Chapter 21, Section 4 Star Systems and Galaxies Based on Prentice Hall Textbook by Rusty Sturken May, 2009 Background imaghttp://mayda.com/astro/Img/M31_LRGB-03C-1k.jpge from http://mayda.com/astro/Img/M31_LRGB-03C-1k.jpg

Star Systems More than half of all stars are members of groups of two or more stars. Our sun is not. Star systems with two stars are called double stars or binary stars. Star systems with three stars are called triple stars.

Binary Systems Often astronomers can detect the presence of a star in a binary system without seeing it, they can tell it is there by observing the effect of its gravity on the second star Sometimes with binary stars, one star blocks the light from the other star and the system is called an eclipsing binary

Eclipsing Binary http://calgary.rasc.ca/images/Algol_Eclipsing.gif

Planets around other stars Scientists have discovered planets around stars by observing how a star “wobbles” very slightly back and forth Over 300 “extrasolar” planets have been found according to Space.com Most of the extrasolar planets found so far are massive gas giants with large influence on their star’s gravity.

Saturday, April 2nd, 2005 Astronomers Photograph Extrasolar Planet “First ever photo of an extrasolar planet, a Jupiter-sized gas giant.” http://www.utahskies.org/image_library/deepsky/misc/top.extrasolar.planet.photo.jpg

Where to look for Earthlike planets The so-called "habitable zone" around a star is a belt in which liquid water could exist on the surface in lakes, rivers or oceans. Too close to its stellar parent and a planet would be too hot, while an orbit too far out would yield only a frozen world, NASA scientists have said. Quote from http://www.space.com/scienceastronomy/090416-kepler-first-images.html

Galaxies Galaxies are giant structures that contain hundreds of billions of stars, Oh, by the way…There are billions of galaxies in the universe Galaxies contain single stars, double stars, star systems and lots of gas and dust between the stars. Astronomers classify most galaxies into three main categories: spiral galaxies, elliptical galaxies, irregular galaxies

Spiral Galaxies Spiral galaxies have arms that spiral outward, like pinwheels http://zoo1.galaxyzoo.org/images/ tutorial/example_face_on_spiral.jpg http://www.spacetoday.org/images/Hubble/ HubbleBeauty/NGC1512BarredSpiralGalaxy.jpg

The Milky Way Our solar system exists in the Milky Way galaxy, and is about 25,000 light-years away from the center of the Milky Way Our solar system is about two-thirds of the way out on one of the spiral arms of the Milky Way We can’t see the center of the Milky Way due to the massive cloud of gas and dust between the sun and the center

The Milky Way http://abyss.uoregon.edu/%7Ejs/images/milky_way_large.jpg

The Milky Way http://www.crystalinks.com/galaxymilkyway.jpg

Elliptical Galaxies Elliptical galaxies look like flattened balls Have little gas and dust between the stars so new stars can not form Ellliptical galaxies only contain old stars http://photojournal.jpl.nasa.gov/ jpegMod/PIA08696_modest.jpg

Elliptical Galaxy http://zuserver2.star.ucl.ac.uk/%7Eidh/apod/image/0406/m87_cfht.jpg

Irregular Galaxies Some galaxies don’t have a regular shape, they are called irregular galaxies The Large Magellanic Cloud is an irregular galaxy http://www.nasa.gov/images/content/ 159426main_image_feature_666_ys_4.jpg

Irregular Galaxy http://starchild.gsfc.nasa.gov/Images/StarChild/universe_level2/ngc6822.gif

Irregular Galaxy http://www.astro.utu.fi/news/img/RGB_bird_idl600.jpeg