1. Part 1: Distances in Space
And
Part 2: Comparing Planets to the Stars
(4.13A-01a)

2. Interplanetary Distances
Compared to how far away the stars are, separation of the planets is a relatively small distance.
Examples: Distance from Earth to the Sun ~ km and the distance between Earth and Mars is km.
Units of Distance used to describe the distance between planets is Kilometers

3. Kilometers are of limited use because distances in space are very large and we usually must express the number of kilometers in scientific notation.
e.g. the average distance from Earth to the Sun is km, but we write it 1.5x108km
Bill Nye distances between planets (4:17 min):
Bill Nye distances between planets soccer field (2:07 min):

4. Useful measurement units because,
Astronomical Units
Useful measurement units because,
1. They allow comparisons and the use of smaller numbers.
2. Compares distances to a common known distance (the distance from the Earth to the Sun).
ACK! That Brain has a comparative size of 3.5 H.B.’s
Comparing is easy. My brain is 3.5 times the size of HUMAN BRAINS

5. Why use the sun as a reference point?
1 astronomical unit = 1 a.u.
1a.u. = average distance between Earth and Sun
Earth is km, or 1 a.u. away from the Sun.
Mars is km, from the sun, or approximately 1.5 a.u. from the Sun. So Mars is 1.5 times as far from the sun as Earth is from the sun.
Why use the sun as a reference point?

6. Interstellar Distances
Interstellar distances are relatively very, VERY large distances.
Examples: Distance between Earth and Alpha Centauri (the next closest star) is 3.8x1013 km [or km]
Units of Distance used to measure the distance from Earth to a star or galaxy are LIGHT YEARS

7. How far can a photon (light particle) travel in 1 year?!?
1 light year is the distance that light can travel in 1 year, at its speed of km/s
1 light year = 9.5x1012 km
How far can a photon (light particle) travel in 1 year?!?
1 Light year !!!

8. Is that like looking into the past?b
Example: The nearest star (other than the Sun) to us is Alpha Centauri. Alpha Centauri is 4.3 light years away or 4.3x9.5x1012 km = 3.8x1013 km away from earth.
This means that the light that we see from Alpha Centauri left that star 4.3 years ago.
Is that like looking into the past?

9. The Andromeda Galaxy is 2.2 million light years away from Earth.
Light years are large, and there are no washroom stops between galaxies.
2.2 million light years
The Andromeda Galaxy is 2.2 million light years away from Earth.
This Means that the light we see from Andromeda Galaxy left there 2.2 million years ago.
It is therefore very possible that some of the stars in Andromeda have exploded as a supernova or gone out long ago. The message of these star finishing events just has not gotten to us yet!

10. Part 2: Comparing Planets and Stars

11. Features Planet Star Location Distance from the Earth Real Size
Reason we are able to see it
Surface Temperature
What are they made of?
Observable Features
Long Term Observable Features
In our solar system.
Beyond our solar system. The Sun is the closest one.
Closer than the sun or other stars.
Generally VERY VERY far away, (light years away) except for the Sun.
Varies, but much smaller than a star.
VERY VERY large compared to planets
Reflect the sun’s light and are called “Non-Luminous” (not light giving)
Gives off own light and are called “Luminous” (light giving)
Varies, depending on closeness to sun and insulation effects of atmosphere.
Extremely Hot
The Sun is ~5500oC
Some are rock (e.g. Earth, Mars)
Some are gas (e.g. Jupiter)
Gases … that are going through nuclear reactions.
Don’t “Twinkle” – give off steady light.
“Twinkle”
Slowly appear to move through constellations.
Varies, but our Sun has extreme solar flares every 11yrs.

12. Reviewing Lights in the Sky
In our own solar system we see 8 other planets, some of their moons and our own local star (Sol), which the solar system is named after.
We can see nearby planets because they reflect the light produced by our sun.
Luminous: stars are called luminous because they make the light that illuminates space.
Non-luminous: Objects like Planets are called non-luminous because they do not make their own light but only reflect the light of stars.