celestial sphere sk
TRANSCRIPT
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