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ASTROMETRICS: DSO Visual Susceptibility Calculator

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(Calculator uses JavaScript1.2 extensively. Problems may occur with some browsers. Program always under further development. GET INVOLVED: Your help with validation encouraged!)

Calculation Input:

Telescope Type: Refractor
Deepsky Object Type:
Published Magnitude:
Magnitude Type: Visual Photo
Unaided Limiting Magnitude at Zenith:
Degrees Above Horizon:
Object Width (arc-minutes):
Object Height (arc-minutes):

Calculation Results:

Visual Magnitude:
Average Surface Brightness at 60X:
Adjusted Surface Brightness at 60X:
Recommended Magnification to Find (X):
Visible Surface Brightness at Find X:
Recommended Magnification to View (X):
Adjusted Surface Brightness at View X:
Field Stars Brighter than Adjusted View Brightness:
Distance to Average Object of Type (KLY):
Threshold Scope Aperture (mm):
Optimal Scope Aperture (mm):


Average Surface Brightness: Straight mathematical treatment based on apparent size and listed magnitude of the object. This is the mean average luminosity of all 1 "square" arc-minute regions on the object.

Adjusted Surface Brightness: Since the luminosity of many deepsky objects tends to coelesce around certain brighter regions, this is the expected luminosity of the brightest portions. (Those parts a small telescope is most likely to reveal.)

Adjusted Surface Brightness at Find Magnification: The smaller the image size in the eyepiece, the greater the concentration of light presented to the eye. This effect is offset however, by the fact that sky brightness also increases with lower magnification.

Threshold Scope Size: This is the smallest aperture scope of the pre-selected type which may just reveal the object at find magnification to the un-averted eye of an observer who already knows its exact location.

ASTROMETRICS: DSO Visual Susceptibility Calculator - Courtesy Jeff Barbour, Astro.Geekjoy.Com


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