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Ch. 15-1 Stars
Chapter 19, Section 1
Part 1
Stars
• Stars are huge, hot, brilliant
spheres of gas.
• To learn about stars, scientists
study starlight.
Color of Stars
• Look at the candle and Bunsen
burner. Which is hotter?
• The blue flame of the Bunsen
burner is much hotter than the
yellow flame of the candle.
• Stars are different colors too,
so we know they are different
temperatures.
Composition of Stars
• The rainbow of colors
produced when white
light passes through a
prism is the spectrum.
• A spectrograph is used
to spread starlight out
into its colors.
Making an ID
• Absorption spectra shows
what elements are in a star’s
atmosphere.
• For example, this spectrum
shows the presence of
hydrogen.
Absorption Spectrum of the Sun
• Our sun shows absorption lines for
hydrogen (marked with an H) and other
heavier elements.
Ch. 15-1 Stars
Chapter 19, Section 1
Part 2
Classifying Stars
Stars are classified by how
hot they are. Different surface
temperatures result in different colors.
Brightness of Stars
• The lower the magnitude = the brighter
the star. (Sun = -26.8)
• Magnitude means size,
or in this case brightness.
2 Ways To Look At
Brightness
• Apparent Magnitude – How bright the
star really looks from Earth. The
farther away from us, the dimmer
the star looks.
• Absolute Magnitude – How bright the
star really is. If all stars were the
same distance from us, how bright
would it look compared to the other
stars?
Ch. 15-1 Stars
Chapter 19, Section 1
Part 3
Distance To The Stars
• A light-year is the distance light will
travel in one year or:
6,000,000,000,000 miles!
• The nearest star to our sun is 4.3
light-years away.
• Some stars are billions of light-years
away.
Parallax
• Stars near the Earth appear to move
more than distant stars.
• This apparent shift
in position is called
parallax.
Motions of Stars
• Because of the earth’s tilt and revolution
around the sun, we see different parts of the
sky at night. We see different constellations
at different times of the year.
Motion of Stars (con’t)
Because of the earth’s rotation,
the stars all seem to circle
Polaris (the north star) once
every 24 hours.
Motion of Stars (con’t)
• Even though the stars are moving in
space, they are so far away the
constellations look the same to us now
as they did to the Greeks who named
them thousands of years ago.
Review
• Is a yellow star hotter or cooler than an
orange star?
• Suppose you see two stars of
the same apparent magnitude.
If one star is actually four
times as far away as the other,
how much brighter would the
farther star really be?