Our sun is just a star…but Our sun is just a star…but it’s OUR star!it’s OUR star!

What are STARs?What are STARs?

“…“…. balls of gas burning billions . balls of gas burning billions of miles away” of miles away”

The SunThe Sun

a a main-sequence main-sequence star star generates energy by nuclear generates energy by nuclear fusion of H into Hefusion of H into He

in a state of equilibrium in a state of equilibrium (pressure out = pressure (pressure out = pressure in/gravity)in/gravity)

about 5 billion years old about 5 billion years old (middle- aged)(middle- aged)

Birth of a StarBirth of a Star NebulaNebula: swirling cloud of dust and : swirling cloud of dust and gas that, if it begins to form gas that, if it begins to form ‘clumps,’ will begin to attract ‘clumps,’ will begin to attract more matter due to gravity more matter due to gravity protostarprotostar

As protostar grows, the ‘clumps’ As protostar grows, the ‘clumps’ begin to condense, the pressure begin to condense, the pressure goes up, so heat also goes upgoes up, so heat also goes up

If heats up enough(18,000,000°F), If heats up enough(18,000,000°F), then nuclear fusionthen nuclear fusion begins and begins and VOILA.. a star is born!!VOILA.. a star is born!!

Life Cycle of a Life Cycle of a Star=Stellar EvolutionStar=Stellar Evolution

The Sunlight We SeeThe Sunlight We See Light travels at 186,000 mi/sec Light travels at 186,000 mi/sec (300,000km/sec)(300,000km/sec)

The sunlight that is currently reaching The sunlight that is currently reaching the Earth was generated inside the sun the Earth was generated inside the sun about 100,000 years agoabout 100,000 years ago

WHAT?!? How can this be?WHAT?!? How can this be?

It takes a VERY long time for a photon It takes a VERY long time for a photon of light to get from the core to the of light to get from the core to the surface because the sun is so densesurface because the sun is so dense

The 8-minute travel time to The 8-minute travel time to Earth by sunlight hides a many Earth by sunlight hides a many

thousand-year journey that thousand-year journey that actually began in the core.actually began in the core.

DAY and NIGHT…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 Earth revolves around the sunthe sun

What causes the different What causes the different seasons of the year? seasons of the year? The The

Earth’s tiltEarth’s tilt

Summer in the Northern Hemisphere

Winter in the Southern Hemisphere

Winter in the Northern 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 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 The Earth’s atmosphere absorbs some of the absorbs some of the sun’s heat energysun’s heat energy

(Daytime = nighttime)

(Daytime = nighttime)

Longest Day

Longest Night

Born under the sign Born under the sign of…of…

Constellation QuizConstellation Quiz1.1.What is changing at the same What is changing at the same (annual) timescale that we are (annual) timescale that we are observing the changing zodiac?observing the changing zodiac?

Constellation QuizConstellation Quiz1.1.What is changing at the same What is changing at the same (annual) timescale that we are (annual) timescale that we are observing the changing zodiac?observing the changing zodiac?

2.2.Do the constellations appear to Do the constellations appear to change positions in the night sky as change positions in the night sky as Earth travels around our Sun Earth travels around our Sun throughout the year? throughout the year?

Constellation QuizConstellation Quiz1.1.What is changing at the same What is changing at the same (annual) timescale that we are (annual) timescale that we are observing the changing zodiac?observing the changing zodiac?

2.2.Do the constellations appear to Do the constellations appear to change positions in the night sky as change positions in the night sky as Earth travels around our Sun Earth travels around our Sun throughout the year? throughout the year?

3.3.Are the constellations themselves Are the constellations themselves moving? moving?

Constellation QuizConstellation Quiz1.1.What is changing at the same (annual) What is changing at the same (annual) timescale that we are observing the timescale that we are observing the changing zodiac?changing zodiac?

2.2.Do the constellations appear to change Do the constellations appear to change positions in the night sky as Earth positions in the night sky as Earth travels around our Sun throughout the travels around our Sun throughout the year? year?

3.3.Are the constellations themselves Are the constellations themselves moving? moving?

4.4.What causes this apparent change in What causes this apparent change in positions? positions?

Constellation QuizConstellation Quiz1.1.What is changing at the same (annual) What is changing at the same (annual) timescale that we are observing the timescale that we are observing the changing zodiac?changing zodiac?

2.2.Do the constellations appear to change Do the constellations appear to change positions in the night sky as Earth travels positions in the night sky as Earth travels around our Sun throughout the year? around our Sun throughout the year?

3.3.Are the constellations themselves moving? Are the constellations themselves moving?

4.4.What causes this apparent change in What causes this apparent change in positions? positions?

5.5.Do all stars appear in different positions Do all stars appear in different positions at different times of the year? at different times of the year?

Constellation QuizConstellation Quiz1.1.What is changing at the same (annual) What is changing at the same (annual) timescale that we are observing the changing timescale that we are observing the changing zodiac?zodiac?

2.2.Do the constellations appear to change Do the constellations appear to change positions in the night sky as Earth travels positions in the night sky as Earth travels around our Sun throughout the year? around our Sun throughout the year?

3.3.Are the constellations themselves moving? Are the constellations themselves moving?

4.4.What causes this apparent change in What causes this apparent change in positions? positions?

5.5.Do all stars appear in different positions at Do all stars appear in different positions at different times of the year? different times of the year?

6.6.Why is Polaris the only star that appears Why is Polaris the only star that appears “fixed”? “fixed”?