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Aries the Golden Ram
Aries is one of the oldest constellations, and has represented a ram to different cultures for over three thousand years. It's an interesting constellation mythologically, and it was once significant as the location of the spring equinox. However if you're looking at the sky, you might find it a bit humdrum. Its stars aren’t very bright, and although it has a number of galaxies, it isn't rich in deep-sky objects.
In the very earliest Babylonian star charts, the stars of Aries rather prosaically represented a farm laborer, only later being associated with a ram. The Greek stories however were full of drama.
Aries wasn't just any old ram, but a golden winged one. In answer to the pleas of Queen Nephele of Boeotia, Zeus sent the ram to save Nephele's children from the plotting of the King's second wife. Aries carried Nephele's son Phrixus to safety in Colchis, but, sadly, her daughter Helle lost her grip and fell into the Dardanelles and drowned. The Greek name for this stretch of water is the Hellespont.
In Colchis, Phrixus sacrificed the ram to Zeus and presented the fleece to King Aeëtes, who in turn presented Phrixus with his daughter in marriage.
The fleece shows up again in a later myth when Jason and his Argonauts come for it. The king refused to part with it, but with the help of the king's daughter Medea, Jason stole it.
Aries and the vernal equinox
Aries is a zodiac constellation. It lies on the ecliptic, the apparent path of the Sun through the sky during the year. But more importantly, it was the first constellation of the zodiac. From around 2000 BCE to 100 CE the vernal equinox - the start of the year - occurred in Aries. This is when the Sun crosses the celestial equator from north to south.
The celestial equator is the celestial coordinate equivalent to the equator on Earth. The place where the ecliptic and the celestial equator intersect is the celestial counterpart to 0o longitude. (You can find out more about this by clicking on the link below this article for “Ecliptic and Equinoxes”.)
The Earth's axis has a little wobble in it, so over long periods of time it's noticeable that the location of the equinox changes. Over a span of 26,000 years, the vernal equinox passes through all of the zodiac constellations. In fact, although it's sometimes still called the First Point of Aries, today the equinox occurs in the constellation Pisces.
Aries is represented as a ram who seems to be looking over his shoulder. Despite his flying ability, no wings are shown. The three brightest stars of Aries, Alpha, Beta and Gamma Arietis, look like a crooked line. This is supposed to be the ram's head, and the rest of the constellation doesn't look much like a ram either. Aries is best seen in late autumn and winter. It lies between the Pleiades star cluster in Taurus and the Great Square of Pegasus.
The three brightest stars of Aries are actually larger and hotter than the Sun, but their distance from us dims them in our sight. Alpha Arietis (Hamal) is a second magnitude star, Beta (Sheratan) is of the third magnitude, and Gamma Arietis (Mesarthim) is only fourth magnitude. (Remember that dimmer stars have higher magnitudes.)
Alpha Arietis has at least one planet orbiting it. There are also a few other stars in Aries known to have planets, including HIP 14810 which has at least three. We don't know of any planets orbiting Gamma Arietis, but it's a triple star system. A pair of stars, each about sixty times the luminosity of the Sun, orbit each other. English scientist Robert Hooke first discovered that Gamma Arietis was a double star in 1664. What he couldn't see through a seventeenth-century telescope was that there is also a third star orbiting the double.
There are a number of galaxies in Aries, some of which can be seen in a small telescope. One of the most interesting is the spiral galaxy NGC 772 which is some 100 thousand light years across. That's about the size of the Milky Way. It's also listed in the Arp catalog of peculiar galaxies because of its distorted shape. The distortion is due to gravitational interactions with its companion galaxies.
But I think the most intriguing object in Aries is Segue 2, a dwarf spheroidal galaxy discovered in 2007. Segue 2, a satellite galaxy of the Milky Way, is only about 800 times as luminous as the Sun, but its mass is a whopping half a million times greater than the Sun. It's the smallest galaxy yet discovered and seems to be bound together with dark matter. The stars are extremely old, probably among the first stars to form in the Universe.
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