1. Astronomy – the Study of the Universe

2. Speculation about the nature of the universe is an ancient tradition.

3. Modern astronomy relies on observations and inferences using the most advanced technology and mathematics.

4. The laws of physics are used to explore the universe, and occasionally refined by astrophysical observations/theory.

5. The solar system reveals clues to the formation of the earth and other planets

6. Studying stars had led to insight into how stars are born, grow old, and die.

7. The creation and fate of the universe is under active discussion
In recent years, the age of the universe has been nailed down
(13.7 billion years).

8. Accelerating Universe?

9. It is a great time to be an astronomer!
Within your lifetime, it is likely that habitable planets will be identified around in our galactic neighborhood.

10. The Earth’s Place in the Universe
Starlight is a historical record of the past – we see the star as it was when the light left it.
Star light can travel for years to billions of years; the farther away the star is, the farther back in time we are observing.

11. Astronomers use the light-year to measure the vast distances in space.
Light travels very fast: 3 x 108m/s. How fast is this?
It takes about 8 minutes for the sun’s light to reach us (150 million km away)
Light could make 7 trips around the equator in a second!
The nearest star system is the Centuri system, 4.3 light years away.
The nearest galaxy to the milky way, the Andromeda galaxy is about 1 million light years away (and closing).
The farthest stars are around 12 billion l-y away.

12. What are galaxies?
Systems containing billions of stars; the largest contain upwards of a trillion stars!
Three types of galaxies:
Spiral
Elliptical
Irregular

14. The Milky Way
Our galaxy, a spiral, measures 100,000 l-y in diameter, and 15,000 l-y thick.
Our solar system is located on one of the spiral arms, 30,000 l-y from the nucleus – pretty far out.
The nucleus is composed of dust, gas, and high densities of stars. At the center is a massive “black hole” that contains the remains of millions of stars!
It takes 230 million years for our galaxy to rotate on its axis.

15. Properties of Galaxies
It is not clear why galaxies are the shape they are; stars at the edge of galaxies move at a similar speed to ones closer in. According to the laws of physics, this shouldn’t be!
One proposal is that galaxies (and us) are embedded in stuff called “dark matter” which has mass, but doesn’t interact with ordinary matter.

16. The Galactic Neigborhood

17. The Galactic Neighborhood
Galaxies are moving in massive clusters, like filaments.
The Milky Way is part of small band called “the local group,” which consists of Andromeda (1 trillion stars), the Milky Way (2-400 billion), and M33 (40 billion), as well as dozens of smaller satellite galaxies.
The local group is part of a larger group of galaxies called the Virgo Supercluster.

19. Andromeda vs. Milky Way
Although Andromeda has more stars, the Milky Way has been estimated to have equal or greater mass. Star formation is more common in our galaxy than our neighbor.
The two galaxies are 2.5 million l-y apart, yet are getting closer at the rate of 120 km/s. At this rate, in 2.5 billion years, the galaxies will collide!
Galactic collisions are fairly common. The largest galaxies, ellipticals, are the product of collisions between large galaxies such as ours and Andromeda.

20. Galaxies colliding