Making intensity estimates
How to make accurate visual brightness evaluations in different sections of Saturn
Using a telescope and your eyes, intensity estimates can be made of Saturn. You’ll need a planetary blank to show the correct outline of the planet for the observing date. WinJupos can generate blanks by selecting Saturn from the ‘Program’ > ‘Celestial body…’ option, before choosing ‘Tools > Ephemerides…’ and going to the ‘Graphics’ tab. Make sure the date is set correctly and turn off any textures, etc, to show a planetary outline which can be printed.
At the eyepiece, the intensity estimate is done by dividing the planet into areas of equal brightness. A numeric scale of 0 to 10 is then used to annotate each area according to its brightness, 0 being bright, 10 dark. Intermediate, decimal values may be used if required. In order to calibrate any estimates, two fixed areas are used. The outer part of ring B, the brightest of Saturn’s rings, is given an intensity of 1. The dark shadow of the planet’s globe on the rings is given a value of 10. In the case of the brightness value, brighter areas may be seen and these should be given decimal values less than one, up to a maximum of 0 for an exceptionally bright region.
Observer bias can be eliminated by first labelling regions brightest to darkest. Once complete, start on a new blank but label darkest to brightest. Although tricky at first, it doesn’t take long before making accurate estimates becomes second nature. The technique is also a great way to connect to Saturn visually, forcing you to look at every part of the planet.