ASTRON 89 1nd Edition Lecture 6Outline of Last Lecture • Seasons: Concept Check • Phases of the Moon: What causes them? Outline of Current Lecture • The Moon • Eclipses Current Lecture• The Moon • Has synchronous rotation: two rotations that are taking place at the sametime • The rotation of moon around its own axis (1 day) = the revolution of the moon around the Earth • Time it takes for moon to spin around its axis is same time it takes for moon to go around the Earth • The orbit of the moon is “locked” with that of the Earth • Which is why we always see one face of the moon• Eclipses • The moon’s orbit is tilted with respect to the Earth’s sunlight • With respect to the ecliptic • Earth goes around the sun, and the Moon’s orbit around the Earth occurs at an angle (about 5 degrees) • Line of nodes – when the moon is on the line of nodes, eclipses can occur • The moon lies or very near the line of nodes • The line of nodes passes through the Earth pointing at a particular direction in space • Ascending node: pointing north• Descending node: pointing south • Solar Eclipses and Lunar Eclipses • Lunar: sunlight will not reach the moon; the moon looks darker • Solar:• Annular: When the moon appears too small to cover the Sun completely, and a thin ring of the Sun is seen aroundthe edge of the Moon. • Partial: The Moon’s penumbra covers a large position of the Earth’s surface. Anyone standing inside the penumbra sees a partial solar eclipse. • Total Solar Eclipse: the tip of the Moon’s umbra reaches Earth’s surface. People within the eclipse path see a total solar eclipse as the tip moves over them. Anyone in the penumbra sees partial solar eclipse. • Conditions favorable for Eclipses• Alignment:• When the three are aligned (sun, moon, Earth) • Moon is between Earth and the Sun, moon will cover up Sun and you will see solar eclipse • Eclipses occur in pairs because line holds over 2 weeks • 2 weeks later, conditions might still be favorable for a lunar eclipse • Alignment doesn’t work when moon is above or below theecliptic • Ecliptic is where the sun is (path of the sun, where all the planets are) • When the moon is on the plane, you see eclipses • ALIGNMENTS ARE RARE • You don’t see eclipses often for this reason • Depending on where the moon is you see different amounts of SHADOW • The darkest part of the Earth’s shadow called the Umbra, is in the center • No light falling space where the Earth’s shadow is • The lightest part is called the Penumbra (towards the outside) • Some sunlight grazes on sides of the Earth (“cones of shadow” are cast depending on where the Earth) • If moon passes through darkest part of shadow, there will be total eclipse of the moon • Moon is completely in the shadow • Deep red color • If moon grazes darkest part, you see partial eclipse, and some of itis lit up a little bit. • Penumbral eclipse, the moon is only going through the lighter partof the Earth’s shadow. • The moon is moving AWAY from the Earth’s shadow• When the moon leaves the penumbra, it returns back to its full lit up shape• The moon is fully lit when it is outside the penumbra• Draw a cone from the edges of the moon down to the