Experience Astronomy Study Guide for the Midterm

The Purpose of Astronomy

Astrology is focused the meanings of heavenly movements (predicting what will happen here on Earth, impacting things on Earth, or inluencing our personality).

Astronomy, however, is a scientiic study of the sky.

The irst chapter of Genesis says God created the stars for very practical reasons: • to give us light on the Earth • to separate day from night • to help us create calendars that guide our different seasons of planting, harvesting, and celebrating, and to help us mark different years so we could keep records of history • to help us use the signs in the sky to navigate around and ind our way

The Celestial Sphere

Celestial Sphere – a spherical representation or map of the ixed stars we see in the sky; divided into 88 regions called constellations

Celestial Poles - the axis of the Earth points at these northernmost and southernmost points on the celestial sphere

Celestial Equator - if the Earth’s equator was projected out into space, the line it would make on the celestial sphere is the celestial equator

Ecliptic - the path the sun takes through the celestial sphere over the course of a whole year; it is tilted in respect to the celestial equator because the Earth’s axis is tilted 23.5°

The Direction of Spin - Looking down on the north pole, the Earth spins counterclockwise. Looking straight on at the Earth, it spins in an Eastward direction. This means the celestial sphere overhead moves in a westward direction from our perspective on Earth.

Latitude Lines - a geographic coordinate that indicates the north-south position of a point on the Earth, ranging from 0° at the Equator to 90° at the North and South poles; your latitude position determines what part of the celestial sphere you see (for instance, standing at 90°N, the north pole, means the North Celestial Pole will be at your zenith)

1 Terms

Absolute Magnitude - how bright a star really is if all stars were the same distance from us

A.M. - Ante Meridiem, meaning before the middle of the day

Apparent Magnitude - how bright a star appears in our sky

The Arctic Circle - the latitude line where the sun doesn’t set on the summer solstice

Autumnal (Fall) and Vernal (Spring) Equinoxes - the two days of the year when the sun rises and sets on the celestial equator, making an equal amount of daylight and nighttime

Axis - the line around with the Earth (or any planetary body) rotates

Day - the amount of time it takes for the Earth to spin on its own axis one time

The Galilean Moons - four largest moons of Jupiter: Europa, Io, Callisto, and Ganymede

Geocentric Model – a model or understanding of the universe where the Earth is at the center, and the sun, moon, planets and stars revolve around the Earth

Horizon – from your perspective, the place where the sky meets the land

Jupiter - a planet named after king god of the Romans; the most massive, fastest spinning planet in the solar system, with more moons than any other planet

The Land of the Midnight Sun - a name for the region north of the Arctic circle because the sun doesn’t set during the summer months

Light Year – the distance light travels in a year (about 5.8 trillion miles)

Meridian - the line on the celestial sphere going from due south, straight over your head through the zenith, to due north; it means “middle of the day”

The Milky Way - a cloudy band circling the celestial sphere which is actually about 100 billion distant stars in our Milky Way Galaxy

Planet - a word meaning “wandering star”; the ive classical planets are Mercury, Venus, Mars, Jupiter, and Saturn

P.M. - Post Meridiem, meaning after the middle of the day

Polar Night - the phenomenon where the sun doesn’t rise north of the Arctic circle during the winter months

2 Retrograde motion - when a planet stops going eastward against the background stars, turns around, and starts moving westward

Saturn - a planet named after the Roman god of agriculture and wealth; known for its rings

Summer solstice - from the perspective of the Northern hemisphere, the day of the year when the Sun rises and sets at the northernmost place on the horizon, making a large arc through the sky (the day with the most amount of sunlight)

Terminator - the line on the surface of the globe where the night side of the Earth meets the day side

Titan - the largest moon of Saturn, known for its atmosphere and liquid lakes

The Tropic of Cancer - the latitude line where the sun is at the zenith at high noon on the summer solstice

The Tropic of Capricorn - the latitude line where the sun is at the zenith at high noon on the winter solstice

The Tropics - The region between the Tropic of Cancer and the Tropic of Capricorn

Winter solstice - from the perspective of the Northern hemisphere, the day of the year when the Sun rises and sets at the southernmost place on the horizon, making a shallow arc through the sky (the day with the least amount of sunlight)

Zenith – from your perspective, the part of the celestial sphere that is right over your head

People

Aristotle • one of the most famous philosophers of all time • argued for a spherical shape to the Earth • argued for a geocentric model to the universe

Aristarchus • irst person we know about who proposed a heliocentric model of the universe

Ptolemy • Greek astronomer • created a catalogue of 48 constellations which much later became the basis for our 88 constellations • followed a geocentric model, creating a mathematical system for predicting the movements of the planets and the stars

3 Copernicus • resurrected the idea of a sun-centered model in the middle ages

Kepler • discovered the three laws of planetary motion

Galileo • one of the irst to use a telescope to observe the sky • discovered the four largest moons of Jupiter

Constellations and Stars

Polaris - meaning “pole star”; this star in Ursa Minor is commonly called the North Star

The Zodiac - 12 traditional constellations that touch the ecliptic: Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpius, Sagittarius, Capricornus, Aquarius, and Pisces

The Summer Triangle - an asterism made up of the three very bright stars Vega, Deneb, and Altair

Fomalhaut - meaning “mouth of the ish”; a 1st magnitude star in Pisces Austrinus

Pollux and Castor - two bright stars in the constellation Gemini

Aldebaran - a 1st magnitude star in the constellation Taurus

Betelgeuse and Rigel - two 1st magnitude stars in the constellation Orion

Aquila the eagle

4 Lyra the lyre

Cygnus the swan

5 Hercules

Pisces Austrinus the southern ish

Aquarius the Water Bearer

6 Pisces the ish

Pegasus the lying horse

Andromeda

7 Perseus

Cassiopeia

Gemini the twins

8 Ursa Major the big bear

Taurus the bull

9 Aries the ram

Capricornus the sea-goat

Orion the hunter

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