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Sat, 17 Sep 2016 - See Chi Cygni at maximum

There is an "extra" star to look for in Cygnus this month.

This is the variable star Chi Cygni.

If you have a dark observing site, you may be able to spot it using this finder chart. If you can't see it with the naked eye from your location, it should be fairly easy to spot it using binoculars.

For most of the time, Chi Cygni is too faint to be seen with the naked eye and at times observers need a sizeable telescope in order to see it. At its brightest, it can reach magnitude 3.4 (somewhat brighter than Eta Cygni) whereas in its deepest minima it can go all the way down to magnitude 14.2.

Chi Cygni only rarely hits these extreme limits. Having said that, however, it did come within a magnitude of the upper limit in May 2013 and again in August 2015. The June 2014 peak, in contrast, only reached about mag 6.5.

This second chart will allow you to monitor Chi Cygni as it fades from maximum. This chart also offers extra detail that should resolve any uncertainty you may have when identifying Chi Cygni near maximum.

Chi Cygni is a Mira type variable, a red giant star whose brightness variations are primarily due to pulsations in its outer layers. The brightness variations don't repeat exactly from one cycle to the next. The gap between maxima average about 407 days (just over 13 months), but individual gaps can be a couple of weeks shorter or longer. All of this means that we don't know in advance how Chi Cygni will become each time or the exact date on which the peak will occur.

The best that we could do in advance was to say that the 2016 peak would occur around mid September.

At the start of 2016, Chi Cygni was down near minimum. Observations by Variable Star section members showed Chi Cygni to have brightened to mag 9.8 by late June, to mag 8.0 by late July and to mag 5.5 by late August. Reports from September suggest that Chi Cygni has reached a brightness similar to that of the star labelled "Fl17", but is somewhat fainter than Eta Cygni . Thus, in contrast with the "extremes" seen during 2013-2015, it seems that Chi Cyg may be producing a relatively "normal" maximum this time.

Imagers may find it rewarding to capture a wide field image of Cygnus while Chi Cyg is near maximum and then capture another image at a later date when Chi Cyg has faded.

More information about Chi Cygni can be found in this guide


Added by: Tracie Heywood