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Astronomy > Observing the Heavens > Flashcards

Observing the Heavens Flashcards

1
Q

Why is astronomy considered a science?

A

It tests theoretical predictions with observations

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2
Q

Examples of historical astronomical observations

A

•Mayan long count Callander
•Egyptian 365-day calendar
•Khoisan used shape, orientation of moon, Milky Way to mark when to hunt, harvest
•Chinese predicted eclipses, meticulously detailed comets, supernovae

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3
Q

The ecliptic

A

•path that planets and sun follow
•made up from 12 zodiacal constellations
•takes 12 months for sun to move through

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4
Q

Greeks philosophers understanding 500BCE

A

•spheres considered perfect so heavens made of spheres
•Heliocentric model vs Aristotle’s geocentric model

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5
Q

Which model was favored by Ptolemy?

A

Geocentric
Accepted by western religions

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6
Q

What could geocentric model explain?

A

•nightly rotation of the heavens around earth
•phases of the moon
•solar and lunar eclipses
•simple planetary motion
•lack of motion of stars relative to each other

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7
Q

Problems with Aristotle model

A

Failed to explain why mercury and Venus stay close to the sun, retrograde motion, why planets moved at different rates at different times

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8
Q

How many epicycles did Ptolemy require to match observations?

A

> 40

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9
Q

What did Copernicus argue?

A

•sun is at centre of universe
•earth-sun distance ting compared to distance to stars
•rotation of earth makes stars go around, and annual motion of sun caused by earth going around it
•retrograde motion caused by motion of our vantage point on earth
•mercury and Venus closer to sun than earth

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10
Q

What is the Copernican Principle?

A

There is nothing special about the Earth, the sun, our galaxy

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11
Q

What did Galileo discover with the telescope?

A

•Jupiter had its own moons
•moon had craters and imperfection (not perfect sphere)
•saw more stars and deduced Milky Way was many stars blended together

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12
Q

What did Kepler propose about planetary motion?

A

They move in ellipses not circles

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13
Q

What were keplers laws?

A
  1. Each planets orbit is an ellipse with the sun at one focus
  2. Planets sweep out equal areas in equal times
  3. For each planet, its orbital period squared is proportional to its semimajor axis cubed
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14
Q

When does parallax arise?

A

When you change viewpoint

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15
Q

Why can’t we see positions of stars change relative to each other

A

Stars are so far away that changes aren’t measurable

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16
Q

Why do planets farther out have longer orbits?

A

•higher up things have more potential energy, lower down have more kinetic energy
•more kinetic energy so more speed so moves around faster so smaller period

17
Q

When are suns, moon, planets at highest point in sky? (North hemisphere)

A

When due south

18
Q

When does sun rise furthest north?

A

Summer solstice

19
Q

When does sun rise furthest south?

A

Winter solstice

20
Q

When does sun rise due east?

A

Spring and autumn equinoxes

21
Q

What is declination?

A

•like latitude
•+90 at north celestial pole, -90 at south

22
Q

What is right ascension?

A

•like longitude
•ranges 0-360, or 0-24h around equator

23
Q

What is coordinates at spring equinox?

A

0,0

24
Q

New moon

A

Moon in same direction as sun
•rises at dawn, sets at sunset

25
Q

Waxing moon

A

•inverted C in northern hemisphere
•visible in evening, sun illuminates west side of moon

26
Q

Full moon

A

Moon in opposite direction to sun
Rises at sunset, sets at dawn

27
Q

Waning moon

A

C shape, visible in morning

28
Q

Sidereal period

A

•moon goes round earth every 27.3 days
•moon rises 50 mins later each day
•sets things like tides

29
Q

Synodic period

A

•moon faces same direction to sun every 29.5 days
•sets moons phases

30
Q

Lunar eclipses

A

•occur when moon passes through shadow cast by earth
•only occur at full moon

31
Q

Solar eclipse

A

•occur when moon blocks light from sun
•only occur at new moon

32
Q

What is the lunar oribit tilt?

A

Orbit of moon round earth inclined at 5 degrees relative to ecliptic

Astronomy (23 decks)

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