What is a constellation?

Constellations are groups of bright stars that move opposite to the moon, planets, and comets. The stars we see are all in the Milky Way Galaxy, they are light years apart, but we see them as a set. They are usually named after their apparent form, animals, mythological creatures, or heroines and heroes in Greek mythology. Constellations are very symbolic, but they do not always resemble what they are supposed to be. Since the constellations are projected in groups of stars at the same time for centuries, they assisted ancient civilizations for planting their crops, guided navigators throughout explorations, and were used for telling time.
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Types of Constellations

Constellations are divided into 88 areas in the northern and southern hemispheres, and into two major groups, depending on their latitude. The first group is the circumpolar constellations. These are constellations that neither rise into the sky, nor set. The other half of constellations are seasonal, they are only visible during certain times of the year because of earth's movement around the sun. The appearance or disappearance of stars in the sky shows the change in season. "Fixed stars" are stars that are in permanent positions. Patterns that are visibly formed by fixed stars today, are the same as they were 3,000 years ago. Most stars in constellations have no connection with each other and have very different distances from the sun. Coincidental alignments of stars are what create patterns. From earth, constellations look very close together. But in space, they are much farther apart and have no relation to one another. Constellations are changing all the time, though it takes thousands of years to notice changes.

Studying Constellations

Although the discovery of constellations is unknown, many astronomers have contributed to increase the world's knowledge on them. In 150 A.D., Greek scientist Ptolemy published the book, "The Almagest." It contained a catalog of 1,022 stars, which are arranged into 48 constellations. These 48 formed the base for our constellation system. On one of the first trading expeditions to the East Indies in the 1600's, Dutch cartographer Gerardus Mercator, Pieter Keyser, and Frederick de Hautmann mapped the southern sky's constellations. The remains of constellations that were not mapped in the northern or southern skies, were completed in 1690 by Polish astronomer Johannes Hevelius and in 1750 by French astronomer Nicolas Louis de Lacaille. In 1922, the International Astronomical Union officially adopted the 88 constellations. Through the years, astronomers have added constellations to fill in gaps between Ptolemy's figures and map unknown places of the sky. Andromeda, Orion, Pegasus, Ursa Major, and Ursa Minor are among the visible and well-known constellations.

Zodiac Constellations

Since ancient times, people have thought their lives were foretold by the stars. This became known as Astrology which made interpretations based on 12 constellations of the Zodiac. These Zodiac constellations include Aries, Taurus, Gemini, Leo, Virgo, Libra, Scorpio, Sagittarius, Capricorn, Aquarius, Pisces, and Cancer.
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Cancer - The Crab

Cancer is the faintest of the constellations, yet it is the 31st largest of all constellations, recorded by Greek astronomer Ptolemy in the 2nd century. It is located in the second quadrant of the northern hemisphere and occupies 506 square degrees, between the constellations Leo and Gemini. In the northern hemisphere, it is most visible in the spring. But in the southern hemisphere, it can be viewed the best during fall. Cancer has many major stars such as; Alpha, Beta, Gamma, Delta, Lambda, Xi, and Zeta Cancri. It's star system is occulted by the moon, and sometimes by planets. The Cancer Constellation is also well known for being the reason for the Tropic of Cancer's name.

Although Cancer is meant to look like a crab, it is hard to see the resemblance. The crab was introduced in the story of the Twelve Labours of Hercules. Hercules was fighting with a monster named Hydra, when another woman named Hera sent a crab to distract Hercules from hurting Hydra. He ended up crushing the crab, and Hera put the remains of it into the sky, forming the Cancer constellation.

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