1. Lecture 31 – Structure of the Milky Way. Let’s check our answer
Are there other objects in the sky which resemble the MW?

2. M31 The Andromeda Galaxy

3. M104 The Sombrero Galaxy

4. The Sky is filled with objects with the same shape and size of the Milky Way. The term for these objects is spiral galaxy. So we figured out the structure of the MW pretty well from the inside, and there is a universe filled with similar objects

5. Next topic: motions of stars in galaxies
There are internal motions In galaxies, a “procession of stars”.
How can we tell?

6. The Doppler Effect (p104)
If a source of waves is in motion with respect to an observer, the observer measures a different wavelength than was emitted

7. The Doppler Effect: Say it in equations
W-W0 V W0 c
DEMO

8. How the Doppler Effect effects spectral lines

9. Results for the motion of the Sun in the Milky Way
Doppler shifts measured for many objects outside the Milky Way, or not a part of the galactic disk.
The Sun is moving on an orbit around the galactic center at a speed of V=220 km/sec
The motion of our orbit is in the direction of Cygnus

10. An independent proof that the Sun is moving on an orbit in the Milky Way
DEMO
VLBI observations