INTRODUCTION

There are many types of astronomical photoelectric photometry projects. Some of the projects an amateur might consider are Lunar photometry, solar photometry, planetary photometry, planetary satellite occultation photometry, asteroid photometry, comet photometry, deep sky photometry (including Nova, Supernova, and galactic photometry), and several varieties of stellar photometry.

LUNAR PHOTOMETRY

Lunar photometry is important and an area where few astronomers do photometric observations. Lunar photometry of transient events such as the brightening or fading of certain areas and discolorations of the crater floors can be done. For additional information, refer to LUNAR PHOTOMETRY by Peter Hedervari, section 4 of the SOLAR SYSTEM PHOTOMETRY HANDBOOK.

Perhaps one of the most interesting of Lunar photometry is the measurement of Lunar occultations of stars. The darkened limb of the moon provides a knife edge for the star light. Much can be learned from the data obtained. High-speed photometry is used and data points may be logged into a computer at 1 millisecond intervals. The resulting light curve, and resulting diffraction pattern, of the light from the star as it is sliced by the darkened edge of the moon, can reveal multiple stars and information about their configurations. This is a very exciting project because you only get one chance and everything must be just right.

These measurements can be made with either a waxing or waning moon. Measurements can be made from stars disappearing or re-appearing from the darken Lunar limb. Unless you have an exceptionally fine telescope setup and very accurate clock drive, projects involving the disappearance of the stars are the best ones to tackle. At professional observatories where pointing and tracking accuracy of the telescopes is in a few arc seconds, the re-appearance of stars from the darkened Lunar limb can be measure.

For the average amateur, however, being able to point to within a few arc seconds of where the star is to re-appear, and sit waiting many seconds or minutes, is usually beyond the amateur's equipment capability. SKY and TELESCOPE magazine publishes a list of the more popular Lunar occultations occurring during the year, in each January issue. For additional information, refer to LUNAR OCCULTATIONS by Graham L. Blow, section 9 of the SOLAR SYSTEM PHOTOMETRY HANDBOOK.

SOLAR PHOTOMETRY

Solar photometry offers some unique challenges. Certainly only a small telescope is needed. The problem with solar photometry is just the reverse of other photometry. It's too bright! Because the Sun is a star and we are totally dependent on it, its study is of great importance.

Areas that can be investigated are Sun spots and a quiet (no Sun spot activity) Sun's limb darkening.

For additional information, refer to SOLAR PHOTOMETRY by Gary A. Chapman, section 5 of the SOLAR SYSTEM PHOTOMETRY HANDBOOK.

PLANETARY PHOTOMETRY

There has been a growing interest lately in planetary photometry. By observing the light changes as a function of the solar phase angle, information about the objects surface composition can be obtained. There has been recent interest in photometry of the Galilean satellites of Jupiter and work is being done on Saturn's satellites.

For additional information on Planetary Photometry, refer to PHOTOMETRY OF PLANETS AND SATELLITES by G. Wesley Lockwood, section 2 of the SOLAR SYSTEM PHOTOMETRY HANDBOOK.

PLANETARY SATELLITE PHOTOMETRY

Photometry of planetary occultations is another project suitable for the smaller observatory. Doing photometry of Pluto and Charon as the occult each other has been a recent organized project. Recent data published that used UBV photometry were able to show different colors of Pluto and Charon as the occulted each other.

Refer to OCCULTATIONS BY PLANETS AND SATELLITES by Robert L. Millis, section 7 of the SOLAR SYSTEM PHOTOMETRY HANDBOOK.

COMET PHOTOMETRY

As mentioned in earlier, the appearance of Comet Halley caused a new interest in comet photometry. This is a very specialized form of photometry and special filters are usually needed. The photometrist with a UBV or VRI photometer can still make valuable observations, however. Before getting too far into comet photometry, it is advisable to contact some of the comet photometry experts. Also, keep an eye out for any new comets. You may be the first to do photometry on them.

For additional information, refer to PHOTOMETRY OF COMETS by Michael F. A'Hearn, section 3 of the SOLAR SYSTEM PHOTOMETRY HANDBOOK, Edited by Russell M. Genet, 1983, Published by Willmann-Bell, Inc., P.O. Box 3125, Richmond, Virginia 23235 USA.

STELLAR PHOTOMETRY

Stellar photometry is probably the most popular and useful project undertaken by amateur astronomers doing photometry. A great many stars have light that is not constant. These form the class known as variable stars. Projects from just timing of eclipses to detailed filter photometry are well within the capability of the amateur astronomer with modest equipment. For more information on variable star projects contact the AAVSO or IAPPP.

Variable light output from stars can be caused by several phenomena. Basically there are three types of variable stars, intrinsic variables, eruptive variable, and extrinsic variables. With some variable star projects, only timing of the period is important. Others require filter photometry and careful calibration of the system and comparison stars. The following is a list of characteristics of the different types of variable stars:

Intrinsic Variables
The intrinsic variables have their light variations caused by internal phenomena. The stars may pulsate, e.g., Cepheid variables. This pulsation may be a long period or short period pulsation, semi-regular, or irregular. Also, a relatively new group of stars, known as RS CVn variables are believed to have large star spots (similar to sun spots only much larger) that travel around on the surface of the star. These spots are cooler than the rest of the surface so as they migrate they cause the star's brightness to change.

Eruptive Variables
The eruptive variables are those that tend to produce sudden outbursts of energy. Examples are Flare stars, Nova and Supernova types.

Extrinsic Variables
The extrinsic variables have there light variations caused by external reasons, e.g., another object (star) passing in front of them. These are known as eclipsing binaries. While they may be eclipsing binaries, the systems may contain more than two stars and may have intrinsic and eruptive variables within the system. Much information about the star system can be learned from the light curves. By using filters, e.g., UBV filters, additional information about the system can be obtained.

NOVA AND SUPERNOVA PHOTOMETRY

While Nova and Supernova photometry are certainly important, it is rare that amateurs have the opportunity for these. They are frequent in other galaxies but are usually beyond the means of most amateur's equipment. Photometry of galaxies is a different story and may well be within the limits of the amateur's equipment.

ASTEROID PHOTOMETRY

Asteroid photometry is a real challenge and requires dark skies and a lot of skill. Asteroids are usually very faint and hard to find. Data obtained on asteroids are of great interest to professional astronomers. Asteroids may someday provide space stations for exploration of the solar system and mining bases for their rich mineral content. By observing asteroid light curves, their rotation rate and surface colors can be investigated.

For additional information, refer to PHOTOMETRY OF ASTEROIDS by Richard P. Binzel, section 1 of the SOLAR SYSTEM PHOTOMETRY HANDBOOK. and ASTEROID OCCULTATIONS by Alan W. Harris, section 8 of the SOLAR SYSTEM PHOTOMETRY HANDBOOK.

Note: The International Occultation Timing Association (I.O.T.A.) is devoted to timing of lunar, asteroid, and planetary occultations. SKY and TELESCOPE magazine usually has details of current projects.