AstronomyAstronomy

What is Astronomy?

1. Astronomy is the study of the universe.

• This includes planets, stars, galaxies, black holes, moons, meteors, comets, asteroids and all of the matter that exists in space.

2. Astronomers are people who observe and study space.

Modern CalendarModern Calendar

1. Our modern 1. Our modern calendar is based on calendar is based on the observations of bodies in our the observations of bodies in our solar system.solar system.

2. A year is the time it takes for the 2. A year is the time it takes for the Earth to orbit the sun.Earth to orbit the sun.

3. A month is the time it takes for the 3. A month is the time it takes for the moon to orbit the Earth.moon to orbit the Earth.

4. A day is the time it takes for the 4. A day is the time it takes for the Earth to rotate once on its axis.Earth to rotate once on its axis.

The The Size and Scale of our UniverseSize and Scale of our Universe

1. It is 1. It is important to consider scale important to consider scale when we think about the universe.when we think about the universe.

2. Stars appear to be very small when 2. Stars appear to be very small when viewed from Earth, but they are viewed from Earth, but they are actually very large, some, like our actually very large, some, like our sun, are bigger than Earth.sun, are bigger than Earth.

The Scale of our Solar System

Earth

Scale of the Universe

Mercury

SUN

Our Galaxy and Scale• Our Milky Way galaxy is simply huge. Just how big is

our galaxy?• Let's now pretend that our galaxy is a kid's sandbox,

and our sun is a grain of sand in a sandbox.• The Earth is a miniscule dust speck near the grain of

sand, too small to be seen without a microscope.• If our sun were a grain of sand in this sandbox

representing the Milky Way galaxy, the sandbox would be somewhat oval and yet flat, and would be about 20 feet in diameter.

• The sand would be about 12 inches thick in the center, and thinner towards the edges.

•

Milky Way GalaxyMilky Way Galaxy

Distance in SpaceDistance in Space

1. Distance in space is measured in light 1. Distance in space is measured in light years.years.

2. A light year is used to measure large 2. A light year is used to measure large differences in space.differences in space.

3. A light year is the distance light travels 3. A light year is the distance light travels in a year, 5.88 trillion miles.in a year, 5.88 trillion miles.

4. Light travels at 186,000 miles per 4. Light travels at 186,000 miles per second.second.

•Each swirling object you see is a galaxy in our universe.

1. We can estimate that there are about 100 billion stars in our galaxy.

2. Andromeda is the nearest major galaxy to our own Milky Way Galaxy.

3. Most scientists believe that Andromeda is about 2 million light years away from the Milky Way.

THE MILKY WAY GALAXY

What is a Galaxy?What is a Galaxy?

1. 1. A large group of stars, gas, and dust A large group of stars, gas, and dust held together by gravitational held together by gravitational attraction.attraction.

2. 2. A system of about 100 billion stars.A system of about 100 billion stars.

3. 3. There are billions of galaxies in the There are billions of galaxies in the observable universeobservable universe..

3 Types of Galaxies3 Types of Galaxies

1. 1. SpiralSpiral 2. 2. EllipticalElliptical 3. 3. IrregularIrregular

Spiral GalaxySpiral Galaxy

1. Spiral 1. Spiral galaxies galaxies consist of a consist of a flat, rotating flat, rotating diskdisk of of starsstars, , gas and dustgas and dust, , and a central and a central concentration of concentration of stars known as stars known as the the bulgebulge..

2. 2. The Milky The Milky Way galaxy is Way galaxy is a spiral a spiral galaxy.galaxy.

Irregular Irregular GalaxyGalaxy

1. These are 1. These are galaxies that galaxies that feature feature neither neither spiralspiral nor nor ellipticalelliptical morphology morphology..

2. They are 2. They are often often chaotic in chaotic in appearance, with appearance, with neither a nuclear neither a nuclear bulge nor any bulge nor any trace of spiral arm trace of spiral arm structure. structure.

Elliptical GalaxyElliptical Galaxy

1. Elliptical galaxies 1. Elliptical galaxies have have smooth, smooth, featureless light-featureless light-profiles.profiles.

2. There is 2. There is very little very little interstellar matterinterstellar matter (neither gas nor (neither gas nor dust),dust), which results which results in low rates of in low rates of star formationstar formation..

3. Elliptical galaxies 3. Elliptical galaxies are are dominated by dominated by old stellar populationold stellar populationss, or old stars. , or old stars.

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