1. Astronomy & Space Science Association
in
University of Kelaniya
Astro Night 2014
Lecture 2
Coordination Systems in the
Sky & Celestial Sphere
Eranga Jayashantha
Hon. mentd Dip in Astronomy & Astrophysics ( IOAA – China )
National Representative at Space Generation Advisory Council ( UN )
Sri Lanka national Astrophysics Olympiad Team Trainer at Institute of Physics Sri Lanka
2. Latitude and Longitude
Latitude (f) meas from
equator
Longitude (l) point of
reference – Greenwich
UK
Units of measure:
Deg, arcmin, arcsec
O ‘ “
3.
4.
5. Two types of Coordination Systems are used to
describe the position of an object in the Sky
1) Horizon System
2) Equator System
6. The Horizon System
Altitude (h) – angle
measured from the
horizon to Zenith (Z)
Azimuth – the angle
measured from NE
along horizon
Problem as a celestial
system?
7.
8.
9. What is an Equator System?
Based on
Right Ascension
&
Declination
10. Celestial Sphere
Imaginary sphere where stars
reside
Extension of Earth’s equator,
poles
Celestial Equator
Celestial poles
Zenith & Nadir
11.
12.
13.
14. • Celestial equator
divides the sky into
northern and southern
hemispheres
•Celestial poles are
where the Earth’s axis
of rotation would
intersect the celestial
sphere
• Polaris is less than 1°
away from the north
celestial pole, which is
why it is called the
North Star or the Pole
Star.
•Point in the sky directly
overhead an observer
anywhere on Earth is
called that observer’s
zenith.
– Nadir is directly
opposite the zenith
15. Declination & Right Ascension
Declination = Latitude
Celestial Equator d = 0
Latitude, NCP elevation
Units: deg, arcmin, ‘’
The Celestial Meridian
Great circle going through
zenith & NCP
Right Ascension =
Longitude
Units: hh:mm:ss
360o = 24 hr (1 hr = 15o)
Where to start RA?
16.
17. How the Equatorial Coordinates are changed over a long time?
Due to two main reasons
1) Precision of Equinoxes
2) Lunar orbit is getting far from Earth by ~3cm per year
( Earth’s rotational angle is getting changed )