The variable star R Leonis

R Leonis was the first variable star identified in Leo the Lion. It is currently below naked-eye magnitude, but you can easily find it with binoculars or a telescope.

An hour after sunset, you’ll find the constellation Leo the Lion pointing head-down toward the horizon in the southwest. The brightest star in this constellation is Alpha (α) Leonis, also known as Regulus. And just over 5° west of this star is a sun called R Leonis, the first variable star identified in the Lion. 

R Leonis shines with a noticeably red hue, thanks to its advanced age and thus cooler temperature. It is a Mira-type variable, a class of variable stars named after Mira in Cetus, the first such star of this type ever identified. 

Discovered in 1782, astronomers estimate R Leo is less than 300 light-years away. This aging star undergoes huge brightness changes, swinging between magnitude 5 and 10.5 over the course of nearly a year (312 days). It has most recently been observed near the faint end of its range, roughly 9th magnitude, meaning you will need binoculars or a telescope to find it. One of the easiest ways to identify it is to look for a deep red star forming one point of a triangle with a pair of yellower stars. 

R Leo is now approaching its faintest, which means in a few months it will begin brightening again. So, make note of its location and brightness now, to compare with your observations when Leo becomes a morning constellation rising in the east before the Sun in the fall. 

Sunrise: 5:41 A.M.
Sunset: 8:12 P.M.
Moonrise: 1:31 A.M.
Moonset: 11:35 A.M.
Moon Phase: Waning gibbous (59%)
*Times for sunrise, sunset, moonrise, and moonset are given in local time from 40° N 90° W. The Moon’s illumination is given at 12 P.M. local time from the same location.

For a look ahead at more upcoming sky events, check out our full Sky This Week column.