1. Astronomical Distances

2. Scientific Notation Power of 10 Decimal Equivalent 107 10 000 000 104
102
100
10-5
10-7

3. Scientific Notation This is a number in scientific notation:
1.3 x 106
4.45 x 103
3.444 x 10-6
These are those same numbers written without scientific notation
4450

4. Scientific Notation
1) To determine the exponent count the number of places you have to move the decimal point to to give a number between 1 and 10.
E.g We would have to move the decimal point 5 decimal places to get a number between 1 and 10 (the number being 1).
Therefore your exponent will be 5.

5. Scientific Notation
2) To form the coefficient, place the decimal point after the first digit. Drop all trailing zeros unless all the numbers after the decimal are zeros, then keep one. But always keep significant figures (numbers other than zero)
E.g In our example our coefficient is 1.2

6. Scientific Notation
Combine the coefficient by multiplying it by base 10 and the exponent.
E.g. Remember our exponent was 5, our coefficient was 1.2.
Thus written in scientific notation is:
1.2 x 105

7. Measuring Distances In the Solar System
Kilometers can be an appropriate measurement on Earth, but astronomers need a more convenient unit.
The Astronomical Unit (AU):
149, 599, 000 kilometers; the average distance from Earth to the Sun.

8. Average Sun to Earth Distance 1 Astronomical Unit (AU)
93,000,000 Miles
1 AU = 149, 599, 000 km

9. Example In Astronomical Units
Jupiter is 780 million km from the Sun. How many Astronomical Units away is that?
Remembering: 1 AU = 149, 599, 000.
km / 149, 599, 000 km
= AU / 149, 599, 000 km
= AU
= 5.21 AU
**ALWAYS SHOW YOUR WORK.
Just the division portion.

10. The Light Year
Astronomers use light years to measure the distance to stars or other celestial objects.
Although it sounds like a unit of time, light years is, in fact, A UNIT OF DISTANCE.
Light Year: the distance that light travels in a vacuum (empty space) in 1 year (365 days); equal to 9.46 x 1012 km.
In space, light travels at a constant speed of approximately km/s

11. Example In Light Years
An unknown planet is 4.01 x 1013 km from Earth, what is it’s distance from Earth in light years?
Remember: 1 light year (ly) = 9.46 x 1012 km
= 4.01 x 1013 ly / 9.46 x 1012
= 4.24 ly.
Just the division

12. Going from light years to km?
What is the distance in km of one light year?
Distance in 1 light year
= speed of light x number of seconds in 1 year
= 300, 000 km/s x 60s/min x 60 min/ hr x 24h/ days x 365 days
= x 1012 km

13. The Parsec (pc)
The largest unit measurement in science, useful for the distant stars, and the large scale structure of the universe.
1 pc = x 1013 Km = 3.26 light years

14. Homework
Pg. 369 # 1-3, 6, 7.