The Sky, Earth, and Moon; Eclipses Flashcards
Great circle
any circle on the surface of a sphere whose center is at the center of the sphere; ex: Earth’s equator. Same center and circumferences.
Meridian
series of great circles that pass through both the N and S poles; they are perpendicular to the equator, crossing it at right angles. Any point on Earth will have a meridian passing through it (specifies longitude which is 0-180 degrees)
Latitude
the number of degrees of arc you are away from the equator along your meridian (N/S; 0-90 degrees)
What causes the seasons?
Significant variations of heat we receive from the Sun each year which is caused by the 23.5 degree tilt of the Earth’s axis. The axis points in the same direction throughout the year depends on which hemisphere is “leaning” into the sun
Why do daylight hours differ in summer and winter?
Where we see the Sun changes as the year goes on b/c of Earth’s axis, the Sun spends more time where there’s more direct sunlight (longer days) and less time where there’s less direct sunlight (shorter days)
Tropic of Cancer
At 23 degrees north, the Sun is at the zenith at noon on the 1st day of summer
Tropic of Capricorn
At 23 degrees south latitude the Sun passes through the zenith at noon
Arctic Circle
The Sun is as far north on the 1st day of summer; places within 23 degrees of the south pole has sunshine for 24 hours
Antarctic Circle
Places within 23 degrees of the south pole do not see Sun for 24 hours
Vernal and Autumnal
(Spring/Fall; points where the Sun crosses the celestial equator)- Halfway between the solstices every place on Earth receives roughly 12 hours of sunshine and night
Why are all the seasons the same at the equator?
It’s always 12 hours of day and night; determine seasons by the amount of rain
Mean Solar Time
Based on the average value of the solar day over the course of the year (exactly 24 hours; everyday timekeeping); inconvenient for practical use b/c it depends on the position of the Sun, so it’s not strictly observed
Daylight saving time
Local standard time of the place plus 1 hour
International Date Line
Run approximately along the 180 degrees meridian of longitude; runs down the middle of the Pacific Ocean
What makes the moon glow?
The moon glows with reflected sunlight
Phases
Different (planetary) appearances
Lunar Phases
The moon moves completely around the Earth, depending on the angle the Sun makes with the Moon. Moon moves about 12 degrees every day for 30 days= 365 degrees around earth
Waxing (or growing) gibbous
Increase of moons illuminating hemisphere
Sidereal period
The period of the Moon’s revolution about Earth measured with respect to the stars (a little over 27 days). Sidereal month: 27.3217 days
Solar month
The time interval in which the phases repeat from full to full
Synchronous rotation
The moon rotates on its axis at the same time that it takes to revolve about Earth; the Moon always keeps the same face turned toward Earth. The Moon’s appearance is due to a change in illumination, not rotation, so there’s no regular dark side of the moon.
Differential forces
The difference among the forces of the Moon’s attraction on different parts of Earth that cause Earth to distort slightly and stretch slightly into a prolate spheroid with its long diameter pointing towards the moon → tide-raising forces
Spring tides
Tides are greater than normal
Neap tides
Sun produced tides partly cancel the Moon produced tides making them lower than usual
What other factors affect the tides?
Landmasses, friction b/w and in oceans, Earth’s rotation, wind, ocean depth, etc.
How can eclipses occur?
The Sun and Moon have the same angular size of ½ degrees
