Wednesday March 23 Thursday March 24 Unit Question What do we know about the universe? How do we know it? Guiding Question / Learning Target How do we know what we know about the universe? Warm-up What kind of spectra is this? Agenda Finish Spectroscopy Doppler effect Homework Quiz Friday Absorption Spectrum

All missing work for Astronomy (March) due Friday next week! Quarter ends next week. Get stuff in!

Finish Spectrum Lab If you did Part 1 Monday/Tuesday, you will start on part 2 today. If you did Part 2 Monday/Tuesday, you will start on part 1 today.

Do your spectrums match? Hydrogen Helium Neon Xenon Krypton Mercury Nitrogen

How can you tell what this star is made of based off the first blue question mark? Hydrogen or Magnesium

Today: We are looking at how we can tell how fast/far galaxies are moving. Fill out your worksheet as we move through the powerpoint.

Slinky Which wave moved toward us? Away from us?

Doppler shift Doppler shift short

Car Honking Which wave represents high pitch? Low pitch?

Wavelength and Light Blue Red Starts looking bluer Light with a shorter wave length looks: Light with a longer wave length looks: What would happen to the color of a light if it moves toward us? What would happen to the color of a light if it moves away from us? Red Starts looking bluer Starts looking redder

Stephan's Quintet  The first identified compact galaxy group, Stephan's Quintet is featured in this eye-catching image constructed with data drawn from the extensiveHubble Legacy Archive. About 300 million light-years away, only four of these five galaxies are actually locked in a cosmic dance of repeated close encounters. The odd man out is easy to spot, though. The interacting galaxies, NGC 7319, 7318A, 7318B, and 7317 have an overall yellowish cast. They also tend to have distorted loops and tails, grown under the influence of disruptive gravitational tides. But the predominantly bluish galaxy, NGC 7320, is closer, just 40 million light-years distant, and isn't part of the interacting group. Stephan's Quintet lies within the boundaries of the high flying constellation Pegasus. At the estimated distance of the quartet of interacting galaxies, this field of view spans about 500,000 light-years. However, moving just beyond this field, above and to the left, astronomers can identify another galaxy, NGC 7320C, that is also 300 million light-years distant. Of course, including it would bring the interacting quartet back up to quintet status.

Here are spectra lines from some distant galaxies. Remember from your notes, that each element gives it’s own spectral pattern. Hydrogen normally looks like this: 656,3

Look at the patterns of lines on your sheet. What do you notice? Using the Brightest (representing red) line on the spectrum, list the velocity (speed) that each galaxy is travelling. On the next page, graph distance vs. velocity. Finish the questions

Hubble’s law

Farther galaxies move faster 4. What is the Doppler shift (effect)? How does it affect light? 5. How do astronomers know the speeds of galaxies moving away from us? 6. What is Hubble's Law? (Use your graph above, and summarize its findings into a sentence or two). 7. If you could travel backward in time, what would you notice about the motion of galaxies (how and where would galaxies appear)? As waves move away they stretch, toward they compress. Light looks redder as it moves away. How much they redshift depends on speed of motion Farther galaxies move faster Closer and slower until they meet at a standstill

Exit Question If a universe appears to be blue, is it moving towards us, or away from us?