Lesson 2 Flashcards
1
Q
Constellation
A
- Region of the sky with well-defined borders
- 88 official constellations
2
Q
Celestial sphere
A
- Imaginary sphere that surrounds Earth, where all the stars lie
3
Q
North celestial pole
A
point directly over earth’s north pole
4
Q
South celestial pole
A
point directly over earth’s south pole
5
Q
Celestial equator
A
projection of earth’s equator into space
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)
7
Q
Local Sky
A
sky as seen from wherever you stand
8
Q
Horizon
A
boundary between Earth and sky
9
Q
Zenith
A
Point directly overhead
10
Q
Meridian
A
imaginary half circle from our horizon South to North
11
Q
Azimuth
A
degrees clockwise from due north - direction along horizon
12
Q
Altitude
A
degrees above horizon
13
Q
Angular size
A
Angle an object appears to span in your field of view
Moon and Sun are both 0.5 degrees
14
Q
Angular distance
A
angle that appears to separate two objects
15
Q
Arcminutes and arcseconds
A
- Arcminutes: divide each degree into 60 arcminutes
- Arcseconds: divide each arcminute by 60 arcseconds
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)
17
Q
Latitude and longitude
A
- Latitude measures north-south position
- Longitude measures east-west position
- Latitude affects how we see constellations
18
Q
Zodiac
A
- the constellations along the ecliptic
- 13 constellations
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
Lunar Phase
- moons orbit around sun takes 29.5 days (synodic period)
| - inclination of lunar orbit to ecliptic plane is 5 degrees
26
Moon phases: New Moon
New Moon: rises and sets with the sun; can't see it in night
- moon is between earth and sun
27
Moon phases: Waxing Crescent
Waxing crescent: rises mid-morning, highest in mid-afternoon and sets late evening; sliver getting bigger
28
Moon phases: First Quarter
First Quarter: rises noon, highest sunset, sets midnight; looks like a half moon getting bigger
29
Moon phases: Waxing Gibbous
- Waxing Gibbous: rises mid-afternoon, highest late evening, sets before dawn; looks like three quarter full moon and getting bigger
30
Moon phases: Full moon
Full moon: rises sunset, highest midnight, sets sunrise; full because sun illuminates it fully
31
Moon phases: Waning Gibbous
Waning Gibbous: rises late evening, highest before dawn, sets mid-morning; looks three quarter full getting smaller
32
Moon phases: Third Quarter
Third Quarter: rises midnight, highest sunrise, sets noon; looks half full getting smaller
33
Moon phases: Waning Crescent
Waning crescent: rises before dawn, highest mid morning, sets mid-afternoon; looks like crescent getting smaller
34
Synchronous Rotation
We always see same face of Moon
35
Lunar eclipse
- 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
Solar Eclipse
- 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
Nodes
- 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
Eclipse season
- nodes of the moon's orbit are closely aligned with the Sun
- lasts <5 weeks; usually one lunar and one solar eclipse
39
Saros cycle
- eclipses recur in a cycle of ~ 18 years and 11.25 days
40
Planets easy to see with naked eye
- Mercury, Venus, Mars, Jupiter, and Saturn
41
Apparent retrograde motion
- occasionally the planets look like they go east to west instead of west to east because Earth is passing other planets
42
Stellar Parallax
- 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
Sidereal vs. Solar day
- 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
Solar day increase
- solar day is increasing 1.4 milliseconds every century
45
Daytime
- 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
Synodic month vs. Sidereal month:
- Synodic: 29 days 12 hours and 44 minutes
| - Sidereal: 27.322 days
