Galaxy Dopper

Geology 105
Introduction to Astronomy

Timothy McDonnell - Instructor


Astronomy Puts the Universe at Your Fingertips!

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The distances to planets are measured in astronomic units, which is the average distance of the Earth to the Sun (93 million miles). Venus is around 0.72 AU from the Sun, or 67 million miles. This distance can also be measured in light-minutes. It takes 5.5 minutes for the light of the Sun to reach Venus.

Moon Phases

The emission specturm given off from hydrogen gas consists of a series of lines. Four are especially prominent in even a cheap spectroscope. Each line represents a different change in electron energy levels.

Wien's Law

Generally the hotter the star, the more intense the energy emitted will be. Also, the hotter the star, the smaller the wavelength of its peak radiation. This can be expressed as Wien's Law:


Practice Questions for
Chapters 1 and 2

Chapter 1:
1. The Sun is on average 150 million kilometers from the Earth. If a comet is 20 A.U.'s from the Sun, how many km away is it?

2. A star is 100 trillion miles from Earth. Express that number as a power of ten.

3. If we represent the Earth as a golf ball 4 cm across, how should we model Jupiter - a baseball, a marble, beach ball, hot air balloon?  (To find their actual diameters, see the chart on p. A-2 in back of The Cosmos.)

4. Let's make Solar System one light-year across (that includes the most distant comets). If we represent the Solar System as a 1-cm dime, what object should we use to model the Milky Way Galaxy, which is 100,000 ly across? (round table, CD, round swimming pool, domed stadium). Explain your answer!

Chapter 2:
1. What evidence do we have (before the Space Age) that the Earth rotates once every 24 hours?

2. How do the stars tell us that we have completed one revolution around the Sun.

3. Why did Copernicus choose to devise the Heliocentric Model (Sun-Centered)? What does retrograde motion of planets have to do with it?

4. How do you draw an ellipse? How does this model the orbit of a planet? Where do you put the sun? (NOT the center!)

5. Galileo discovered the phases of Venus and the moons of Jupiter. Why did this lead him to accept the Copernican model of the universe?

6. According to Kepler, the distance of a planet to the sun cubed is equal to the period of revolution squared (P2 = A3). If the semi-major axis of a comet is 400 AU, then what is its period of revolution?

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