Eclipse Calculator
Calculate the dates and visibility of upcoming solar and lunar eclipses for your location. Enter values for instant results with step-by-step formulas.
Calculator
Adjust values & calculateSolar Eclipses
Lunar Eclipses
Formula
Eclipses repeat in predictable cycles. The Saros cycle of 6,585.32 days (approximately 18 years, 11 days) results from the alignment of three lunar periods: 223 synodic months, 242 draconic months, and 239 anomalistic months, producing geometrically similar eclipses.
Last reviewed: December 2025
Worked Examples
Example 1: Eclipses Visible from North America 2025-2028
Example 2: Next Total Solar Eclipse
Background & Theory
The Eclipse Calculator applies the following established principles and formulas. Astronomy and space science rely on a set of precisely defined physical relationships that allow distances, sizes, motions, and energies of celestial objects to be calculated from observational data. Kepler's three laws of planetary motion, derived empirically in the early seventeenth century, describe elliptical orbits, equal areas swept in equal times, and the harmonic law T² = a³, where T is the orbital period in Earth years and a is the semi-major axis in astronomical units (AU). This relationship holds for any object orbiting the Sun and can be generalized using Newton's law of gravitation. Distances in astronomy are expressed in multiple units: one light-year equals approximately 9.461 × 10¹⁵ meters, one parsec equals 3.086 × 10¹⁶ meters or about 3.26 light-years, defined as the distance at which one AU subtends one arcsecond of parallax. Angular size is calculated as θ = 206,265 × (d / D) arcseconds, where d is the physical diameter and D is the distance. The stellar magnitude system uses Pogson's formula: m1 − m2 = −2.5 × log10(F1 / F2), where F represents flux. Each magnitude step corresponds to a flux ratio of approximately 2.512, meaning a first-magnitude star is 100 times brighter than a sixth-magnitude star. Hubble's Law relates recessional velocity to distance: v = H₀d, where the Hubble constant H₀ is approximately 70 km/s/Mpc. Escape velocity from any body is given by v = √(2GM/r), yielding 11.2 km/s for Earth. Orbital period for a circular orbit follows T = 2π√(r³/GM). Luminosity and distance are linked by the inverse square law: F = L / (4πd²). Stars are classified by spectral type using the mnemonic OBAFGKM, corresponding to surface temperatures from approximately 30,000 K (O-type) to under 3,500 K (M-type). Each type reflects characteristic absorption spectra tied to ionization states of elements in the stellar photosphere.
History
The history behind the Eclipse Calculator traces back through the following developments. The history of astronomy is one of progressive scale — each era expanding humanity's conception of the universe's size and structure. The Copernican revolution of 1543, when Nicolaus Copernicus published De revolutionibus orbium coelestium, displaced Earth from the center of the cosmos and placed the Sun at the center of the planetary system. Decades later, Galileo Galilei turned a Dutch-invented telescope toward the sky in 1609, discovering the moons of Jupiter, the phases of Venus, and the cratered surface of the Moon — observations that provided compelling evidence for the heliocentric model and led to his conflict with the Catholic Church. Johannes Kepler, working from Tycho Brahe's meticulous naked-eye observations, derived his three laws of planetary motion between 1609 and 1619. Isaac Newton unified celestial and terrestrial mechanics with his law of universal gravitation in 1687, explaining the cause behind Kepler's empirical laws and enabling precise prediction of planetary positions. The eighteenth and nineteenth centuries brought systematic sky surveys, stellar parallax measurements, and the discovery that the Milky Way is itself a galaxy among many. Edwin Hubble's 1929 observations using the 100-inch Hooker Telescope at Mount Wilson demonstrated that galaxies are receding from us at velocities proportional to their distance — the first direct evidence for an expanding universe and the empirical basis for Big Bang cosmology. NASA was founded in 1958 following the Sputnik shock, and the Apollo 11 mission landed humans on the Moon on July 20, 1969. The Hubble Space Telescope, launched in 1990, revolutionized observational astronomy by operating above Earth's atmosphere and producing imagery from ultraviolet to near-infrared wavelengths. The first confirmed exoplanet around a Sun-like star was detected in 1995 by Michel Mayor and Didier Queloz using the radial velocity method. The James Webb Space Telescope, launched in December 2021 and fully operational by 2022, extended infrared observations to probe the earliest galaxies formed after the Big Bang.
Frequently Asked Questions
Formula
Saros Cycle = 6,585.32 days (223 synodic months)
Eclipses repeat in predictable cycles. The Saros cycle of 6,585.32 days (approximately 18 years, 11 days) results from the alignment of three lunar periods: 223 synodic months, 242 draconic months, and 239 anomalistic months, producing geometrically similar eclipses.
Worked Examples
Example 1: Eclipses Visible from North America 2025-2028
Problem: Find all eclipses occurring between 2025 and 2028 that may be visible from a latitude of 40 degrees North (United States).
Solution: Filter eclipse database for years 2025-2028\nCheck visibility regions against 40N latitude\nSolar eclipses: match regions including Americas, North America, Arctic\nLunar eclipses: visible from night side during eclipse\n2025: 2 solar (partial), 2 lunar (total)\n2026: 2 solar, 2 lunar\n2027: 2 solar, 2 lunar\n2028: 2 solar, 3 lunar
Result: Approximately 8-10 eclipses potentially visible from latitude 40N between 2025-2028, including multiple total lunar eclipses
Example 2: Next Total Solar Eclipse
Problem: When is the next total solar eclipse after 2025?
Solution: Searching known eclipse data after 2025:\nAugust 12, 2026: Total Solar Eclipse visible from Arctic, Greenland, Spain\nAugust 2, 2027: Total Solar Eclipse visible from N. Africa, Middle East\nJuly 22, 2028: Total Solar Eclipse visible from Australia, New Zealand\nSaros cycle confirms these dates align with predicted eclipse series
Result: Next total solar eclipse: August 12, 2026, visible from Arctic regions, Greenland, and Spain
Frequently Asked Questions
What causes a solar eclipse?
A solar eclipse occurs when the Moon passes directly between the Sun and Earth, casting a shadow on Earth surface. This alignment can only happen during a new moon when the Moon is on the same side of Earth as the Sun. However, eclipses do not happen at every new moon because the Moon orbital plane is tilted about 5 degrees relative to Earth orbital plane around the Sun. Solar eclipses only occur when the new moon coincides with the Moon crossing the ecliptic plane at points called lunar nodes. The remarkable coincidence that the Moon apparent size closely matches the Sun apparent size, despite the Sun being 400 times larger but also 400 times farther away, is what makes total solar eclipses so spectacular.
What causes a lunar eclipse?
A lunar eclipse occurs when Earth passes between the Sun and the Moon, causing Earth shadow to fall on the Moon surface. Unlike solar eclipses, lunar eclipses can only happen during a full moon when the Moon is on the opposite side of Earth from the Sun. Earth shadow has two parts: the darker inner shadow called the umbra and the lighter outer shadow called the penumbra. A total lunar eclipse occurs when the Moon passes entirely through the umbra, often turning a dramatic red color due to sunlight being filtered and refracted through Earth atmosphere. Lunar eclipses are visible from the entire night side of Earth, making them far more commonly observed than solar eclipses from any given location.
Why does the Moon turn red during a total lunar eclipse?
During a total lunar eclipse, the Moon often appears deep red or copper-colored, earning the popular name blood moon. This coloring occurs because Earth atmosphere bends and filters sunlight around the planet edges and onto the Moon surface. Short-wavelength blue light is scattered away by the atmosphere through the same Rayleigh scattering process that makes our sky blue, while longer-wavelength red light passes through and is refracted toward the Moon. The exact shade depends on atmospheric conditions at the time. Volcanic eruptions can inject particles into the upper atmosphere that darken the eclipse significantly, while clear atmospheric conditions produce a brighter, more orange-red appearance. Astronomers rate lunar eclipse darkness on the Danjon scale from 0 to 4.
Is it safe to look at an eclipse?
Looking directly at a solar eclipse with the naked eye is extremely dangerous and can cause permanent eye damage or blindness. The Sun intense ultraviolet and infrared radiation can burn the retina even when most of the Sun is covered by the Moon. Special eclipse glasses with ISO 12312-2 certified solar filters must be used during partial and annular phases. The only time it is safe to look without protection is during the brief period of totality in a total solar eclipse when the Sun disk is completely covered. Lunar eclipses, by contrast, are completely safe to observe with the naked eye, binoculars, or telescopes without any filters, since you are only viewing reflected and refracted sunlight that is dramatically dimmed.
How do eclipse seasons work?
Eclipse seasons are periods roughly 34 to 38 days long when the Sun is close enough to one of the Moon orbital nodes for eclipses to occur. There are two eclipse seasons per year, spaced about 173 days apart. At least one solar eclipse must occur during each eclipse season, and often a lunar eclipse will occur about two weeks before or after. Because 173 days is less than half a year, eclipse seasons gradually shift earlier each year, completing a full cycle in about 18.6 years. During each eclipse season, there are typically two eclipses (one solar and one lunar), giving a minimum of four eclipses per year. In some years, the geometry allows for five, six, or rarely seven eclipses.
Is my data stored or sent to a server?
No. All calculations run entirely in your browser using JavaScript. No data you enter is ever transmitted to any server or stored anywhere. Your inputs remain completely private.
References
Reviewed by Daniel Agrici, Founder & Lead Developer · Editorial policy