Mrs. Degl1 All about the Stars Click here Click here for the Astronomy picture of the day!!! The distances to stars are very large so astronomers use light years as units. A light year is the distance light can travel in one year. 1 light year = 9.5 trillion kilometers or 5.8 trillion miles. (Light travels at a rate of 300,000 km per second.) A stars brightness is controlled by 3 factors: 1.The size of the star 2.The temperature of the star 3.The distance from the viewer (this is the most important one) Absolute Magnitude/Luminosity = The true brightness of a star Apparent Magnitude = How bright a star appears to us on Earth As the Earth’s distance from a star increases, it’s apparent magnitude _______________.

Mrs. Degl2 Stellar Evolution (How stars form) In outer space there is plenty of material, but it is very spaced out. Over time, gravity begins to pull this material together. Hydrogen is the most common element that gets pulled in by gravity. Eventually large, dark, cool clouds of matter form. Because of the mass increase, gravity begins to contract the cloud further. The temperature begins to rise and the cloud radiates heat (infrared). This is a Protostar (infant star). The gravity contraction continues, and the star reaches 10 million K. Hydrogen nuclei begin to fuse (join together). This is called Nuclear Fusion or Hydrogen Fusion. The hydrogen turns into Helium when it fuses. A star is formed by hydrogen fusing into helium. This is what all stars are made of and why they continue to burn and explode today.

Mrs. Degl3 Take out page 15 in your Earth Science Reference Tables. Let’s compare the two charts.

Mrs. Degl4 The Life Cycle of the Stars ( the short summary) All stars are born in the Red Dwarf Phase. Stars are coolest at this point and relatively small. Stars stay in this phase for a few million years. As they grow, they enter the Main Sequence Phase. This phase has a temperature range from 5,000 ºC to 16,000 ºC. Stars that are born small will have a lower temperature than stars that are born larger. Stars stay in this phase for about 9.5 billion years. Larger stars will leave this phase quicker than smaller stars. After the Main Sequence, larger stars now enter the Blue Supergiant phase. These are the largest stars. The smaller/medium stars will enter the Red Giant after leaving the Main Sequence. Now on to the death of stars………

Mrs. Degl5 How Stars Die Out The Blue Supergiants will begin to burn up all of the hydrogen that they have after a few million years. When this happens, the outer shell of the star begins to expand. It grows to about triple the size that it currently is. The Blue Supergiant now becomes a Supergiant. Supergiants are orange/yellow and are mostly helium. This is the last stage before it blows up. Blue Supergiants can have one of two fates. They will Supernova (explode) and become a Neutron Star or a Black Hole. Only the high mass stars can do these two things. The small/medium stars have a completely different death. After staying put in the Main Sequence stage for a a while, they also run out of hydrogen, and expand to the Red Giant stage. This is also about three times the size of the original star. Once the small/medium stars run out of gas, they will Nova and end up as White Dwarfs. In this stage, the stars slowly burn out. (very short summary)

Mrs. Degl6 Neutron Star Black Hole These can form after a Supernova. A major explosion causes all of the star matter to contract together. All of this contraction creates an area of extremely high gravity and density. A pea sized sample of neutron star would weigh 100 million tons. It is like taking each person in the world and combining them into an area the size of a sugar cube. These have very strong magnetic fields and can turn into stars, called Pulsars, which emit radio waves, in a pulse like manner. These are more dense than a Neutron Star. The intense surface gravity does not allow light to escape. All surrounding matter is pulled into it. These areas give off X-rays. That is how we can detect them.

Mrs. Degl7 Crab Nebula - Neutron Star

Mrs. Degl8 The relative sizes of the planets compared to the Sun.

Mrs. Degl9 The Pillars of Creation Eagle nebula, a nearby star-forming region 7,000 light-years from Earth in the constellation Serpens.

Mrs. Degl10 The Spitzer image shows the eastern edge of a region known as W5, in the Cassiopeia constellation 7,000 light-years away. This region is dominated by a single massive star, whose location outside the pictured area is "pointed out" by the finger-like pillars. These pillars themselves are colossal, together resembling a mountain range. These are more than 10 times the size of those in the Pillars of Creation, in the Eagle Nebula. Mountains of Creation