Mr. Mac’s Earth Science Classroom

Galaxies

- Group of stars, gas, and dust.- There are over 40 billion galaxies in the universe!- 1000 to 1,000,000 light years wide.

Mr. Mac’s Earth Science Classroom

New Vocab Worddddd….

Light Year (ly): distance light travels in one year.

A light year is not a measure of time. Light travels 9.5 trillion kilometers in one year. That’s a lot!

Star: 4.3 ly away It will take light 4.3 years to reach our eyes. (Proxima Centauri)

Mr. Mac’s Earth Science Classroom

What is a galaxy?

Mr. Mac’s Earth Science Classroom

Spiral Galaxies

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Elliptical Galaxies

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Elliptical Galaxies

Most are tiny

Mr. Mac’s Earth Science Classroom

Irregular Galaxies

D. Hunter (Lowell Observatory), Z. Levay (STScI)

Mr. Mac’s Earth Science Classroom

Irregular Galaxies

These galaxies are not spiral or elliptical. They are irregularly shaped.

They contain lots of gas and dust which means that lots of stars are forming.

D. Hunter (Lowell Observatory), Z. Levay (STScI)

Local G

roup Galaxies S

urvey Team

, N

OA

O, A

UR

A, N

SF

Mr. Mac’s Earth Science Classroom

The Milky Way

“face-on” view

“edge-on” (looking from the edge)

view

25 kpc = 25 kiloparsecs = 25,000 parsecs

75,000 light-years

8.5 kpc (2/3 of the way out)

Mr. Mac’s Earth Science Classroom

The Big Bang Theory: 10 billion to 20 billion years ago:

An expansion of space from a single point..

Mr. Mac’s Earth Science Classroom

The Big Bang Theory: 10 billion to 20 billion years ago:

• Over time the universe has cooled, but is still expanding today.

(What proof do we have?Stay Tuned!) …

• After about 1 billion years, the first stars and galaxies started to form….

The galaxies are expanding WITH space!!!

The Big Bang Theory: 10 billion to 20 billion years ago:

Mr. Mac’s Earth Science Classroom

The Big Bang Theory: 10 billion to 20 billion years ago:

The “raisin bread” analogyraisins galaxies, dough space

Mr. Mac’s Earth Science Classroom

The Big Bang Theory: 10 billion to 20 billion years ago:

The “raisin bread” analogyraisins galaxies, dough space

Mr. Mac’s Earth Science Classroom

The Big Bang Theory: 10 billion to 20 billion years ago:

The “raisin bread” analogyraisins galaxies, dough space

Note: raisins are not moving through dough.

Rather, blobs of dough are expanding, and

pushing the raisins farther apart.

Note: galaxies are not moving through space.

Rather, blobs of space are expanding, and

pushing the galaxies farther apart.