Popular Astronomy

Share to Facebook Share to Twitter Stumble It More...

Guide to T Cephei

A circumpolar Mira type variable that can be followed over most of its brightness range using binoculars.

The brightness changes don't repeat exactly from one cycle to the next. As can be also seen in the above light curve, the brightness doesn't rise and fall at a constant rate - it is quite normal to T Cep to "pause" for several weeks close to mag 8.0 during its rise to maximum (the six week "pause" in early 2015 was unusually long!  Long pauses also occurred during the rises to the 2016 and 2017 maxima).

T Cephei is a red giant star. The brightness changes seen are primarily due to pulsations in the star's outer layers. However, these outer layers are also sufficiently "cool" for it to be possible for some very simple molecules to form when the expansion phase causes further cooling and to then break up when the subsequent contraction causes the temperature to rise again.

Extreme brightness range 5.4 - 11.0
More typical range 6.0 - 10.5
Period of variation 389 days  (nearly 13 months)
Frequency of observation Worth checking a few times per month
Observe using 40mm or 50mm binoculars will suffice when the star is near maximum, but 50-80mm binoculars will be required when it gets fainter and a telescope will be needed at minimum
Visibility Can be observed all year round
Dates of maxima late May 2017, late June 2018, mid July 2018

Here are three charts that show the location of T Cephei. All have north at the top.

Comparison stars are marked with their magnitudes with the decimal points removed (so, for example, '54' labels a star of magnitude 5.4)

This next chart, approx 8 degrees by 6 degrees, covers the brighter part of the binocular range:

This final chart covers the fainter binocular range and telescopic range: