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Review Questions for Chapter 21 – Stars, Galaxies and the Big Bang


1.      What are constellations?  What are some examples?

Constellations are groupings of stars that form a picture in the sky.  Example Orion or Ursa Major.

2.      What is a circumpolar constellation?  What are some examples?

Constellations that are visible all year long, they never go below the horizon.  Example: Ursa Minor

3.      Explain Earth’s movement and how it relates to the movement of the stars.

Earth rotates west to east, but the sky appears to be moving east to west because of our perspective.  The earth is so big that we cannot see the whole thing in relation to the sky, so all we see moving is the sky.  That is why everything seems to rise in the East and set in the West.

4.      What is Polaris, and what is unique about it?

     The North star, which all circumpolar constellations such as the Big Dipper revolve around all year long.  This happens because Polaris is along the Earth’s axis of rotation, and creates a fixed North position.  Mariners used it to determine their latitude using an astrolabe or sextant.

5.      What is the zodiac, and what is the difference between its use by astronomers and astrologers?

     The thirteen (13) constellations which ring the horizon throughout the calendar year.  Astrologers use the sequence of 12 constellations which were in a similar position thousands of years ago as a pseudoscience tool.  Astronomers simply recognize these constellations as 13 of the 88 officially recognized constellations

6.      What unit of measure is usually used within our solar system, and what is it equal to?

     Astronomical unit (AU), 150,000,000 Km

7.      What is meant by light year?

     The distance light travels in a year.

8.      What is one light year?

     9.5 trillion Km

9.      How do stars differ from each other?

     Size, density, color, temperature, spectra (remember emission spectra), distance from us, and brightness

10.  How do we really tell one star from another (what is the “fingerprint”)?

     Its spectra (hydrogen and helium are the two most abundant elements, but each star has slightly different amounts of these elements and others)

11.  What is apparent magnitude?

     How bright a star appears to be looking at it from Earth.

12.  What is luminosity? What does it depend on?

     The actual brightness of a star which is dependant upon its temperature and size.

13.  What is absolute magnitude?  How does it relate to luminosity?

     Absolute magnitude measures the luminosity of stars as if they were at the same distance from Earth.

14.  Which is brighter, an apparent magnitude of -2 or +3?


15.  What is the process in stars that produces light and what are the elements involved?

     Fusion, the explosive reaction between two hydrogen nuclei to form one helium nuclei and energy (mostly light energy)

16.  What is the expected life cycle of our Sun?

     Our Sun is a Main Sequence star, and expected to remain stable for another 5 billion years, then it will become a Red Giant and eventually collapse and become a White Dwarf.

17.  What are the characteristics of giants, supergiants, white dwarfs, and main sequence stars?

     Giants and Supergiants are very large stars with low densities, low temperatures, and high absolute magnitudes (because of their size)

     Main sequence stars make up 90% of stars in space and range from cool to hot, high luminosity to low luminosity.  Our Sun is an example.
White Dwarfs are small, dense stars of low luminosity but higher temperature.

18.  How are the above star types related to the Hertsprung-Russell (H-R) diagram?

     Make sure you know the area on the HR diagram each star type belongs.

19.  What is each axis in an H-R diagram?

     X axis is temperature which increases from right to left; Y axis is luminosity (apparent magnitude) which increases from bottom to top.

20.  What is a neutron star?

     Very, very dense stars at the end of their life cycle that result from the collapse of massive stars.  Produce limited amount of light waves.

21.  What is a black hole?

     Also the result of the collapse of a very massive star.  It is so dense that light cannot escape its gravity.

22.  What is a super-nova?

     Explosion of a dense star, signaling its death.

23.  What are nebulae?

     Huge clouds of dust and gas in space.  Stars are thought to form from nebulae.

24.  What is the major factor in determining whether a star dies by becoming a white dwarf, or exploding and becoming a neutron star or black hole?

     Its size and density.

25.  What is our galaxy, and what type is it?

     Milky Way.  It is a spiral galaxy.

26.  What are the four evidences supporting the Big Bang Theory?

     1.  Universe is continuously expanding, measured by the Red Shift in light from stars – discovered by Edwin Hubble in 1929.

     2.  Cosmic Background Radiation – the leftovers or echo from the explosion – is coming from everywhere in space – discovered by Arno Penzias and Bob Wilson in 1964.

     3.  Small differences in temperature across the Universe as measured by COBE satellite – another echo of the explosion – work done by George Smoot in 1992

     4.  Uniform presence of hydrogen and helium throughout the Universe.

27.  When did the Big Bang occur, and was our planet created at the same time?  If not, what happened (in general)?

     15 billion years ago.  Our planet was not created immediately.  It took time for matter to “congeal”.  It is estimated that our planet and the solar system began around 10 billion years ago.