
Astronomy Packet: 1 
Astronomy Basics:
What is an Astronomical Unit (AU)
In science we use a lot of really big numbers. To make these numbers easier to work with, we have invented units of measurement which make the numbers smaller. For example, it is easier to say that you live one mile from the park than it is to say you live 66,000 inches from the park. Rather than saying the Sun is 93 million miles from the Earth, which is true, it is easier to say the Sun is one Astronomical Unit (AU) from the Earth. The distance from the Sun to the Earth is one (AU).
What is a light year?
When we talk about distances in the Solar System, it is convenient to use AUs. However, when we start to talk about distances to other stars, even using AUs gives us a number which is very large. To make the number smaller, once we leave the Solar System we measure things using light years.
A light year is 6 trillion miles (6,000,000,000,000). That is the distance light can travel in a year. But don't let that confuse you, it is not a measurement of time. It is a measurement of distance. The distance is 6 trillion miles.
Other units of measurement:
The Universe is unimaginably large. Even using light years eventually gets too difficult. Scientists have created another unit of measurement even larger than a light year. This is called a Parsec. A parsec is 3.6 light years. We also use kiloparsecs, which means 1000 parsecs, and megaparsecs, which means one million parsecs.
Even using megaparsecs can still give us very large numbers because in astronomy distances are huge. Scientists have one more trick they use to make math with such large numbers easier. They use what is called Scientific Notation.
Scientific Notation is a special way to write down large numbers. Instead of 1,000,000, in scientific notation you would write 1x10^6. The 6 should be little and written as a power. The rules of scientific notation say that after the first number you count how many numbers there are to the right and put that number to the power of ten, so that 1,000 is written as 1x10^3, because there are three numbers to the right of the 1. 30,000 is written as 3x10^4. 50,000 is written as 5x10^4.
Assignment # 3.
How would you write the following in scientific notation?
100
5,000
9,000
20,000,000
500,000,000,000,000,000,000
40,000
60,000,000