Materials:

• Calculators
• Astronomy reference books
• String or clothesline
• 4 x 6 inch index cards
• Paper hole punch
• Paper clips

Procedures:

Distances to stars and celestial objects are immense. Cars travel at an average of 60 miles/hour, jets fly at about 600 miles/hour, and rockets travel through space at 25,000 miles/hour. Imagine that with new technolgy you can build a time machine that travels at light speed, or 186,000 miles/second. The unit used to express stellar distance is the light-year, which is the distance that light travels in a year (5.8 trillion miles or 9.46 x 10¹² kilometers). With the unit of light-years, we can begin to make sense of the very great distances between objects in the universe and begin our time travel exploration.

1. Using the chart below, calculate the travel time from the Earth to the destinations given.

Planets & Galaxies	Destination Distance from Earth (light-years)	Time at Light Speed
Moon	0.000000038	1.1991888 seconds
Sun	0.000016	8.41536 minutes
Mercury	0.0000095	4.99662 minutes
Venus	0.00000476	2.5035696 minutes
Mars	0.0000076	3.997296 minutes
Jupiter	0.0000666	35.028936 minutes
Saturn	0.000135	1.18341 hours
Uranus	0.000285	2.49831 hours
Neptune	0.00046	4.03236 hours
Pluto	0.0006183	5.4200178 hours
Alpha Centauri	4.27	4.27 years
Sirius (Dog star)	8.7	8.7 years
Arcturus	36	36 years
Pleiades Cluster	400	400 years
Betelgeuse	520	520 years
Deneb	1,600	1,600 years
Crab Nebula	4,000	4,000 years
Center of Milky Way	38,000	38,000 years
Magellanic Clouds	150,000	150,000 years
Andromeda Galaxy	2,200,000	2,200,000 years

2. Suspend the string or clothesline from the ceiling in your classroom or stretch it along the length of the hallway. Determine an appropriate scale, depending on whether you want to show the edge of the universe, approximately
15 billion light-years away, or the objects closer to the Earth, for which you will use a scale of 3 million light-years. Mark the scale on the string or clothesline.

3. Give each student a card. Have them record the name of the object that is their destination and the time distance to travel there. Use paper clips to attach the cards to the string at the appropriate distances on your scale. (Extension: Use the images from the Hubble Space Telescope and add artwork to each card. Select additional locations for students to add to their time line from the program and from the Hubble Space Telescope observations.)

4. The chart and travel time line represent a glimpse into the past. In a sense, our time travel is like a time machine. When we look at the history of the universe, what can we learn? What evidence have scientists gathered with new technologies and the Hubble Deep Field Project?

5. Because of the finite speed of light, we are restricted to studying our observable universe. Discuss with your class the question, "Are there other universes?" What hypotheses can they make?

Extensions:

• Middle School Extensions -- Give students the light-year calculation and have them construct the time line by using the known distances. Have students use an astronomical globe that shows the position of the stars and the planets in relation to Earth.

• Advanced High School Students -- Have students design and conduct experiments to study the correlation between a star's brightness and its distance. Use light meters to perform experiments and make measurements. Discuss how the brightness of a star is determined by how large it is, how hot it is, and how far away it is.

• Extension for All Students -- Find out about NASA's Discovery Program called STARDUST, which plans to sample a comet and an interstellar dust stream and return the material to Earth. The samples may provide a window to the distant past.