NEW! Astronomy Projects for Amateurs, Educators & Students

Project 11: Visual Photometry Project
Charts, Stars & Magnitudes

M39: Heidi Schweiker/NOAO/AURA/NSF
M45: Tad Denton/Adam Block/NOAO/AURA/NSF

Visual photometry is the process of determining the brightnesses of an unknown star by comparing its brightnesses to nearby standard stars of known brightness.  This comparison is made by eye. The standard stars that match the unknown closest in brightness set limits on what the visual magnitude of the unknown star can be; if the unknown is fainter than standard A but is brighter than standard B, then its visual magnitude is somewhere between those of A and B.

This project uses the star cluster M39, M44 orM45 (39th, 44th, 45th objects in the catalog compiled by Messier.) viewed through the telescope eyepiece. M39 is good for summer/fall, M45 for fall/winter, M44 for spring/summer. Using the finding chart (in the project) to identify the standards and unknown stars in the image on the computer screen, compare standard stars to unknown stars to estimate the magnitudes of the unknown stars.

Enjoy, and we solicit your comments/suggetions/critique at

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