Stars and Galaxies

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Slide 31

There are different types of spectra

Continuous

Emission or Bright Line (from ionized gas, like a nebula or a neon sign)

Absorption or dark line (from stars)

Slide 32

Radiation

All stars emit radiation

Radio, infrared, visible, ultraviolet, x-ray and even some gamma rays

Most sunlight is yellow-green visible light or close to it

The Sun at X-ray wavelengths

Image at http://imagine.gsfc.nasa.gov/docs/science/know_l1/sun.html

Image and info at http://imagine.gsfc.nasa.gov/docs/teachers/gammaraybursts/imagine/page18.html

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Slide 33

Using a Star’s Spectrum

We can use a star’s spectrum to classify it.

NOAO/AURA/NSF image at http://antwrp.gsfc.nasa.gov/apod/ap010530.html

Slide 34

Stellar Evolution

Slide 35

Time to Create a Stellar Graph

Everyone will receive several “stars”

Place them on the large paper, according to their color and their brightness

This is a version of the Hertzsprung-Russell diagram.

Slide 36

Hertzsprung-Russell Diagram

Slide 37

Young stars form in nebulae from Small Magellanic Cloud

Slide 38

Star-forming region in the Large Magellanic Cloud

Slide 39

Slide 40

Interstellar “eggs”

Movie at

Slide 41

Our Sun is a Regular/ Small Star

On the “Main Sequence”

Slide 42

In a few Billion years… Red Giant

Slide 43

Our Sun’s Habitable Zone

Billions of years ago, things may have been different

The Sun was cooler (by up to 30%!)

Earth’s atmosphere was different (thicker, carbon dioxide)

Conditions will be different in the future

By many accounts, increases in the Sun’s temperature will make Earth uninhabitable in 1 billion years or less

These changes will also affect other planets… Mars?