Page 19 - BBC Sky at Night Beginners Guide to Astronomy - 2017 UK

NEED TO KNOW

THE CELESTIAL

SPHERE

This has a grid which is the North celestial pole
starry version of latitude and
longitude on Earth

Declination

+60°

Apparent
rotation
of the Equator +30°
night sky

12h

Right ascension Celestial equator

-30°
South celestial pole

For example, crossing the celestial equator at day of spring (known as the vernal equinox in the
two points is the ‘ecliptic’. This line represents northern hemisphere), but it also defi nes the zero
the path of the Sun through the year, with the tilt point for the entire grid – we call this 0 hours right
due to Earth’s changing tilt in relation to the Sun. ascension and 0° declination. See the ‘Using charts’
When the Sun (ecliptic line) crosses the celestial box, left, for a full explanation of how this works –
equator northwards it not only represents the fi rst and then happy hunting!

5˚ 10˚ 15˚ 25˚

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