Stars

A Star is…. A ball of matter that is pulled together by gravity, and that gives off energy as a result of NUCLEAR FUSION. Nuclear fusion- when two atoms bond together to make one heavier atom. The process releases large amounts of energy.

1. Composition of Stars The two most abundant elements in stars are HYDROGEN and HELIUM. Scientists determine the composition by studying the LIGHT that comes from a star.

How Light shows composition When elements in a star burn, they give off certain colors of light. The color of light corresponds to a specific wavelength of the light.

How Light Shows Composition Scientists look at the light from a star through a SPECTROSCOPE. A spectroscope breaks light apart and shows the wavelengths of the light. Example: Color Spectrum of calcium: The bright lines on the spectrum tell you the wavelength of the light given off.

How Light Shows Composition Each element gives off a unique pattern, or color spectrum. If scientists find that pattern in a stars light, then they know that element is present in the star. Example: When you burn sodium, it produces a yellow flame. If a star’s spectrum has two lines in the same place, that star contains sodium.

How Light Shows Composition Astronomers match up the lines on the spectrum coming from a star with the dark lines different elements produce when they burn to determine the composition of the star.

2. Temperature Scientists estimate the temperature of stars by the COLOR of the star. Hottest: Coldest: Blue White Yellow Orange Red

3. Magnitude The Brightness of a star depends on three things: Size Temperature Distance from us Apparent Magnitude: How bright a star is when viewed from Earth. A very large, hot star could look dim just because it is so far away. (how bright we see it) Absolute Magnitude: the amount of light that is actually given off by a star. (how bright it actually is)

4. Measuring the Distance to Stars We measure the distance between objects in space using PARALLAX. Parallax is the apparent change in position of a star in the sky when viewed from two different positions in earth’s revolution. The closer a star is, the larger its parallax, or apparent movement. The farther away a star is, the smaller its parallax.

Location 1 When we observe Star X from Location 1, it appears to be beside Star B. When we observe Star X from Location 2, it appears to be beside Star A. Did Star X really move? Star A Star B Star X Location 2

5. Measuring Distance in Space Light-Year- The DISTANCE that light can travel in one year. 5,865,696,000,000 miles Astronomical Unit (AU)- the distance between the sun and the earth (93 million miles)

6. Constellations Constellations are patterns of stars in the sky. Circumpolar Constellations: Constellations that appear to revolve around the North Star. Major constellations: Orion Big Dipper

7. Important Stars Polaris: The North Star: The star directly above the earth’s axis of rotation, or the north pole. It appears to stay in the same place all year, and other constellations revolve around it. Alpha Centauri: Closest star to us (other than the sun)