Stars Galaxies and Constellations l l l Stars

Stars, Galaxies, and Constellations

l l l Stars are born when there is a large amount of gas and dust in a small area that becomes so hot that nuclear fusion starts. The gas continues to burn until it runs out. More burning gas = a bigger and brighter star!

Our Sun is a star and is the largest object in our solar system. It is the only star in our solar system

Our Sun Billions of years ago, things may have been different l l l The Sun was cooler (by up to 30%!) Earth’s atmosphere was different (thicker, carbon dioxide) Conditions will be different in the future l By many accounts, increases in the Sun’s temperature will make Earth uninhabitable in 1 billion years or less

Our Sun The Sun will spend most of its life in the main sequence. l It will expand into a red giant l In about 5 billion years, it will turn into a white dwarf. l

The Sun compared to other stars in our galaxy…

And yet larger stars…

Temperature of a Star l l l l 3, 000° – 6, 000° Fahrenheit (1, 649° – 3, 316° Celsius): Red 6, 000° – 8, 500° F (3, 316° – 4, 704° Celsius): Orange 8, 500° - 10, 500° F (4, 704° – 5, 816° Celsius): Yellow/ White 10, 500° – 13, 000° F(5, 816° – 7, 204° Celsius): Type F -White 13, 000° - 17, 500° F(7, 204° – 9, 704° Celsius): Type A -White 17, 500° – 50, 000° F (9, 704° – 27, 760° Celsius): Blue -White 50, 000° - 100, 000° F (27, 760° – 55, 538° Celsius): Blue

What is a Galaxy? l l A large group of stars outside of our own Milky Way Made of billions to trillions of stars l l Also may have gas and dust Spiral, or elliptical, or irregular shaped

Types of Galaxies Spiral Galaxies l l Have arms of stars, gas and dust that curve away from the center of the galaxy in a spiral form. There is a central disk of older stars at the center. The youngest stars are on the outer arms There is a lot of dust and gas

The Milky Way Galaxy l l l We live in the Milky Way galaxy. The Milky Way is a spiral galaxy. It has about 200 billion stars, and lots of gas and dust. All the stars in the Milky Way have their own motion, some are moving towards the sun while others are moving away from our sun. Our Sun is halfway to the edge of an arm, revolving at half a million miles per hour around the center of the galaxy

The Milky Way Galaxy l l The Milky Way has a diameter of about 100, 000 light years. The nucleus is 2000 light years thick. Our sun is located 30, 000 light years from the nucleus. It takes the sun 200 million years to make one Revolution around the center.

The Milky Way Galaxy l l You can look outside on a clear dark night and see the Milky Way!!! In the night sky it will appear as a band of stars that stretches across the sky. It will appear “milky” in the sky. You are actually looking at one of the arms of the galaxy!

Types of Galaxies Elliptical Galaxies l l l Elliptical galaxies contain many older stars, up to one trillion, but little dust and gas. They are typically larger galaxies. There are no young stars.

Types of Galaxies Irregular Galaxies l l They lack shape They are the smallest galaxies with the fewest stars. Could be formed from the collision of two different galaxies. Stars are of low mass and cannot organize into a pattern

The next closest galaxy to us is Andromeda, which is also a spiral galaxy. Andromeda is about 2. 5 million light years away. There an estimated 50 billion to 1 trillion galaxies in the known universe!

What is a Nebula? l l A cloud in space Made of gas and dust l Can have stars inside Most of the ones we see are inside our Milky Way Galaxy l Young stars form in nebulae l

WHAT ELSE IS IN A GALAXY? The Nebula’s cometh l Galaxies also contain gases and dust. l There are two bright nebulas. l One glows bright from the hot gases within. l The other shines by reflecting light from nearby stars.

THE DARK SIDE OF THE NEBULA. The dark nebula. l Other nebula’s are dark in nature. l Dark nebulas are visible as dark areas among the stars. l Dark nebulas absorb light of more distant stars behind them. l The Horsehead Nebula is an example of a dark nebula.

Leftovers from an Explosion l Supernova- A Massive Star Explodes

Neutron Star or Pulsar A neutron star is a type of stellar remnant that can result from the gravitational collapse of a massive star

Black Holes • A black hole is a region of spacetime from which nothing, not even light, can escape. • Black holes of stellar mass are expected to form when very massive stars collapse at the end of their life cycle. • After a black hole has formed it can continue to grow by absorbing mass from its surroundings. • There is general consensus that supermassive black holes exist in the centers of most galaxies

Light Years l What is a Light Year? l l A light year is the distance light travels in a year. Light moves at a velocity of about 300, 000 kilometers (km) each second; how far would it move in a year? About 10 trillion km (or about 6 trillion miles).

Parallax is a difference in the apparent position of an object viewed along two different lines of sight. [ l Astronomers use the principle of parallax to measure distances to celestial objects including to the Moon, the Sun, and to stars beyond the Solar System. l

Binary Star Systems A pair of stars that revolve around each other. l Multiple star systems- have more than two stars. Two will orbit rapidly around one another while a third will move slowly at a greater distance away. l

Constellations l All the stars that we can see from Earth are in our galaxy. l Constellations are patterns of stars in the sky.

Ancient Greeks and Romans saw pictures in the stars of the night sky. l These pictures were later associated with myths. l

Astronomers recognize 88 constellations including… Ø 14 men and women Ø 9 birds Ø 2 insects Ø 19 land animals Ø 10 water creatures Ø 2 centaurs ØA serpent Ø A dragon Ø A flying horse Ø A river Ø 1 head of hair Ø 29 inanimate objects

Example: Scorpius l l l The scorpion is believed to be responsible for the death of the great hunter, Orion was stung and killed after he was boasting that he could defeat any beast. Scorpius was placed in the sky opposite from Orion to avoid any further contact.

Stars as Tools for Navigation l Earth rotates on its axis, this makes most constellations appear to rise in the east and set in the west during the night. l There is a group of stars that appear in the sky all night long and all year long. It seems that these stars do not rise and set, but circle the Earth’s north pole each night. These stars are called circumpolar.

Stars as Tools for Navigation l l The North Star is called Polaris and located directly above the North Pole. This star appears in the same place every night all year long. In the Northern Hemisphere, if you find Polaris you will be able to tell which direction is north. l l The Southern Hemisphere does not have a star to help you find its pole. In stead it has what is known as the Southern Cross. The Southern Cross consists of 4 bright stars and some dimmer ones. All of these together point to the south pole.

Extra Info. l The brightest constellation is Crux (the Southern Cross). The constellation with the greatest number of visible stars in it is Centaurus (the Centaur - with 101 stars). The largest constellation is Hydra (The Water Snake) which extends over 3. 158% of the sky.