Guide to RW Bootis

A star that shows periodic variations in brightness, sometimes with a range of over a magnitude, over the course of about 7 months (supposedly).

RW Bootis is a red giant star. The brightness changes seen are due to pulsations in the star’s outer layers.

It is classed as being a semi-regular variable star. This means that it shows periodic variations, but these don’t repeat exactly from one cycle to the next. The brightness range in some cycles will exceed one magnitude, but may be smaller in others.

Extreme brightness range 6.4 – 9.2
More typical range 7.9 – 8.7
Period of variation Listed as about 7 months, but recent observations suggest it is more like 10-11 months
Frequency of observation Worth checking a few times per month
Observe using 50 – 80mm binoculars will suffice for most of the time. However, 70 – 80mm binoculars may be required if your observing site is not particularly dark and may also be needed when RW Boo is low in the sky
Visibility Can be observed all year round, but is rather low in the evening sky during November and December. Not visible in the evening sky for most of January. Can be observed in the morning sky from late October onwards.

The finder charts which follow show the location of RW Bootis. North is at the top in each case.

The first shows the position of RW Bootis relative to the brighter starts of Bootes.

The second chart, which is approx 7 degrees by 5 degrees, shows the area around RW Bootis in more detail.

You can use the lettered comparison stars to make brightness estimates of RW Bootis.

When locating RW Bootis, bear in mind that it might be brighter than comparison D or might be as faint as comparison F!

RV Bootis is another semi regular variable, but is usually somewhat fainter than RW Bootis.