Welcome to AST 111!

Instructor: Adam Blake

Planets

• Earth is a planet in the solar system.• The planets in the solar system revolve around

the Sun.

The Solar System

• The Solar System consists of:– The Sun– All objects that have been captured by the Sun’s

gravity (these objects orbit the Sun)• Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus,

Neptune• Asteroid Belt• The Kupier Belt• The Oort Cloud

Stars

Are stars the largest “element” in the Universe?

Galaxies

The Milky Way

• The Sun is one star among one hundred BILLION in the Milky Way Galaxy:

The Milky Way NOT the Milky Way (why not?)

Structure of a Galaxy• Galaxies generally consist of:

– A supermassive black hole• 100,000 solar masses to 18 billion

solar masses (largest known)

– The central bulge– The disk– Spiral arms (sometimes)– The halo

• Large galaxies often have smaller satellite galaxies in orbit

• Sometimes they get absorbed by the larger galaxy

Nebulae live in galaxies.

Star clusters also live in galaxies.

Galactic Collisions

Sometimes they duke it out for millions of years!

Galaxy Clusters

• The Milky Way Galaxy is one galaxy among 30+ in the Local Group

Galaxy Clusters

Galaxy Superclusters

• The Local Group is one galaxy cluster among 100+ in the Virgo Supercluster

Hubble Ultra Deep Field

The Universe

• Do superclusters form larger-scale structures?

• What are the largest-scale structures in the Universe?

Cosmology

How it’s Built

• The hierarchy:– Planets– Stars– Galaxies– Galaxy Clusters– Galaxy Superclusters– The rest of the Universe

Two questions to ponder…

• When you look at the night sky, what is and what is not in our galaxy?

• Why don’t galaxies look like a pile of sprinkles? They’re composed of lots of stars, right?

The Scale of the Solar System (Size Comparison)

The Scale of the Solar System(Orbit Comparison)

• From the Sun to the Earth: 93 million miles• From the Sun to Neptune: 2.79 billion miles

• The solar system is conveniently measured in Astronomical Units (AU)– 1 AU = 93 million miles– Distance from Sun to Earth

The Scale of the Galaxy

• We need to use light years to describe the galaxy.– 1 LY is how far light

travels in 1 year– Light travels 186,000

miles / second– 1 LY = 5.88 trillion miles

The Scale of the Galaxy

• The star nearest to the Sun is Alpha Centauri

• It is 4.4 light years from the Sun!

• Side note: many of the stars that you can see are multiple stars

The Scale of the Galaxy

• The diameter of the Milky Way is 100,000 LY

• If the Milky Way were a football field:– Solar System becomes

microscopic dot– Alpha Centauri is 4.4mm

away– Millions of star systems

are within arms reach

The Nearest Galaxy

• The nearest “heavyweight” galaxy is the Andromeda Galaxy

• 2.1 million light years away!

The Farthest Galaxy (that we can see)

13+ billion light years away and 600 million years old

Looking Back In Time

Light travels 186,000 miles per second.

On Earth, it seems instantaneous.

But if we observe light from an object 2.1 million light years away, we see the object as it was

2.1 million years ago.

“The Universe is full of magical things, patiently waiting for our wits to grow sharper.”