What does the spectrum tell us about
in space? How does the spectra differ depending on temperature and
Cycles of the Sky
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
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
What are Kepler's Three Laws of Planetary Motion?
How did Galileo use his telescope to add more evidence to a
What do the Sir Isaac Newton's Laws of Motion prove that the universe
is not geocentric?
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.
Concept of the Week!!
1. Scaling the Universe...
The distances in the universe are
large that it is very difficult for us to comprehend based on our
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
Keeping to scale, what object would best represent the Moon
SOLUTION: Set up the
following proportion, and substitute known actual diameters of the
(12,800 km) and the Moon
This means that the tennis ball
seems to fit best.
Now, how far apart should we place them?
average distance between the Earth and the Moon is 385,000 km.
SOLUTION: Set up the following proportion,
This means that the 12-in. globe
and the 3.3-in. tennis ball need to be on the opposite sides of a
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,
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
Click on one of the links below to
find out more about
Introduction to Astronomy: