CRCT QuestionGroups of two or more stars are

called: a. Star clusters b. Star systems c. Galaxies d. Solar systems

When’s The

Test?

Are stars still present in the sky during the day time?

Yes, we just can’t see them because their dim light is

overwhelmed by the brightness of the sun during the day.

Galaxies are based on their:

Size

Shape

Brightne

ss

Densit

y

11%6%6%

78%1. Size2. Shape3. Brightness4. Density

What is it most based on?

Life of a Star

1. The Origin of Stars• Nebula: A large cloud of gas (helium and

hydrogen) and dust which forms into a star.• Dust and gas particles exert a gravitational force

on each other which keeps pulling them closer together.

Orion Nebula

More Nebulas• As the particles pull closer together the

temperature increases.• At 10,000,000o C fusion takes place and

energy radiates outward through the condensing ball of gas.

• Another view of Orion

Hydrogen Fusion: Energy of the Stars

• Stars have large amounts of hydrogen gas.• Four hydrogen atoms fuse forming 1 atom of

helium• The mass of 4 hydrogen atoms is greater than the

mass of 1 helium atom; the excess mass is converted to a tremendous amount of energy.

• This hydrogen helium fusion can power a star for billions of years

Step 2: Stellar Evolution• Fusion uses up a star’s hydrogen supply rapidly

casing the core to heat up and the outer temperature to fall. (Life cycle of the star)

• Star expands and becomes a red giant

• Red Giant

Stellar Evolution• Core continues to heat and star expands to a

super giant.• As the core uses up its helium supply, the outer

layers escape into space and the remaining core is white hot and called a white dwarf.

• White dwarfs

3. More Stellar Evolution• When no more material is left in the core it

explodes into a supernova.• Smaller stars become neutron stars and most

massive will collapse into a black hole.

• Neutron Star

Black Holes-nothing can escape, even light!

A. Earth’s Galaxy—and Others• Galaxy: A large group of stars, gas, and dust held

together by gravity.• Milky Way: Our galaxy which contains about 200

billion stars and many nebulas

• Spiral Galaxies

Spiral Galaxies• Spiral Galaxies: Circular galaxies that have arms

curve outward from a central hub.• Arms are made up of stars and dust

Two spiral galaxies!!

Irregular Galaxies• Irregular Galaxies: Come in many different shapes

and are smaller and less common than elliptical or spiral galaxies.

Do you know the Milky Way?• 100,000 light years in diameter•Our sun orbits the center of the galaxy once every 240 million years• Probably a barred spiral galaxy• Contains over 200 billion stars• Its where I live!!!!!

Name Game

Constellation Homework

Need to include: •Picture •Major stars •Brief background

Stars as Tools for Navigation Earth rotates on its axis, this makes most

constellations appear to rise in the east and set in the west during the night.

Most constellations appear in many different positions in the sky as the Earth revolves around the sun.

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 Calendars It seems that the constellations in the east rise a

little earlier each evening. This means that the seasons are changing and we are seeing different constellations. An example is in the Northern Hemisphere, Orion is high in the sky during the winter and Scorpio can only be seen during the summer.

People of ancient times used these seasonal changes in the stars as calendars. It is believed that the ancient people used the

constellations to tell them when to plant and harvest crops. An example would be Leo and Virgo in the night sky would signify that the last frosts of the year have happened and it is safe to plant. This worked much like our paper calendars work for us today.

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.

OrionOrion is one of the brightest constellations and is a mythological character.

According to Greek myths, Orion was a hunter who used to brag all the time. This bother the gods.

When the gods were tired of him, the sent a scorpion to bite and kill him.

The gods felt bad for doing having Orion killed, they they placed him in the sky.

Constellation List• Andromeda • Canis Major-the dog• The swan• Gemini-the twins • Leo-the lion• Orion-the hunter• Scorpius-the scorpion• Taurus-the bull• Big dipper• Little dipper