DSST Astronomy notes 1

A the earths rotation axis is not fixed in space it

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a) The Earth's rotation axis is not fixed in space; it is moving like the top of a wobbly top a.i) By human standards, this conical motion is imperceptible--with a precession period of 26,000 years, it takes 26,000 years for the Earth's axis to do a full rotation. a.ii) Another way to look at this is that right now the North Star is Polaris, but in 13,000 years the star Vega will be approximately at the North Celestial Pole. a.iii) Then in 26,000 years, the pole will be pointing in the same direction again--back at Polaris. 168) The twenty brightest stars as seen from Earth are classified in that manner because they have high Luminosity and/or are nearby. a.i) Those stars are: Sun, Sirius, Canopus, Arcturus, Alpha Centauri, Vega, Rigel, Procyon, Achernar, Betelgeuse, Hadar (Agena), Capella A, Altair, Aldebaran, Capella B, Spica, Antares, Pollux, Fomalhaut, and Deneb.
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a.ii) Sirius is the brightest star after the sun. 169) A visual grouping of five galaxies of which four form the first compact galaxy group ever discovered is called the Stephan's Quintet. a) This group was discovered by Edouard Stephan in 1877 and is one of the most studied of all the compact galaxy groups. 170) The length 206,265 AU (astronomical units) is defined as a Parsec. a) A parsec is 206,265 AU, which is about 30 trillion kilometers (19 trillion miles) or 3.262 light years. b) The name parsec stands for "parallax of one second of arc" and the concept is based on trigonometry. c) A parsec is too big of a unit to use within our solar system, which is only around 1/2600th of a parsec across (c.i.1.a) Typically you would describe the distance between nearby stars in parsecs, kiloparsecs for the distance between parts of a galaxy or within galaxy groups, and megaparsecs for distances between galaxy clusters. 171) Parallax is the change of angular position of two observations of a single object relative to each other as seen by an observer, caused by the motion of the observer. a) This is the apparent shift of an object against the background that is caused when the observer changes positions. b) When standing in one place it looks one way; if the observer moves, the background changes and the object looks different. 172) Pulsars are highly magnetized rotating neutron stars which emit a beam of detectable electromagnetic radiation in the form of radio waves. a) The radiation can only be observed when the beam of emission is pointing towards the Earth. b) Most pulsars actually are detectable only by their radio radiation--they release too little visible light to be seen with the human eye. c) Because neutron stars are very dense objects, the rotation period and the interval between observed pulses are very regular. 173) A Quasar is an extremely bright and distant active galactic nucleus--the very bright center of a distant galaxy powered by a black hole in the galaxy in which it's located. a) Quasars were first identified as high redshift sources of electromagnetic energy including radio waves and visible light. b) They are considered the most distant objects discovered by astronomers, so far away that their light takes billions of years to reach the Earth. c)
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a The Earths rotation axis is not fixed in space it is...

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