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Alongside the sight of Venus, Mars and Jupiter in the pre-dawn sky, the constellation of Leo is also emerging from the morning twilight.
Leo does not contain many bright variable stars, but it does include one of the brighter Mira type variables.
This is R Leonis, which has an extreme magnitude range of 4.8-11.0 and an average period of 310 days. Not all maxima are equally bright however and on average R Leonis reaches about mag 5.8 at maximum.
The latest maximum is predicted for mid September 2015, so if you can drag yourself from your bed just before dawn, now is a good time to see R Leonis. It you can observe before the twilight becomes too bright, it should readily be visible in binoculars. As the autumn progresses, it will steadily fade and by early 2016 will only be visible in a telescope.
The next maximum is due to occur in July 2016, when Leo is close to conjunction with the Sun, so the coming weeks will see R Leonis brighter than it will be for the rest of its 2015-16 apparition.
You can locate R Leonis using this finder chart, which has north at the top and is approx 9 degrees by 5 degrees:
As is the norm on many variable star charts, the comparison stars are labelled with their magnitudes but with the decimal point omitted. Thus, for example, '57' labels a star of magnitude 5.7.
A good way to locate R Leonis when using binoculars is to first locate the star Regulus and then 'star hop' to R Leonis via the stars labelled 53, 65 and 57 .
More information about R Leonis can be found in this SPA Guide to R Leonis
Added by: Tracie Heywood