Download Chapter 21, Section 4 Star Systems and Galaxies

 More
than half of all stars are
members of star systems
(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.
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.

http://calgary.rasc.ca/images/Algol_Eclipsing.gif
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.

“First ever photo of an extrasolar planet, a Jupiter-sized gas giant.”
 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 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 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
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

http://abyss.uoregon.edu/%7Ejs/images/milky_way_large.jpg
http://www.crystalinks.com/galaxymilkyway.jpg
 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
http://zuserver2.star.ucl.ac.uk/%7Eidh/apod/image/0406/m87_cfht.jpg
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
http://starchild.gsfc.nasa.gov/Images/StarChild/universe_level2/ngc6822.gif
http://www.astro.utu.fi/news/img/RGB_bird_idl600.jpeg