Before there were proper calendars people had no way of determining when to sow, or harvest except by the stars. Constellations made the patterns of the stars easy to remember. The ancient peoples knew for example that when the constellation Orion started to be fully visible winter was coming soon.
Consequently, what stars are used for navigation?
The star Polaris, often called the "North Star", is treated specially due to its proximity to the north celestial pole. When navigating in the Northern Hemisphere, special techniques can be used with Polaris to determine latitude or gyrocompass error.
Each different culture developed their own interpretation. A more practical use for constellations was agriculture. The stars allowed farmers to plan ahead and form agriculture, and constellations made it easier to recognize and interpret the patterns in the sky. The constellations also helped with navigation.
Are the constellations permanent? Ancient astronomers often spoke of the "fixed stars," which maintained permanent positions in the sky. And, indeed, the stars do seem almost fixed in place; the patterns they form look much the same today as they did when the constellations were first named nearly 3000 years ago.
The stars themselves don't appear to move with respect to each other. (In fact, they do, but it takes careful measurement to notice it.) The apparent motion is caused by the Earth's rotation and its orbit around the Sun. This means that we see the stars (and constellations) drift from east to west every night.
Constellations are formed of bright stars which appear close to each other on the sky, but are really far apart in space. The shapes you see all depend on your point of view. Many societies saw patterns among the stars with gods and goddesses or stories from their culture.
If observed through the year, the constellations shift gradually to the west. This is caused by Earth's orbit around our Sun. In the summer, viewers are looking in a different direction in space at night than they are during the winter. Earth orbits our Sun once each year.
The stars allowed farmers to plan ahead and form agriculture, and constellations made it easier to recognize and interpret the patterns in the sky. The constellations also helped with navigation. It is fairly easy to spot Polaris (The North Star) once you've found Ursa Minor (Little Dipper constellation).
There are 88 official constellations. But astronomers haven't made up new constellations for hundreds of years! When new stars are discovered, they are considered to be a part of whatever constellation they are closest to.
They represent stories from many different cultures and are also important because they serve as a celestial map. Astronomers refer to zodiac constellations when describing the location of the planets in our solar system. Constellations are also useful for navigation. Just think of the North Star!
Here the sailors would use the locations of particular stars, especially those of the constellation Ursa Major, to orient the ship in the correct direction. The pole stars were used to navigate because they did not disappear below the horizon and could be seen consistently throughout the night.
88 Officially Recognized Constellations
|Latin Name||English Name or Description|
|Andromeda||Princess of Ethiopia|
|Apus||Bird of Paradise|
Astronomers can measure a star's position once, and then again 6 months later and calculate the apparent change in position. The star's apparent motion is called stellar parallax. The distance d is measured in parsecs and the parallax angle p is measured in arcseconds.
The Earth's axis rotates (precesses) just as a spinning top does. The period of precession is about 26,000 years.
Hydra is sometimes called the female water serpent and Hydrus the male water serpent. The description of Hydra as the largest constellation in the sky refers to its total area in square degrees, according to the official boundaries established by the International Astronomical Union (IAU).
The Big Dipper is an asterism in the constellation Ursa Major (the Great Bear). One of the most familiar star shapes in the northern sky, it is a useful navigation tool. In this case, the Big Dipper has eight stars in it.
The Zodiac is the ring of constellations that the Sun seems to pass through each year as the Earth orbits around it. Contrary to popular belief, there are actually 13 zodiacal constellations, if you pay attention to the way astronomers define them.
CONSTELLATION NAMES AND MEANINGS
- ANDROMEDA – THE CHAINED MAIDEN. Genitive: Andromedae.
- ANTLIA – THE AIR PUMP. Genitive: Antliae.
- APUS – THE BIRD OF PARADISE. Genitive: Apodis.
- AQUARIUS – THE WATER BEARER. Genitive: Aquarii.
- AQUILA – THE EAGLE. Genitive: Aquilae.
- ARA – THE ALTAR.
- ARIES – THE RAM.
- AURIGA – THE CHARIOTEER.
If a star looks red, that means its surface temperature is approximately 2,500 Kelvin. Just for comparison, our Sun, which actually looks white from space, measures about 6,000 Kelvin. The hotter the star, the further up the spectrum you go. The hottest stars are the blue stars.