StarWindow Tools Overview

Every tool on the site, free and with no account needed. They are grouped into dark skies, sun and moon, and coast and outdoors.

Popular planning calculators

Free tools for stargazing, dark skies, the Sun, Moon, tides, and outdoor planning. No sign-up required.

Stargazing & Moon Viewing Score — Use moonlight, night windows, and nearby sky events to judge whether a night is good for stargazing or moon viewing.
Taiwan Dark-Sky Map —
Sky Map — The real sky for a city or your current location: find something now, explore any moment, or plan what to look at on a chosen night.
Where to go this week? — We combine the sunset glow forecast, moonlight stargazing conditions, and weather into one score per day for the next 7 days — so you know which day is worth heading out.
Aurora Forecast — Tonight's odds of seeing the aurora from New Zealand and the Arctic, using NOAA's OVATION model together with cloud, darkness and which way to look.
Photography Golden Hour Planner — Choose a city, date, and subject to get blue hour, golden hour, moon phase, and shooting tips. Use it before heading out for sunsets, city lights, coastlines, or a moonrise in the frame.
Tide Forecast — Check today and tomorrow tide times, tide charts, high tide, and low tide information for coastal planning and outdoor activities.
Intertidal Field Guide — Move from tide tables to the shore with three Taiwan field sites, their wildlife, access rules and safety limits.
Fishing Index — Today's best fishing windows computed from tide changes and the moon (solunar theory), for fishing ports and beaches around Taiwan, with a 7-day outlook.
Sunrise & Sunset — Calculate sunrise time, sunset time, golden hour, blue hour, and twilight periods by location and date for photography, travel, and daily planning.
Moon Phases — Check today's moon phase, last night's moon, upcoming full moon dates, lunar illumination, moonrise, moonset, and a monthly moon calendar.
UV Index — Check UV index by location and understand ultraviolet exposure levels for sun protection and outdoor planning.
Astronomy Calendar — Browse astronomical events by year, including meteor showers, solar eclipses, lunar eclipses, planetary oppositions, and other sky events.
Widgets — One iframe snippet adds a daily auto-updating sunrise & sunset card to your blog, B&B or surf-shop website. Completely free.
Go Timing — Combine sunrise, sunset, golden hour, moon, weather, UV, and tide data to decide whether today is good for photography, stargazing, or outdoor plans.

Astronomy Classroom

Why does sunset change time? Why does the Moon change shape? Start with things you can see, then follow the links between light, position and motion. Most lessons include interactive diagrams: change a condition, compare the result and read what causes it.

The two clocks behind sunrise and sunset: solstices, tilt and latitude — Change date, latitude and axial tilt to see how day length and solar noon set sunrise and sunset—and why their four extremes miss the solstices.
Sky colours: from blue daylight to sunset and twilight — Turn your view and lower the Sun to explore blue sky, warm sunlight and high clouds after sunset. Learn Rayleigh and Mie scattering, optical depth and twilight.
How auroras form — Follow the chain from sunspots and CMEs to the auroral oval, then use it to plan a realistic aurora trip.
How a meteor lights up — Textbooks say meteors burn from friction with the air. That sentence points at the wrong heat source. Drag altitude, speed and size, and see what is doing the heating.
Moon phases are not Earth's shadow: Why does the Moon change shape? — Move the Moon and compare sunlight in space, the disk seen from Earth, and approximate viewing times.
Moon, seasons and the leap month: how a traditional calendar stitches two clocks together — Use a nineteen-year timeline to compare solar, lunar and lunisolar calendars, see months drift against the seasons, and examine how principal solar terms guide leap-month placement.
Solar and Lunar Eclipses — The Moon's orbit leans 5.16 degrees, so most new and full moons do nothing at all. Turn the nodes and build a total eclipse, a ring, and a blood moon yourself.
Tides: reading the Moon and Sun from the shore — Move the Moon, follow the change in tidal range, and learn where an astronomical model ends and a harbour forecast begins.
Tidal locking: why does the Moon keep the same face toward us? — Try no spin, half speed, and synchronous rotation to see why one spin per orbit is the only setting that keeps one lunar face aimed at Earth.
Why planets appear to move backwards — Scrub through time and draw the loop Mars traces backwards across the stars yourself.
Opposition and conjunction — Use elongation to tell when a planet is visible all night or close to the Sun, and compare different Mars oppositions.
Greatest elongation — Why the two inner planets are always twilight objects, and why Venus is brightest as a crescent.
Ptolemaic and heliocentric — One geometry, two choices of origin. Move the origin and the epicycles appear on their own.
Solar System Orrery — All eight planets on the ecliptic plane at true scale and true period, with free zoom and a speed ladder.
The ecliptic plane — The solar system is a disc. Seen from the side it is a line, which is why the diagram has to say how much it is exaggerating.
Comets: from icy nucleus to extreme orbit — Move perihelion and aphelion to explain the coma, two tails, high eccentricity, and SL9's impact on Jupiter.
Lagrange points: why do telescopes and space colonies talk about L1–L5? — Start with Webb, Roman and Gundam, then operate Sun–Earth and Earth–Moon models to find five fixed locations.
Perihelion precession — The orbit itself turns. Watch the long axis sweep a few degrees over six thousand years, and meet Mercury's extra 43 arcseconds.
How to read a star map: direction, one night, and the changing seasons — Drag a real star chart to find your bearings, then hold your view steady while time and month change.
Why dark skies reveal more stars: magnitude and light pollution — Change sky background and limiting magnitude over one fixed Orion field, then compare Bortle, SQM, VIIRS, and international dark-sky designations.
Where do astronomy and astrology part ways? — Turn one ecliptic dial, then use Sirius, ancient calendars, and two studies to trace the line between observation, interpretation, and prediction.
The Milky Way and its centre: when and where to look — Pick a city and a date, find the galactic centre on a real star chart, then see how the hour, month and latitude change its overlap with darkness.

Tonight: stars, the Milky Way, sunset glow, or a cloud sea?

Stop cross-checking page by page. Start with tonight's stargazing index, find a dark-sky spot, confirm the galactic-core direction, or switch to sunset and cloud-sea planning.

Is tonight good for stars? — Cloud, transparency, moonlight and darkness are combined into the best observing window tonight.
Where is the sky darker? — Compare mountains, coasts and islands with Bortle, SQM, elevation, Milky Way timing and tonight's sky.
Which way is the Milky Way? — The live sky map marks the galactic core, planets, constellations and compass directions for field use.
Sunset glow or cloud sea? — A 7-day outdoor outlook blends sunset glow, stargazing and weather for photo and mountain plans.
Japan Milky Way travel — Achi, Bisei, Iriomote-Ishigaki, Kozushima and other Japanese star destinations with tonight's conditions.
Alert me when it is good — Dark-sky spot pages can be subscribed to with Telegram for evening stargazing alerts.

Related tools: Go Timing · Sunrise & Sunset · Tide Forecast