The topic this week is the "Celestial Sphere", the earliest representation
of the Universe. Nowadays we know that everything in the Universe isn't on
the surface of a big sphere that rotates round the Earth once a day, but the
device of the celestial sphere is still a useful tool for finding one's way
round the sky. The "motions" of the sky and Sun show that the
Earth is rotating on its axis and orbiting round the Sun.
Constellations
Polaris, day & night, and the Earth's rotation
The Celestial Sphere
Coordinates: right ascension & declination, altitude & azimuth
Navigation: Polaris and the bright stars
Motion of the Sun & the ecliptic
Solstices & equinoxes, tropics & arctic circles, seasons and
the tilt of the Earth