Astronomy

Kepler's Three Laws

1. The orbital paths of the planets are elliptical, with the sun at one focus 2. An imaginary line connecting the sun to any planet sweeps out equal areas of the ellipse in equal intervals of time 3. The square of a planet's orbital period is proportional to the cube of its semimajor axis.

What are the three types of solar eclipses?

1. Total 2. Partial 3. Annular

why is there a difference between a sidereal day and a solar day?

A sidereal day is the time it takes for the Earth to rotate about its axis so that the distant stars appear in the same position in the sky. A solar day is the time it takes for the Earth to rotate about its axis so that the Sun appears in the same position in the sky.

Moon motion

Although the Moon is moving eastward around the Earth, the Earth is also turning to the east and much faster, for it goes all the way around its axis of rotation in just under a day. As a result, although the Moon is moving to the east relative to the stars, the much faster westward motion of the sky is carrying it to the west, so despite its eastward motion relative to the center of the Earth, it rises in the east and sets in the west, just like any other celestial body. The Moon's eastward motion is much slower than the sky's westward motion. So though moving to the east from day to day, it still has a net motion toward the west each day. This means that it still rises in the east and sets in the west like the stars, but a little later each day.

What would happen to the seasons if the Earth's spin axis were perpendicular to the Earth's orbital plane?

First would be that the length of day and night would be exactly equal, over the whole planet. There would be no seasons, just one average of the current four. Weather patterns would be very different; much more uniform.

Why does Polaris not move?

Polaris, the North Star, appears stationary in the sky because it is positioned close to the line of Earth's axis projected into space.

Why are a tropical year and a sidereal year different?

Sidereal year: the time is takes Earth to complete one orbit relative to the stars Tropical year: how long it takes from one spring equinox to the next (20 min shorter than sidereal year)

Why are a synodic month and a sidereal month different?

The sidereal month is the time the Moon takes to complete one full revolution around the Earth with respect to the background stars. However, because the Earth is constantly moving along its orbit about the Sun, the Moon must travel slightly more than 360° to get from one new moon to the next. Thus, the synodic month, or lunar month, is longer than the sidereal month. A sidereal month lasts 27.322 days, while a synodic month lasts 29.531 days.

What causes the seasons?

The tilt of the earth's rotation axis relative to the ecliptic is responsible for the seasons we experience- the marked difference in temperature between the hot summer and cold winter months.

By which "day" do we set our watches? Why?

We set our watches by solar days. It measures from noon to noon.

What is the direction of the apparent annual motion of the planets in our sky?

West to east

superior conjunction

a conjunction of Mercury or Venus with the sun, when the planet and the earth are on opposite sides of the sun.

What is the eccentricity of an ellipse?

a measure of how flat it is

Ancient Chinese

attached particular importance to omens such as comets and "guest stars"

AU

average distance from the Earth to the Sun. = 1.4960 x 10^11 m

Declination and Ascension

declination- latitude above or below the celestial equator on the celestial sphere right ascension- longitude on the celestial sphere (East & West) measured in hours (1 hr= 15 degrees) 0 hr= position of the sun

light years

distance light travels in one year. 1 ly = 9.46x 10^15 m

How much of the overall sky is above the celestial equator in the northern hemisphere?

exactly 1/2

Where is the sun in its path in the sky during the summer solstice?

farthest north in the northern hemisphere or farthest south in the southern hemisphere when the summer solstice happens in the N.H, the North pole is tilted toward the sun.

Blackbody

object that absorbs all radiation falling on it

Arab Astronomers

preserved and augmented the knowledge of the Greeks through the dark ages. developed trigonometry terminology- zenith, azimuth, rigel, Betelgeuse, vega

Babylonian Astronomy

records over long periods of time showed regularities and patterns in the motion of the moon and the planets.

parsec

the distance at which 1 AU fills an angular size of 1 arc second. = 3.26ly

Inferior conjunction

when a planet is directly between the earth and Sun.