Hamal: alpha Arietis

α Arietis

Alpha Arietis is called Hamal, "Sheep".

The constellation is quite insignificant now, compared to its original function, of signalling the arrival of the Spring Equinox.

Some two or three millennia ago the Sun's arrival in Aries marked the return of the Spring. Thus it was that Hipparchus chose to begin mapping the heavens using Aries as the starting point, at 00h. This "zero hour" has since moved over to Pisces.

Finding the three is an easy naked-eye exercise. From the Pleiades in Taurus move to the west (about five binocular fields) until, at the same declination, you come to the distinctive asterism.

An interesting point about Aries is the group of stars formed by its brightest members, best seen with the naked eye (as gamma Arietis is just out of view, half a binocular field below beta Ari.): stars. Hamal is a yellow giant while Sheratan (beta Arietis) is blue-white.

Alpha Arietis is also a spectroscopic binary, with a companion orbiting the star every 1.1 days.

In the same field as alpha and beta is lambda Arietis, a wide binary: 4.8, 7.7, PA 46 and separation 37.4".

Gamma Arietis (a lovely binary) comes into view by moving just south of beta: binoculars. Click on gamma on the map for further information.

Alpha Arietis is a convenient jumping off point for finding a number of other stars, such as alpha Piscium, which is 20 directly south of the Aries group.

A much smaller constellation can also be conveniently visited after locating Hamal. Triangulum is just to the north of Aries. It houses the binocular Messier object, M33, three binocular fields northwest of alpha Arietis.

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1999-2014 by Richard Dibon-Smith.