Stars & Galaxy 2.1 The Sky Above

Geocentric

The idea that the Earth is the center of the universe.

Zenith

The point of the imaginary ‘dome’ directly above your head.

Changes depending on your position on Earth.

Horizon

Where the imaginary ‘dome’ meets the Earth.

Stars rise and set from?

All stars rise from the eastern horizon and set on the western horizon

North & South Celestial Poles

An imaginary line from North to South poles that extends out to the Celestial Sphere.

Earth’s axis rotates around these poles.

Celestial Sphere

3D projected surface of objects in the night sky.

Imaginary.

As Earth rotates, the sky appears to turn in what direction?

the opposite direction in which it is turning.

Celestial Equator

Halfway between the celestial poles.

Exactly where Earth’s equator is, just extended out.

The apparent motion of the celestial sphere depends on your latitude.

Examples: If you’re at the North Pole, it would appear as though the stars would not rise or set. Just ‘circle’ around the celestial poles.

If you’re on the Northern half of the equator, you can only see the Northern half of the sky (vice versa).

If you’re on the equator, all the stars rise and set

Latitude

Position North or South of the equator.

Lines perpendicular to the equator.

0 degrees to 90 degrees.

Altitude

Angular height.

Equal to the observer’s latitude.

Example: When the latitude is 38 degrees North, the altitude to the North Pole is 38 degrees above the horizon.

North Circumpolar Zone

Within a given location, the stars that surround Polaris and the North Celestial Pole that NEVER set for YOU depending on your latitude.

Example: In the US the Big Dipper, Little Dipper, and Cassiopeia are a part of the circumpolar zone. These stars are always visible.

Polaris Star

Very close to the North Celestial Pole.

Barely moves.

Fun Facts About the Sun

Moves 1 degree each day to the East (along with the stars).

The sun rises 4 minutes later(?) each day (along with the stars)

Ecliptic

The path the sun takes around the celestial sphere each year.

It is a 23.5 degree angle from the imaginary vertical line of our planet.

So it aligns oppositely with Earth’s tilt.

Constellations

New ones every month.

Grouping of stars.

Used for navigation.

One of the 88 sectors divided in the sky (made up of imaginary lines going north, south, east, and west. Each point in the sky falls in a specific constellation).

Asterism

Noticeable star pattern within a constellation.

Example: the Big Dipper is an asterism within the constellation of Ursa Major

Fixed Stars

Those that maintain fixed patterns among themselves through many generations

Wandering Stars

Planets

Zodiac

Planets, sun, and moon are centered on the ecliptic and always found in the sky within an 18 degree-wide belt.

Meridian

The line passing through the Zenith and connecting North and South points on the horizon.

Conceptual Model

The night sky appears to an observer on Earth as a sphere surrounding Earth.

The Earth rotates and we see new objects on the sphere.

Longitude

Lines parallel to the equator.

X-axis.

0 degrees to 180 degrees.

Arcminutes and Arcseconds

Full circle: 360 degrees

1 degree = 60’ arcminutes

1’ arcminute = 60” arcseconds

Right Ascension (RA) & Declination

Describes the location of the sky.

Latitude and longitude but extend it outwards, encompassing the celestial sphere.

Right Ascension

Would be space’s version of longitude.

Measured in hours.

1 hour = 15 degrees

Declination

Space’s version of latitude.

0 degrees-90 degrees

Azimuth

The angle across the horizon