Methodology

Every specification comes from the manufacturer's own page with a check date. Everything the planner shows is calculated in your browser from public astronomy data; nothing is guessed.

Specifications

We take aperture, focal length, field of view, sensor, weight, battery and price from official product pages and record the date we checked them. Where a maker publishes only a diagonal field or a full-frame equivalent focal length, we derive width and height and label the value "derived". Conflicting official figures are noted on the product page.

"Fits well", "larger than the frame", "small in the frame"

We divide the object's longest dimension by the short side of the native frame. Between 0.2 and 0.95 counts as fitting well; above 0.95 the object is larger than the frame and needs a mosaic; below 0.2 it is small in the frame. This is an editorial rule of thumb, not a quality score.

"Sky needed"

For each Messier object we calculate the mean surface brightness from its magnitude and apparent size. Bright, compact objects and star clusters cope with city skies; faint, spread-out objects need darker skies. Galaxies get a stricter threshold because filters cannot separate them from sky glow. It is a calculated guide, not an observation.

The sky planner

Star positions come from the Hipparcos catalogue (via d3-celestial), Messier objects from the same dataset and Sun, Moon and planet positions from Astronomy Engine. Star positions are not corrected for precession, which shifts them by well under a degree. An object counts as visible when it is at least 5° above your horizon while the Sun is more than 12° below the horizon, for at least 30 minutes. The cloud forecast comes from MET Norway.

Difficulty

"Easy", "doable" and "challenging" combine the object's magnitude with the sky quality you set (Bortle scale). It is a rough guide for planning, not a promise of results.

Corrections

Found an error? Tell us via the contact address on the about page and we will correct it with a new check date.