1. Ask students to consider what life was like on Earth in the 1400s, when there were no telescopes and no pictures from space. The average person's knowledge of the universe was based only on the science that was supported by the Church and on what they were able to observe with their own eyes.

1. Based on this information, what do you think people believed about the Sun and the Moon in the 1400s? The stars? Earth's place in the universe?
2. In Europe at that time, most beliefs, including theories of science, were governed by religion. How do you think new scientific theories were regarded if they differed from the teachings of the Church?
3. Show the Galileo: Sun-Centered System QuickTime Video . How did Galileo's observations fit with the Copernican system? Do you think Galileo's findings were accepted?

2. Discuss the scientific process and how researchers rely on observations and experiments to gather data to better understand the world. Have students theorize how scientists study the universe despite being grounded on Earth. Emphasize the importance of light for astronomical research. As an example, discuss Galileo's observations that supported the Copernican system as described in the Galileo: Sun-Centered System QuickTime Video .

3. Have students consider how the physics of light affects our knowledge of the universe. Remind students that the speed of light is about 299,792 kilometers per second (186,282 miles per second) in a vacuum. What does that mean about the light that we see from faraway objects? What does that mean about how we see objects that are different distances away from us?

Recall that one light- year is the distance that light travels in one year, about 9.46 trillion kilometers (9.46 x 10¹² km). You may want to go through sample calculations to demonstrate how the distance of an astronomical object is related to the time it takes for its light to reach Earth.

Example conversion to calculate how long it takes for the light from the Sun to reach Earth: 150 million km x (1 ly/9.46 x 10¹² km) x (365 days/yr) x (24 hr/day) x (60 min/hr) ≈ 8 light minutes

For your reference:

1. Distance to Sun ≈ 1.6 x 10^-5 ly (8 light minutes) ≈ 150 million km
2. Distance to Moon ≈ 4.1 x 10^-8 ly (1 light second) ≈ 384,000 km
3. Distance to Proxima Centauri ≈ 4.3 ly ≈ 4 x 10¹³ km
4. Distance to the Andromeda Galaxy ≈ 2 million ly ≈ 2 x 10¹⁹ km

4. Discuss student preconceptions about the universe. Compare the relative sizes of planets, stars, and galaxies. Visit the Spin a Spiral Galaxy QuickTime Interactive to bring a galaxy to life in 3-D. You may want to talk about Earth's galactic address.

5. Show the Hubble's Expanding Universe QuickTime Video . Explain that not only has our knowledge of the universe expanded over time, but we've also discovered that the universe itself is expanding! Discuss the following:

1. How has the telescope changed human understanding about Earth's place in the universe?
2. The discoveries by both Hubble and Galileo led to major advances in astronomy. What similarities do you see in their stories?
3. What is the Big Bang theory? Do you think there is any way to prove the theory?

6. Working alone or in pairs, have students explore the How Big Is Our Universe? HTML Interactive . Emphasize how distance is related to age - the age of the universe limits how far we can see.

7. Working in groups, have students create a timeline of the history of the universe, scaled to one "calendar year." For example, they should record the Big Bang on January 1, and the present day 12 months later, on December 31 of that year. More advanced students can do their own research to find significant events, such as the formation of the solar system or the development of life, and calculate placement in the calendar. For less advanced students, distribute the Events in the History of the Universe Worksheet PDF Document .

8. Have students examine the current state of astronomy. New technology has made astronomy one of the most exciting sciences today, but not all the answers have been found. Watch the Gravity and the Expanding Universe QuickTime Video and discuss the following:

1. Why did Einstein hypothesize the cosmological constant? Why did he later discard it?
2. What does it mean to say that the universe is accelerating?
3. What are the difficulties in studying and understanding the universe? How much do you think we still don't understand?

9. Working alone or in pairs, have students look at the Infrared Search for Origins Flash Interactive . This activity contains very recent images of the universe, observed by great telescopes such as the Hubble Space Telescope and the Spitzer Space Telescope. Distribute the Search for Origins Worksheet PDF Document .