Hello....hope you are having a better time than me, some day it was for me, I FEEL SOO BAD! It wasn't my fault someone stole it, even though I didn't get told off by them, but I know the problems right now, and this problem suddenly comes and I'm part of the whole problem now, ahh...hopefully he'll get what he wants towards the end of this week.
Anyway..today's blog is about celestial co - ordinates..I think I should have posted this some time ago, but I just found it recently, so hopefully I am not too late.
Celestial spheres
From Earth all stars and planets appear equally remote.
This can be depicted as the celestial sphere that spins westwards in rotation of the Earth.
North celestial pole (NCP) and south celestial pole (SCP) lie above geographic poles of Earth.
Celestial equator is above terrestrial equator.
Local Reference Lines
Describes the location of a object in the sky with respect to the horizon.
The point that is directly above the observer is called the Zenith.
Celestial horizon is circle 90 degrees away from Zenith.
Local or observer’s meridian is great circle running through the north point on the horizon, the zenith and south point on the horizon (and directly beneath observer too). You'll probably recognize the picture in the last post.Sorry.
Rotation of the Earth is East to West direction (anti - clockwise) when viewed from above the North Pole, which means that stars appear to move in arcs across the sky in an east to west direction.
Looking towards south in northern hemisphere, stars move from left to right across the sky; looking towards north, stars move from right to left. (In the southern hemisphere these relations are reversed.)
In northern hemisphere a celestial body (star, planet, whatever) reaches its maximum altitude as it crosses the local meridian in the southern half of the sky. This is the upper transit or culmination of the body.
Location of stars and planets are described using the altitude and the azimuth.
Altitude changes from 0° at horizon to 90° at zenith.
Azimuth measures clockwise direction around horizon; 0° is due north, 90° is due east, 180° is due south, 270° is due west.
Celestial Co-ordinates.
Declination (Dec, d ) analogous to latitude. Measures star’s position north or south of celestial equator, runs from +90° at NCP through 0° at equator down to -90° at SCP
Right ascension (RA, a) similar to longitude. Measured eastwards from north-south line containing first point of Aries – position of Sun at vernal equinox. RA measured in hours, with 24h marking complete circle from 0h at vernal equinox. Each hour of RA corresponds to angle of 15° RA and Dec. of star will be same all over world and only change over long timescale due to the wobble of Earth’s rotation axis (precession)
RA and Dec coordinates on star maps altered every 50 years to account for precession. Last altered in 2000; these are labelled Epoch 2000 maps.
Circumpolar stars
Circumpolar are stars are stars that never sets.
Star is circumpolar if distance from pole is less than or equal to observer’s latitude. Stars of declination are circumpolar if Declination is less than or equal to 90 degrees take away observer's latitude.
The Ecliptic
Orbit of Earth around the Sun causes the apparent motion of from west to east background stars. The line of this path is called the ecliptic.
If the ecliptic is spotted on star chart based of the RA and Dec, then you'll see that a curve appear in the graph
Zodiac Constellations
Most planets move though a band in the sky centred ecliptic - the zodiac. There are thirteen zodiac constellations: Pisces, Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpius, Ophiuchus, Sagittarius, Capricornus (ME!) and Aquarius.
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Simplicity is the ultimate sophistication. Leonardo da Vinci
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