Discovering the Night Sky

Flashcards based on the lecture notes from 'Discovering the Universe' Chapter 1

What is scientific notation used for in astronomy?

Describing numbers much smaller or much greater than 1 using powers of ten.

What are the names of the metric prefixes for 10^3 and 10^9?

Kilo and Giga, respectively.

What are constellations?

Regions of the sky named after familiar patterns of stars.

How many official constellations do modern astronomers recognize?

88

What is the celestial sphere?

An imaginary sphere surrounding the Earth on which all objects in the sky can be located.

What are the north and south celestial poles?

Axis points around which the celestial sphere appears to rotate, located directly above the Earth’s poles.

What is the celestial equator?

The line that divides the celestial sphere into northern and southern hemispheres.

What are right ascension and declination?

Two coordinates used to define the position of an object on the celestial sphere.

Define rotation in the context of Earth's motion.

The spin of the Earth on its axis, taking one day to complete.

Define revolution in the context of Earth's motion.

The movement of the Earth in orbit around the Sun, taking one year to complete.

Define precession in the context of Earth's motion.

The slow conical motion of the Earth’s axis of rotation, taking 26,000 years for one cycle.

What causes the apparent westward motion of the Sun, Moon, and stars across our sky each day?

Earth’s rotation.

What type of motion do stars seen from the North or South Pole appear to have?

Huge, horizontal circles.

What is the ecliptic?

The special path that the Sun appears to move through the stars along. It also defines the plane of Earth's orbit around the Sun.

What causes the seasons?

The tilt of the Earth’s axis and the Earth's revolution around the Sun combined effect on the amount of direct sunlight.

What are the summer and winter solstices?

The points of the Sun’s path farthest north and south on the celestial sphere, respectively (June 21 and December 21).

What are equinoxes?

The two points on the ecliptic where the Sun crosses the celestial equator (vernal in March, autumnal in September).

What is the effect of precession on the North Celestial Pole?

It causes the position of the North Celestial Pole to slowly change over time.

What creates the phases of the Moon?

The changing amount of the Moon's lit side facing the Earth as it orbits the Earth.

What is the synodic period of the Moon?

29 1/2 Days

What is the difference between a synodic and sidereal month?

A synodic month is with respect to the Sun (29½ days), while a sidereal month is with respect to the stars (27.3 days).

What causes eclipses?

During a new or full moon phase, when the Moon, Sun, and Earth are aligned, the Moon may enter the shadow of the Earth, or the shadow of the Moon may reach the Earth.

Define penumbral lunar eclipse.

The Moon appears dimmed.

Define partial lunar eclipse.

Part of the Moon enters the umbra of the Earth’s shadow and is darkened.

Define total lunar eclipse.

All of the Moon enters the Earth’s shadow and becomes a reddish color, only lit from light bending around the Earth’s atmosphere.

What happens during a total solar eclipse?

The entire disk of the Sun is covered by the Moon, revealing the faint solar corona surrounding the Sun.

What is an annular solar eclipse?

An eclipse that occurs when the Moon is too far away from the Earth to completely cover the Sun, leaving a thin ring of light around the Moon.

What are the names of the two parts of a shadow?

Umbra and Penumbra.

What is the tilt of the Earth's axis of rotation from the perpendicular to the plane of the Earth’s orbit?

23 1/2 degrees