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Lecture 4

Astronomy 1021 Lecture Notes - Lecture 4: Scientific Revolution, Earth Radius, Deferent And Epicycle

Course Code
ASTR 1021
Robert Cockcroft

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Eclipse types:
- lunar :
- Order: Sun-Earth-Moon
- Earth’s shadow falls on the Moon
- Dark red or brown-ish colour
- “Umbra” (darkest); “penumbra” (edge)
- Next:
- 2018 Jan 31 (sunrise)
- 2019 Jan 20/21 (~midnight)
- Can be totally red
- Why does the moon turn red?
- Earth’s atmosphere scatters the light (same reason why sunsets are red)
- If you were on the Moon, it would be like seeing all the sunsets
- Solar:
- “Umbra” (darkest); “penumbra” (edge)
- Only see total solar eclipse if you are in the umbra
- Umbral line is called “path of totality”
- Solar eclipse order: Sun-Moon-Earth
- Lunar eclipse order: Sun-Earth-Moon
- When moon is completely over the sun
- Totality is the only time it’s safe to look at the Sun
- Solar corona and flares visible
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- Bailey’s beads or “diamond ring” effect (red dots from sun's atmosphere coming through)
- Could use pinhole camera or solar glasses at other times
Apparent Sizes of Sun and Moon
- Orbits not perfectly circular (Moon’s around Earth and Earth’s around Sun)
- Apparent sizes are different, sometimes moon is closer or farther(e.g., “super” Moon)
- A very small moon compared to sun Leads to annular (and hybrid) solar eclipses
Eclipse frequency:
- Alignment needed: the three celestial bodies and the orbital planes
- The moon's orbital plane is slightly tilted from the earth, so the shadows are not always
Early western science:
- Ancient Egyptians
- Ancient Greeks
- Dark Ages
- Scientific Revolution
Motion of Celestial Bear:
- Daily motion of the Big Dipper shows the Celestial Bear and the Hunters
- Annual change of the sky means that only at the correct time of year is this format seen in
the sky
- The Bear and the Hunters running across the horizon is specific to this region’s latitude
- Based off of old tale about hunters chasing after a magic bear with their dog (cayuga)
Ancient Greeks and Scientific Revolution:
- Observations and Construction:
- Building large dedicated structures requires:
- Careful observations
- Repeated for validity
- Over generations
- Record observations
- Important elements in modern science: Accurate, repeatable, recorded
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