1.4 The Earth-Sun-Moon interactions

1.4 The Earth-Sun-Moon interactions

1. Lunar Phases

   • the mon undergoes its familiar cycle of phases in a period of 29.5 days.
   • the cycle begins with a new moon , waxes through its crescent and gibbous phases until it is directly opposite the sun and appears as a full moon it then wanes through gibbous and (de) crescent phases until the cycle ends with another new moon
   • the lunar month is 2.2 days longer than the moons orbital period around the earth

2. Solar and lunar eclipses

   • When the moon passes directly in front of the sun, it can obscure light from the suns photosphere and produce a spectacular total solar eclipse for observers in the dark shadow on earth
   • • The diagram show the beginning of totality in which bright solar prominences are also visible above the suns edge.
     • During totality, the sky darkens , some of the brighter stars can be seen , the temperature drops and the suns corona is visible.
   • Baily's Beads
     • Small bright spots of sunlight caused by the suns rays shing through valleys on the moon
     • It is possible to observe Baily's Beads at the beginning and end of totality.
     • When just one bead is visible, this is known as the Diamond ring effect
   • Solar eclipses occur at a full moon and generally last a few minutes. However they do not occur every new moon due to the plane of the moons orbit around earth being slightly tilted
   • If the moon only partly obscures light from the sun then an observer views a partial solar eclipse.
   • when the moon is full, it is possible to observe a lunar eclipse. This time it is the earth that casts the shadow and prevents sunlight from reaching the moon.
   • total lunar eclipses are visible from most of the earth's hemisphere facing the moon and therefore more common than solar eclipses from a given location

3. Time and its determination

   • The earth spins from west to east in a time of 23 hours and 56 minutes. This is known as a sidereal day
   • in contrast to a sidereal day a solar day is 24 hours exactly

4. Shadow sticks and sundials

5. aurorae

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