Stars and Galaxies

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takes our Solar System about 200 million years to revolve once around our galaxy

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The Milky Way

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Mapping the Milky Way

We can see stars

star clusters

nebulae

Galaxies

Let’s try to Map our Galaxy

How do we know what our Galaxy looks like?

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Measuring Distances

Parallax (let’s model it)

As Earth orbits the Sun, we see nearby stars move relative to more distant stars

How many degrees did the plate move, relative to the background?

Can you calculate the distance to the plate?

Sine of the parallax (angle) x Earth’s distance to the Sun = Distance to the star

The angles involved for strellar observations are very small and difficult to measure. Proxima Centauri, has a parallax of 0.77 arcsec. This angle is approximately the angle subtended by an object about 2 centimeters in diameter located about 5.3 kilometers away.

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Measuring Distances

What is a Light Year?

A light year is the distance light travels in a year. Light moves at a velocity of about 300,000 kilometers (km) each second; how far would it move in a year?

About 10 trillion km (or about 6 trillion miles).

Why do we use light years?

Show me how far 5 centimeters is.

Now show me 50 centimeters.

Now tell me (without thinking about it, or calculating it in meters) how far 500 centemeters is. 2000? 20,000?

We need numbers that make sense to us in relationship to objects; we scale up and use meters and kilometers for large numbers.

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Time for a Break! Next Up

Our Place in the Universe

The Electromagnetic Spectrum

Classifying Stars

Classifying Galaxies

History of the Universe

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Let’s check your knowledge

Please draw an electromagnetic spectrum on a sheet of paper, and label the parts.

You can work in groups.

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Radiation

There are lots of types of light (radiation), including visible and invisible

Electromagnetic spectrum

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Let’s Observe A Spectrum

What will the spectrum look like with a red filter in front of your eyes? A blue filter?

Hypothesize and test your hypothesis.

Now let’s examine the invisible parts—using our cell phones and a solar cell.