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Lecture 4

ASTA01H3 Lecture Notes - Lecture 4: Solar Wind, The Moons

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Kristen Menou

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- There are two important points to note about the phases of the moon:
1. The moon always keeps the same side facing Earth, and you never see the far side of the
Moon. *spin & orbit are in 1:1 period ratio
2. The changing shape of the Moon as it passes through its cycle of phases is produced by
sunlight illuminating different parts of the side of the moon you see
- Eclipses are due to a complicated combination of apparent motions of the Sun and the Moon
- Because the Sun is 400 times larger times than the Moon and roughly 390 times farther away,
the Sun and Moon have nearly equal angular apparent diameters so therefore, the Moon is just
about the right size to cover the bright disk of the Sun and cause a solar eclipse
- A solar eclipse, it is the Sun that is being hidden and the Moon is in the way
- A shadow consists of two parts: The umbra (the region of total shadow) and The Penumbra
- Corona is the white streamers which are the upper layers of the solar atmosphere
- The corona is a non-uniform, outflowing part of the Sun, gradually becoming the rarified solar
wind that flows past the Earth and the planets
- The Sun gets it’s Corona from: Hot Temperatures causing the outflow (1 mil degrees C),
Magnetic fields
- When the Moon crosses in front of the Sun, it is too small to fully cover the Sun which would
create an annular eclipse
- An annular eclipse is in which an annulus of the Sun’s disk is visible around the disk of the Moon
- A lunar eclipse is when the Moon darkens and turn copper-red. It occurs at full Moon when the
Moon moves through the Earth’s shadow
- As the Moon shines only by reflected sunlight, you see the Moon gradually darken as it enters
the shadow
- If the orbit of the Moon carries it through the umbra of Earth’s shadow, you can see a total lunar
- When the Moon is totally eclipsed, it does not disappear completely, though it receives no
direct sunlight, the Moon in the umbra receives some sunlight that is refracted through Earth’s
- The red glow from the ring consisting of all the Earth’s simultaneous sunsets and sunrises
illuminates the Moon during totality and makes it glow coppery red
- Lunar eclipses always occur at full moon but not at every single one
- The Moon’s orbit is tipped about 5 degrees to the ecliptic
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