Observatory Calibration Worksheet

Dome & Mount Geometry → NINA Settings

Formulas used
Up/Down = (mount axis height) − (dome center height) · N/S and E/W = signed floor-mark distances · GEM Axis Length = raw measurement + 0.5 × guidescope offset (if used) · Radius = as measured (or diameter ÷ 2).

These are direct geometric inputs — NINA computes the live dome azimuth internally from these plus your mount's current RA/Dec and pier side. Once entered, turn on dome synchronization and nudge one value at a time only if you re-measure it and find it wrong; don't tune values arbitrarily to patch a specific slew position, or it'll get worse elsewhere in the sky.

NINA · Options → Dome

Mount TypeEquatorial

+N/-S—

+E/-W—

+Up/-Down—

Dome Radius—

GEM Axis—

Lateral Axis—

Az Tolerance—

Live Dome Aim

Telescope points at—

Required Dome Az—

Intersection Alt—

Aperture Clearance—

Mount Position

1Mount Position

Walks through plumb-bob and tape-measure steps and converts them into NINA's signed values.

Height of dome center above floorgeometric center of the sphere, not the rim

Height of mount RA/Dec intersection above floor

North/South distance

East/West distancemount mark relative to dome center mark

Dome & Rotator

2Dome & Rotator

Dome radiusmeasured center-to-rim, along the base

I only measured the diameter — halve it for me

Shutter (slit) widthstraight-line width of the open gap

Smallest azimuth step your rotator can reliably slew toolder NexDome units were 1°

Wall height, floor to springlinewhere the hemisphere shell actually starts — only affects the 3D preview, not the NINA math

Optical Axis Offset

3Optical Axis Offset

Mount type changes what NINA needs here.

GEM Axis Length (raw) Slew RA to ±90° from the meridian and measure the lateral distance from the RA axis to the center of the OTA aperture.

I'm using a guide scope — add its correction

Dual saddle with side-by-side OTAs — set Lateral Axis Length

Telescope dimensions — used for the 3D preview and aperture clearance check.

OTA tube length

OTA clear aperture

Sky Coverage

Sweeps a grid across the whole sky and checks whether the shutter actually clears at each point — for both pier sides side by side, so a meridian flip's effect is visible directly rather than found by trial and error.

Pier East

Pier West

Reading this

Center = zenith, edge = horizon, up = North, right = East. Updates live as you change your setup.

● Green — shutter clears
● Red — vignettes or misses the dome entirely
● Brown — below your local horizon, not observable regardless
● Grey — mount geometry invalid there

Local Horizon

Buildings, trees, or terrain that block the sky below a certain altitude — drawn as a wireframe skyline in the 3D preview so you can see where the dome slit would be pointed at something other than open sky.

Minimum observation altitude

Telescope Pointing

4Telescope Pointing

Drives the live azimuth calculation and the 3D preview, using the exact same math NINA runs internally.

Site latitude

Hour Angle0 = on the meridian, + = west of meridian

Declination

1°

Step size

Hold to keep jogging. Nudges whichever pointing mode is active above.

Pier side

Auto-flip at the meridian (HA=0) — East while approaching, West once past

3D Preview

Show local horizon

Show celestial equator

● Clears ● Blocked ● Tight margin

Drag to orbit, scroll to zoom.