies/history.html 

Since stars from our own galaxy are critical for discoveries of evolution of the universe and its distance, next Friday's entry will touch on stars.