Solar Eclipse Visibility Calculator

What this tool checks, and how

Solar eclipses occur when the Moon passes directly between the Sun and Earth, casting a shadow on the planet’s surface. The darkest central part of the shadow, called the umbra, produces a total eclipse for locations it touches. Surrounding this is the penumbra, where a partial eclipse is visible. Predicting exact visibility traditionally requires complex celestial mechanics, but for educational purposes, this calculator uses a simplified geometric model. Each upcoming eclipse is represented by a central reference point along the path of totality and approximate radii for the total and partial regions. By computing the great-circle distance between your coordinates and the reference point, the script determines whether you fall within the total or partial boundary.

The distance calculation employs the well-known haversine formula, which relates spherical coordinates to linear distance on a sphere. Let $\varphi$ and $\lambda$ denote latitude and longitude in radians for two points. The surface distance $d$ is:

Here, $R$ represents Earth’s mean radius, approximately 6,371 kilometers. If the computed distance is less than the radius representing the umbra, the calculator reports a total eclipse. If it falls between the umbral and penumbral radii, a partial eclipse is indicated. Distances beyond both radii yield a result of no visible eclipse for that event.

The eclipses this tool knows about

The following table lists the eclipses currently included in this tool. The radii are coarse approximations intended for educational use; actual eclipse paths are irregular and require detailed astronomical data to model precisely.

Each row provides a representative point near the eclipse’s central path. For example, the April 8, 2024 event cuts across North America from Mexico to Canada; we use a reference near Texas as a midpoint. The Aug 12, 2026 eclipse sweeps across Greenland, Iceland, and Spain, while the Aug 2, 2027 eclipse journeys over North Africa and the Arabian Peninsula. Actual visibility at your site depends on many factors including local weather, terrain, and the precise geometry of the Moon’s shadow. Nevertheless, the table offers a quick way to gauge potential viewing opportunities.

Why totality tracks are so narrow

Understanding why solar eclipses are so geographically limited requires a brief tour of celestial geometry. The Moon’s diameter is roughly 3,474 kilometers, while the Sun’s is about 1.39 million kilometers. Despite this vast difference, the Sun is also about 400 times farther away, so the two bodies appear nearly the same size in Earth’s sky. A total eclipse occurs when the Moon’s apparent diameter slightly exceeds that of the Sun. The region experiencing totality is typically less than 200 kilometers wide, racing across Earth’s surface at thousands of kilometers per hour. Outside this narrow track, observers see only a partial eclipse, with a portion of the Sun obscured.

The size of the umbra depends on the Moon’s distance from Earth and the orbital geometry at the time. When the Moon is near apogee, its shadow may not reach Earth, resulting in an annular eclipse where a ring of sunlight remains visible. The calculator focuses on total eclipses, but the same distance approach could be extended to annular events by assigning appropriate radii. Astronomers typically use complex ephemerides and numerical integrations to predict exact paths, but simplified models illustrate the main concepts effectively for educational outreach.

In addition to distance, observers must consider the local circumstances of eclipse timing. The shadow reaches different locations at different times, and some areas experience only a partial eclipse because the Sun sets before totality arrives or rises after the shadow has passed. Detailed predictions require accounting for Earth’s rotation and the relative motions of the Sun and Moon. While this calculator cannot provide timing information, it introduces the spatial aspect of eclipse visibility, which is a crucial first step in planning an observation.

Entering your coordinates

To use the tool, enter your coordinates in decimal degrees. Positive latitudes indicate the Northern Hemisphere, negative latitudes the Southern. Longitudes east of the prime meridian are positive; western longitudes are negative. Choose an eclipse from the dropdown list and click Check Visibility. The script converts inputs to radians, applies the haversine formula to compute distance to the event’s reference point, and compares the result with stored radii. The output states whether you can expect a total eclipse, a partial eclipse, or no event. You can copy the textual result for quick sharing with friends or to include in planning notes.

Because the model uses rough radii, its results should be interpreted cautiously. Being within 100 kilometers of the reference point does not guarantee totality if you are outside the actual path, which may curve or shift. Conversely, some locations outside the listed partial radius may still experience a shallow partial eclipse. The purpose is to provide a first approximation that encourages further exploration using authoritative resources such as NASA’s eclipse maps or dedicated astronomy software.

Turning a result into an observing plan

Witnessing a solar eclipse safely requires proper eye protection. During partial phases, observers must use certified solar filters or projection techniques to avoid eye damage. Only during the brief moment of totality is it safe to view the Sun directly, and even then, caution is warranted because the bright photosphere returns quickly. Weather conditions also play a critical role; clouds can obscure the event entirely. Many eclipse chasers travel long distances seeking clear skies. If the calculator suggests a partial eclipse from your home, consider whether traveling into the path of totality is feasible to experience the dramatic full corona.

Planning ahead ensures a successful experience. Lodging near the path of totality often sells out months in advance, and traffic can be heavy on eclipse day. Pack necessary equipment such as solar glasses, tripods, and cameras, and familiarize yourself with camera settings for photographing the event. The table below outlines common items and their purposes:

By considering equipment and logistics alongside the spatial analysis provided by this calculator, you can maximize your chances of a memorable eclipse experience.

A worked example: Cleveland and the 2024 eclipse

Cleveland, Ohio sits near 41.5°N, 81.7°W and lay squarely inside the path of totality on April 8, 2024. Feed those coordinates into the tool with the 2024 event selected. The haversine distance to the model's Texas reference point (30°N, 96°W) works out to roughly 1,900 km — well beyond the 100 km "total" radius but comfortably inside the 4,000 km "partial" radius, so the tool reports a partial eclipse.

That result is worth sitting with, because Cleveland actually saw a full four minutes of totality. It is the clearest illustration of the model's core limitation: a single reference point plus a circular radius cannot reproduce a 3,000-mile diagonal shadow track. The 100 km total radius only "lights up" for coordinates within a hundred kilometers of the one stored midpoint, whereas the real umbra swept from Mazatlán to Newfoundland. Read a partial-or-better result here as "this eclipse crosses your continent, now go check a real path map," not as a verdict on totality.

Where this model breaks down

Each eclipse is compressed into one latitude/longitude point and two circular radii, so the tool answers a coarse question — is this event roughly in your part of the world — rather than the precise one. A location can be flagged "partial" while genuinely enjoying totality (as Cleveland shows above), or flagged "total" only when it happens to sit near the stored midpoint. The radii are round numbers chosen for teaching, not fitted to the actual umbral and penumbral geometry, which is an elongated, curving band a couple of hundred kilometres wide at most.

The model is also silent on everything time-related: it will not tell you whether the Sun is above your horizon when the shadow arrives, how long totality lasts, or the local start and end times. It ignores annular eclipses, weather, and elevation. Before you book travel or promise anyone four minutes of darkness, confirm your spot against an authoritative source such as NASA's eclipse maps or Xavier Jubier's interactive path viewer, which model the Besselian elements properly.