1. Astronomical Distances

2. Warm-up
What is a light year?

3. Light year is a unit of distance, NOT time
Light Year: the distance light travels in one year (9.5 trillion km!!!)
Kilometers are too small to use in astronomy
one light-year is equal to 9,500,000,000,000 kilometers or 5,879,000,000,000 miles

4. Light Year

5. Parsec is used to measure greater distances between stars and galaxies
1 parsec = 3.26 light years

6. Astronomical Units (AUs) measure distances between planets (our solar system)
AU is the average distance between the Earth and Sun (1 AU)
1 AU is about 150 million km

7. Mercury is the closest at 0.39 AUs while Neptune is the farthest at 30.06 AUs

8. Stars that seem to be close may actually be very far away from each other.

9. The universe is immense in size
Astronomers use units and methods of measuring that are not used to on Earth

10. Parallax is used to measure the distance to nearby stars
Parallax: when objects appear to move or shift due to earth’s orbit
This method uses trigonometry
nearby stars = 300 light years or less

11. Parallax
Jan.
draw this
June

13. Standard Candle Class of objects which have known luminosity
Luminosity =  total amount of energy emitted by an object
Ex: H-R Diagram, Supernova, and Cepheid Variable Stars

15. The Distance Ladder
Each stage in the ladder overlaps the previous and next
Cepheid distances are critical
Tully-Fisher, fundamental plane apply to whole galaxies
Supernova are now the best estimators at large distances