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.

• 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 AStar B

Star X

Location 1

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:

Big DipperOrion

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)