Choosing stars to observe

Which type of variable star is suitable for you?

This depends on how often you can observe in a given month and how long you can observe for on each occasion.

The variable stars on the programme of the SPA VSS can be divided into five categories:

1. One-Nighters

Tracie Heywood’s light curve for the Primary eclipse of RZ Cas on 2018 Jan 8

These are stars for which it is possible to see significant variation in brightness in the course of several hours on a single night, although not necessarily on every night.

This category includes RR Lyrae and the Algol type eclipsing variables.

One such eclipsing variable is RZ Cassiopeiae, whose primary eclipse is shown in the accompanying light curve.

In the case of RZ Cas, the whole eclipse lasts for nearly 5 hours but, as can be seen in this light curve, most of the brightness changes occur during the middle 3 hours.

Algol (beta Persei) is the most famous example, although its eclipses are about twice as long as those of RZ Cas.

2. One-Weekers

delta cep
All observations from 2016 combined into a single light curve showing the 5.37 day cycle

These are stars for which significant changes in brightness can be seen over the course of a week or two, in some cases from one night to the next.

These would suit people who are able to observe on every clear night, but only short a short time.

This category includes the Cepheid variables, such as Delta Cephei,  and the beta Lyrae type eclipsing variables.

 

3. Medium-Rangers

A 4-year light curve for the semi-regular variable Z UMa

These are stars that vary more slowly, but which show significant changes in brightness over the course of several months or a year.

The brightness changes don’t repeat exactly from one cycle to the next, although there are clear signs of periodicity, all is illustrated by the accompanying light curve for Z Ursae Majoris.

Sometimes these stars spring surprises – by brightening beyond the published upper limits of their brightness ranges or fading below the published lower limits. During 2015 and 2016 the minima of Z UMa were unusually deep

They would suit people who can observe several times per month, but not necessarily on every clear night.

This category includes R Scuti and the semi-regular variables.

4. Big-Rangers

A 2-year light curve for the  Mira type variable S UMa

These are stars that show large changes in brightness over the course of a year.

Their brightness changes are so large that for several months they become too faint to be seen using binoculars and are only visible telescopically.

The accompanying light curve for S Ursae Majoris shows its brightness changes during 2016 and 2017. The maxima were observable using binoculars, but a telescope was required to follow it down to minimum.

These stars would also suit people who can observe several times per month, but not necessarily on every clear night.

This category includes the Mira type variables.

5. Rebels

r crb

These are variable stars that are totally unpredictable.

These variables would mostly appeal to people who can observe on every clear night, but other observers may also enjoy monitoring them when their circumstances permit.

The category includes R Coronae Borealis and Novae.