Astronomy

Front 1

Celestial Sphere

Back 1

The dome of the sky

Front 2

Celestial Equator and Celestial Poles

Back 2

Projection of the Earth's equator and poles on the sky

Front 3

Constellations

Back 3

The 88 regions into which the sky is segmented

Front 4

Ecliptic

Back 4

Path of the sun on the sky defined by the plane of the Earth's orbit around the Sun

Front 5

Signs of the Zodiac

Back 5

Constellations that lie along the ecliptic

Front 6

Horoscope

Back 6

"Hour of first Rising"

Front 7

Local Meridian

Back 7

Line on the celestial sphere drawn from the North point on the horizon through the zenith to the South point on the horizon

Front 8

Zenith

Back 8

Point direct directly overhead on the sky

Front 9

Vernal Equinox

Back 9

Points on the sky that define the event where the Sun on the ecliptic crosses the Celestial Equator going from South to North

Front 10

Autumnal Equinox

Back 10

Points on the sky that define the event where the Sun on the ecliptic crosses the Celestial Equator going from North to South

Front 11

Tilt of the Celestial Equater and Ecliptic

Back 11

23 1/2 degrees to each other since the Earth is tilted at 23 1/2 degrees to the orbit of the Earth around the sun which defines the Ecliptic

Front 12

Pole Star

Back 12

The altitude of the celestial pole about the North horizon is equal to your latitude. The Celestial Equator is zero of the celestial latitude or declination. One can measure positions on the celestial sphere North or South of the celestial equator.

Front 13

Angular Measure

Back 13

Degrees, minutes of arc, seconds of arc;

There are 360 degrees in a circle. There are 60 arcminutes (60') in a degree and 60 arcseconds (60") in an arcminute. There are 360 degrees all the way around the horizon.

Used rather than miles or yards to indicate the separation of objects on the Sky because this a relative measure independent of the distance to the objects.

Front 14

Declination and Right Ascension

Back 14

Positions of objects on the sky are specified by these two coordinates. Coordinates on the sky are analogous to latitude and longitude on the Earth; used to ascertain what time it is at your location.

Front 15

Right Ascension

Back 15

Measured in hours, minutes and seconds of time

Front 16

Declination

Back 16

Measured in degrees, minutes, and seconds of arc

Front 17

Daily Motion

Back 17

Celestial Motion of the Sun, Moon, and stars due to the rotation of the Earth. As a result, celestial object move from East to West as the Earth rotates from West to East through 360 degrees in 24 hours or 15 degrees/hour.

Front 18

Monthly Motion

Back 18

Celestial motion of the Moon in its orbit around the Earth is West to East on the sky. The Moon still rises in the East and sets in the West as the Earth rotates on its axis.

Front 19

Yearly Motion

Back 19

Celestial Motion of the Sun against the background stars is West to East about 1 degree/day due to the revolution of the Earth around the Sun. Note that all constellations appear to move towards the West at the same time each night as the months go by. This is why we see different constellations a different nights in different seasons.

Front 20

Path of the Sun through the Sky

Back 20

Changes not only with position on Earth, but also with the time of the year. This is due to the 23 1/2 degree tilt of the Earth's Rotation axis to its orbital plane

Front 21

Seasons

Back 21

Caused by the tilt of the Earth's axis

Front 22

Winter

Back 22

Days are shorter and the Sun is lower on the horizon meaning less direct sunlight reaches us

Front 23

Summer

Back 23

Days are longer and the Sun is higher in the sky meaning more direct sunlight reaches us

Front 24

Phases of the Moon

Back 24

Produced by the Moon orbiting Earth where we see only the portion of the face towards the Earth as illuminated; note that we always see the same face of the Moon, which implies that the Moon rotates once on its axis per orbit around the Earth (with respect to the background stars)

Front 25

Eastern Horizon

Back 25

Where an object is rising, i.e. just coming into view or in a direction of 90 degrees counterclockwise of your local meridian (overhead point)

Front 26

Western Horizon

Back 26

Where an object is setting, i.e. disappearing from view or in a direction of 90 degrees clockwise of your local meridian (overhead point)

Front 27

Solar Eclipses

Back 27

Occur when the New moon covers the Sun. They can be partial, annular, or total. Only a small portion of the Earth lies along the path of the Moon's shadow; occur since the Moon and the Sun are approximately the same angular size on the sky.

Front 28

Conditions for a Total Solar Eclipse

Back 28

1. Must be a new moon

2. The moon must be close enough to the Earth to completely block the Sun

3. The moon must be at a nodal point in its orbit around the Earth, i.e. lie in the ecliptic plane

Front 29

Moon's Orbit

Back 29

Not circular, but rather elliptical so at times it is farther or closer to Earth than on average; orbit around the Earth does not line in the ecliptic plane, but is tilted by 5 degrees to the ecliptic plane

Front 30

Lunar Eclipse

Back 30

Occur when the Moon is Full and lies in the Earth's shadow; They can be partial, total, or prenumbral

Front 31

Parallax

Back 31

An apparent change in the position of a foreground object with respect to the fixed background because of the motion of an observer.

Front 32

Earth - Sun Distance

Back 32

1 Astronomical Unit

Front 33

Planetary Motion

Back 33

Generally West to East direct motion, except when retrograde motion, East to West, independent of daily motion of the sky

Front 34

Inferior Conjucntion

Back 34

Between the Earth and Sun

Front 35

Superior Conjunction

Back 35

On the opposite side of the Sun from the Earth

Front 36

Oppositon

Back 36

On the opposite side of the Earth from the Sun

Front 37

Hipparchus and Luni-Solar Precession

Back 37

The effect on the Earth's spin axis is similar to that of the spinning axis on the toy gyroscope which wobbles in a circular pattern instead of falling over as the gyroscope rotates

Front 38

Earth's Axis of Rotation

Back 38

Completes a circle on the sky roughly every 26,000 years

Front 39

Copernicus

Back 39

Placed the Sun at the center of the Solar System

Front 40

Tycho Brahe

Back 40

Noted from his very accurate observations of motions on the sky; was not able to observe stellar parallax

Front 41

Kepler

Back 41

Introduced the idea of elliptical orbits

Front 42

Kepler's 1st Law

Back 42

Planets move in elliptical orbits

Front 43

Kepler's 2nd Law

Back 43

Planets move fastest when they are closest to the Sun and slowest when they are farthest from the Sun

Front 44

Kepler's 3rd Law

Back 44

Period, in years, squared = semi-major axis, in A.U., cubed, where the period is the time for a complete orbit around the Sun

Front 45

Galileo

Back 45

Observed moons going around Jupiter to indicate that not all celestial objects revolve around the Earth. Observed mountains on the Moon and sun spots to show celestial bodies are not perfect. Observed that Venus had phases like our Moon and thus had to be going around the Sun.

Front 46

Newton

Back 46

Explained how gravity worked, knew that the force of gravity produces an acceleration on objects due to Earth's mass. The moon is constantly being pulled towards the Earth just like an apple falls to the Earth.

Front 47

Universal Law of Attraction

Back 47

Any two objects (masses), independent of compositions, attract each other with a force proportional to the product of their masses directly divided by the square of the distance between them.