Geology 105
Introduction to Astronomy

Timothy McDonnell - Instructor


Astronomy Puts the Universe at Your Fingertips!

Astronomy Home


Practice section

Concept of the Week


Coming Attractions!

Chapter 2:
The Spectrum

Celestial Sphere
What does the spectrum tell us about objects in space? How does the spectra differ depending on temperature and  other factors?

Chapter 4:
Cycles of the Sky

Lunar Eclipse

How do we account for the changes we see on Earth, such as day and night and the seasons?
What is the cause of the phases of the moon? Why does the moon eclipse the sun? Why does the Earth eclipse the Moon?

Chapter 5: The Origins of Astronomy

Phases of Venus

Why did astronomers of the ancient world think that the Earth was the center of the universe?

How is retrograde motion of the planets explained in both the geocentric and heliocentric models of the universe?
What are Kepler's Three Laws of Planetary Motion?
How did Galileo use his telescope to add more evidence to a Sun-centered universe?
What do the Sir Isaac Newton's Laws of Motion prove that the universe is not geocentric?

Chapters 6-8
Early solar system

The Solar System probably began around 5 billion years ago from a swirling cloud of gas formed from the remains of an ancient supernova. From this the Sun, the terrestrial planets, the Jovian planets, and the comets, asteroids, and meteoroids were formed.

The Concept of the Week!!

1. Scaling the Universe...
The distances in the universe are so large that it is very difficult for us to comprehend based on our limited experience. After all, when have you traveled one light-year?
So it helps to scale important objects and distances in space to a more manageable size.

Suppose, for example, that the Earth is the size of a 12-inch globe.


Keeping to scale, what object would best represent the Moon?




Tennis ball
Beach Ball: 24 inches
Softball: 3 inches
Golf Ball:
1.5 inches
0.5 inches

SOLUTION: Set up the following proportion, and substitute known actual diameters of the Earth (12,800 km) and the Moon (3500 km).


This means that the tennis ball seems to fit best.

Now, how far apart should we place them? The average distance between the Earth and the Moon is 385,000 km.

SOLUTION: Set up the following proportion, and substitute:


This means that the 12-in. globe and the 3.3-in. tennis ball need to be on the opposite sides of a classroom! Models showing the Earth and Moon just inches apart are way off.

2. Powers of Ten...
Numbers in space can be very large. Even close stars are trillions of miles away. Who wants to write a number with all those zeroes?
To simplify this, we write large numbers as powers of ten. For example 1000 is equal to
10 x 10 x10 or ten to the third power.
How do you write one million, one billion, one trillion?
Powers of 10
Now think opposite! What do the following numbers mean?

There are also negative powers of ten. They are used for very small numbers, such as the time of the Big Bang. That we'll save for another lesson!

If you would like to practice some similar problems to those above, visit the Practice Questions section.

Click on one of the links below to find out more about
Introduction to Astronomy:






Due Dates


What's New in


Links in Astronomy


NY Geography
Go to the Monroe
Community College Website

Email Mr. McDonnell
New York Geography Home Page

Content Copyright (c) Timothy McDonnell - Layout Copyright (c) GingerSKW
Design downloaded from

Free web design, web templates, web layouts, and website resources!