THE CELESTIAL SPHEREA scientific model

THE CELESTIAL SPHEREBIG QUESTIONS:

Why do we use the model of the celestial sphere when studying the night sky, even though it does not accurately represent three-dimensional space?

How can you locate constellations and other sky objects using the coordinate system of the celestial sphere?

Why are different constellations visible in the sky at different times of the year or from different places on Earth?

WHAT IS THE CELESTIAL SPHERE?

An imaginary sphere used to help locate celestial objects.

The Earth is at the center and the celestial bodies (stars, planets, galaxies, etc) are “painted on” the surface of the sphere

It is considered a scientific model

GUIDEPOSTS ON THE CELESTIAL SPHERE

Horizon – the visual boundary between Earth and the sky (with cardinal points N, S, E, and W)

Zenith - Point on the celestial sphere directly overhead

Nadir -Point on the celestial sphere directly underneath the observer’s feet

Celestial equator - a projection of Earth’s equator onto the celestial sphere, always crosses the horizon directly East and West

Celestial Poles projection of Earth’s north and south poles onto the celestial sphere

• From geographic latitude l you will see the celestial north pole (l) degrees above the Northern horizon

l

Locating the Celestial North Pole and Celestial Equator in your sky

zenith

The Celestial South Pole isn’t visible from the Northern Hemisphere.Celestial Equator is visible in the sky 90o south of the CNP

Horizon

Looking North

Celestial North Pole

40.70

Example: New York City: l ≈ 40.7º

Polaris

Zenith (90o above horizon)

Same as latitude (l)

COORDINATE SYSTEM ON THE GLOBE: Latitude: (parallels) marks locations

north and south of the equator Longitude: (meridians) marks locations

east and west of the Prime Meridian

COORDINATE SYSTEM OF THE SKY Declination (Dec): imaginary lines on the

celestial sphere that show positions north and south of the celestial equator +60o is north and -60o is south Similar to latitude lines on the

Earth 0o declination is at the

celestial equator

COORDINATE SYSTEM OF THE SKY

Similar to longitude on Earth Usually measured from 0 – 24

hours. Right ascension is a unit

of angle As you face north, the stars

will appear to rise (ascend) from the east (your right).

The celestial meridian (0 hour) is a semicircle connecting the celestial poles and passing through the vernal equinox on the celestial equator

• Right Ascension (RA): The E-W position of a celestial body

SPECIFIC COORDINATES

Constellations, stars, galaxies, etc. can be given an “address” in the sky using RA and Dec.

Degrees of Declination (Dec) can be divided into 60 arcminutes and each minute of arc can be divided into 60 arcseconds.

Hours of Right Ascension (RA) can be divided into minutes and seconds as well.

So, the specific “address” for the star Antares is Dec: -26o25’55” RA: 16h29m30s

THE ECLIPTIC

The Sun’s apparent path on the sky is called the Ecliptic.

OR

The Ecliptic is the projection of Earth’s orbit onto the celestial sphere.

ECLIPTIC VIDEO

http://www.youtube.com/watch?v=2-TtcfmbrkI

THE CELESTIAL SPHEREBIG QUESTIONS:

Why do we use the model of the celestial sphere when studying the night sky, even though it does not accurately represent three-dimensional space?

How can you locate constellations and other sky objects using the coordinate system of the celestial sphere?

Why are different constellations visible in the sky at different times of the year or from different places on Earth?