How to Use the ISS Pass Predictor
Find the next International Space Station pass worth going outside for, with its time, compass bearings, brightness and path across your sky.
What this tool answers
When will the ISS cross my sky, and which of those passes can I actually see? The tool lists every pass that climbs at least 5° above your horizon in the next 21 days. It labels each one by sky brightness and sunlight on the station, and searches 45 days ahead for passes worth a trip outside. Times follow your pin's time zone, not your device's, and carry its label. For a pin in Guyana that is America/Guyana, labelled GMT-4 (UTC-4, no daylight saving).
What you see on the screen
- Location bar: your pin's place name and coordinates, with My location and Change buttons.
- Next worth going out: date, peak time, countdown, peak elevation, compass direction and magnitude, then Appear (time and direction), Gone (time and minutes) and Sky (the label), and a Show path & sky button.
- Best upcoming: a second block when a better pass falls within 7 days.
- Add to calendar: downloads a calendar file for the Next worth going out pass.
- Upcoming: the pass list, with a Spottable only checkbox.
- Sky path and Sky sim: two charts for the selected pass. On a phone they sit in tabs under the list.
- A Tip box with a count such as "5/9 near-term hard to see". On a wide screen an Observer box sits above it.
- Next step links: Email sky alerts, Check your Bortle, What's in the sky and Stargazing weather.
Step by step
- Open the ISS Pass Predictor.
- Check the place name. Tap My location for GPS, or Change to pick a Guyana Presets town or type Manual Coordinates.
- Wait for "Finding passes worth going outside for" to give way to the Next worth going out card.
- Tap Show path & sky to draw that pass in the charts.
- Tick Spottable only to hide passes you cannot see.
- Tap any row to draw it in the charts and show why it is easy or hard to see, with its Appear and Gone times.
- Tap Add to calendar to save the pass.
- Go outside a few minutes before the Appear time and face the Appear direction.
The ISS Pass Predictor for Georgetown with a dated orbit: the next pass worth going out for, the best one, the list and Spottable only.
The coming passes for Georgetown or Lethem as the predictor finds them, with its Next worth going out pick and each pass's path on a compass dial.
How to read the results
| Sky label | What it means | Can you see it? | |---|---|---| | Good to spot | Sun at least 6° below your horizon at the peak, station in sunlight | Yes, the best case | | Twilight | Sun between about 0.8° and 6° below the horizon, station in sunlight | Maybe, if the sky is clear | | Daylight | Sun up | No | | Near sun | Station within 35° of the Sun while the Sun is up or less than 12° down | No, and keep optics away from the Sun | | Eclipsed | Station in Earth's shadow, shown as "unlit" | No |
Good to spot and Twilight count as spottable. A pass is worth going out when it is spottable, peaks at 15° or higher, lasts at least 3 minutes and reaches magnitude 0.5 or brighter. If none qualifies, the card falls back to the next spottable pass lasting 2 minutes or more and reads Next worth going out · marginal. If nothing is spottable in 45 days, it says "None practical in the next 45 days". Best upcoming rates passes by brightness (half the weight), height (30%) and length (20%), with a small penalty for later dates.
Earth and its shadow to scale: why a station 420 km up shines in a dark sky, and when it goes dark.
A pass in the list is labelled Near sun. What should you do?
- Use binoculars to find it in the glare
- Skip it, and keep binoculars and cameras away from the Sun (the right answer)
- Wait for it to brighten at the peak
- Tick Spottable only to make it visible
A Near sun pass is within 35° of the Sun while the Sun is up or less than 12° down: you cannot see it, and optics pointed near the Sun can hurt your eyes.
Each list row shows the peak time, peak elevation, magnitude and a countdown. Tags in front of the time mark Next, Best, Bright (magnitude -1 or brighter), Worth it and Marginal. The second line adds the label, "high" for a spottable pass peaking at 40° or more, the length and the start, peak and end bearings (only the peak bearing on a narrow phone screen).
Magnitude is a brightness scale: more negative is brighter. The estimate comes from distance and lighting angle, so treat it as a guide. The Sky sim sets it beside Venus at -4.0 and Jupiter at -2.4.
Sky path is a compass dial with north up: the outer ring is the horizon, the centre is overhead and the filled dot is the peak. Sky sim shows the view facing the peak direction, with Appear and Gone marks on the trail.
Appear and Gone are when the station crosses 5° above the horizon, found in 1-minute steps.
Using it from Guyana
- In Georgetown and Lethem the Sun is 6° or more below the horizon from 21 to 23 minutes after sunset until 21 to 23 minutes before sunrise. Lit passes closer to sunset or sunrise get the Twilight label.
- Pick your town under Guyana Presets so bearings match your sky.
- Check the forecast before you wait outside. The Tonight Observing Score and Stargazing Weather cover cloud and rain.
What it does not do
- It does not know the weather.
- It does not send alerts itself. Email sky alerts opens the alerts page, which can email you before ISS passes.
- It tracks the ISS only, not other satellites, and shows no live map.
- It labels each pass at its peak only. A pass can slip into Earth's shadow before its Gone time.
- It has no refresh button. Reload the page to recalculate.
Common mistakes
- Treating every row as visible. Tick Spottable only.
- Looking toward the peak direction at the start. The station rises from the Appear direction.
- Hunting a Near sun pass. Never point binoculars or a camera near the Sun.
- Pinning a place in another time zone and reading the times as your own clock. Times follow the pin's zone, so check the label.
A pass reads Appear 19:02 WSW, peak 19:05 NNW at 62°. Where do you look at 19:01?
- Low in the west-south-west, where it will appear (the right answer)
- High in the north-north-west, at the peak
- Straight overhead
- Wherever the Moon is
The station rises from the Appear direction, 5° above the horizon, and only reaches the peak bearing a few minutes later.