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2. What is a light-year and how is it used?? - NASA

   starchild.gsfc.nasa.gov/docs/StarChild/questions/question19.html

   For distances to other parts of the Milky Way Galaxy (or even further), astronomers use units of the light-year or the parsec . The light-year we have already defined. The parsec is equal to 3.3 light-years. Using the light-year, we can say that : The Crab supernova remnant is about 4,000 light-years away. The Milky Way Galaxy is about 150,000 ...

3. Just How Big is this Place? - NASA

   starchild.gsfc.nasa.gov/docs/StarChild/teachers/how_big.html

   A light year is equal to 9,500,000,000,000 km and is the distance that light travels in one year. A light year can be expressed as 9.5 trillion km or in scientific notation as 9.5 x 10 12 km. The star outside of our solar system that is closest to Earth is Alpha Centauri C. It is 40,000,000,000,000 (40 trillion) km away. How many light years is ...

4. Parallax - NASA

   starchild.gsfc.nasa.gov/docs/StarChild/questions/parallax.html

   From the image above, you can see that by knowing the size of Earth's orbit and measuring the angles of the light from the star at two points in the orbit, the distance to the star can be derived. The farther the star is, the smaller the angles. For stars more than about 100 light-years from Earth, we cannot measure any shift and the method fails.

5. Redshift and Hubble's Law - NASA

   starchild.gsfc.nasa.gov/docs/StarChild/questions/redshift.html

   (A megaparsec is given by 1 Mpc = 3 x 10 6 light-years). This means that a galaxy 1 megaparsec away will be moving away from us at a speed of 65 km/sec, while another galaxy 100 megaparsecs away will be receding at 100 times this speed. So essentially, the Hubble constant reflects the rate at which the universe is expanding.

6. Why is there day and night? - NASA

   starchild.gsfc.nasa.gov/docs/StarChild/questions/question31.html

   Find where you live on the globe. Now slowly spin the globe on its axis so that if you look down on the north pole, it is rotating counterclockwise. Watch what happens to the place where you live. Do you see that it is sometimes pointed toward the light (which represents the Sun) and sometimes away from the light? Hey, you've made day and night!

7. Galileo Galilei - NASA

   starchild.gsfc.nasa.gov/docs/StarChild/whos_who_level2/galileo.html

   Galileo Galilei was an Italian physicist and astronomer.He was born in Pisa on February 15, 1564. Galileo's father, Vincenzo Galilei, was a well-known musician.

8. What causes a "falling star"? - NASA

   starchild.gsfc.nasa.gov/docs/StarChild/questions/question12.html

   A "falling star" or a "shooting star" has nothing at all to do with a star! These amazing streaks of light you can sometimes see in the night sky are caused by tiny bits of dust and rock called meteoroids falling into the Earth's atmosphere and burning up. The short-lived trail of light the burning meteoroid produces is called a meteor. Meteors ...

9. Does the Sun move around the Milky Way? - NASA

   starchild.gsfc.nasa.gov/docs/StarChild/questions/question18.html

   The Sun (and, of course, the rest of our solar system) is located near the Orion arm, between two major arms (Perseus and Sagittarius). The diameter of the Milky Way is about 100,000 light-years and the Sun is located about 28,000 light-years from the Galactic Center. You can see a drawing of the Milky Way below which shows what our Galaxy ...

10. Why does the Sun rise in the east and set in the west? - NASA

    starchild.gsfc.nasa.gov/docs/StarChild/questions/question14.html

    Question: Why does the Sun rise in the east and set in the west? Answer: The Sun, the Moon, the planets, and the stars all rise in the east and set in the west.

11. StarChild: The Milky Way - NASA

    starchild.gsfc.nasa.gov/docs/StarChild/universe_level2/milky_way.html

    Stars, dust, and gas fan out from the center of the Galaxy in long spiraling arms. The Milky Way is approximately 100,000 light-years in diameter. Our solar system is 26,000 light-years from the center of the Galaxy. All objects in the Galaxy revolve around the Galaxy's center. It takes 250 million years for our Sun to pull us through one ...