Meridian

Location & time

Click the map or drag the marker to set your location. Place search by OpenStreetMap Nominatim.

Latitude

Longitude

Decimal degrees; north and east are positive.

Night of

Time zone

Time format

12-hour 24-hour

Observing window

Window	Start	End
Astronomical twilight
Nautical twilight
Civil twilight
Sunset to sunrise
Custom times

Filters

Object types

Catalogues

OpenNGC Messier objects only

Minimum altitude: 20°

Your local horizon. Rise and set times are when objects cross this altitude.

Brighter than (mag):

Surface brightness under:

Size:

Any Any

Minimum uses the minor axis

Apex altitude at least:

Visible at least:

Moon distance at least:

Tonight score at least: 0

Scoring

Tonight's score rates each object from 0 to 100. Tune what it rewards and how hard moonlight and light pollution count against it.

Light pollution: Bortle 1 · SQM 22.0

Inner city Pristine

Light pollution at your site, as read by a sky quality meter (SQM), or look it up on lightpollutionmap.info. Not changed by Restore defaults.

What the score rewards

Blended in proportion to each other; the percentages show each one's share.

Altitude: 35%

How high it climbs above your minimum altitude.

Time visible: 25%

How long it stays above your minimum altitude.

Brightness: 40%

Its magnitude, and surface brightness for galaxies and nebulae.

Full marks for time visible: 4 h

Objects up for this long get the whole time-visible share. On shorter nights the whole window is enough.

Penalties

The most each can take off a faint galaxy or nebula; clusters lose half as much, stars and planets a tenth.

Moonlight: up to 60%

Strongest for a bright Moon that is up most of the night and close by.

Light pollution: up to 70%

Scaled by the light pollution setting above.

Meridian – Observing Planner

Meridian helps plan a night of observing by showing which objects are well placed from your location, and scores them by how worthwhile they are tonight. It can also work out times of year an object is ideally positioned.

Location, settings and filters are saved in the browser; no account needed.

Data and credits

Deep-sky objects from OpenNGC by Mattia Verga, licensed CC BY-SA 4.0.
Sun and Moon positions follow Jean Meeus's Astronomical Algorithms; the planets use JPL's approximate orbital elements (E. M. Standish). They are good to about an arcminute: plenty for planning, but use your telescope's own catalogue to point it.
Map and place search from OpenStreetMap contributors, through its Nominatim search service.
Sky views in Stellarium Web.