Part 1: Distances in Space

And

Part 2: Comparing Planets to the Stars

(4.13A-01a)

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 ~150 000 000 km and the distance between Earth and Mars is 75 000 000 km.

• Units of Distance used to describe the distance between planets is Kilometers

• 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 150 000 000km, but we write it 1.5x108km

Bill Nye distances between planets (4:17 min): http://www.youtube.com/watch?v=97Ob0xR0Ut8

Bill Nye distances between planets soccer field (2:07 min): http://www.youtube.com/watch?v=BdAqq-wEQV0&feature=related

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).

Comparing is easy. My brain is 3.5 times the size of HUMAN BRAINS

ACK! That Brain has a

comparative size of 3.5 H.B.’s

Why use the sun as a reference point?

• 1 astronomical unit = 1 a.u.• 1a.u. = average distance between Earth and Sun• Earth is 150 000 000 km, or 1 a.u. away from the Sun.• Mars is 230 000 000 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.

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 38 000 000 000 000 km]

• Units of Distance used to measure the distance from Earth to a star or galaxy are LIGHT YEARS

• 1 light year is the distance that light can travel in 1 year, at its speed of 300 000 km/s

• 1 light year = 9.5x1012 km

How far can a photon (light particle) travel in 1 year?!?

1 Light year !!!

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?

• 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!

2.2 million light years

Light years are large, and there

are no washroom stops

between galaxies.

Part 2: Comparing Planets and Stars

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.

Reflect the sun’s light and are called “Non-Luminous” (not light giving)

Varies, depending on closeness to sun and insulation effects of atmosphere.

Some are rock (e.g. Earth, Mars)

Some are gas (e.g. Jupiter)

Don’t “Twinkle” – give off steady light.

Slowly appear to move through constellations.

VERY VERY large compared to planets

Gives off own light and are called “Luminous” (light giving)

Extremely Hot

The Sun is ~5500oC

Gases … that are going through nuclear reactions.

Varies, but our Sun has extreme solar flares every 11yrs.

“Twinkle”

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:Luminous: stars are called luminous because stars are called luminous because they make the light that illuminates space.they make the light that illuminates space.

Non-luminous:Non-luminous: Objects like Planets are Objects like Planets are called non-luminous because they do not called non-luminous because they do not make their own light but only reflect the light of make their own light but only reflect the light of stars.stars.