Hamal is a bright star shining away at mag. +2.0, located in the constellation Aries.
The name Hamal means ‘the lamb’ and it’s the brightest star in Aries, as well as being the 50th brightest star in the sky.
Aries is often described as looking like a bent line. Although this does the much larger form of the celestial ram a great injustice, it does provide a convenient method of identifying Hamal (Alpha (α) Arietis), the star marking the eastern end of the ‘bent line’.
It lies at the relatively close distance of 65.8 lightyears from Earth and is believed to play host to a large orbiting exoplanet, 1.8x more massive than Jupiter and orbiting its primary every 381 days.
Hamal classification, size and brightness
Hamal is a cool orange giant, 14.9x larger than our Sun and 1.5x as massive.
Its bolometric luminosity – that is its luminosity across all wavelengths – is 91x larger than the Sun’s.
Hamal has exhausted its core hydrogen and is now evolving along the path of becoming a red giant star.
This is one of the few stars that has had its diameter accurately measured. In this case, Hamal’s disc subtends an angle of 0.00680 arcseconds.
This measurement also revealed the presence of limb darkening, a phenomenon that makes the limb regions of a star appear darker than those in the centre.
This is a well-known effect that has been seen on our own Sun and results from looking into cooler layers of the star at the edges than when you’re looking straight at its centre.
In our star guides we often reveal exciting facts about the stars hat give them a hidden persona and make them stand out against their neighbours.
In the case of Hamal, the star is characterised by being utterly normal.
Although this may sound a little dull, it’s actually an important attribute because it provides a useful baseline against which you can compare other stars.
The only unusual thing about Hamal is that its metallicity is around half that of our Sun’s.
A star’s metallicity describes the amount of elements it contains other than hydrogen or helium.
This article appeared in the October 2024 issue of BBC Sky at Night Magazine
