# Eclipse Simulator - Umbra and Penumbra, Saros Cycle, Eclipses 2026–2035

> See why eclipses are total or annular with real Sun, Moon and Earth sizes: shadow cones, magnitude, lunar eclipse durations, Saros series and a 2026–2035 table.

- URL: https://qilingtools.com/en/physics/eclipse
- Category: Physics Tools (https://qilingtools.com/en/physics)
- Tags: [Physics](https://qilingtools.com/en/tags/physics), [Education](https://qilingtools.com/en/tags/education)
- Last updated: 2026-10-29
- Price: Free, no sign-up
- Privacy: Runs locally in the browser; files are never uploaded

This tool explains eclipses with real sizes and distances. Drag the Moon between perigee and apogee to see whether its umbra reaches the ground, giving a total or an annular eclipse, with the shadow width on Earth, the magnitude and the obscuration. The lunar eclipse page draws Earth's umbra and penumbra to scale at the Moon's distance, computes magnitudes and how long each phase lasts, and explains the red colour. It also lists every eclipse of any year with Meeus' algorithm, shows its Saros series, and gives a table of notable eclipses for 2026–2035.

## How to use

1. On the geometry tab, drag the Moon or use the sliders for the Earth–Moon and Earth–Sun distances and watch the umbra tip
2. Move the Moon across the Sun with the offset slider or Play to see the magnitude and obscuration
3. On the lunar tab, set the closest approach γ and play the Moon through Earth's shadow
4. Enter a year on the Seasons & Saros tab to list its eclipses, click one for its Saros series, and see the 2026–2035 table

## Features

- Shadow cones from real radii and distances: umbra length, umbra/antumbra width on the ground, penumbra size
- Animated partial phases with live magnitude and obscuration, plus the corona at totality
- Lunar eclipses to scale: umbral and penumbral magnitudes, durations and the Danjon scale
- Meeus chapter 54: all eclipses in any year with type, γ and magnitude
- Saros calculator showing four members either side, with the 223/242/239 month coincidence
- 2026–2035 eclipse table from the NASA catalogue, cross-checked by independent computation

## FAQ

### Why are some solar eclipses total and others annular?

The Moon's umbra, the cone where the Sun is completely hidden, is about L = R☾ × Sun–Moon distance / (R☉ − R☾) ≈ 374,000 km long, while the distance from the Moon's centre to Earth's surface ranges from about 350,000 to 400,000 km. Near perigee the umbra reaches the ground and makes a path of totality one or two hundred kilometres wide. Near apogee the tip falls short, the ground lies in the antumbra, the Moon looks smaller than the Sun and you see a ring. When the tip sits right at the surface, part of the track is total and part annular: a hybrid eclipse.

### What is the difference between magnitude and obscuration?

Magnitude is the fraction of the Sun's diameter covered; obscuration is the fraction of its area covered. In a partial eclipse the same magnitude means a smaller obscuration: at magnitude 0.5 only about 39% of the area is covered. A total eclipse has magnitude above 1 (the Moon looks bigger than the Sun); an annular one has magnitude below 1, and obscuration of at most (Moon/Sun diameter)². The eye adapts so well that the sky only darkens noticeably beyond about 90% obscuration.

### Why is the Moon red during a total lunar eclipse?

Inside Earth's umbra the Moon doesn't vanish. Sunlight passing through Earth's atmosphere loses its blue light to Rayleigh scattering, and the remaining red light is refracted into the shadow, as if every sunrise and sunset on Earth lit the Moon at once. Volcanic dust and clouds make it darker; the Danjon scale runs from L0 (almost invisible) to L4 (bright copper-red). The umbra at the Moon's distance is about 2.7 Moon diameters across, so totality can last up to about an hour and three quarters.

### What is the Saros cycle?

A Saros is 223 synodic months, about 6,585.32 days or 18 years 11 days 8 hours. It is almost exactly 242 draconic months and 239 anomalistic months, so the Sun, Moon and lunar node line up again with the Moon at nearly the same distance, and a very similar eclipse recurs. The extra ≈8 hours means Earth turns an extra third, shifting the track about 120° west; after three Saros (about 54 years and a month) it returns to similar longitudes.

### Why isn't there an eclipse every month?

The Moon's orbit is tilted about 5.1° to the ecliptic, so most new moons pass above or below the Sun and most full moons miss Earth's shadow. Eclipses happen only when the Sun is near one of the Moon's nodes. These eclipse seasons last a bit over a month and come about every 173 days, roughly twice a year. So every year has at least two solar eclipses, and at most five solar eclipses or seven eclipses in total.

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