Observer
Remote observatory
{{ o.label }}
Latitude (°N)
Longitude (°E)
Use my location
Reset site
Save these coordinates as
Save
Delete
{{ geoMsg }}
{{ t.label }}
Hours above altitude threshold
Latitude {{ latLabel }}
Export PNG
DECLINATION (°)
HOURS ABOVE ALTITUDE
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{{ svgLegend }}
Usable dark hours by RA / Dec
{{ darkInfo }}
Date
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>
Altitude threshold
{{ thrLabel }}
Mask
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Falloff
{{ falloffLabel }}
Milky way
{{ milkyLabel }}
Constellations
{{ starsLabel }}
Frame
Full sky
Center usable
Fit usable
Auto
Reset chart
Export PNG
Chart ·
scroll
to zoom ·
drag
to pan or rotate ·
ctrl-drag
to box-select a region ·
click
for usable hours at a point
Layers
· click to toggle
usable boundary
all-night boundary
ecliptic
Moon ± 30° dimming radius
Sun
Planets
Planets at local midnight
Planet
RA
Dec
Usable
{{ p.name }}
{{ p.raLabel }}
{{ p.decLabel }}
{{ p.hoursLabel }}
cos H = (sin alt − sin φ sin δ) / (cos φ cos δ) · usable = overlap of [RA − H, RA + H] with the astronomical dark window (Sun below −18°), in local sidereal time