Star Party Planner Calculator

Plan a star party by estimating sunset time, moon phase, visible planets, and observable deep-sky objects for your location and date.

Inputs

Month (1-12)

Latitude (°N)

Bortle Class (1-9)

Tab to move between fields

Results

Observable DSOs

Est. Sunset (24h)19.1 hr

Moon Illumination100%

Visible Planets3

How to Use This Calculator

Enter Month (1-12), Latitude (°N), and Bortle Class (1-9).
Review the Observable DSOs result.
Use Est. Sunset (24h) (hr) and Moon Illumination (%) to inform your decision.
Use the chart to visualize the results and explore different scenarios by adjusting inputs.

How the result changes with Bortle Class (1-9)

Bortle Class (1-9)	Observable DSOs
1.8	77
3.8	58
6.2	35
8.2	17

What each input means

Month (1-12): Month of the planned observing session (1 = January, 12 = December)
Latitude (°N): Your geographic latitude (positive = north, negative = south)
Bortle Class (1-9): Light pollution level: 1 = pristine dark sky, 5 = suburban, 9 = inner city

How this is calculated

Worked example, using the default values

Identify Input Parameters
Month (1-12) = 6, Latitude (°N) = 40, Bortle Class (1-9) = 4 = 3 input(s) provided
Calculate Est. Sunset
Est. Sunset
19.1 = 19.1
Calculate Moon Illumination
Moon Illumination
100 = 100

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