Stars and galaxies

1. Stars and galaxies Part I: A Trip Through the Universe What We Will See

2. First Stop – Alpha Centauri Multiple Star Systems • More than 80% of stars are part of multiple star systems that consist of two or more stars in orbit with each other • Most common are binary systems with 2 stars • Alpha Centauri is actually a multiple star system consisting of three stars;Proxima Centauri is the closest to Earth.

3. Constellations • Groups of stars in which people at one time thought they saw imaginary figures of animals and people • Helped farmers to know when to plant and harvest as they appear at different times of the year • In 1929 the International Astronomical Union (IAU) defined the 88 official constellations that exist today

4. Asterisms • Patterns of stars that are not the defined constellations, but nonetheless are widely recognized Examples: • The Big Dipper which is part of the large constellation Ursa Major • The Summer Triangle (the bright stars Altair, Deneb and Vega) Original Photo at: http://www.flickr.com/photos/jbmac/3935287615/

5. A Nova • A star that suddenly increases in brightness and then slowly dims • Always a part of a binary star system with a white dwarf star • Gas from the companion star hits the surface of the white dwarf star causing a nuclear explosion  Nova: Before and after images

6. Star Clusters Open Cluster • Not well organized • Contains hundreds of stars • Over 1,100 known, thought to be many more • Example: Pleiades

7. Star Clusters Globular Cluster • Stars gravitationally bound in a spherical shape • Contains 10,000-1,000,000 stars • Appear to the eye as a single star or a faint, white cloud • As of 2011, there are 157 known clusters The Messier 80 globular cluster in the constellation Scorpius is located about 28,000 light-years from the Sun and contains hundreds of thousands of stars. A light year is the distance light can travel in one year. It is equal to 9.46 x 1012km.

8. Nebulae • Huge clouds of dust and gas between the stars • Some are the birthplace of new stars • Often formed when old stars “die” • Seen using infrared telescopes Eagle Nebula Crab Nebula

9. The Boomerang Nebula FYI: In 1995, astronomers revealed that it is the coldest place in the Universe found so far. With a temperature of -272°C, it is only 1 degree warmer than absolute zero (the lowest limit for temperature). Even the -270°C background glow from the Big Bang is warmer than this nebula. It is the only object found so far that has a temperature lower than the background radiation.

10. Galaxies • There are believed to be more than 100 billion galaxies. • There are three basic types of galaxies: • Spiral • Elliptical • Irregular • Galaxies, which contain various star groups, are the major feature of the universe. • Existence of galaxies was first hypothesized in 1755 by German philosopher-scientist Immanuel Kant. • Confirmed in the 1920s, when Edwin Hubble found the distance to stars located outside our own galaxy.

11. This image reveals 100s of galaxies in just a tiny area of sky (the whole sky contains 12.7 million times more area). View a short video at: http://hubblesite.org/hubble_discoveries/hubble_deep_field/

12. Spiral Galaxies • Pin-wheel shaped Examples: • The Milky Way • Andromeda – 2 million light years away • Whirlpool Galaxy • Sunflower Galaxy Messier 101 (M101, also known as NGC 5457 and also nicknamed the Pinwheel Galaxy)

13. FYI: MAY 31, 2012: NASA astronomers announced Thursday they can now predict with certainty the next major cosmic event to affect our galaxy, Sun, and solar system: the titanic collision of our Milky Way galaxy with the neighboring Andromeda galaxy. The Milky Way is destined to get a major makeover during the encounter, which is predicted to happen four billion years from now. It is likely the Sun will be flung into a new region of our galaxy, but our Earth and solar system are in no danger of being destroyed.

14. Elliptical Galaxies • Vary in shape from nearly spherical to flat discs • Contain little dust or gas and generally have older stars than in other types of galaxies Maffei1,in the constellation Cassiopeia, is the closest known giant elliptical galaxy  Atlas Image [or Atlas Image mosaic] obtained as part of the Two Micron All Sky Survey (2MASS), a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation

15. Irregular Galaxies • No orderly shape • Thought to make up about ¼ of all galaxies NGC 1427A, an example of an irregular galaxy about 52 Mlydistant NASA, ESA, and The Hubble Heritage Team (STScI/AURA)

16. The Milky Way • Seen as a band of light stretching across the sky • Composed primarily of stars that are too faint to be resolved so that we see their combined light as a faint glow • An example of a gigantic collection of stars, gas, and dust that we call a galaxy

17. The Milky Way Galaxy • Because we are within the galaxy we have no actual picture of it, but scientists have figured out that the Milky Way is a barred spiral galaxy. • Contains 200-400 billion stars • 100,000-120,000 light years in diameter; 12,000+ light years thick • The sun is in one of the spiral arms, far from the center, about half way to the edge, rotating around the center Artist's conception of the spiral structure of the Milky Way; from NASA

18. Image of the night sky above Paranal on 21 July 2007, taken by ESO astronomer Yuri Beletsky. A wide band of stars and dust clouds, spanning more than 100 degrees on the sky, is seen. This is the Milky Way, the Galaxy we belong to.