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Every solar and lunar eclipse from 2020 to 2050 with its times and how much you'll see from your place — contacts, magnitude, obscuration, the path of totality on a world map — and the meteor showers of the IMO list, with the rate you can expect tonight after the radiant's height, your sky and the moon.
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Conjunctions of planets with each other, the Moon and bright stars, planet "parades", oppositions, greatest elongations, stations and retrograde loops, Mars's closest approach and lunar occultations — for the next year or twenty, filtered to what you can actually see from your place, each with a picture of the sky at the best moment and an .ics file for your calendar.
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Convert between the Bortle class, sky brightness in mag/arcsec² (an SQM reading), naked-eye limiting magnitude and how much brighter than natural your sky is; see what each class shows and a simulated star field at that darkness; and estimate tonight's limiting magnitude by altitude with the Moon up.
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A star chart for your place and time — the whole sky as a dome or a zoomable view, with stars to magnitude 6.5, constellations, the Milky Way, Messier objects, the planets and the Moon's phase; a time slider, search, rise/transit/set for anything you tap, a red night mode, and a mode that shows what your phone is pointing at.
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Film + developer + dilution + EI → development time from Ilford and Kodak datasheets, corrected for temperature and continuous agitation, with push and pull; your own combinations; and a step timer for pre-soak, developer with agitation prompts, stop, fix and the Ilford wash, with sound and vibration — plus C-41 and E-6.
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Pixels ↔ print size at any ppi; the resolution the eye can use at a viewing distance (1 arcminute acuity); a photo cropped to a paper's shape with an overlay on your own image; how much upscaling a print needs; and mat window, borders and the standard frame that fits.
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Event duration ↔ clip length ↔ interval at your frame rate; frames, card space and batteries; shutter angle and the ND filter for natural motion blur; and a day-to-night exposure ramp laid over the real sunset and twilight times for a place and date.
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Depth of field with near and far limits, hyperfocal distance and a diagram; circle of confusion by sensor from phones to 4×5; two set-ups side by side; field of view and framing; equivalent focal length, aperture and ISO across formats; megapixels for a print; diffraction against pixel pitch; and macro with extension tubes.
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Drop a folder of photos — JPEG, HEIC, DNG or camera RAW — and see which focal lengths, apertures, shutter speeds and ISOs you really use, which lenses and cameras, and when you shoot; export the table as CSV. Read in your browser; nothing is uploaded.
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The exposure triangle with EV at ISO 100 — lock any two of aperture, shutter and ISO and see the third — plus stops arithmetic in ⅓ and ½ stops, Sunny 16 and a light-level table, ND filters with a long-exposure countdown, reciprocity failure for film, and the shutter speed that freezes a moving subject or a shaky hand.
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Guide number, distance, aperture and ISO solved from any three; flash power in ⅓ stops from 1/1 to 1/128; inverse-square falloff to the background; several flashes together; the light lost to high-speed sync, with flash balanced against the ambient; and key:fill lighting ratios, softbox size and distance, and a top-down diagram of where the lights go.
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A sequential lens design bench: build a prescription of spherical and conic surfaces in N-BK7, N-SF11, F2, N-SK16, fused silica, CaF₂ and plastics (Sellmeier data), trace paraxial and real rays, get the cardinal points, Seidel aberrations and longitudinal colour, spot diagrams, ray fans and an MTF estimate, bend a singlet, design an achromatic doublet, and export the prescription as CSV or JSON — with a full-screen layout.
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The longest shutter speed for pinpoint stars — the 500 rule against the NPF rule, from your sensor's pixel pitch, aperture, focal length and where you point — a star-trail planner (frames, gaps, total time, arc swept, card space), and when the Milky Way's core is up in a dark sky, tonight and through the year.
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"What's that plane?" — point your phone at the sky and see the aircraft labelled where they are, with callsign, type, altitude and distance, using your location, the phone's compass and tilt, and optionally the camera; a sky plot and a list work everywhere else.
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Plan the light for a place and date: sunrise and sunset, golden and blue hour, civil, nautical and astronomical twilight, the sun's azimuth and elevation through the day, and moonrise, moonset, phase and illumination — with a day chart and a sky compass, in the place's own time zone.
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Telescope and eyepiece arithmetic (magnification, focal ratio, exit pupil, true field, useful power, Dawes and Rayleigh limits, limiting magnitude, Barlows and reducers), a camera on a telescope (arcseconds per pixel and sampling), binoculars, an interactive ray-tracing bench where you drag lenses and mirrors and watch images form, the lensmaker's equation and Snell's law with total internal reflection.
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Resize, crop, rotate, and re-encode images as JPEG, PNG, WebP, or AVIF with a before-and-after comparison; strip EXIF; extract a palette; and build favicon and app-icon sets.
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ffmpeg compiled to WebAssembly, in your browser — convert, trim, crop, resize, rotate, re-time and watermark video; make GIFs and animated WebP; extract audio; split video into frames or build video from images; join clips; or run any ffmpeg command.
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Read text from photos, screenshots, scans and PDFs with Tesseract compiled to WebAssembly — clean up the image (threshold, deskew, upscale), pick a region, see every word's confidence, and export text, hOCR, TSV or JSON.