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Ras Elased Borealis, Alshemali, Mu Leonis, 24 Leonis

One of the arc of stars that run northward from Regulus in the western parts of Leo, forming a pattern that represents the Lion's head, a group commonly known as the 'Sickle'. Rasalas is the northernmost of these stars, marking the crown of the Lion's head. Its name indeed comes from Ras Elased, 'head of the lion', a name that it shares with another star to the southwest. This pair of stars were traditionally named Ras Elased Borealis (where Borealis means 'northern', referring to Rasalas itself) and Ras Elased Australis (the 'southern' neighbour). While Ras Elased Australis retained that name, the northern star is now formally recogised by the variant Rasalas.

Imagery provided by Aladin sky atlas

Rasalas lies some 125 light years from the Solar System. It is an evolved orange giant star that has consumed its reserves of hydrogen and expanded to some fourteen times the diameter of the Sun, and generates far more light and heat. Nonetheless it is only approximately 1.5 times the Sun's mass, and is therefore far less dense. Its relatively tenuous atmosphere shows unusually high levels of certain compounds and elements, specifically cyanogen and calcium.

There is one known planet in orbit around this star, designated Rasalas b or Mu Leonis b. At a distance from its star of 1.1. AU, this planet follows an orbit comparable with that of Earth around the Sun, and has a similar length of year at some 358 days. This planet is an immense gas giant, with more than twice the mass of Jupiter. Because Rasalas is much more energetic than the Sun, its planet Rasalas b receives far more energy than Earth, and it lies far within the inner limit of the star's habitable zone.


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