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An imaginary pattern of stars in the sky

Apparent magnitude

The brightness of a star as seen from Earth.

Absolute magnitude

the brightness a star would have if it were at a standard distance from earth


light distance travels in one year (9.5 trillion km)


the apparent change in position of an object when seen from different places

Hertzsprung-Russell diagram

a graph relating the surface temperatures and absolute brightnesses of stars

Main sequence

A diagonal area on an H-R diagram that includes more than 90 percent of all stars


A large cloud of gas and dust in space, spread out in a immense volume. Where stars are "born."


When gravity pulls some of the gas and dust in a nebula together and there is enough mass to form a star (nuclear fusion has not begun)

planetary nebula

A huge cloud of gas that is created when the outer layers of a red giant star drift out into space

white dwarf

The blue-white hot core of a star that is left behind after its outer layers have expanded and defined out into space. The death of low to medium-mass stars


The brilliant explosion of a dying supergiant star. Stage after main sequence for high mass stars.

neutron star

The small, dense remains of a high-mass star after a supernova explosion (less than 5 solar masses, with a diameter of only 20 km)


A rapidly spinning neutron star that produces pulses of radio waves

black hole

An object whose gravity is so strong that nothing, not even light, can escape (formed after supernova with 5 or greater solar mass remaining)

3 main characteristics used to classify stars

temperature (color), mass, and absolute magnitude (also diameter size, stage in life cycle)

Our Sun

main sequence star, 4.6 billion years old, middle of life, medium sized, yellow- 6,000 degrees celsius, center of our solar system

Solar Mass

the mass of our sun. So, three solar mass is three times the mass of our sun

How are mass and the length of a star's life related?

Inversely related. The greater the mass, the shorter the life span. Small mass stars have the longest life spans.

Where are most stars located on the H-R Diagram?

Main Sequence

When a low mass star runs out of hydrogen fuel, what happens next?

The outer layer expands and becomes a red giant.

After a supernova explosion, if the core remaining is greater than 5 solar masses, what is formed?

a black hole

Two pieces of evidence that astronomers use as evidence of the presence of a black hole:

1) x-rays detected coming from rotating hot gas near a black hole. 2) The effect of gravity on nearby stars and objects.

A medium-mass star will become what at the end of it's life?

white dwarf

When is a star "born?"

When the contracting gas and dust becomes so hot that nuclear fusion starts.

What is the vertical axis on the H-R Diagram?

Absolute magnitude

What is the horizontal axis on the H-R Diagram?

Decreasing surface temperature

Where are white dwarfs located on a H-R Diagram?

bottom/middle (blue.white, yellow and dim)

Where are main sequence stars located on a H-R Diagram?

Diagonally across the diagram from bright and hot to dim and cold.

Where are giants located on a H-R Diagram?

far right (orange/red) and middle from top to bottom.

Where are supergiants located on a H-R Diagram?

top (very bright), and broad range of temperatures (blue, white, yellow and orange)

Where is the sun located on a H-R Diagram?

yellow and middle (pretty close to center)

Label on a H-R Diagram the following: Main sequence, red giant, supergiant, white dwarf, and our sun.

see H-R Diagram in book and on worksheets

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