Elementary Astronomy Ch. 1

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Aster
Star
Nomie
Naming, Organization
How many “stars” can the naked eye see on a clear night?
~6000
Do stars change relative position to each other?
No
What direction do the stars seem to travel from the equator?
Perpendicular to horizon
Constellation
Regions of sky, familiar patterns
What do constellations help do?
Locate specific celestial bodies.
How many constellations do astronomers recognize?
88
Winter Triangle
Procyon, Sirius, Betelgeuse
Summer Triangle
Vega, Deneb, Altair
Celestial Sphere
A way to describe the universe surrounding Earth
Where are the Celestial Poles
Directly above Earth’s poles
Celestial Equator
Divides Celestial sphere into two hemispheres
Right Ascension
Longitude on Celestial Sphere
Right Declination
Latitude on Celestial Sphere
Altitude-Azimuth Coordinate System
Coordinate system thats universal. Altitude is the angle straight up from horizon, Azimuth is angle eastward from north along horizon.
Ecliptic
Annual path of sun on celestial sphere.
Annual path of Earth around sun.
What is the angle of deviance from perpendicular of Earth’s axis from the ecliptic?
23.5 degrees
What two measurements do we need to locate a “star”?
Direction and Angular separation from some reference point
Rotation
Earth’s rotation around its own axis, causes day and night
Revolution
Earth’s orbit around the sun, causes seasons and years
Precesses
Earth’s axis forming a cone rotation over course of 26000 years
Moon’s orbit causes…
lunar phases, cycle of tides, eclipses
What causes seasonal changes?
The tilt of Earth’s axis
Summer Solstice
Point of sun’s path farthest north on ecliptic. June 21st
Winter Solstice
Point of sun’s path farthest south on ecliptic. December 22th
Vernal Equinox
Sun crosses celestial equator while sun is moving north. March 20th
Autumnal Equinox
Sun crosses celestial equator while sun is moving south. September 22nd
Day and night are of equal length
Equinox
Longest day of the year
Summer Solstice
Shortest day of the year
Winter Solstice
Seasonal names of the solstices and equinoxes refer to which hemisphere?
Northern. Southern hemisphere’s seasons are exactly opposite.
Sidereal Days
4 min. shorter than solar day. Measured in respect to stars fixed on celestial sphere.
Solar Days
Measured in respect to the rotation of the Earth around its own axis.
Terminator
Boundary between bright and dark regions of the moon.
Synodic period
Phase cycle of the moon. 29 1/2 days long.
Sidereal Months
Time it takes the Moon to complete one revolution with respect to background stars. About 27.3 days.
Synodic Months
Time between consecutive new moons/ full moons. 29.5 days.
What moon phases can eclipses occur?
New/ Full moon
Eclipse
Moon, Sun, and Earth are aligned. Moon can be shadowed by Earth (Lunar Eclipse). Moon casts a shadow on Earth (solar eclipse).
Why doesn’t an eclipse occur during every full/ new moon?
Moon’s orbit is tilted 5 degrees from ecliptic plane.
Penumbral Lunar Eclipse
Moon appears dim
Partial Lunar Eclipse
Part of the Moon enters the umbra of Earth’s shadow and darkens
Total Lunar Eclipse
All of Moon enters earth’s shadow and becomes reddish. Lit by light bending around Earth’s atmosphere.
Total Solar Eclipse
Entirety of sun is covered by Moon.
Annular Eclipse of sun
Moon is too far from earth to cover all of sun, so a ring of sun appears around moon.
Categories: Astronomy