Noteworthy ISS Passes: January 31, 2025

The visible passes of the International Space Station (ISS) are remarkable events that can be seen with the naked eye from various locations on Earth.

Why is the ISS visible?

The ISS reflects sunlight due to its large surfaces, including solar panels and its external structure. Although it orbits approximately 400 km above the Earth, it becomes visible when illuminated by the Sun while the observer's sky is dark, typically at dawn or dusk. At times, a shadow cone from the Earth may obscure the station, causing it to seemingly vanish even when it is high in the sky.

The ISS appears as a bright point moving swiftly across the sky, without blinking (unlike airplanes): it travels at around 28,000 km/h, completing an orbit around the Earth in about 90 minutes. Its brightness can fluctuate based on the angle of sunlight reflection and the observer's position, sometimes reaching a magnitude of -4, comparable to or even brighter than Venus.

Visible passes typically last from a few seconds to 5-6 minutes, as the ISS crosses the sky from one horizon to another.

These passes follow a trajectory from west to east, as the ISS orbits in the same direction as the Earth's rotation. The orbit's inclination of approximately 51.6° allows it to pass over many populated areas.

Visibility depends on the observer's geographical location, making it crucial to select an appropriate observation point. It is ineffective to rely on generic maps found online, as they may not correspond to the observer's specific location. To assist with this, our portal allows you to:

1. Set your observation location;
2. Check visible passes on the dedicated page, updated every night.

The skies are not only graced by the ISS; they are increasingly filled with satellites. You can monitor the passage of any satellite in orbit from this page.

When passes occur at higher altitudes, they tend to be more spectacular, as the station appears brighter and the pass itself is generally longer-lasting.

The Pass on January 31, 2025, at Approximately 17:55

The significance of the pass on January 31 is evident from the map showing the station's projection over Earth (see the section below in the following image).

The pass over Italy of the ISS on January 31, 2025, around 18:00. Credits: AstronomiAmo

This pass covers the entire Italian territory, from North to South, maintaining a high altitude throughout the country. Typically, passes do not occur at an angle that reflects the shape of Italy, often favoring the North, South, or Center at different times. However, in this instance, the height will be approximately uniform across the nation.

It is important to note that visibility conditions will vary across Italy. Along the red line, populations will see the station at zenith, but as one moves away from this line, the ISS will appear lower in the sky. For example, here are three timings for the North, Center, and South, encouraging readers to adjust the site to optimize for their observation point. It’s worth noting that while we highlight this pass as an example of "democracy" for all of Italy, individual municipalities may experience even better passes than that of January 31, 2025.

Northern Italy (Turin): begins at 17:54 from the Northwest, peaks at 17:58 at 76° altitude, ends at 18:04 in the Southeast;

Central Italy (Rome): begins at 17:55 from the Northwest, peaks at 17:59 at 87° altitude, ends at 18:05 in the Southeast;

Southern Italy (Vibo Valentia): begins at 17:56 from the Northwest, peaks at 18:00 at 80° altitude, ends at 18:06 in the Southeast.

If you wish to capture the pass, prepare for a long-exposure shot, ranging from 5 to 10 seconds depending on the light conditions in the sky: you will obtain a "streak" of the ISS's passage overhead!

Happy observing!