Where are you observing from?
Location estimated from your device's time zone. Pass times change from one city to the next: set your location for accurate times. It is stored only on this device.
Astrophotography
Plan a session from
A detailed sky chart to plan a session: your sensor’s frame, mosaics, moonless nights, the night’s weather and exposure calculators.
Planning chart
Chart display
Orientation
Grids
Reference lines
Sky
auto
Field of view
Mosaic
CSV file in the Telescopius mosaic format, also for a single frame. N.I.N.A.: simple sequencer, “Import targets” (one panel per target, with its angle). KStars and StellarMate: Framing Assistant, “Import Mosaic from Telescopius”, with the centre row, which they require; leave it out for N.I.N.A., which would turn it into an extra target.
Panels are numbered row by row from the top of the image, left to right. J2000 coordinates are copied as hh:mm:ss and ±dd:mm:ss. Without a rotator, the camera keeps the same angle from one panel to the next: if the angles in the table differ by more than 2°, as near the pole, allow a wider overlap.
The frame stays at the centre of the chart: drag the sky to compose the image. Angle measured from north through east, as in N.I.N.A.: at 0°, the long side is horizontal and the top of the image, marked with a triangle, points north.
Real sky image: the DSS2 colour survey (Digitized Sky Survey, STScI/NASA, colourised by CDS), cut out on request by the CDS hips2fits service in Strasbourg when you settle the frame. Only the coordinates of that patch of sky are sent to it, never your location.
Moonless nights over the next two weeks
Moonless night: astronomical night (Sun more than 18° below the horizon) with the Moon below the horizon. Tap a night to plan it.
TwilightAstronomical nightMoon upMoonless night
- Computing nights…
Altitude tonight
Tap the curve to set the chart time. Solid line: the object; dashes: the Moon.
Weather for the night
Loading the forecast…
Highlighted rows: moonless-night hours. Clouds as a percentage of the sky. Dew: gap between temperature and dew point (high under 2 °C, possible under 4 °C).
Well-placed targets for this frame
Exposure time without trails
On a fixed tripod, without tracking, using the sensor, focal length and focal ratio of the field of view.
NPF rule by Frédéric Michaud (Société astronomique du Havre): t = (16.856 × N + 0.0997 × f + 13.713 × p) ÷ (f × cos δ), where N is the effective focal ratio (reducer included), f the effective focal length in mm, p the pixel size in µm and δ the declination. 500 rule: 500 ÷ (focal length × crop factor), older and meant for film prints; it accounts for neither pixels nor declination.
Image scale
The patch of sky covered by one pixel, compared with the seeing at your site.
Image scale = 206.265 × pixel (µm) ÷ focal length (mm). The usual aim is between a third and a half of the seeing: above that, stars turn square; below, light is spread over too many pixels (2 × 2 binning helps).
About this tool
What it does
A sky chart to compose an image before the session: find a target, frame it with your sensor and focal length, plan a mosaic, pick a moonless night and check the weather. The coordinates of any point appear on hover or tap. For the planets, the Moon and the eclipse calendar, see tonight's sky.
The calculations
J2000 and of-date coordinates (precession, nutation, aberration), refracted altitude and azimuth: astronomy-engine, on your device. Stereographic chart; frame drawn in gnomonic projection, angle measured from north through east as in N.I.N.A. Positions checked against JPL Horizons and SIMBAD to within one arcsecond.
The sources
99,049 stars down to magnitude 9.5 (HYG v4.1), 1,941 deep-sky objects (OpenNGC), constellations from d3-celestial, weather from Open-Meteo. The catalogues load only on this page, then stay available offline.
How long can I expose without trails?
On a fixed tripod, the NPF rule gives the longest exposure before stars start to trail, from the f-ratio, focal length, pixel size and the target's declination. It does not apply on a motorised equatorial mount: take care of polar alignment with the position of Polaris in the polar scope.
What sampling should I aim for?
Between a third and half of the seeing, in arcseconds per pixel: 0.83 to 1.25 ″/px for 2.5″ seeing, the default value. Above that, stars may look square; below it, 2 × 2 binning suits better.
How do I import the mosaic into N.I.N.A.?
Export it as CSV, then open N.I.N.A.'s simple sequencer and choose “Import targets”: each panel becomes a target, with its angle. KStars and StellarMate read it with “Import Mosaic from Telescopius”, with the centre row ticked.