Astrophotography is one of the most popular activities in astronomy. To spend hours outside in the cold taking images and then later during the day (and in the warmth) processing all of your saved images to create a final masterpiece is a very rewarding experience.
Apart from imaging deep sky objects, have you ever considered using your equipment to take images to obtain scientifically useful data that can be used for research purposes? Enter the world of astronomical photometry!
There are many types of celestial objects you can image and investigate. Variable star photometric observations cover many types of objects such as Supernovae, Dwarf Novae (or Cataclysmic Variables), Mira and Semi-Regular variables, Wolf-Rayet stars and even Extra Solar Planets too. Brightness variations can range from 0.01 up to +10 magnitudes with timescales from hours, days to years depending on the object. Furthermore, observations of Minor planets can help provide clues about their surface physical properties, compositions and also rotational periods.
In order to obtain photometric observations with your imaging equipment you will need a suitable photometric filter or filterset.
Baader offer UBVRI filters that adheres to the widely used astronomical Johnson/Bessel filter transmission specification.
The filters are available in two sizes:
- 1.25″ mounted for use in many popular sized imaging cameras
- 50x50mm square unmounted for larger sensors
Older style filters had cemented absorption glass elements which could potentially lead to internal reflections. They also often had glass thicknesses of 5mm or more which would be too thick for use in the more modern slimline width filter wheels and also add more weight to the overall imaging train payload too. The Baader-filters are made of a combination of dielectric layers as well as absorption glass which results in a thinner filter glass thickness of 4mm. The filters each have a very good light transmission and provide steep off-band-blocking.
If you want to dabble into the world of astronomical imaging photometry, you could start off with the (popular and widely used) V-band filter. For the 1.25″ filter(s), if you do not have a filterwheel you can just use it in the nosepiece of your camera. If you do not have space in your filterwheel for any more additional filters, you could use the Baader Universal Filter Changer for your photometric filter(s) (for either filter size) to easily swap between them if you are using more than one filter.
So what can you investigate and where can you find out more about programmes that may be of interest?
To start with there is the British Astronomical Association (BAA). They have a Variable Star Section (BAA VSS) which is the world’s longest established variable star observing group. You can find more details of the group and their observational programmes here. There is the American Association of Variable Star Observers (AAVSO), founded in 1911, is an international non-profit organisation dedicated to enable anyone to participate in scientific discovery through variable star astronomy. More information about the AAVSO and its work and programmes can be found here. Professional astronomers have, and do continue to use, the results of observing campaigns from both these organisations.
Over the next few months we will explore the topic of photometry in a little more detail – from observing programmes, celestial target suggestions, techniques and analysis and more. So stay tuned!