Formation and Classification

H-R Diagram

- In 1911 a Danish astronomer, Ejnar Hertzprung, compared the temperature and brightness of stars on a graph. Two years later, an American astronomer, Henry Russell, made some similar graphs. The combination is a graph showing the relationship between a stars surface temperature and its absolute magnitude.

- All stars begin as a ball of gas and dust. Gravity pulls the gas and dust together into a sphere. As the sphere becomes denser, it gets hotter and the hydrogen turns into helium in a process called nuclear fusion.

- Main Sequence Star: A major grouping of stars that forms a relatively narrow band from the upper left to the lower right when plotted according to luminosity and surface temperature on the Hertzsprung-Russell diagram.

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Basic Star Information

- Color - has to do with how “hot” the star is. Blue stars are the hottest. Red stars are the coolest.

- Composition – stars are made up of gases. The star itself is very dense and hot. Its atmosphere is made up of cooler gases. Because different elements absorb different wavelengths of light, astronomers use a star’s light to learn what it is made up of.

Apparent Magnitude – how bright a star LOOKS

Absolute Magnitude – the actual brightness of a star (calculated using the apparent magnitude and the star’s distance from the Earth).

- A light year – a unit of length that is equal to the distance that light travels through space in about 1 year. Because the speed of light through space is about 300,000 km/s, it travels approximately 9.46 trillion kilometers in a year.

- Circumpolar stars – stars that can be seen at all times of the year and all times of the night

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When Stars Die

- Super novas – the death of a large star by explosion

- Neutron Star – a star in which nearly all the particles have become neutrons; the collapsed remains of a super nova

- Pulsars – a spinning neutron star that emits rapid pulses of light

- Black Holes – an object with more than three solar masses squeezed into a ball only 10km across whose gravity is so strong that not even light can escape.