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Our sun is just a star…but it’s OUR star!
What are STARs?
“…. balls of gas burning billions of miles away”
The Sun
 a main-sequence star
generates energy by nuclear fusion of H
into He
in a state of equilibrium (pressure out =
pressure in/gravity)
 about 5 billion years old (middleaged)
Birth of a Star
 Nebula: swirling cloud of dust and gas that, if it
begins to form ‘clumps,’ will begin to attract
more matter due to gravity  protostar
 As protostar grows, the ‘clumps’ begin to
condense, the pressure goes up, so heat also goes
up
 If heats up enough(18,000,000°F), then
nuclear fusion begins and VOILA.. a star is
born!!
Life Cycle of a Star=Stellar Evolution
The Sunlight We See
 Light travels at 186,000 mi/sec (300,000km/sec)
 The sunlight that is currently reaching the Earth was
generated inside the sun about 100,000 years ago
WHAT?!? How can this be?
It takes a VERY long time for a photon of light
to get from the core to the surface because the
sun is so dense
The 8-minute travel time to Earth by
sunlight hides a many thousand-year
journey that actually began in the core.
DAY and NIGHT…
Light travels in
straight lines so only
half the world can
be lit up by the Sun;
the other half must
be in darkness.
…caused by rotation of the Earth on its own axis
Earth revolves around the sun
What causes the different seasons
of the year? The Earth’s tilt
Summer in the Northern Hemisphere
Winter in the Northern Hemisphere
Winter in the Southern Hemisphere
Summer in the Southern Hemisphere
SUMMER
WINTER
•The amount of heat received in any one spot is
directly related to the angle at which it is received
•The greater the angle, the less concentrated are the
sun’s rays
The Earth’s atmosphere absorbs
some of the sun’s heat energy
(Daytime = nighttime)
Longest
Night
Longest
Day
(Daytime = nighttime)
Born under the sign of…
Constellation Quiz
1. What is changing at the same (annual) timescale
that we are observing the changing zodiac?
Constellation Quiz
1. What is changing at the same (annual) timescale
that we are observing the changing zodiac?
2. Do the constellations appear to change positions in
the night sky as Earth travels around our Sun
throughout the year?
Constellation Quiz
1. What is changing at the same (annual) timescale
that we are observing the changing zodiac?
2. Do the constellations appear to change positions in
the night sky as Earth travels around our Sun
throughout the year?
3. Are the constellations themselves moving?
Constellation Quiz
1. What is changing at the same (annual) timescale
that we are observing the changing zodiac?
2. Do the constellations appear to change positions in
the night sky as Earth travels around our Sun
throughout the year?
3. Are the constellations themselves moving?
4. What causes this apparent change in positions?
Constellation Quiz
1. What is changing at the same (annual) timescale
that we are observing the changing zodiac?
2. Do the constellations appear to change positions in
the night sky as Earth travels around our Sun
throughout the year?
3. Are the constellations themselves moving?
4. What causes this apparent change in positions?
5. Do all stars appear in different positions at
different times of the year?
Constellation Quiz
1. What is changing at the same (annual) timescale that
we are observing the changing zodiac?
2. Do the constellations appear to change positions in the
night sky as Earth travels around our Sun throughout
the year?
3. Are the constellations themselves moving?
4. What causes this apparent change in positions?
5. Do all stars appear in different positions at different
times of the year?
6. Why is Polaris the only star that appears “fixed”?