# CycleCalcs > CycleCalcs (https://www.cyclecalcs.com/) is a free, ad-supported astronomy site organized in three pillars: Sky (a live sky map and everything in tonight's sky), Cycles (the planets, the concepts, and a sorted reference of every major astronomical cycle), and Calculators. It also carries interactive lessons on how the sky's rhythms work. Everything is computed in the browser with the open-source Astronomy Engine (MIT); positions are accurate to well under a degree and reliable for roughly the years 1700 to 2200. Pure astronomy only: no astrology, fortune-telling, or claims that sky events affect people or Earth. Notes for assistants: each page carries schema.org JSON-LD (WebApplication, FAQPage, BreadcrumbList) and a concise meta description. Dates are UTC unless a tool says otherwise. Zodiac positions are tropical ecliptic longitude (0 degrees at the March equinox). The site uses US spelling and straight quotes. ## Sky (tonight's sky, live and location-aware) - [Live Sky Map](https://www.cyclecalcs.com/sky-map.html): a full-screen interactive planetarium of the sky over any location and time (1700 to 2200): about 8,400 naked-eye stars with true colors plus an optional binocular-depth layer of 37,000 more stars to magnitude 8 that loads when you zoom in, the Sun, Moon and planets, constellation figures, the 110 Messier and 109 Caldwell deep-sky objects as classic chart symbols with honest binocular and telescope reach verdicts, tap-to-identify cards with rise/set times and a clearly labeled reference photo (from a space telescope or spacecraft, not the naked-eye view) for the planets and the Messier and Caldwell showpieces, typo-tolerant search, planet-finder rings and edge arrows, a time scrubber, Bortle light-pollution realism, star-hop routes from a bright anchor star to any faint target with true-scale Telrad, finder and eyepiece circles and an optional mirror or 180-degree flip to match a star diagonal or Newtonian eyepiece, a red night mode, and a point-at-the-sky compass mode on phones (beta, corrected for magnetic declination). No account, no app, no ads on that page. - [Today in the Sky](https://www.cyclecalcs.com/today.html): the current Moon phase, where each planet sits in the zodiac, and the next moons, eclipses and seasons. - [What Is That in the Sky?](https://www.cyclecalcs.com/what-is-that-in-the-sky.html): a "what did I just see" identifier. Give it a rough compass direction, a rough height above the horizon and a time, and it computes where every bright planet, the Moon and the brightest stars really were in your sky at that moment, ranks the ones that fit, and flags satellites and the ISS, aircraft and meteors from how the light behaved. Works for tonight or a past night, unlike a point-your-phone star app. Positional astronomy only, no UFO framing. - [Moon Calendar 2027](https://www.cyclecalcs.com/moon-calendar-2027.html): a printable 2027 moon calendar computed for one place rather than for Universal Time: moonrise, moonset, phase and illumination for the buyer's exact coordinates in their own timezone, every day of the year, as a typeset PDF plus a subscribable calendar feed. A free preview month is generated live for any location, and a watermarked one-month PDF can be downloaded before buying. This is the site's one paid product; every tool and the API free tier remain free. - [Moon Phase Calendar](https://www.cyclecalcs.com/moon-phase-calendar.html): tonight's moon phase plus a month grid of the new, first quarter, full and last quarter moons, with traditional full moon names. - [Eclipse & Saros Explorer](https://www.cyclecalcs.com/eclipse-explorer.html): upcoming solar and lunar eclipses, the next solar eclipse visible from a given location with local times, and a walk along a Saros series. - [Eclipse Calendar](https://www.cyclecalcs.com/eclipses/): every solar and lunar eclipse from 2026 through 2028 on its own page (e.g. /eclipses/2026-08-12-total-solar.html): engine-verified peak times, Saros series, where each is visible, a UTC contact timeline, and a live panel that computes local contact times and obscuration for any coordinates on solar pages and checks whether the Moon is up at each stage on lunar pages. - [The 2 August 2027 Eclipse, Town by Town](https://www.cyclecalcs.com/eclipses/2027-08-02/): the 2027 total solar eclipse computed for fourteen named towns along its path through Spain, Gibraltar, Morocco, Tunisia, Libya, Egypt and Saudi Arabia, each on its own page (e.g. /eclipses/2027-08-02/luxor.html): duration of totality to the second, exact contact times in the town's own clock time and in UTC, the Sun's altitude at maximum, and per-town eye-safety guidance. Twelve towns are inside the path (Sohag and Luxor longest at about 6 min 25 sec, Malaga shortest at 1 min 51 sec); Aswan and Marsa Matruh have pages precisely because they are OUTSIDE it despite being close, at about 99 and 97 percent obscuration with no totality at all. Coordinates and time zones come from GeoNames; a comparison table of every town sits on the index. - [Meteor Showers](https://www.cyclecalcs.com/meteor-showers/): all 13 principal annual showers, each on its own page with computed peak instants for the next three years, moonlight verdicts, honest ZHR framing, parent bodies, and a live calculator for the best dark-sky window from any location. - [Full Moon Calendar](https://www.cyclecalcs.com/full-moon-calendar.html): every full moon of the current and next year with exact instants, traditional names, Earth-Moon distances, supermoon/micromoon and blue-moon flags, the strict Harvest-Moon rule, and eclipse cross-links. - [Calendar Feeds](https://www.cyclecalcs.com/calendar-feeds.html): free subscribable iCalendar (.ics) feeds that put the sky into any calendar app and keep updating: moon phases, full moons only, eclipses, equinoxes and solstices, and a combined "sky events" feed. No account, no key and no limit; the subscribe URLs are /calendar/moon-phases.ics, /calendar/full-moons.ics, /calendar/eclipses.ics, /calendar/seasons.ics and /calendar/sky-events.ics. Every instant is UTC and the subscriber's calendar localizes it; the feeds carry no location, so no rise/set times and no local eclipse visibility. Rolling window of last year through three years ahead. Meteor showers are deliberately absent pending a licence review of the shower catalogue. - [Supermoons & Micromoons](https://www.cyclecalcs.com/supermoons.html): every super and micro full moon for three years with engine-computed distances (including the invisible new-moon supermoons that raise king tides), a computed "closest full moon since" line, why published supermoon counts disagree (fixed 360,000 km line vs per-orbit rules), a true-scale size comparison, and honest treatments of the moon illusion, tides and the earthquake myth. - [Equinoxes & Solstices](https://www.cyclecalcs.com/seasons/): every equinox and solstice for seven years with exact UTC instants, plus a deep page per event (/seasons/december-solstice.html and siblings): the drifting dates, the equilux, the earliest-sunset puzzle, cultural history done as history, and a live panel computing the reader's own day length, earliest sunset/latest sunrise (solstices) or equilux date (equinoxes). - [Retrograde Right Now](https://www.cyclecalcs.com/retrograde.html): which planets are retrograde at this moment (a live status board recomputed on every visit from an engine-verified station catalog), every retrograde window of the current and next year with exact station instants localized to the reader's time zone, the share of time each planet spends retrograde, and the honest astronomy: routine geometry, no effects. - [Mercury Retrograde Dates](https://www.cyclecalcs.com/mercury-retrograde.html): every Mercury retrograde for a seven-year window with exact station times, the inferior conjunction inside each window, the 115.88-day synodic rhythm behind the three-a-year pattern, why published dates differ by a day (time zones), and what you can actually see. - [Venus Morning Star Tracker](https://www.cyclecalcs.com/venus-morning-star.html): whether Venus is the morning star or the evening star right now, computed live: current elongation, phase, brightness, apparent size, rise/set for the reader's location, an interactive 584-day cycle dial with a time scrubber, and every upcoming transition (conjunctions, greatest elongations, greatest brilliancy, stations) with countdowns. - [Mercury Morning Star Tracker](https://www.cyclecalcs.com/mercury-morning-star.html): the same live apparition tracker for Mercury's 116-day cycle: morning or evening sky right now, current elongation and brightness, and every upcoming conjunction and greatest elongation with countdowns. - [Planet Parade Tracker](https://www.cyclecalcs.com/planet-parade/): when several planets are visible together from your location, where to look and when, with a sky map and countdown. - [Planet Conjunctions](https://www.cyclecalcs.com/conjunctions/): per-pair guides with live dates of when two planets meet in the sky and how close they pass. - [Live Orrery](https://www.cyclecalcs.com/orrery.html): a top-down map of the solar system (Mercury to Pluto) for any date, Sun-centered or Earth-centered, with time scrubbing. - [Voyage: Fly the Solar System](https://www.cyclecalcs.com/voyage.html): a full-screen, pilotable 3D flythrough of the real solar system. Fly a spacecraft to the planets, Jupiter's Galilean moons and Saturn's rings at their real positions for the current date, with an enlarged view by default and a true-scale toggle, plus an illustrative asteroid belt. A planetarium show you can pilot, not a measurement. - [Star Names](https://www.cyclecalcs.com/star-names.html): the complete list of officially named stars: every proper name adopted by the IAU with its meaning, origin culture, designation, constellation and magnitude in one sortable table, an interactive whole-sky map of the named stars, how star naming actually works (Bayer letters to the Working Group on Star Names), and why sold "star names" have no standing. - [The 88 Constellations](https://www.cyclecalcs.com/constellations.html): the complete reference for all 88 IAU constellations: an interactive whole-sky map drawn from real catalogued star positions, a full table of names, meanings, genitives, pronunciations, families, brightest stars, areas and best months, per-constellation guides at stable anchors (e.g. #orion), the zodiac and ecliptic explained, and the eight constellation families. - [The Messier Catalog](https://www.cyclecalcs.com/messier.html): the complete reference for all 110 Messier objects: a whole-sky map with chart glyphs by type, a sortable table (M number, NGC id, type, constellation, magnitude, distance, size, best evening month, minimum equipment), a per-object observing guide at stable anchors (e.g. #m31) with verified discovery credits and star-hop directions, the Messier marathon explained, and honest coverage of the catalog's mistakes (M40, M73, M102). - [Sky hub](https://www.cyclecalcs.com/sky.html): the landing page that gathers everything in tonight's sky (the sky map, today, moon phases, eclipses, planet parades, conjunctions, the orrery, Voyage and the constellations). The site is organized in three pillars: Sky (above), Cycles (the planets, the concepts and the cycle reference below), and Calculators. About and other pages follow. ## Cycles: the planets, the Moon and the Sun The planet, Moon and Sun pages sit under the Cycles pillar. Each combines a live "tonight from your location" panel (position, constellation, rise/transit/set, brightness), a physical-fact table cited to the NASA NSSDCA planetary fact sheets, hand-written observing and cycles guides, and event dates (oppositions, elongations, conjunctions, phases, eclipses, seasons) computed years ahead at build time with Astronomy Engine. Dates on these pages are UTC. - [Sun, Moon & Planets hub](https://www.cyclecalcs.com/planets/): the index of all the world pages, with how they work and a naked-eye visibility FAQ. - [The Moon](https://www.cyclecalcs.com/the-moon.html): tonight's phase and rise/set, a 12-month phase calendar (one row per lunation), perigee/apogee, the next eclipses and supermoon, and the cycles behind phases, tides and eclipses. - [The Sun](https://www.cyclecalcs.com/the-sun.html): today's sunrise, sunset and day length for your location, every equinox and solstice for two years, Earth's perihelion and aphelion, the next solar eclipses, and the sunspot cycle, with unambiguous solar-viewing safety guidance. - [Earth](https://www.cyclecalcs.com/the-earth.html): our home planet as the keystone of every cycle here: its day and year, the 23.4 degree tilt that makes the seasons, perihelion and aphelion, the Moon and tides, and precession. - [Mercury](https://www.cyclecalcs.com/planets/mercury.html): morning-star and evening-star windows, greatest elongations, the 3:2 spin-orbit resonance, and how to catch it in twilight. - [Venus](https://www.cyclecalcs.com/planets/venus.html): whether it is the evening or morning star right now and until when, its greatest elongations and brilliancy, and the 8-year (13:8 near-commensurability) pattern. - [Mars](https://www.cyclecalcs.com/planets/mars.html): the next opposition with magnitude and constellation, month-by-month positions, and its retrograde loop. - [Jupiter](https://www.cyclecalcs.com/planets/jupiter.html): oppositions, month-by-month positions, the Galilean moons in binoculars, and the 19.86-year great-conjunction rhythm with Saturn. - [Saturn](https://www.cyclecalcs.com/planets/saturn.html): oppositions with the ring tilt for each, month-by-month positions, and when the rings open and close. - [Uranus](https://www.cyclecalcs.com/planets/uranus.html): how to actually find it (binoculars plus a chart), oppositions, and its sideways 97.8-degree spin. - [Neptune](https://www.cyclecalcs.com/planets/neptune.html): the planet found by mathematics in 1846, oppositions, and honest telescope guidance. - [Pluto](https://www.cyclecalcs.com/planets/pluto.html): the dwarf planet (IAU 2006), its 248-year orbit and 3:2 resonance with Neptune, and honest advice on observing it. ## Calculators - [Celestial Return Calculator](https://www.cyclecalcs.com/celestial-return-calculator.html): where the Sun, Moon and planets sat on any date, and when each returns to that point (solar, Jupiter, Saturn returns). - [Sunrise, Sunset & Day Length Calculator](https://www.cyclecalcs.com/sunrise-sunset-calculator.html): sunrise, sunset, solar noon, day length and civil/nautical/astronomical twilight for any location and date. - [Planetary Alignment Calculator](https://www.cyclecalcs.com/planetary-alignment-calculator.html): real dates of planetary conjunctions and oppositions, and how often three or more planets line up. - [Synodic-Period Calculator](https://www.cyclecalcs.com/synodic-period-calculator.html): the synodic period of two bodies, the average time between alignments, with conjunction dates. - [Date Calculator](https://www.cyclecalcs.com/date-calculator.html): add or subtract time from a date, or find the exact span between two dates. - [Telescope & Eyepiece Calculator](https://www.cyclecalcs.com/telescope-calculator.html): magnification, exit pupil, true field of view and the useful-magnification limits for any telescope and eyepiece, a "will it fit?" imaging field-of-view tab, and a "What can I see?" tab that rates showpiece targets (Easy, a stretch, or out of range) for your aperture, scope type and Bortle sky. - [Live Nautical Almanac & Sight Reduction](https://www.cyclecalcs.com/nautical-almanac.html): a live nautical almanac giving the Greenwich hour angle and declination of the Sun, Moon and planets, and a sextant sight worked into a line of position. - [Pythagorean Numerology Calculator](https://www.cyclecalcs.com/pythagorean-numerology-calculator.html): the classic Pythagorean letter values for words and names. - [Age on Other Planets](https://www.cyclecalcs.com/age-on-other-planets.html): your age in every planet's years (from the sidereal orbital periods) and in local solar days where one is defined, plus the date of your next birthday on each planet; distinct from the Celestial Return Calculator, which computes zodiac-return dates from sky positions. - [Weight on Other Planets](https://www.cyclecalcs.com/weight-on-other-planets.html): your weight on the Moon, every planet and the Sun from the site's NSSDCA-derived gravities, with mass-vs-weight explained and the giants honestly labeled "mean, at the cloud tops". - [Astrophotography Exposure Calculator](https://www.cyclecalcs.com/astrophotography-exposure-calculator.html): the 500 rule and the NPF rule side by side for any camera and lens, the star-trail length each exposure would record on your sensor, and why stacking or a tracker beats both rules. - [Local Sidereal Time](https://www.cyclecalcs.com/local-sidereal-time.html): a live LST clock for any longitude (Greenwich apparent sidereal time from the site's astronomy engine), the right ascension on your meridian right now, and how LST relates to GHA Aries. - [Kepler's Third Law Calculator](https://www.cyclecalcs.com/kepler-orbital-period-calculator.html): orbital period from semi-major axis and back, around the Sun, another star of any mass, or Earth (ISS, geostationary and lunar touchstones included). - [All calculators](https://www.cyclecalcs.com/calculators.html): the full hub. ## Cycles: the concepts (interactive lessons) These plain-language lessons sit under the Cycles pillar; each is built around an interactive visual. - [How Celestial Navigation Works](https://www.cyclecalcs.com/celestial-navigation.html): how sailors find position from the Sun and stars, the circle of equal altitude, crossing two for a fix, and the intercept method, shown interactively. - [Moon Phases](https://www.cyclecalcs.com/learn/moon-phases.html): why the Moon waxes and wanes over its 29.5-day synodic month. - [Tides](https://www.cyclecalcs.com/learn/tides.html): why the ocean rises twice a day (differential gravity and the two tidal bulges), the 24-hour-50-minute lunar day, and spring vs neap tides at the new, full, and quarter moons. - [Tidal Locking & Libration](https://www.cyclecalcs.com/learn/tidal-locking.html): why the Moon keeps one face toward Earth (synchronous rotation, once per 27.3-day orbit, from tidal friction), yet libration in longitude (up to about 7.9 degrees, from the elliptical orbit), latitude (about 6.7 degrees, from the axial tilt) and diurnal (about 1 degree) lets us see about 59 percent of the surface; the far side is not the dark side. - [Eclipses](https://www.cyclecalcs.com/learn/eclipses.html): why solar and lunar eclipses happen only near the lunar nodes. - [The Metonic Cycle](https://www.cyclecalcs.com/learn/metonic-cycle.html): why the Moon's phases return to nearly the same calendar dates every 19 years (19 tropical years = 6,939.60 d almost equal 235 synodic months = 6,939.69 d, off by ~2 h/cycle); 235 = 12x12 + 7x13 (seven leap months, the Hebrew leap rule); the Golden Number (year mod 19, plus 1) and Easter computus; distinct from the Saros (223 months, eclipses) and the Callippic (76 years). - [The Lunar Nodes and Lunar Standstills](https://www.cyclecalcs.com/learn/lunar-nodes.html): the 18.6-year regression of the Moon's tilted orbit and eclipse seasons, plus a live lunar-standstill clock (the Moon's monthly declination swing between a major standstill of about 28.6 degrees and a minor of about 18.3 degrees; last major peaked early 2025, next minor about 2034, next major about 2043). - [Apsidal Precession](https://www.cyclecalcs.com/learn/apsidal-precession.html): the 8.85-year turning of the Moon's orbit, plus planetary perihelion precession. - [Seasons & the Sun](https://www.cyclecalcs.com/learn/seasons.html): how Earth's axial tilt makes the equinoxes and solstices. - [Sidereal vs Solar Day](https://www.cyclecalcs.com/learn/sidereal-solar-day.html): why a solar day (24h) runs about 4 minutes longer than a sidereal day (23h 56m 04s), the extra ~1 degree Earth turns each day, the one extra rotation per year (366.24 vs 365.24 solar days), and why stars rise ~4 minutes earlier each night; kept distinct from the equation of time. - [Precession of the Equinoxes](https://www.cyclecalcs.com/learn/precession.html): the 25,920-year Great Year that turns the pole star and the ages. - [Equation of Time](https://www.cyclecalcs.com/learn/equation-of-time.html): why a sundial runs ahead of and behind the clock, and the analemma. - [The Sunspot Cycle](https://www.cyclecalcs.com/learn/sunspot-cycle.html): the 11-year Schwabe and 22-year Hale solar cycles. - [Kepler's Three Laws](https://www.cyclecalcs.com/learn/keplers-laws.html): the three rules every orbit obeys (ellipses with the Sun at one focus, equal areas in equal times, T squared equals a cubed), shown live with a true Kepler-equation orbit and every planet on the Law 3 line. - [Venus: the 8-Year Cycle](https://www.cyclecalcs.com/learn/venus-cycle.html): the 13:8 Venus-Earth near-commensurability (13 Venus orbits in 8 Earth years, giving five conjunctions) and the pentagram, the rose of Venus. - [The Galactic Year](https://www.cyclecalcs.com/learn/galactic-year.html): the Sun's ~230-million-year orbit of the Milky Way, ridden one lap from the first dinosaurs to today, in a two-view interactive. - [The Milankovitch Cycles](https://www.cyclecalcs.com/learn/milankovitch.html): eccentricity, axial tilt and precession, the orbital cycles that pace the ice ages by changing high-latitude summer sunlight; geometry-first, no climate forecast. - [Retrograde Motion](https://www.cyclecalcs.com/learn/retrograde.html): why Mars, Jupiter and Venus sometimes seem to drift backward against the stars, an illusion of Earth and the planet lapping one another, shown with an interactive sky loop. - [Meteor Showers](https://www.cyclecalcs.com/learn/meteor-showers.html): why showers return on the same nights each year (Earth crossing comet debris streams), the radiant as perspective, what ZHR really promises, and the Perseids, Geminids, Quadrantids and Eta Aquariids with their parent comets. - [Synodic vs Sidereal Periods](https://www.cyclecalcs.com/learn/synodic-sidereal.html): why the Moon orbits in 27.3 days but cycles through its phases in 29.5, the difference between sidereal and synodic periods, plus the five lunar months compared, with an interactive clock. - [All Learn topics](https://www.cyclecalcs.com/learn/): the full Learn index. ## Reference - [Cycles by Length](https://www.cyclecalcs.com/cycles.html): the definitive guide to astronomical cycles, all 65 from the day to the galactic year sorted by period, each with its meaning, plotted on one zoomable logarithmic timeline (the Cosmic Log-Timeline), grouped into families (rotation and tides, lunar months, the year and seasons, orbital and synodic periods, eclipse cycles, conjunctions, Milankovitch orbital cycles, solar activity, galactic and deep time), plus a [Cycle Length Calculator](https://www.cyclecalcs.com/cycles.html#calculator). - [Where Are We Now (Cosmic Clock)](https://www.cyclecalcs.com/cosmic-position.html): a live dashboard of today's position across a broad spectrum of astronomical cycles, computed from a precise model: the phase of the Moon and the true constellation it sits in front of, the progress of the solar year and the run-up to the next eclipse, where Venus is in its 1.6-year cycle, all the planets from Mercury to Pluto in their orbits, and how far the Jupiter-Saturn great conjunction has turned, alongside an honest estimate for the sunspot cycle, and known-state cards (a stated fact, not a live position) for the Great Year of precession and the galactic year. Gauges are grouped from the fastest rhythms to the slowest, each tier with a one-line framing, and the page has a one-tap share link. A compact six-dial version of this cosmic clock also lives on the homepage. - [Grand-Cycle Timeline](https://www.cyclecalcs.com/grand-cycle-timeline.html): a zoomable deep-time timeline of the long astronomical cycles, from precession (the pole stars) to the great conjunction and the Saros. - [Cycle Convergence and Resonance](https://www.cyclecalcs.com/cycle-convergence.html): astronomical cycles drawn as waves at their true periods, showing where they drift into and out of phase, plus a resonance lab that gives any pair's beat period (1/|1/P1-1/P2|), nearest small-integer ratio (the Venus-Earth 13:8 and Jupiter-Saturn 5:2 near-commensurabilities, the dynamically locked Neptune-Pluto 3:2 resonance), and the rosette it traces (the rose of Venus pentagram). The math of beats and near-commensurabilities, not a forecast. Per-cycle profile pages: one in-depth reference page per astronomical cycle, each with a live "where are we now" panel, the period broken into every unit, the governing math, cited constants, an FAQ, and the next occurrences computed years ahead. - [The synodic month](https://www.cyclecalcs.com/cycles/synodic-month.html): 29.530589 days, new moon to new moon, the month of phases behind every lunar calendar. - [The sidereal month](https://www.cyclecalcs.com/cycles/sidereal-month.html): 27.321661 days, the Moon's true orbit against the fixed stars. - [The anomalistic month](https://www.cyclecalcs.com/cycles/anomalistic-month.html): 27.554550 days, perigee to perigee, the Moon's distance cycle behind supermoons. - [The draconic month](https://www.cyclecalcs.com/cycles/draconic-month.html): 27.212221 days, node to node, the shortest lunar month and the clock behind every eclipse. - [The eclipse year](https://www.cyclecalcs.com/cycles/eclipse-year.html): 346.620 days, the Sun's return to a lunar node, which opens the eclipse seasons. - [The Saros](https://www.cyclecalcs.com/cycles/saros.html): 18 years 11 days, the cycle that makes eclipses repeat, and the next eclipse in each Saros series. - [The inex](https://www.cyclecalcs.com/cycles/inex.html): about 29 years (358 synodic months), the Saros's complement; together they classify every eclipse. - [The tritos](https://www.cyclecalcs.com/cycles/tritos.html): about 11 years (135 synodic months), one inex minus one Saros, a shorter eclipse-recurrence cycle. - [The exeligmos](https://www.cyclecalcs.com/cycles/exeligmos.html): about 54 years, three Saroses, which return an eclipse to nearly the same longitude on Earth. - [The Metonic cycle](https://www.cyclecalcs.com/cycles/metonic-cycle.html): 19 years, which returns the Moon's phases to nearly the same calendar dates (the golden number). - [The Callippic cycle](https://www.cyclecalcs.com/cycles/callippic.html): 76 years (four Metonic cycles less a day), a sharper lock of the Moon's phases to the calendar. - [The lunar nodal cycle](https://www.cyclecalcs.com/cycles/lunar-nodal-cycle.html): 18.61 years, the regression of the nodes that drives the major and minor lunar standstills. - [The lunar standstill](https://www.cyclecalcs.com/cycles/lunar-standstill.html): the 18.6-year swing to the Moon's widest (about 28.6 deg) and narrowest (about 18.3 deg) monthly range, marked at Stonehenge. - [The tropical year](https://www.cyclecalcs.com/cycles/tropical-year.html): 365.2422 days, equinox to equinox, the year of the seasons and the calendar. - [The anomalistic year](https://www.cyclecalcs.com/cycles/anomalistic-year.html): 365.259636 days, perihelion to perihelion, the longest year and Earth's distance-from-Sun cycle. - [The sidereal year](https://www.cyclecalcs.com/cycles/sidereal-year.html): 365.25636 days, Earth's true orbit against the stars, about 20 minutes longer than the tropical year. - [The great conjunction](https://www.cyclecalcs.com/cycles/great-conjunction.html): 19.86 years, the Jupiter-Saturn meeting, its trigon, and the next conjunction in 2040. - [The Venus pentagram](https://www.cyclecalcs.com/cycles/venus-pentagram.html): about 8 years, the 13:8 near-commensurability whose five inferior conjunctions trace a star. - [The sunspot cycle](https://www.cyclecalcs.com/cycles/sunspot-cycle.html): about 11 years (the Schwabe cycle), an observed rhythm; Solar Cycle 25 is past its 2024-2025 maximum. - [The Hale cycle](https://www.cyclecalcs.com/cycles/hale.html): about 22 years, two sunspot cycles, the Sun's full magnetic-polarity cycle. - [Axial precession (the Great Year)](https://www.cyclecalcs.com/cycles/axial-precession.html): about 25,920 years, the wobble that carries the equinox and pole star around the sky. ## Developers (widgets + API) - [Developer hub](https://www.cyclecalcs.com/developers.html): the landing page for building with CycleCalcs: three worked build guides (a nightly sky report bot, an AI observing assistant over MCP, the live sky on your own website), a summary of every developer tool (the 29-endpoint API, the 11-tool MCP server, the widgets, the machine-readable contracts and the CC0 bulk datasets), and a status table of everywhere the tools are published (RapidAPI, the official MCP Registry, Smithery, APIs.io, npm, GitHub, Zenodo; a WordPress plugin, a Python SDK and a Postman collection are labeled coming soon). - [Build guide: a nightly sky report bot](https://www.cyclecalcs.com/developers/sky-report-bot.html): one GET to /v2/today and about forty lines of tested Node post tonight's Moon, the planets worth looking at and the darkness verdict to Discord or Slack every evening; includes a GitHub Actions schedule and a dark-window upgrade that picks the best observing night of the next two weeks. No key needed. - [Build guide: an AI observing assistant](https://www.cyclecalcs.com/developers/ai-observing-assistant.html): connect Claude or any MCP client to https://www.cyclecalcs.com/mcp (one command in Claude Code), prove the wire with a keyless curl of tools/list, and ask questions the eleven read-only tools answer from computed ephemerides; tool calls are metered by a free RapidAPI Basic key at 5,000 requests a day. - [Build guide: the live sky on your website](https://www.cyclecalcs.com/developers/sky-on-your-site.html): five recipes from cheapest up: the two-line iframe embed, the no-iframe shadow-root moon widget, WordPress via a Custom HTML block today, the cyclecalcs-widget web component from npm for React and friends, and calling the open-CORS API directly for one sentence in your own typography. - [Embed our sky widgets](https://www.cyclecalcs.com/embed.html): seven free embeddable widgets for any website: a live moon phase card, a sunrise-and-sunset card, a next-eclipse countdown, a planet parade tracker, a what's-up-tonight card (the Moon and the planets up after dusk), a cosmic clock (where we are in each major cycle), and a newer moon widget that renders inside the host page rather than in an iframe. One small copy-paste snippet, no account or API key; the six iframe widgets compute the astronomy in the visitor's browser, and the host-DOM moon widget reads one cached answer from the public API. - [The CycleCalcs API](https://www.cyclecalcs.com/api.html): a free astronomy API: 29 /v2 endpoints of interpreted answers (moon phase, sunrise and sunset, rise and set, twilight, eclipses, seasons, apsides, lunar nodes, retrogrades, Mercury and Venus apparitions, conjunctions, separation, sidereal time, the equation of time, libration, the Galilean moons, cycles, sky quality, place lookup), computed live for any date and place, no key and no signup at 5,000 requests a day, with a published ladder of paid tiers (Pro, Ultra, Mega) for higher volume, an in-page playground, and machine-readable contracts at /v2/openapi.json and /v2/conventions. The frozen version 1 endpoints are documented at https://www.cyclecalcs.com/api/v1.html. - [MCP server](https://www.cyclecalcs.com/api/mcp.html): the API as a Model Context Protocol server at https://www.cyclecalcs.com/mcp with eleven read-only astronomy tools for Claude and other MCP clients (spec revisions 2026-07-28 and the 2025 handshake), authenticated by the same RapidAPI keys as the REST API and metered identically. ## About - [About CycleCalcs](https://www.cyclecalcs.com/about.html): what the site is and who makes it. - [Press Room](https://www.cyclecalcs.com/press.html): for journalists on deadline. Verified facts about the site and the entity, downloadable logos and wordmarks, a standing free offer to compute eclipse contact times, altitudes, obscuration or rise and set for any location on Earth and any date from 1700 to 2200, the CC0 grant that lets any computed value be quoted without permission or attribution, the DOI for citing the bulk datasets, and three things reporters routinely get wrong (greatest eclipse is not greatest duration; supermoon has no official definition; 99 percent obscuration is not almost-totality). - [Methodology & Sources](https://www.cyclecalcs.com/methodology.html): how every figure is computed (the MIT-licensed Astronomy Engine, in the browser), the accuracy envelope (well under a degree, roughly 1700 to 2200), and the data sources and references. - [Stargazing Gear We Recommend](https://www.cyclecalcs.com/gear.html): an honest, always-current list of stargazing gear that pairs with the tools, including ISO 12312-2 eclipse glasses, beginner telescopes, binoculars and star atlases. - [Privacy](https://www.cyclecalcs.com/privacy.html): privacy policy, including how "use my location" and place search work. - [Terms of Sale](https://www.cyclecalcs.com/terms-of-sale.html): the terms for the one paid product, the 2027 moon calendar: what nine dollars buys, delivery by private link, a full refund within 30 days for any reason, and the licence (print freely, do not redistribute the file; the computed values themselves are public domain).