NAME _________________________
Period _________
January 12-16, 2015
HOMEWORK INSTRUCTIONS:
1. Learn the correct meaning and use of the vocabulary words listed below. You may use any study strategies you
wish such as, flashcards, the Quizlet app, memory games, etc. You will have a quiz over the meaning of these words
AND the content we covered IN CLASS throughout the week on Friday, January 16, 2015.
2. Complete the assignment on the back of this sheet. Due Friday, January 16, 2015. You may turn in your work early,
but be sure you have copied the words and definitions elsewhere (or taken a picture with a device) in order to
continue studying them throughout the week.
VOCABULARY
KNOW THE CORRECT MEANING AND USE OF THE FOLLOWING TERMS
1. Light year – a unit of length in astronomy (NOT A UNIT OF TIME); equal to just under 10 trillion kilometers (or
about 6 trillion miles); the distance that light travels in a vacuum in one year.
2. Nuclear fusion – the joining of the nuclei from two atoms that results in massive amounts of heat and light;
the process that takes place in stars like our sun.
3. Galaxy - a system of millions or billions of stars, together with gas and dust, held together by gravitational
attraction; three basic galaxy shapes are spiral, irregular, and elliptical.
4. Convection Zone – the outermost layer of the sun’s interior; convection forms loops of energy that move
towards the sun’s surface; generates the sun’s magnetic field.
5. Corona – outer layer of the sun’s atmosphere; visible during total solar eclipse; extends into space for millions
of kilometers and gradually thins.
6. Photosphere – inner layer of the sun’s atmosphere; considered the sun’s surface layer; gives off visible light.
7. Sunspots – areas of gas on the sun’s surface that are cooler than those around it; they appear darker and
helped to prove that the sun rotates on an axis.
NAME _________________________
Period _________
This picture contains a link to the web site
Background: How Are Galaxies Classified? What Do They Look Like?
Edwin Hubble classified galaxies into four major types: spiral, barred spiral, elliptical, and
irregular. Most galaxies are spirals, barred spirals, or ellipticals.
Spiral galaxies are made up of a flattened disk containing spiral (pinwheel-shaped) arms, a bulge
at its center, and a halo. Spiral galaxies have a variety of shapes and are classified according to the
size of the bulge and the tightness and appearance of the arms. The spiral arms, which wrap around
the bulge, contain numerous young blue stars and lots of gas and dust. Stars in the bulge tend to be
older and redder. Yellow stars like our Sun are found throughout the disk of a spiral galaxy. These
galaxies rotate somewhat like a hurricane or a whirlpool.
Barred spiral galaxies are spirals that have a bar running across the center of the galaxy.
Elliptical galaxies do not have a disk or arms. Instead, they are characterized by a smooth, ballshaped appearance. Ellipticals contain old stars, and possess little gas or dust. They are classified by
the shape of the ball, which can range from round to oval (baseball-shaped to football-shaped). The
smallest elliptical galaxies (called "dwarf ellipticals") are probably the most common type of galaxy in
the nearby universe. In contrast to spirals, the stars in ellipticals do not revolve around the center in
an organized way. The stars move on randomly oriented orbits within the galaxy like a swarm of
bees.
Irregular galaxies are galaxies that are neither spiral nor elliptical. They tend to be smaller objects
that are without definite shape and tend to have very hot newer stars mixed in with lots of gas and
dust. These galaxies often have active regions of star formation. Sometimes the irregular shape of
these galaxies results from interactions or collisions between galaxies. Observations such as the
Hubble Deep Fields show that irregular galaxies were more common in the distant (early) universe.
How Do You Classify Galaxies Today?
Today we classify galaxies mainly into two major groups following Hubble’s examples (top of next
page). Elliptical galaxies range from round shapes (E0) to oval shapes (E7). Spiral galaxies have a
pinwheel shape and are classified according to their bulge, as well as how tightly their arms are
wrapped around the bulge. They range from (Sa), which has a large bulge and tight, smooth arms, to
(Sc), which has a small bulge and loose, lumpy arms. Barred spiral galaxies classified as (SB) are
pinwheel-shaped and have a distinct "bar" of stars, dust and gas across their bulge. They range from
an (SBa), which has a bar across its large bulge and tight, smooth arms, to an (SBc), which has a bar
across its small bulge and loose, lumpy arms. Irregular galaxies have no definite shape but still
contain new stars, gas, and dust. The chart below summarizes the properties of the main classes of
galaxies.
NAME _________________________
Period _________
1.
2.
3.
4.
1. What are the three main classifications of galaxies?
_____________________________
Put your name on THIS page.
Detach this page.
Turn in only this page!
Keep first page for your records.
_____________________________
_____________________________
2. Which type of galaxy contains younger blue stars in the center and older, redder stars around the
bulge? _____________________________
3. Which type of galaxy has no disk or arms? _____________________________
4. Which galaxy type tends to have newer, very hot stars? _____________________________
5. Which type of galaxy is characterized by having gas and stars that rotate around the center?
_____________________________
6. Which type of galaxy is a result of a collision between galaxies?
_____________________________
7. Galaxies that contain little or no dust are classified as? _____________________________
8. What is the two letter code for a galaxy that has a pinwheel shape and a distinct bar of stars across
the bulge? _____________________________
9. The classification (E7) describes which type of galaxy? With what shape?
________________________________________________________________________
10. The Milky Way Galaxy is which classification of galaxy? ______________________________
Classify the galaxies below:
11.
12.
E for elliptical, S for spiral, I for irregular
13.
14.
15.