Ursa Major

FIELDS OF STUDY: Stellar Astronomy; Observational Astronomy

ABSTRACT: Ursa Major is a constellation best seen in the Northern Hemisphere. The main stars in Ursa Major form a shape that many observers believe resembles a bear. The name Ursa Major means "great bear." Some of the brightest stars in the constellation form a scoop-like shape, which is called the Big Dipper. In addition, Ursa Major includes interesting varieties of stars, many galaxies (groups of stars and planets), and a nebula (a huge cloud of gas and dust). People have been aware of this constellation for thousands of years. Ursa Major has a very rich, colorful history in myth and lore from cultures around the world.

The Great Bear Constellation

Ursa Major is a constellation. A constellation is a region of space defined by a group of stars that resembles a pattern or picture when seen from Earth. For thousands of years, people have searched for such patterns among the stars. People used these patterns to track the changing seasons. Some believed the images held spiritual significance as well. Many constellations have been identified by world cultures, and astronomers recognize eighty-eight constellations today.

Possibly the best-known of all constellations is Ursa Major, also known as the Great Bear. The stars of this constellation form a quadrangle with extensions on each corner that many observers believe resembles a bear. In some regions, people are most familiar with one portion of this constellation, which they call the Big Dipper.

Attributes of Ursa Major

Ursa Major is a prominent Northern Hemisphere constellation best seen between the latitudes of 90 degrees north and 30 degrees south. Its right ascension is 9 hours, 46 minutes, and 31.7 seconds. Its declination is about +57 degrees from the celestial equator. Although it is visible to stargazers throughout the year, this constellation is clearest during its culmination, or highest point, in April. Ursa Major is the third largest of all eighty-eight constellations recognized by the International Astronomical Union.

Although the image of the bear is the definitive symbol of Ursa Major, the constellation is better known in many regions as the Big Dipper. This name comes from the distinctive shape of one asterism, or star pattern, within Ursa Major. This asterism resembles a large scoop or spoon as might be dipped into food or water. The Big Dipper shares many stars of the larger constellation.

The stars of the Big Dipper are designated by letters of the Greek alphabet as well as individual names. These stars include alpha (Dubhe), beta (Merak), gamma (Phad or Phecda), delta (Megrez), epsilon (Alioth), zeta (Mizar), and eta (Alkaid or Benetnash) Ursae Majoris. These stars, particularly Alioth, Dubhe, Alkaid, Mizar, and Merak, are among the brightest in the entire constellation. These bright stars make the Big Dipper highly distinct in the night sky.

Many of the stars of Ursa Major are notable for their variations. Mizar, for example, is considered a double star because it appears to be right next to another star, 80 Ursae Majoris (Alcor). Alcor itself is a binary star. A binary star is a pair of stars that orbit around a common center of mass. Xi Ursae Majoris (Alula Australis) is another binary star. Some other named stars from Ursa Major include iota (Talitha), lambda (Tania Borealis), mu (Tania Australis), and omicron (Muscida) Ursae Majoris.

Aside from stars, several deep-space objects exist within the Ursa Major constellation. These include a vast assortment of galaxies that take on various forms. Some are irregular galaxies that do not take on a specific shape. Among the notable spiral galaxies within Ursa Major are Messier 81 (M81), also called Bode’s galaxy; M82, the Cigar galaxy; and M101, the Pinwheel galaxy.

Finally, Ursa Major also contains a planetary nebula, M97. A planetary nebula is a vast cloud of gases surrounding an expanding star. In 1848, astronomer William Parsons, the third earl of Rosse, named M97 the Owl Nebula for the two distinct holes in the cloud, which reminded him of an owl’s eyes. As of 2022, astronomers have discovered more than five thousand exoplanets orbiting stars other than our sun. Forty-eight of these planets have been found in Ursa Major.

Tales from the Past

The first clearly recorded references to Ursa Major date back to ancient times. The Greek Egyptian astronomer Ptolemy (ca. 100–170 CE) listed it among the constellations he recognized. Although cultures around the world speculated on the meaning of this constellation, Greek myths are the most well-known today. The most famous Greek myth about Ursa Major has several minor variations. The main idea of the myth, however, deals with the chief god, Zeus.

In this myth, Zeus fell in love with a beautiful nymph, or spirit, named Callisto. Zeus’s wife, the goddess Hera, noticed his interest and became jealous of the nymph. Hera used her power to transform Callisto into a bear. Shortly afterward, Callisto’s son Actas was hunting when he spotted the bear. Without realizing it was actually his mother, he prepared to shoot it with his bow. Zeus intervened by turning Actas into a bear as well and then hurling them both into the stars. There, they formed the Great Bear (Ursa Major) and Small Bear (Ursa Minor) constellations.

Some American Indian cultures also had bear stories for Ursa Major. According to Iroquois and Mi’kmaq lore, the constellation represents human hunters who are forever pursuing the bear, hoping to kill and eat it. Similarly, the Zuni people believed that the stars were a magic bear that moderated the seasons. Every spring the bear would appear and chase away the cold. In the winter, the bear would fade into hibernation, allowing the cold to return.

Other cultures did not see a bear at all. In the Basque region of Spain, people told stories of the constellation representing a group of people searching for stolen oxen. In some Arabian lands, people interpreted the stars as a funeral procession. Four stars of the quadrangle represented the coffin and other nearby stars stood for mourners. Many groups saw vehicles in the sky. North Pacific peoples in the Marshall Islands believed the stars formed a canoe. In German mythology, the stars were a large wagon. English people thought that the legendary King Arthur lived in the sky near the constellation, which was later known as King Arthur’s Chariot, while some people in Ireland believed it represented a chariot belonging to King David.

Other interpretations dealt with scoops or drinking vessels. In ancient China, farmers thought these star patterns looked like containers for grain. In North America, many people saw a ladle or pan, thus leading to the name Big Dipper. (Ursa Minor, the companion constellation, is often called the Little Dipper.) In the early nineteenth century, when slavery was still legal in the American South, enslaved people sang songs about the stars forming a "drinking gourd" that offered happiness. These songs had a hidden meaning. If escaped slaves walked toward the "gourd" in the northern sky, they would eventually find themselves in the northern states, where slavery was outlawed.

Studying Ursa Minor Today

Astronomers search the constellations to gather scientific information about their diverse stars and planets. Constellations are a handy way of mapping features of space so they can be located easily. For both amateur and professional stargazers, Ursa Major is a good starting point for a visual exploration of the night sky. From it, stargazers can locate the constellations Ursa Minor, Auriga, and Gemini.

Ursa Major contains double and binary stars, a nebula, and a striking number of galaxies within its boundaries. Scientists have noted that the star called Groombridge 1830, unlike the vast majority of stars, never moves. In addition, Earth observers often look to Ursa Major to see meteor showers, including the Alpha Ursa-Majorids, Ursids, and Leonids-Ursids.

PRINCIPAL TERM

• celestial equator: the imaginary line above Earth’s equator that halves the celestial sphere; it is equally distant from the celestial poles.
• constellation: a region of space defined by a pattern of stars that can be seen in the night sky from Earth.
• declination: a space object’s angular distance north or south of the celestial equator, expressed in degrees of arc.
• International Astronomical Union: an association of professional astronomers from all over the world who define astronomical constants while promoting research, education, and discussion on important astronomical topics.
• right ascension: a space object’s longitudinal arc along the celestial equator, measured eastward from the vernal equinox and expressed in hours.

Bibliography

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