Some Quick and Sloppy Procedures
Bruce L. Gary, Hereford Arizona Observatory (G95)
Last updated 2007.09.02

This web page was inspired by the realization that asteroid astrometry observations reported to the Minor Planet Center often include brightness estimates that are typically too faint by 1 or 2 magnitudes (for the faint asteroids). I'm accustomed to sweating long hours to produce photometry sequences with an accuracy of 0.03 magnitude, which is about 2 orders of magnitude better than these MPC submissions. "Surely," I told myself, "by deleting a few terms from my complete equations it should be possible to achieve an accuracy on the order of 0.15 magnitude." Indeed, if this accuracy is acceptable the "color terms" can be dropped, atmospheric extinction can be treated carelessly, subtle considerations in choosing photometry aperture sizes can be ignored, and a host of other details that consume the bulk of effort can be neglected. This hope was fulfilled as I developed the short-cut methods described below.

However, something completely unexpected happened, which has slowly diminished the importance of these clever short-cut procedures: It's the advent of J and K magnitudes for nearly every star that an amateur will come in contact with, and the ability to convert from J and K to B, V, Rc and Ic. These conversions are so accurate that there is no longer a need for most of the other short-cut methods. I now recommend that if 0.05 magnitude is going to be adequate for your needs, do the 2-minute solution for BVRcIc using J and K and forget about the other procedures. It's for a good reason that I assign the J and K procedure the name "Method #0" in the following list.

Links to Specific Photometry Procedures:

    Method #0: 0.05 mag SE, J and K to BVRcIc (2-minute effort)
        Converts J and K magnitudes to BVRcIc using Warner and Harris (2007) coefficients

    Method #1: 0.25 mag SE, planetarium program using Tycho or UCAC2 catalog (3-minute effort)
        Uses a Tycho or UCAC2 star to establish calibration. User must "measure" that star & asteroid in image and convert to magnitude.

    Method #2: 0.15 mag SE, planetarium program using several Tycho or UCAC2 reference stars (5-minute effort)
        Uses several Tycho or UCAC2 stars. User may employ Photometry Tool to combine them as mulit-reference star standard.
    Method #3: 0.15 mag SE, counts equation magnitude (5-minute effort, plus once/year system cal)
        Converts measured intensity directly to magnitude, but user must perform a telescope system calibration once per year. Must know air mass.

    Method #4: 0.15 to 0.30 mag SE, R-filter, using Tycho or UCAC2 reference stars (10-minute effort)
          Must convert catalog mag's to R, then same as method #2

    Method #5. 0.10 to 0.20 mag SE, UNSO-A2.0 Download Method (30-minute effort)
          Download B & R mag's for FOV of interest; convert to V; build consensus using several stars

     Method #6: 0.03 mag SE, Photometry for Smarties (1-day effort)
          (almost as good as the pro's do using 127 transformation equations)
          Simplified Magnitude Equations (SME) for differential and all-sky photometry

    Method #7: 0.025 mag SE, (2-day effort)
          Best procedure for the really serious amateur; slow-paced intro

    Method #8: 0.020 mag SE, ask Arne (1-minute effort, but good luck!)

    Method #9: 0.043 mag SE, (30 minute effort)
          Good choice!

Other Links:

    Definitions and good observing practices
       Use of median combine to remove interfering stars. Flat field mini-tutorial. Stochastic SE & calibration SE tutorial.

    Measuring Flux
        Aperture dimensions, recovery factors, interfering stars, etc

    Flat Frames
         Twilight, screen, dark sky, superflats, noise considerations

    Catalog Photometry Comparisons: Tycho, UCAC2 & GSC Accuracy
       Compares accuracy of star catalog photometry used in planetarium programs.

    External Links to Photometry Matters


If you want to view all of the above material on one large web page, click All.

You may e-mail me at:  B G A R Y @ c i s - b r o a d b a n d . c o m


This site opened:  January 1, 2005 Last Update:  2010.12.16