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Stars
• The apparent twinkling of the stars is a
product of the turbulence and motion of
the Earth’s atmosphere
• Stars have different colors depending on
how hot they are. The HOTTEST stars are
BLUE, the COLDEST stars are RED.
(Note- this is opposite to what we are used
to associating with temperature.)
• Color is used to determine ages – stages
– in life cycle.
Spectroscope
• A tool that is used to separate light into the
visible spectrum. Used to help determine
elements in the stars.
Absorption Spectroscopy
Star Colors
•
•
•
•
•
•
•
Blue (HOT) 11-40,000C
Blue-White
White
Yellow
Orange
Red (COLD)
7.5-11,000C
6-7,500C
5-6,000C
3.5-5,000C
3-3,500C
(young)
Beta Centauri
Rigel (supergiant)
Vega
_____
Aldebaran
(old)
Betelgeuse
Hadar (r) and Alpha Centauri (l)
Vega – upper left
Star Life Cycle
• Nebula: a large cloud of gas and dust in space
that is the beginning of a star (PLANETS are
also formed this way)
• Dwarf: a main sequence star or, the smallest of stars (up to 20
times larger than our sun and up to 20,000 times brighter. Our sun is
a dwarf star.)
• Red Giant: star is dying (red=cold) and energy
is expanding outward
• White Dwarf: a dying star that is extremely
massive and may soon become a black hole
• Supernova: an exploding star; usually occurring after a dying star
becomes too dense to be supported
• Binary star (double star): a stellar system
consisting of two stars orbiting around
their center of mass
• Our Sun is unusual in that it is NOT part of
a binary system
Hubble image of the Sirius binary system,
in which Sirius B can be clearly seen (lower left)
Star forming region in the nebula NCG 604, in the nearby spiral galaxy M33,
Diminutive by stellar standards,
white dwarf stars are also intensely hot ...but they are cooling.
No longer do their interior nuclear fires burn,
so they will continue to cool (turn more red) until they fade away
E0102-72 is a supernova remnant in the Small Magellanic Cloud,
a satellite galaxy of the Milky Way. This galaxy is 190,000 light years
from Earth. E0102 -72, which is approximately a thousand years old,
is believed to have resulted from the explosion of a massive star.
Stretching across forty light years of space, the multi-million degree
source resembles a flaming cosmic wheel.
Star Vocabulary
• Luminosity: the brightness of a star compared to
the brightness of the Sun. In other words, the Sun’s
luminosity is 1, Sirius is 23, Adhara is 5,000. Luminosity is measured in
ergs per second.
–
The apparent brightness of the sun is 63 billion times brighter than Arcturus,
although intrinsically the Sun is 100 times fainter.
• Apparent Magnitude: stars closer to Earth
appear brighter than those that are farther away
• Absolute Magnitude: big stars are brighter than
small stars. This is the ACTUAL brightness of
the star
– If all the stars were lined up equi-distant from Earth, we would be
able to compare their actual brightness
Magnitude
• The SMALLER the magnitude, the
BRIGHTER the star
– For example, Vega with an apparent
magnitude of +.02 seems about 2 ½ times
brighter than Antares whose apparent
magnitude is +.98
– Antares is actually almost 100 times as bright
as Vega, since Antares has an absolute
magnitude of -4.0 and Vega ‘s is +.5
Magnitude cont.
• As a comparison, the Sun has an apparent
magnitude of -27, but an absolute
magnitude of +5. this is because the Sun
is so close to Earth.
Hertzsprung-Russell Diagram
• An American, Henry Russell and a
Dutchman, Ejnar Hertzsprung noted a
relationship between temperature (color)
and luminosity (brightness) of the stars.
• The significance of the discovery of the
“main sequence” is that for any given
temperature, there is a preferred radius.
Therefore, luminosity is related to
temperature.
HertzsprungRussell
Diagram
Sun
Page 714
In your
book
White dwarfs,
Very hot,
Very dense
Cool, bright
Hot, bright
Hot, dim
_______
Very big
Very bright
cool
Our SUN
• Age:
approx 4.5 billion years old
• Diameter: 1.4 X 106 km
(medium sized star)
• Temperature:
5,800 Kelvin (10,000°F)
• Distance from Earth: 1.5 X 108 km
(150,000,000) (closer than any other star)
• Burns more than 24 billion tons of
Hydrogen gas per minute.
Sun Vocab
• Sunspot: an area of the sun that gives off
less light, due to a disturbance in the sun’s
magnetic field
Sun Vocab
• Solar Flare: an area of the sun that erupts
Sun Vocab
• Corona: the area surrounding the Sun that
can be seen during an eclipse
• Core: center of the sun where the
thermonuclear transmutation of H to He
occurs
• Photosphere: the visible surface of the
Sun – several hundred miles thick
(Visible surface)
(part of the atmosphere)