ISS Transits Across the Sun and Moon

Published October 12, 2026 · Updated October 12, 2026

What a transit is

A transit happens when the International Space Station passes exactly in front of the disk of the Sun or the Moon, as seen from where you're standing. For an instant, the station's silhouette, solar panels and main truss included, stands out against the bright disk. It's one of the most sought-after images in amateur astrophotography, and one of the hardest to get.

Unlike a regular pass, which anyone can see with the naked eye, a transit demands three things: being in exactly the right place, at exactly the right second, with gear ready to shoot or record at that instant.

Why it lasts less than a second

The Sun and the Moon are each about 0.5° across in the sky. When the ISS passes high, it covers a little more than one degree per second, so it crosses the disk in half a second or less. If it's lower and farther away, it moves more slowly across the sky and the transit can stretch to just over a second, but never much longer.

With the naked eye, without magnification, it's practically impossible to notice: the station spans less than one arcminute, a sixtieth of a degree, and against the disk of the Sun or Moon it's a tiny speck that's gone in the blink of an eye. That's why transits are photographed or recorded on video and viewed afterward, frame by frame.

Why it's only visible from a strip a few kilometers wide

For the station to line up in front of the disk, the line running from your eyes to the Sun (or Moon) has to cross the orbit exactly where the ISS is at that moment. Move just a few kilometers and that line passes in front of or behind the station, and there's no transit.

You can work out the width of the strip with some simple math: if the ISS is about 600 km (370 miles) from you, the half-degree disk covers about 5 km (3 miles) at that distance. That's roughly the width of the corridor on the ground from which the transit is visible. At the center of the strip, the station crosses the middle of the disk; at the edges, it just grazes it.

How they're predicted

Transits are calculated from the same orbit data we use for passes, but with much greater precision: the observer's position has to be known to within tens of meters, and the time to the second. Our tracker is built for naked-eye passes and doesn't calculate transits. For that there are specialized calculators, such as Transit Finder, that draw the visibility strip on a map along with the exact time for each point.

The usual steps are:

1. Look for opportunities within 30 to 100 km (20 to 60 miles) of home, several days ahead.
2. Pick a spot as close as possible to the center line of the strip, with the Sun or Moon in clear view above the horizon.
3. Run the numbers again on the day. The station's orbit is adjusted every so often with engine burns, and the prediction can shift by a few seconds or a few hundred meters.
4. Sync your clock to a precise time reference, such as GPS time or a time server.

Safety: never look at the Sun without a filter

There are no shortcuts here. Looking at the Sun through binoculars, a telescope or a camera viewfinder without a proper solar filter can permanently damage your eyes in a fraction of a second. Sunglasses, X-ray film and smoked glass won't protect you either.

• For naked-eye viewing, use only eclipse glasses certified to the ISO 12312-2 standard.
• For telescopes, binoculars and lenses, use a certified solar filter that covers the entire front of the instrument, never one that goes on the eyepiece.
• With a camera, frame the shot on the rear screen, not through the optical viewfinder, and never leave your gear pointed at the Sun without a filter, even for a moment.

The Moon poses no risk at all: you can photograph it without a filter.

Gear and settings

The ISS silhouette is small, so you need plenty of focal length: from 600 mm you can already make out its shape, and with a 1,000 to 2,000 mm telescope the panels show up clearly.

The simplest approach is to start recording video a few seconds before the predicted time and stop a few seconds after. If you shoot in burst mode, start two or three seconds early, because the camera's buffer fills up fast. Focus ahead of time on the edge of the disk or on sunspots, or on craters in the case of the Moon, and don't touch anything in the last minute.

If it's your first time, the Moon is a good place to start: there's no risk to your eyes, and nighttime transits can be set up without rushing. And if you haven't yet photographed the station on a regular pass, start with our guide on how to photograph the ISS.

Frequently asked questions

How long does an ISS transit last?

Usually less than a second. The Sun and the Moon are half a degree across, and the ISS covers about one degree per second when it passes high, so it crosses the disk in half a second or a little more.

Can you see a transit with the naked eye?

Across the Sun, never without certified eclipse glasses. Across the Moon it's possible in theory, but the station is tiny against the disk and gone in the blink of an eye, so in practice it's recorded with a camera and viewed afterward.

Why do I have to travel to see one?

Because a transit is only visible from a strip a few kilometers wide. The usual approach is to look for opportunities within a few dozen kilometers and drive to the center line.

Does your tracker calculate transits?

No. The tracker calculates naked-eye passes. Transits require specialized calculators that work with your exact position and the time down to the second.

Do I need a telescope?

To make out the station's shape, yes, or a telephoto lens of at least 600 mm. With shorter lenses, the ISS shows up as a dot against the disk.