Astronomy Test 1

equinox

The date and time where the sun crosses the celestial equator. There is exactly 12 hours of sunlight and 12 hours of day light.

Vernal Equinox ~ March 20
Autumnal Equinox ~ September 22

celestial equator

A great circle in the celestial sphere that is in the same plane as the Earth's equator.

ecliptic

A great circle on the celestial sphere representing the sun's apparent path during the year, so called because lunar and solar eclipses can occur only when the moon crosses it.

zenith

Point in the celestial sphere that is directly above the observers head.

zodiac

A belt of the heavens within about 8° either side of the ecliptic, in the celestial sphere. This includes all apparent positions of the sun, moon, and most familiar planets. It is divided into twelve equal divisions or signs.

solstice

The highest and lowest point the sun reaches in the celestial sphere. This creates the longest Day and the longest Night.

Winter Solstice ~ December 21(Longest Night)
Summer Solstice ~ June 21(Longest Day)

constellation

From Latin, meaning "set of stars". The defined area of a set of stars which are identified with mythological creatures or other objects.

zodiac constellations

The major Roman constellations that are comprised of stars within the Zodiac (or path of the sun). Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Sagittarius, Capricorn, Aquarius, Pisces

a light year

The amount of time it takes light to travel in a year: 3x10^8 m/s

right ascension

Measurement of distance from East to West in Degrees and Minutes. Analogous to Longitude.

declination

Measurement of 'height' in the sky from the celestial equator in Degrees and Minutes. Analogous to Latitude. Uses negative signs, not North and South (-90 to 90, rather than 90 S to 90 N)

solar/synodic time

The time it takes the sun to appear at the Meridian again. Literal 24 hour day, from sun down to sun-up. Because we are orbiting the thing we are looking at (the sun) our angle doesn't change.

sidereal time

The time it takes a distant star to appear at the Meridian again. 23 hours and 56 minutes. This is because as we orbit around the sun, while we are rotating, the angle to that distant star changes slightly (about 4 minutes).

A.U. (astronomical unit)

The distance from the Sun to the Earth.

Gregorian calendar

Replaced the Julian Calendar in 1582 by Gregory XIII to correct the '3 day creep' of the Julian system.

electromagnetic spectrum

Radio - Micro - Infrared - Visible (ROYGBIV) - Ultra Violet - X-Rays - Gamma Rays

light pollution

The brightening of the night sky caused by street lights and other man-made sources, which has a disruptive effect on natural cycles and inhibits the observation of stars and planets.

Galileo

~1609 He was the first to see craters on the moon and that planets other than our can have moons. He apposed the Catholic Church and said that the Celestial Spheres (Planets & Moons) weren't perfect. Helped champion the idea of Heliocentrism. Made popular the telescope and improved the compass.

astrology

The study of the movements and relative positions of celestial bodies interpreted as having an influence on human affairs and the natural world.

NACA

Founded in 1917 as National Advisory Committee for Aeronautics. Preliminary NASA Agency.

star

Ball of gas that generates its own energy in the core by nuclear fusion

asteroid

Small rocky object that orbits a star

comet

Small icy object that orbits a star

How far is the Sun from the center of the Galaxy

27,000 Light Years

astronomical unit

The average distance between the Sun and the Earth (1.5 x 10^11)

horizon

A great circle on the celestial field, 90 degrees from the zenith

nadir

The point directly below the zenith

meridian

Great circle moving North-South, and passing through the zenith

60 arcminutes

1 degree

60 arcseconds

1 arc minutes

why does the sky look blue

Because the Earth's atmosphere scatters Blue light better than Red light

celestial equator

Intersection of the plane passing through the Earth's equator and the celestial sphere.

summer solstice

Sun reaches most northerly point above the celestial equator

winter solstice

Sun reaches most southerly point below celestial equator

What do short and long wavelengths mean for frequency?

a short wavelength means a high frequency, a long wavelength means a low frequency. They are inversely proportional.

What is a wave?

any disturbance that carries energy without the motion of material from one place to another, often in the form of a repeating pattern.

Define wavelength.

distance between two successive peaks (or troughs).

Define frequency.

the number of waves that pass a given point per second.

Define period.

time required to complete one cycle of a wave if you stay in the same place.

Define amplitude.

height of a wave

How long does it take light from the Sun to reach Earth?

8 min 20 secs

How long does it take light from the closest sun to our sun, Proxima Centauri, take to reach Earth?

about 4 light years

What is the unit used to measure frequency?

hertz

the spectrum

the splitting of light into its components.

Which color has the longest wavelength?

red

the Doppler effect.

motion of a light source toward or away from us, changing our perception of the wavelength of the waves reaching us.

“blue shifted”

the waves of an object approaching crowd together, making wavelengths shorter (like the color blue).

“red shifted”

the waves of an object moving away space apart, making wavelengths longer (like the color red).

If a light source is approaching you, you will observe:

its spectral lines are shorter in wavelength.

scale that refers to temperature in terms of degrees K.

Kelvin Temperature Scale.

What is the equation for the Stefan- Boltzmann Law?

F = o T^4. F is flux (energy per second per unit area) and T is temperature to the fourth power. The o is constant.

When an electron moves from a higher energy level to a lower energy level in an atom:

a photon is emitted

How many regions is the sky divided up into?

88 regions, each with one constellation

celestial sphere

The imaginary sphere on which objects in the sky appear to reside when observed from Earth.

celestial equator

an imaginary circle directly above Earth's equator, dividing the sky into north and south halves.

NCP: north celestial pole

an imaginary pole above the North pole that extends into the sky. 90 degrees away from celestial equator.

SCP: south celestial pole

an imaginary pole above the South pole that extends into the sky. 90 degrees away from celestial equator.

define circumpolar

stars that never set nor rise, near the North celestial pole.

meridian

imaginary line dividing East/ West halves.

the zodiac

constellations that fall upon the ecliptic, the path the sun takes. the Zodiac of the month is determined by the zodiac that is in the sun that month.

define the Earth’s tilt

the North pole is always pointed towards the North Star. it does not change its tilt toward or away from the sun, but remains constant in it's almost perfect circle around the Sun.