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The universe is the totality of all space,
time, matter matter and and energy. |
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| the study of the universe |
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Earth is neither central nor special.
It is an ordinary planet. |
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Is more than 100 times larger in diameter then the sun.
1 million earth's can fit into the sun. |
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1 Ligght-y ( y) year (Ly) = the distance that light, moving
at a constant speed of 300,000 300,000 km/s, travels in one km/s, travels in one year. |
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A typical galaxy contains a few hundred billion stars.
N stars> N people have ever live on Earth |
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A billion light years from earth.
Each contain hundreds of billions of stars and planets. |
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| Nearly 6000 stars are visible to the unaided eye. |
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| A human grouping of stars in the night sky into a recognizable pattern. Constellations are named after mythylogical heroes and animals. |
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| The stars making up a particular constellation are generally not close together in space. So constellations have no physical meaning. |
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• Over the course of a night the constellations appear to cross the sky from east east to est to west.
• First astronomers concluded that stars were attached to a celestial sphere surrounding Earth. |
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Stars appear to move in appear to move incircles around a point very close to the Polaris star.
• Polaris indicates the direction (north) in which Earth's rotation axis points. |
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The apparent apparent motion of the stars is the
result of the spin, or rotation, of Earth. |
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| The earth revolves around the sun. |
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| The apparent motion of the Sun in the sky traces out a path on the celestial celestial sphere known sphere known as the ecliptic plane. |
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The plane defined by the ecliptic is in fact the plane of Earth's
orbit around the Sun. |
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| As the Sun follows the ecliptic path |
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As the Sun follows the ecliptic path, it appears to move
against against a band of a band of 12 constellations called the Zodiac. |
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| The dark side of the earth |
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faces different set of constellations constellations at at
different epochs of the year. |
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23.5 degrees with respect to the celestial equator
because the Earth's rotation axis is tilted by 23.5 degrees with respect to its orbital axis. |
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| The two points where where the ecliptic the ecliptic intersects the celestial equator are known as equinoxes. |
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| Where the Sun is at its northernmost (southernmost) point above (below) the celestial equator is known as the |
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| summer (winter) solstice. |
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| Annual Changes : Northern Hemisphere |
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1 – Summer Solstice: longest day longest day
2 – Autumnal Equinox: day = night
3 – Winter Solstice: the shortest day
4 – Vernal Equinox:day = night
Opposite for Southern Hemisphere |
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We experience seasons because Earth's axis is tilted
with respect to the ecliptic axis. |
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| The interval of time from one vernal equinox to the next (365.2422 solar days) is known as one tropical year. It is the year our calendars measure. |
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One tropical year is not a whole number of solar days
(365 (365 2422d) In order to keep the average length of a calendar year equal to 1 .2422d). In order to keep the average length of a calendar year equal to 1
tropical year, an extra day is inserted into the calendar on leap years. (in average 1 yr = 365.25 d) |
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omit the extra day from years that were multiple of 100,
but retain it in years multiple of 400 (in average 1 yr = 365.2425 d) |
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The Moon shows a regular cycle of changes, or phases: New Moon, quarter Moon, full moon, which takes takes about 29 5 days to about 29.5 days to complete.
Moon emits no light of its own. |
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Fractions of the Moon's sunlit face visible to us.
Note: We always see the same side of the Moon. |
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| Eclipses: From time to time, only during full Moon. |
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When the Sun and the Moon are in exactly opposite directions as seen from Earth, Earth's shadow sweeps across the Moon , temporarily blocking the Sun''s light and darkening the Moon in a lunar eclipse.
• It lasts no more than 100 minutes (the time for the Moon to pass through Earth's shadow.) |
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| Usually the alignment of the Sun, Earth and the Moon is imperfect, so the shadow never completely covers the Moon |
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| the entire lunar surface is obscured |
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| Lunar Eclipse acquires red coloration |
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| Small amount of sunlight reddened by Earth's atmosphere atmosphere and refracted onto the lunar surface. |
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| When the sun and the moon are in exactly the same direction as seen from Earth, the Moon passes directly in front of the Sun (perfect alignment) briefly turning day into night. |
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| During a total solar eclipse, we can often see the the Sun Sun'ss outer outer atmosphere, or corona. |
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The Moon's orbit around around Earth is not Earth is not
exactly circular. Thus, the Moon may be far enough from Earth at the moment of an eclipse that its disk
fails to cover the disk of the Sun completely leaving a ring of sunlight visible around its edge. |
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| Unlike a lunar eclipse, a total solar eclipse can only be seen from only a small portion of the day-time side on Earth. |
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| Within the shadow, but outside the umbra, in the penumbra |
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| Within the shadow, but outside the umbra, in the penumbra |
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| Within the shadow, but outside the umbra, in the penumbra |
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