Ancient people knew a great deal about the sky since knowing the seasons was literally an issue of life and death. To know when to plant and when to harvest is crucial if you are going to starve if the crops fail! And since it was a matter of life and death, then astronomy and the calender got linked into the religion of that culture, so the astronomical alignments of sites like Stonehenge are only part of its function in the ancient culture which built it. Some nice links on archeoastronomy, and a lovely site from the british museum on Babylonian astronomy.
But as well as the cycle of the seasons, there is the more immediate cycle of day and night. While we are all aware of the suns motion, where it rises in the East(ish - depending on the season), has its maximum height above the horizon when its due south, and then sets in the West(ish - depending on the season), that of the stars is not so obvious. These would be more familiar to ancient people than to us, firstly because we live a lot more of our lives indoors in a culture which is not obviously linked to agriculture, and secondly because we mostly live in places where there are many street lamps, and their light drowns out all but the brightest stars. So what do we see in the night sky ?
Stars - and more stars, the Moon, Planets, and a milky band of light called the Milky Way. This lecture concentrates on stars, and we'll deal with the rest later.
The stars do not appear to move relative to each other - we now know that this is because they are so far away that their motions bring no appreciable change in their positions on human timescales. So the same stars in the same relative positions have been seen by all human cultures. And all cultures seemed to have played 'join the dots' and come up with pictures (termed constellations), and stories to weave around them. The way we 'join the dots' is mainly based on the Greeks. More on constellations.
When you look at the stars they have different apparent brightnesses. Starmaps generally use the size of the dot as a measure of stellar brightness. From the Evolving Universe part of this course you now know its because the stars have different intrinsic luminosities AND they are at different distances from us. The Greeks are responsible for a vile way to talk about the apparent brightness of an object - magnitudes. They classified stars into first class, second class, third class all the way down to sixth class (ones which are only just visible to the naked eye on a clear dark night), with the first class ones being the brightest. Each successive magnitude is about 2.5x fainter than the previous one. Sadly this system is still in use! Its now defined so that two stars which differ by a factor of 100 in brightness have magnitudes which are different by 5 units (with the fainter star having the bigger magnitude!). On these definitions then we can relate any brightness to a magnitude. Rigel (blue supergiant bottom right star in Orion) has a magnitude of about zero. Sirius (the brightest star) is about 4x brighter and has a magnitude of -1.5. The Sun has a magnitude of -26.85, while faintest galaxies which can be seen with big telescopes have magnitudes of ~30, i.e. 10 billion times fainter than the faintest stars we can see with our eyes. With just binoculars or a small telesope you can see objects that are 100x fainter (or 5 magnitudes bigger)
Now for some nasty stuff where you have to think in 3 dimensions! Firstly, we think of directions N-S-E-W looking DOWN on the Earths surface. Then west is to the left when we face north. But now we want to use the same dirctions to map the sky not the earth, so east and west reverse on skymaps. (Take a piece of paper, draw the normal points of the compass on it. Then lift it above your head!)
To work out how the stars move during the night and during the year you need to know that the earth goes around the sun once a year and that the earth rotates on its axis once every 24 hours, and that the axis of the earths rotation is tilted with respect to the axis of the earths orbit by 23.5 degrees. Always draw diagrams so that you are looking down on the north pole (i.e. you are looking south). Then the earth rotates anticlockwise on its axis, and anticlockwise around the sun. (All the planets also go anticlockwise around the sun and the moon goes anticlockwise around the earth).
How then do the stars appear to move ? Well, funnily enough, to describe what we see from earth we may as well use the ancient concept of stars fixed onto a sphere. If the earth spins anticlockwise, then this imaginary sphere rotates clockwise. Extrapolate the Earths rotation axis onto this imaginary sphere, and call these the north and south celestial poles. Extrapolate the Earths equator onto the sphere and get the celestial equator. In the Northern hemisphere there is a brightish star which happens to be rather close to the north celestial pole - this is Polaris, or the pole star. There isn't such a convienient star marking the south celestial pole. The key to what you see is then the angle which the point directly above your head (the zenith) makes with the celestial pole. The meridian is the imaginary circle running through the point over your head (the zenith) and through the north and south celestial poles. This is all much easier to see in a diagram of the Celestial sphere.
If you are at the Earths north pole then your zenith is the same as the north celestial pole, so you see all the stars moving in concentric circles centered on the north celestial pole directly above you. If you were looking south then the celestial sphere would rotate clockwise (as the earth goes anticlockwise) but since you are looking north then the celestial sphere goes anticlockwise around the pole star. The celestial equator runs along the horizon so all stars above the celestial equator are circumpolar and never set, while all stars below the celestial equator are never visible. All directions are south, so there is no meridian
Now sit on the equator. the zenith makes an angle of 90 degrees with the north celestial pole so the NCP is on the horizon. the zenith is perpendicular to the earths rotation axis. All stars rise and set, and all stars are visible for 12 hours as we see half of every star's circle around the pole. Stars on the celestial equator rise due east, and set due west. stars above the celestial equator rise north of E, and set N of W. Stars below the celestial equator rise south of E, and set S of W.
now go to intermediate latitudes to, say, Durham, then there is an angle between your zenith and the north celestial pole. So looking north you see some stars moving in anticlockwise circles round the north celestial pole (circumpolar stars) while (turn south) others rise in the East and set in the West like the Sun. Stars on the celestial equator are above the horizon for 12 hours and rise due E and set due W. Stars above it rise N of E, set N of W and are above the horizon for more than 12 hours, stars to the south of the celestial equator rise S of Again, its all much easier to see in pictures of how star motions depend on latitude
So to know what the stars look like we need to know position on the earths surface, and time of day and time of year. You can make your own starchart using yoursky (Durham is at 55 degrees North and 2 degrees West, and it looks best if you only plot stars of magnitude 4.0 and brighter, turn off the ecliptic and equator, deep sky objects, constellation boundaries and star names!). Make one and go out and find Ursa Major (also known as the Great Bear, the plough, the big dipper), use this to find polaris, the (current) pole star. And see if you can spot Orion too.