copyright © 2012 pearson education, inc. the night sky? with the naked eye, we can see more than...
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Copyright © 2012 Pearson Education, Inc.
The night sky?
With the naked eye, we can see more than 2000 stars as well as the Milky Way.
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Constellations
A constellation is a region of the sky.
Eighty-eight constellations fill the entire sky.
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The Celestial Sphere
Stars at different distances all appear to lie on the celestial sphere.
The ecliptic is the Sun’s apparent path through the celestial sphere.
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The 88 official constellations cover the celestial sphere.
The Celestial Sphere
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Question : The celestial equator is ?
A The path of the Sun compared to the stars.
B The path of the Moon compared to the stars.
C Always directly overhead at the Earth's equator.
D The average path of planets on a star chart.
E Always along the horizon for people on Earth's equator.
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The Milky WayA band of light that makes a circle around the celestial sphere
What is it?Our view into the plane of our galaxy
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The Milky Way
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The Local SkyAn object’s altitude (above horizon) and direction (along horizon) specify its location in your local sky.
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The Local Sky
Zenith: The point directly overhead
Horizon: All points 90° away from zenith
Meridian: Line passing through zenith and connecting N and S points on the horizon
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Angular Size
An object’s angular size appears smaller if it is farther away.
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Apparent Brightness
• A bright star in the sky.– Is really very bright? – Or is it very dim but very close?
• A dim star in the sky– Is it really very dim?– Or is it very bright but very far away?
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Why do stars rise and set?
Earth rotates west to east, so stars appear to circle from east to west.
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Question : In the northern hemisphere, the stars rise in the East, set in the West and revolve counter-clockwise around the North celestial pole. In the southern hemisphere the stars?
A. Rise in the East, set in the West and revolve anti-clockwise around the South celestial pole.
B. Rise in the East, set in the West and revolve clockwise around the South celestial pole.
C. Rise in the West, set in the East and revolve clockwise around the South celestial pole.
D. Rise in the West, set in the East and revolve anti-clockwise around the South celestial pole.
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Our view from Earth:• Stars near the north celestial pole are circumpolar and
never set.• We cannot see stars near the south celestial pole.• All other stars (and Sun, Moon, planets) rise in east and
set in west.
celestial equator
your horizon
A circumpolar star never sets.
This star never rises.
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Thought Question
What is the arrow pointing to?A. the zenithB. the north celestial poleC. the celestial equator
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Question : You are standing at the north pole and you look at the stars. Which statement below describes what you would see?
A There are no circumpolar stars.
B. There are only circumpolar stars just after sunset.
C. Some stars will be circumpolar and some will not.
D. Every star you see is circumpolar.
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Question : You are standing on the Equator and you look at northern pole star on the horizon. Which statement below describes what you would see?
A There are no circumpolar stars.
B. There are only circumpolar stars just after sunset.
C. Some stars will be circumpolar and some will not.
D. Every star you see is circumpolar.
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Why do the constellations we see depend on latitude and time of year?
• They depend on latitude because your position on Earth determines which constellations remain below the horizon.
• They depend on time of year because Earth’s orbit changes the apparent location of the Sun among the stars.
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Review: Coordinates on the Earth• Latitude: position north or south of equator• Longitude: position east or west of prime meridian
(runs through Greenwich, England)
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The sky varies with latitude but not longitude.
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Altitude of the celestial pole = your latitude
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Thought Question
A. You are on the equator.
B. You are at the North Pole.
C. You are at latitude 50°N.
D. You are at longitude 50°E.
E. You are at latitude 50°N and longitude 50°E.
The North Star (Polaris) is 50° above your horizon, due north. Where are you?
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The sky varies as Earth orbits the Sun
• As Earth orbits the Sun, the Sun appears to move eastward along the ecliptic.
• At midnight, the stars on our meridian are opposite the Sun in the sky.
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Special Topic: How Long Is a Day?• Solar day = 24 hours• Sidereal day (Earth’s rotation period) = 23 hours,
56 minutes
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Summary Of The Night Sky
• Now work on Page 1-6 of the tutorial book.