Guide to R Leonis

One of the brighter Mira type variables, located only 5 degrees from the bright star Regulus (Alpha Leonis).

r leo

R Leonis, like other Mira type variables, is a red giant star. The brightness variations were first recognised by J A Koch in 1782. The main cause of the brightness variations is pulsations in the star’s outer layers. However, there are also smaller scale changes that are related to the formation of very simple molecules when the pulsations cause the surface layers to cool and then split apart when the contraction phase causes the temperature to rise again.

Extreme brightness range 4.8 – 11.0
More typical range 5.4 – 10.5
Period of variation 310 days (approx 10months)
Frequency of observation Worth checking a few times per month
Observe using 40mm or 50mm binoculars will suffice when near maximum, but 50-80mm binoculars will be required when fainter. A telescope is required to follow R Leo all the way down to minimum
Visibility mid September to early June
Dates of maxima June 2017 , April 2018 and February 2019

The following finder charts show the location of R Leonis. North is at the top of each chart.


The second chart, which is approx 9 degrees by 5 degrees, shows more detail around R Leo.

You can follow the changes in R Leo by comparing its brightness with that of the comparison stars. These are labelled with their magnitudes (with the decimal point omitted). Thus, for example, ’78’ labels a comparison star of magnitude 7.8.