SkyCaramba astronomy blog for the week ending July 23, 2011
Almost everybody these days has at least a general idea which ways are north, south, east, and west. Street signs help. So do some handheld electronic devices. If you don’t have such things around you, maybe you have a built-in sense of direction. If you have none of those, there are time-tested methods that work as long as you have a clear enough sky.
We’ve all heard the sun rises in the east and sets in the west. That’s a good general rule. Remember it’s not due east or due west on most days. And if you’re very far north or south of the equator, the sun may rise and set very far from due east and due west at certain times of the year.
A safer assumption is that the sun will be in a certain direction at high noon. At a middle or high northern latitude, the sun will always be southward then. From a middle or high southern latitude, it will be northward. Close to the equator, however, the sun will be a little north, a little south, or right overhead. If you can track which way the sun appears to be moving midday, that’s a good indicator for east-to-west motion.
It’s a similar set of circumstances for the moon, generally rising in the east and setting in the west. Again, the closer you get to the poles, the farther moonrise and moonset get from east and west most days.
Few sky objects stay in almost the same place all the time and are reliable direction markers. The North Star, or Polaris, is the most well known. It’s not exactly on the celestial north pole. But it’s close enough, you can’t tell the difference just by looking.
If you live north of the equator, there’s almost certainly a spot somewhere near your home or apartment where you can stand at any time on any night, look up just above a building or tree, and find the North Star.
I’m sorry to inform those south of the equator that there is no widely accepted south star. The stars closest to the south celestial pole are very dim. You can’t see them except in dark skies and many of them still can’t be seen except with binoculars. However, it’s not hard to recognize the visible star patterns near the south celestial pole. The Southern Cross points to where an ideal south star would be.
Sailors in centuries past learned methods like these and many more to figure out where they were on the high seas with no landmarks around. But since the stars alone can’t tell us everything we want to know about where we are, much work went into developing new technology. In modern navigation, constellations of satellites have usurped the constellations of stars. Microcomputers have usurped our mental faculties. A thing that fits in a shirt pocket replaces maps and a chest full of navigation instruments.