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Aries, a constellation for December

Contributed by Paul Rodmell, Southland Astronomical Society

ARIES "The Ram".

Chart showing the constellation.

ARIES, "The Ram", of Greek mythology, is the first constellation of the Zodiac, but one of the smallest. It is a very ancient star group, and although known by a variety of names in the historical records of early peoples, seems usually to have represented a sheep or ram. The modern name is due to the Romans for whom and the early Greeks it was associated with the legend of the golden fleece. Ptolemy recorded 13 stars in Aries in AD 150, and five additional stars to the north. The constellation is recognised by the narrow triangle of the brightest stars. In the southern hemisphere the evening rising of this triangle, balanced on its narrow apex, marks the coming of summer.

Despite the faintness of its stars, Aries has assumed great importance in astronomy, because 2000 years ago it contained the point where the Sun passed from south to north across the celestial equator each year. This point, the Vernal Equinox, marked the start of the northern hemisphere spring, and from it the celestial coordinate known as right ascension is measured. Because of the slight wobble of the Earth in space known as precession, this point has now moved into Pisces, and in about 400 years time will move into Aquarius. (The dawning of the age of Aquarius?)

To find Aries, look to the north, find Orion, then the bright star Aldebaran, look further to the west (left) to find the Pleiades star cluster (the seven sisters), and look between the Pleiades and the Great Square of Pegasus.

Chart showing Aries as seen about 10.30 pm (NZDT) mid December. 

Aries chart

Constellation Aquarius Constellation Cetus Constellation Eridanus Constellation Orion Constellation Gemini Constellation Taurus Constellation Auriga Constellation Perseus Constellation Triangulum Constellation Pegasus Constellation Andromeda Constellation Pisces

Some stars in the Constellation

α Arietis (Hamal, from the Arabic for sheep) is a yellow giant star of magnitude 2.0, 66 light years away.

β Ari (Sheratan, the sign) is a white star 60 years away

γ Ari (Mesarthim) is a striking double star 204 light years away at magnitude 2.8. This double star was the first to be discovered, by Robert Hooke in 1664. The stars dominate a field well sprinkled with scattered stars

ε Ari is a challenging double star for larger aperture telescopes. High magnification reveals a tight pair of white stars of magnitudes 5.3 and 5.6. The pair lie 293 light years away.

λ Ari is a white star, magnitude 4.8, 133 light years away with a yellow 7th magnitude companion, easily visible in small telescopes or even good binoculars.

π Ari is a blue-white star of magnitude 5.2, with a close magnitude 8.3 companion, difficult to distinguish in small telescopes. They lie 600 light years away.

Visibility

Aries is north of the equator so fairly low for New Zealand observers. This particularly applies to the brighter stars, Hamal amd Sheraton, which are above the horizon for about 9 hours. The constellation is due north at about 10.30 pm (NZDT) in the middle of December. By the end of January, Hamal is low to the north-west at 10.30 pm.


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