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PHYS 284 - Astronomy > Lesson 2 > Flashcards

Lesson 2 Flashcards

1
Q

Constellation

A
  • Region of the sky with well-defined borders

- 88 official constellations

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2
Q

Celestial sphere

A
  • Imaginary sphere that surrounds Earth, where all the stars lie
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3
Q

North celestial pole

A

point directly over earth’s north pole

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4
Q

South celestial pole

A

point directly over earth’s south pole

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5
Q

Celestial equator

A

projection of earth’s equator into space

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6
Q

Ecliptic

A

Path the Sun follows as it appears to circle around the celestial sphere once a year (crosses celestial equator at 23.5 degrees; because that is the tilt)

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7
Q

Local Sky

A

sky as seen from wherever you stand

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8
Q

Horizon

A

boundary between Earth and sky

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9
Q

Zenith

A

Point directly overhead

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10
Q

Meridian

A

imaginary half circle from our horizon South to North

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11
Q

Azimuth

A

degrees clockwise from due north - direction along horizon

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12
Q

Altitude

A

degrees above horizon

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13
Q

Angular size

A

Angle an object appears to span in your field of view

Moon and Sun are both 0.5 degrees

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14
Q

Angular distance

A

angle that appears to separate two objects

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15
Q

Arcminutes and arcseconds

A
  • Arcminutes: divide each degree into 60 arcminutes

- Arcseconds: divide each arcminute by 60 arcseconds

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16
Q

Rotation of stars

A
  • stars near north celestial pole are circumpolar (they remain where they are, just rotota)
  • Stars near south celestial pole never rise above horizon
  • all other stars have daily circles that are partly above horizon and partly below (appear to rise in East and set in West)
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17
Q

Latitude and longitude

A
  • Latitude measures north-south position
  • Longitude measures east-west position
  • Latitude affects how we see constellations
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18
Q

Zodiac

A
  • the constellations along the ecliptic

- 13 constellations

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19
Q

Why seasons?

A
  • the tilt of Earth’s axis causes sunlight to fall differently on Earth at different times of year
  • North Hemisphere: tipped toward sun in June and away from sun in December
  • Southern Hemisphere: tipped toward sun in December and away from sun in June
20
Q

June Solstice

A
  • Summer solstice in North
  • June 21st
  • North Hemisphere tipped most directly toward the Sun - most direct sunlight
21
Q

December Solstice

A
  • Winter solstice in North
  • December 21st
  • North tipped away; least direct sunlight
22
Q

March equinox

A
  • Spring/vernal equinox in North
  • March 21st
  • moment where North goes from tipped away to tipped toward Sun
23
Q

September equinox

A
  • Fall/autumnal equinox in North
  • September 22nd
  • moment where North goes from tipped toward to tipped away Sun
24
Q

Precession

A
  • gradual wobble that alters orientation of Earth’s axis in space
  • each cycle takes about 26,000 years
  • gradually changes the direction in which the axis points in space (polaris won’t be north star, it’ll be Vega)
  • Only changes what we see in space, not seasons (constellations) - so zodiacs change
  • Tropical year is actually longer by 20.2 minutes
25
Q

Lunar Phase

A
  • moons orbit around sun takes 29.5 days (synodic period)

- inclination of lunar orbit to ecliptic plane is 5 degrees

26
Q

Moon phases: New Moon

A

New Moon: rises and sets with the sun; can’t see it in night
- moon is between earth and sun

27
Q

Moon phases: Waxing Crescent

A

Waxing crescent: rises mid-morning, highest in mid-afternoon and sets late evening; sliver getting bigger

28
Q

Moon phases: First Quarter

A

First Quarter: rises noon, highest sunset, sets midnight; looks like a half moon getting bigger

29
Q

Moon phases: Waxing Gibbous

A
  • Waxing Gibbous: rises mid-afternoon, highest late evening, sets before dawn; looks like three quarter full moon and getting bigger
30
Q

Moon phases: Full moon

A

Full moon: rises sunset, highest midnight, sets sunrise; full because sun illuminates it fully

31
Q

Moon phases: Waning Gibbous

A

Waning Gibbous: rises late evening, highest before dawn, sets mid-morning; looks three quarter full getting smaller

32
Q

Moon phases: Third Quarter

A

Third Quarter: rises midnight, highest sunrise, sets noon; looks half full getting smaller

33
Q

Moon phases: Waning Crescent

A

Waning crescent: rises before dawn, highest mid morning, sets mid-afternoon; looks like crescent getting smaller

34
Q

Synchronous Rotation

A

We always see same face of Moon

35
Q

Lunar eclipse

A
  • Earth lies between Sun and Moon, so Earth’s shadow falls on Moon
  • Total lunar eclipse: sun earth moon almost exactly lined up (all umbra); red during totality
  • Partial lunar eclipse: not quite lined up (part umbra, part penumbra)
  • Penumbral lunar eclipse: all penumbra (most common)
36
Q

Solar Eclipse

A
  • Moon lies between Sun and Earth, so moon’s shadow on Earth
  • Total solar eclipse: moon close to earth so umbra covers lots
  • Annular solar eclipse: moon is farther, umbra may not reach totally, ring of sunlight seen around moon
  • Partial solar eclipse: only part of the sun is blocked from view
37
Q

Nodes

A
  • where the moon crosses through Earth’s ecliptic plane; happens twice an orbit; only have eclipses when moon is near these nodes and full or new moon
  • lunar nodes precess around ecliptic, completing revolution every 18.6 years
38
Q

Eclipse season

A
  • nodes of the moon’s orbit are closely aligned with the Sun
  • lasts <5 weeks; usually one lunar and one solar eclipse
39
Q

Saros cycle

A
  • eclipses recur in a cycle of ~ 18 years and 11.25 days
40
Q

Planets easy to see with naked eye

A
  • Mercury, Venus, Mars, Jupiter, and Saturn
41
Q

Apparent retrograde motion

A
  • occasionally the planets look like they go east to west instead of west to east because Earth is passing other planets
42
Q

Stellar Parallax

A
  • apparent shift of position of any nearby star against distant background
  • more distant the object the smaller it’s stellar parallax
  • made it difficult to abandon Earth centered universe because couldn’t detect stellar parallax
43
Q

Sidereal vs. Solar day

A
  • Sidereal day: Earth goes 360 degrees; orbits the sun once every 366.26 sidereal days
  • Solar day: Earth goes from noon to noon; orbits the sun once every 365.26 solar days
  • Length of solar day varies throughout the year; because ellipse (moves faster closer to sun) and because earth is tilted (seasons)
44
Q

Solar day increase

A
  • solar day is increasing 1.4 milliseconds every century
45
Q

Daytime

A
  • due to refraction and scattering of light of atmosphere, day light earlier than sunrise
  • at equator; daytime and nighttime are equal
  • but not: daytime and nighttime change depending on solstice
46
Q

Synodic month vs. Sidereal month:

A
  • Synodic: 29 days 12 hours and 44 minutes

- Sidereal: 27.322 days

PHYS 284 - Astronomy (5 decks)

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