“Measuring the rotation period of the sun” activity

Discuss with your neighbor(s)

• Does the sun rotate? • How do we measure the rotation of the sun? • About how long does it take the sun to make one complete rotation around its axis? • How long does it take the Earth to make one complete rotation around its axis? • How long does it take the Earth to orbit around the sun? • Does the sun always have the same appearance to us on Earth? If not, in what ways does it change, and why does it change?

Milky Way distances

Activity: What is your cosmic address?

Street number/PO Box, City, State, Country

P.O. Box 3129, Sells, AZ, USA

Our galaxy is called the Milky Way. It is a spiral galaxy.

If we could see it from afar, it would look something like this:

The sun

Because we live inside of the the Milky Way, it looks like this instead:

Distances in astronomy are very large.

Distance from Sells, AZ to Tucson, AZ:

Distances in astronomy are very large.

Distance from Sells, AZ to Tucson, AZ: 63 miles

Distances in astronomy are very large.

Distance from Sells, AZ to Tucson, AZ: 63 miles Distance from Sells, AZ to New York, NY:

Distances in astronomy are very large.

Distance from Sells, AZ to Tucson, AZ: 63 miles Distance from Sells, AZ to New York, NY: 2,496 miles

Distances in astronomy are very large.

Distance from Sells, AZ to Tucson, AZ: 63 miles Distance from Sells, AZ to New York, NY: 2,496 miles Distance from Sells, AZ to alpha Centauri:

Distances in astronomy are very large.

Distance from Sells, AZ to Tucson, AZ: 63 miles Distance from Sells, AZ to New York, NY: 2,496 miles Distance from Sells, AZ to alpha Centauri: 25,671,409,000,000 miles

Distances in astronomy are very large.

Distance from Sells, AZ to Tucson, AZ: 63 miles Distance from Sells, AZ to New York, NY: 2,496 miles Distance from Sells, AZ to alpha Centauri: 25,671,409,000,000 miles Distance from Sells, AZ to the center of the Milky Way:

Distances in astronomy are very large.

Distance from Sells, AZ to Tucson, AZ: 63 miles Distance from Sells, AZ to New York, NY: 2,496 miles Distance from Sells, AZ to alpha Centauri: 25,671,409,000,000 miles Distance from Sells, AZ to the center of the Milky Way: 160,000,000,000,000,000 miles

Distances in astronomy are very large.

Distance from Sells, AZ to Tucson, AZ: 63 miles Distance from Sells, AZ to New York, NY: 2,496 miles Distance from Sells, AZ to alpha Centauri: 25,671,409,000,000 miles Distance from Sells, AZ to the center of the Milky Way: 160,000,000,000,000,000 miles Distance from Sells, AZ to the Andromeda galaxy: 14,919,633,000,000,000,000 miles

Therefore, astronomers use their own units of distance, such as the “light year”.

Distance from Sells, AZ to Tucson, AZ: 63 miles Distance from Sells, AZ to New York, NY: 2,496 miles Distance from Sells, AZ to alpha Centauri: 25,671,409,000,000 miles Distance from Sells, AZ to the center of the Milky Way: 160,000,000,000,000,000 miles Distance from Sells, AZ to the Andromeda galaxy: 14,919,633,000,000,000,000 miles

Therefore, astronomers use their own units of distance, such as the “light year”.

Distance from Sells, AZ to Tucson, AZ: 0.00000000001 light years Distance from Sells, AZ to New York, NY: 0.0000000004 light years Distance from Sells, AZ to alpha Centauri: 4.37 light years Distance from Sells, AZ to the center of the Milky Way: 27,169 light years Distance from Sells, AZ to the Andromeda galaxy: 2,538,000 light years

1 light year (ly) = 5,878,499,810,000 miles

(You do NOT need to memorize this number.)

A distance to a nearby star might be:

(A)  10 inches (B)  10 miles (C)  10 kilometers (D)  10 light years

A light year is a unit of:

(A)  time (B)  distance (C)  temperature (D)  energy

Why did astronomers choose the name “light year” to represent 5,878,499,810,000 miles?

Why did astronomers choose the name “light year” to represent 5,878,499,810,000 miles?

A light year is the distance traveled by light (and all information) in one year.

1 light year = (the speed of light) x (1 year)

Minute physics: How far is a second?

Work in groups Define a new unit of distance called a

“person year” which is the distance a person walks in a year.

Fill in this equation: 1 person year = ________ miles

A light year is the ________ traveled by light in ________.

Lecture Tutorial: Milky Way Scales

pages 135-137