Why Am I Here?Why Am I Here?

To tell you about what’s out there in the To tell you about what’s out there in the Universe.Universe.

I’m an I’m an astronomerastronomer, which is a kind of , which is a kind of scientist.scientist.

I get to study stars and galaxies, and they I get to study stars and galaxies, and they pay me to do it!pay me to do it!

What do we call the star that is What do we call the star that is the nearest star to Earth… by far?the nearest star to Earth… by far?

The Sun!The Sun!

What What IsIs A A Star Star ??Stars look bright and tiny to us, but they are Stars look bright and tiny to us, but they are

huge dense balls of gas huge dense balls of gas lit up from the lit up from the inside by their own internal nuclear power.inside by their own internal nuclear power.

All stars were born from gas and dust that All stars were born from gas and dust that collapsed into a fiery ball because of gravity.collapsed into a fiery ball because of gravity.

Stars have different masses. The heaviest Stars have different masses. The heaviest are 100 times bigger than the lightest ones.are 100 times bigger than the lightest ones.

The Sun is One of Many, The Sun is One of Many, Many Stars in Our GalaxyMany Stars in Our Galaxy

What’s A Galaxy?What’s A Galaxy?

A galaxy is a huge collection of stars, A galaxy is a huge collection of stars, held together in space by gravity.held together in space by gravity.

Stars are very far apart and do not Stars are very far apart and do not bump into each other.bump into each other.

Galaxies also have clouds of gas Galaxies also have clouds of gas and dust between the stars.and dust between the stars.

Those clouds may make new stars Those clouds may make new stars one day, and recycle the dying ones.one day, and recycle the dying ones.

What do we call the galaxy we What do we call the galaxy we live in?live in?

The Milky Way is The Milky Way is Our Our GalaxyGalaxy

Why is it called “Why is it called “MilkyMilky”?”?

What the Milky Way Looks Like from the Inside

Where is the Sun inside the Where is the Sun inside the Milky Way?Milky Way?

TOP VIEW

SIDE VIEW

The Milky Way is The Milky Way is Our Our GalaxyGalaxy

Our galaxy contains about 200 billion Our galaxy contains about 200 billion stars – 200,000,000,000stars – 200,000,000,000 But the total mass of the galaxy is 5 But the total mass of the galaxy is 5 times more than that.times more than that.Loose-floating gas & dust only Loose-floating gas & dust only account for “only” about another 200 account for “only” about another 200 billion stars’ worth. billion stars’ worth. The galaxy is about the same age as The galaxy is about the same age as the universe: 13 billion years old.the universe: 13 billion years old.

The Andromeda Galaxy is similar to ours.

Galaxies com

e In many shapes and sizes.

Elliptical

Spiral

BarredSpiral

The Hubble Ultra Deep Field