E1 – Introduction to the Universe

Let’s make a model!

The Solar System

Let’s answer some questions!

(“Planet patterns”)

Main points

• Know the names of the planets!• They orbit in ellipses with the sun at one foci• Inner planets small and rocky• Outer planets large and mainly gas• Outer planets are much further from the sun• Asteroid belt between Mars and Jupiter

Comets

• Giant dirty snow balls (ice and dust) (diameter 100m - 50 km?)

• Very elliptical orbits• Short period (T < 200 yrs) and long period

(could be thousands of years)• Oort cloud• Tail(s) always point away from the sun• Evaporate as they get closer to the sun

Comets

My address

11507 Meadow Lake DriveHoustonTexas 77077USA

My address

11507 Meadow Lake DriveHoustonTexas 77077USAEarth

My address

11507 Meadow Lake DriveHoustonTexas 77077USAEarthSolar System

My address

11507 Meadow Lake DriveHoustonTexas 77077USAEarthSolar SystemMilky way

My address

11507 Meadow Lake DriveHoustonTexas 77077USAEarthSolar SystemMilky wayLocal groupUniverse

My address

11507 Meadow Lake DriveHoustonTexas 77077USAEarthSolar SystemMilky wayLocal groupUniverse

Galaxy

Galaxies

• A large collection of stars held together by their mutual gravity.

• Dwarf galaxies might have only a few million stars, many galaxies have hundreds of billions.

• The Universe has around 100 billion galaxies

Astronomical unit (1 AU)

An astronomical unit (AU) is the average distance of the earth from the sun which is 150 million km

1 AU = 1.5 x 1011 metres

Light Year

1 ly = 3 x 108 x 365 x 24 x 60 x 60 = 9.46 x 1015 m

Defined as the distance travelled by light in one year

Distance between stars in a galaxy

About one parsec (defined later)

One parsec is 3.26 light years

Distance between galaxies

• 100 kpc for galaxies in clusters• A few Mpc for galaxies in different clusters

Constellations

• The pattern of the stars remains the same from night to night (over the time of a life-time)

• These patterns have been labelled constellations

Orion’s belt

Constellations

• The constellations do not appear in the same place

• Over the period of one night they appear to rotate around the pole star

• Some stars rise above the horizon during the night, and some set behind it.

Constellations

• This same movement is continued during the day. The sun rises in the east and sets in the west. Maximum height at midday (in the south in the Northern hemisphere.

Constellations

• The constellations visible also depends on the time of year

Constellation position

• The location of stars also varies slightly at different times of year due to the change in position of the earth.

Place to place

• The constellation you can see also depends on where you are

I can’t see the pole star!

I’m on top of the world!

Constellations – line of sight effect

• The stars in a constellation only appear to be close

Stellar clusters

• A group of stars that are physically near each other in space, formed from the same gas cloud.

Let’s read!Pages 487 to

492.