Stars

Distances To The Stars

• Stars are separated by vast distances.

• Astronomers use units called light years to measure the distance of stars

• A light-year is the distance that light travels in a vacuum in a year

• Proxima Centauri, is the closest star to the sun.

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Parallax

• Astronomers have developed various methods of determining the distance of stars.

• The change in position of an object with respect to a distant background is called parallax.

• As Earth moves in its orbit, astronomers are able to observe stars from two different positions.

• Astronomers measure the parallax of nearby stars to determine their distance from Earth

Properties of Stars

• Astronomers classify stars by their color, size, and brightness. Other properties of stars are chemical composition and mass.

• Color and Temperature – a stars color indicates the temperature of its’ surface.

• The hottest stars appear blue• The cooler stars appear red• The spectrum of color in a star

is from blues to greens to yellows and reds.

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Brightness

• The brightness of a star as viewed from Earth is dependent on many factors such as color intensity and distance.

• Apparent Brightness – is the brightness of a star as it appears from Earth.

• The apparent brightness decreases as its distance from you increases

• Absolute Brightness – is how bright a star really is. The absolute brightness is a characteristic of the star and is not dependent on its distance from Earth.

Composition

• Each star has its own spectrum.

• Most stars have a chemical makeup that is similar to the sun, with hydrogen and helium together making up to 96 to 99.9 % of a star’s mass.

How Stars Form

• A nebula is a large cloud of gas and dust spread out over a large volume of space.

• Some nebulas are glowing clouds lit from within by bright stars.

• A star is formed when a contacting cloud of gas and dust becomes so dense and hot that nuclear fusion begins.

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Life Cycles of Stars

• Adult Stars – A star’s mass determines the star’s place on the main sequence and how long it will stay.

• The amount of gas and dust available when a star forms determines the mass of each young star.

• The larger the star the more energy produce.

• Since blue stars burn brightly, they use up their fuel quickly and are short lived.

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The Death of a Star

• The dwindling supply of fuel in a star’s core leads to the star’s death as a white dwarf, neutron star, or black hole.

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Groups of Stars

• Astronomers have determined that more than half of all stars are members of star systems.

• There are three basic kinds of star clusters: open clusters, associations, and globular clusters.

• Astronomers classify galaxies into four main types: spiral, barred-spiral, elliptical, and irregular.

Expanding Universe

• The observed red shift in the spectra of galaxies shows that the universe is expanding.

• Astronomers theorize that the universe came into being in an event called the big bang.

• Dark matter can only be detected by observing its gravitational effects on visible matter.

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