Arguably one of the more challenging aspects of amateur astronomy is to electronically record consistently accurate stellar magnitudes. Don’t let this statement deter you. Once the technique is mastered your precious data is highly sought after by the AAVSO and other repositories.
The requirements for photometry are not trivial. A telescope, preferably an all reflecting Classical Cassegrain but any good scope will suffice, a steady and accurate equatorial mount, a good mono CCD ideally without anti blooming gates, a set of UVBI Johnson – Cousins photometric filters or at least the V filter, a computer with appropriate software and a lot of dedication. If you have a DSLR and a good lens your domain is differential photometry.
Photometry is not just photometry. Photometry using a mono CCD has its set of rules and requirements, DSLR photometry requires a completely different approach to achieve accurate results and finally the use of photoelectric photometers, known as PEP, has its unique requirements. Irrespective of which instrument you apply and given that all things being equal the results obtained from each should be within a magnitude range of .01.
Software
There are a number of software packages that are designed to do photometry. Listed are a few of the more popular ones. Included are some acquisition software packages for DSLR cameras. Not all the software is free.
- VPhot – AAVSO – Online photometric tool
- IRIS – Christian Buil – DSLR aquisition software – Aperture photometry – Free
- APT – Aperture Photometry Tool – Free
- AIP4Win – Richard Berry, James Burnell – Willman-Bell
- CCDSoft5 – Software Bisque – Obsolete
- The SKY X Pro – Software Bisque
- IRAF – image processing and photometry tools – Free
- MaximDL – Aquisition software – image processing
- Backyard EOS – Aquisition software for DSLR’s
- Canopus – SBig – Astrometric & Photometric Software
Organisations to join
These bodies have a vast amount of information including excellent tutorials on how to conduct effective photometry.
- AAVSO – American Association of Variable Star Observers – http://www.aavso.org/
- VSS – Variable Stars South (Australia) – http://www.variablestarssouth.org/
Recommended reading
An enormous amount of literature is freely available on the net. For starters, read the two documents listed below.
- CCD Photometry by E. Norman Walker: A very comprehensive page on the subject.
- DSLR Photometry by John E. Hoot: An in-depth analysis of DSLR sensors.
- High-speed multicolour photometry with CMOS cameras by SM Pokhvala, BE Zhilyaev & VM Reshetnyk. This study demonstrates the effective use of CMOS sensors for high-speed, multicolour photometry with a small telescope, highlighting their potential for precise astronomical observations.
- DSLR Photometry, Part 1 and 2 by Dave Blane.
The number and titles available on the subject of photometry are too many to mention here. All deal with photometry at quite a high level but are essential to getting a deeper understanding of the subject.
- Astronomical Photometry: For the Advanced Amateur and Professional Astronomer by Henden and Kaitchuck – Willman-Bell. (Recommended by the AAVSO)
- Introduction to Astronomical Photometry by Edwin Budding and Osman Demircan – Cambridge Online Books. (Observing handbook for research astronomers)
Observing Programs
Your skill at making accurate photometric measurements puts you in a good position to detect large transiting exosolar planets or the flux of asteroids and comets.