Characteristics of Stars Section 27.1

Definition of a star It’s a body of gases that gives off lots of energy in the form of light and heat They vary in size and mass, some are smaller that 20 km in diameter or up to a 1000 times the size of our sun!

Variations in composition and temperature Using a spectrometer, scientists can determine what type of gases compose a star Every chemical element has a characteristic spectrum

Temperature The temperature of a star is indicated by its color The red ones are the coolest and the blues are the hottest Most Temps range between 2800°C to 24,000°C.

Star Temperatures

Motion Actual motion can only be measured by high powered telescopes since stars are so far away Apparent motion of stars is what we see and is only due to the motion of the earth

Actual Motion of Stars They rotate on an axis, they revolve around other stars, and they move towards or away from earth Don’t forget the red shift

Distance to the Stars It’s measured in light years- the distance that light travels in one year ( about 9.5 trillion km) Light from the sun takes about 8 minutes to reach earth

Parallax Scientists can use this to measures stars within 1000 light years of accuracy by measuring the angle between a stars’ apparent position over a period of 6 months The closer the star, the larger the angle

Stellar Magnitudes The visibility of a star depends on its brightness and distance from earth Over 3 billion stars can be seen through a telescope, but only 6000 can be seen with the naked eye The 2 scales that scientists use to measure brightness are apparent magnitude and absolute magnitude

Apparent Magnitude The brightness of a star as is appears from earth The most powerful telescopes can detect stars with an apparent magnitude of about 29 Those stars are 1.5 billion times fainter than those seem with a naked eye

Apparent magnitude

Absolute Magnitude How bright a star would be if it were 32.6 light years away Scientists use this distance because it’s equal to one parsec

Classification of stars Main-sequence stars- stars that are visible in the night sky, this includes the sun Super giants – are bright because they have so much surface area to project light White dwarfs- these stars are hot and dim because of their size