celestial sphere sk

CELESTIAL SPHERE

There are many celestial bodies on the sky…

We can see celestial bodies (stars, planets etc.) on many

parts of the sky but…

How to orient the position of star?

We can spot positions on the Earth with Geographic

coordinates.

Equator, Poles & Other Latitudes

Prime Meridian & Other Longitudes

We imagine the Cosmic Sky that

looks like Sphere.

Celestial Sphere is a sphere that

extends Global sphere

to the Sky faraway.

A person being at each position on the Earth can see half of celestial sphere.

Horizon divides the Celestial sphere to 2 Hemispheres (Overhorizontal &

Undererhorizontal).

Astronomers crated many systems of

coordinates for spotting position

on the sky.

There are 4 coordinating

systems that be popular in using

!

HORIZONTAL COORDINATE SYSTEM

“Azimuth” & “Altitude”

You must know about directional point.

North point is a point on horizon that point to Geographic North Pole.

A point on horizon that is opposite to North point is South point.

West point is to the left and East point is to the right hand of

North point.

Azimuth is the angular distance along horizon from north eastward to

position of object.

360 degrees for azimuth

angle.

Altitude is the angular distance from horizon to object, measured along a

vertical circle.

90 degrees for altitude from

horizon.

There are 90 degrees of altitude at

Zenith (overhead

point).

Zenith distance is the angular distance from

zenith to object,

measured along a vertical

circle.

Altitude + Zenith distance = 90

degrees.

Astrolabe

Simple astrolabe

How to use simple astrolabe to spot the object in horizontal

coordinate .

Simple astrolabe and direction plate

Altitude & Azimuth measurement by hand

Hand signs for altitude & azimuth measurement

(1 – 20 degrees)

Altitude measurement for 35 degrees.

Vertical circle & Meridian

Vertical circle is a circle which pass zenith.

Meridian is a circle which pass zenith,

north and south point.

Problems in using Horizontal Coordinates

Different place…Different horizon

Different time…Different celestial

hemisphere

So…there are other coordinate systems for

unity of spotting.

EQUATORIAL COORDINATE

SYSTEM

“Right Ascension” & “Declination”

“Celestial equator” & “Celestial pole”

“Earth’s axis of rotation”

N“Right hand rule” & “Planet’s rotation”

Rotation of each planets. (Earth, Uranus & Venus)

Apparent motion of the sky is opposite way to Earth’s rotation.

At “Equator”

All stars rise from the east and set to the

west.

At “Mid-North latitude”

Some stars are circumpolar,

some stars can rise and set.

At “North Pole”

All stars that can be seen

are “circumpolar

stars”.

Zenith distance of celestial equator equals “latitude of observer” and “altitude to celestial pole”.

“Declination”

Declination is the angular distance measured north and south of celestial

equator.

Celestial equator has a declination of 0 degree. North celestial pole has +90

degree & South has -90 degree.

Declination at zenith equals to Latitude at observer.

Lowest declination that be circumpolar declination = 90 – latitude of observer

“Ecliptic plane” & “Ecliptic line”

Ecliptic plane is a plane of the Earth’s orbit around the Sun.

Ecliptic line is the apparent path of the Sun on celestial sphere.

Ecliptic line angles to Celestial equator ~23 degrees and half.

Ecliptic line crosses Celestial equator at “Vernal Equinox” and “Autumnal

Equinox”

“Right Ascension”

Right ascension is the angular distance measured eastward along

celestial equator.

Right ascension is measured in hour minute & second with 24 hours

equivalent to a full circle.

0 hour of right ascension begins at “Vernal equinox” point lined from North to South.

Star map in 0 hr – 12 hr in R.A.

Stars map in 12 hr – 24(0) hr in R.A.

Each right ascension can rise from the East and set to the West when the Earth rotates.

So…Each right ascension can reach to highest point at meridian line.

Position of the Sun in Equatorial Coordinate System

The Sun changes position in equatorial coordinate system in each day during

a year .

The Sun is on Dec. 0 at Equinox day. Vernal is on 0 hr and Autumnal is on

12 hr right ascension.

The Sun is on +23.5 Dec. and 6hr R.A. at Summer solstice day.

The Sun is on -23.5 Dec. and 18 hr R.A. at Summer solstice day.

Ecliptic line on Equatorial Coordinate

system

The Sun rises from the east point and sets to the west point at Equinox

day.

Path of the Sun in Equinox day

observing in each latitude.

Equator

Pole

Mid latitude