When is the best time to observe Rasalas?

Rasalas is best observed from January through March, with peak visibility during February when it transits around midnight in the Northern Hemisphere.

Where is Rasalas located in the sky?

Rasalas lies in the constellation Leo at right ascension 09h 53m and declination +26° 00′.

What telescope do I need to see Rasalas?

At magnitude 3.9, Rasalas is visible to the naked eye from dark skies, easy in any binoculars.

Rasalas — Star in Leo

HIP 48455; Mu Leonis; 24 Leonis

Magnitude 3.9^m Star Leo Visible 1 Exoplanet

Star Map + List + Plan

About Rasalas

Description

Rasalas, Mu Leonis, is a K-type giant of spectral class K2 IIIb about 130 light-years away in the northern part of the constellation Leo. It shines at magnitude 3.88 and has an enriched barium content — a chemical signature of past mass transfer from a now white-dwarf companion, though no companion has yet been directly detected. Rasalas hosts a confirmed exoplanet, Mu Leo b, a Jupiter-class giant in a 358-day orbit.

Observing Tips

Rasalas marks the top of the Lion's mane, well north of Regulus. Follow a gentle arc from Algieba (Gamma Leo) up and west: Rasalas is the next prominent yellow-orange star. A small telescope clearly shows its warm color. Best observed February through May.

History

The name Rasalas is a shortening of the Arabic "Ra's al-Asad al-Shamāliyy," meaning "the northern head of the lion." The exoplanet was discovered in 2014 by radial-velocity observations at the Okayama Astrophysical Observatory in Japan — one of a growing family of substellar companions now known around evolved giants.

Fun Facts

Rasalas's chemical peculiarity — elevated barium and strontium abundances — is the fingerprint of an ancient binary evolution: the now-unseen companion, once a red giant itself, polluted Rasalas with s-process elements before collapsing into a faint white dwarf. The planet Mu Leo b, which survived the original companion's red-giant expansion, orbits at about 1.1 AU.