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Lecture

# Lecture 2

Department
Astronomy
Course Code
ASTB03H3
Professor
Eric Shaver

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ASTB03 โ Lecture 2
โขGreek Astronomy
๎Aristotle
๎Tried to prove that Earth was stationary โ was not in motion
๎Evidence: Objects would be left behind by rotating or revolving Earth
๎Moving Earth would produce parallaz shift in stars' positions
โขAstronomical Measurements
๎Relative measurements: comparing 2 things in nature (for example, the moon and the sun)
๎Aristarchus (310 BC)
๎How far the sun and moon are from the Earth in relative form
๎Based on observations of timing of Moon's phases
๎Found that sun is 19x further away than the moon was
โขSun is actually 392x further away
๎Found that Sun is 7x diameter of Earth
โขSun is actually 109x the diameter of Earth
๎Eratosthenes (276 BC)
๎Sun is never directly overhead in Toronto
๎In a particular place in Egypt (Syene), Sun was actually directly overhead
๎Position of Sun was also observed from Alexandria
๎They found the angle between Alexandria & Syene = 70 degrees
๎Measurement unit they used was โstadeโ
๎Distance all around the Earth was 250 000 stade (40 000 km)
๎Appolonius (220 BC)
๎Introduced two ways of describing the motion of things
๎Introduced eccentric circles, deferents & epicycles
๎When planet is father from the earth it would appear to go slower than when it is closer to the
earth (car analogy), even though it's in constant speed
๎This guy tried to explain retrograde motion
๎The planet would go in its own mini circle (epicycle), as it went around the earth in a circle
(deferent)
๎This theory about epicycles seemed to explain retrograde motion well even though it was wrong
๎Hipparchus (190 BC)
๎Looked at the position of stars
๎Discovered the โprecession of the celestial polesโ
๎The point that stars circled around a long time ago is no longer the same
๎Magnitude Scale for Brightness
โขLooked at the importance of the brightness of stars
โขBrightest stars were called Magnitude 1
โขAnd the dimmer ones were Magnitude 2
โขHad no way of describing a star that was Magnitude 1
โขHe was using eyes to judge brightness
โขThese magnitudes are now called apparent magnitude (judging by looking)
โขThe more negative something is, the brighter it is!
โขSun: m= - 26.8
โขMoon: m = - 12.5