Starlink satellites, deployed by SpaceX to provide global internet access, are placed in low orbit (about 550 km altitude). Unlike stars that emit their own light, these satellites are visible because they reflect sunlight. This is why the best observation windows are just after sunset or just before sunrise: the observer is in darkness, but the satellites, still illuminated by the Sun, stand out as aligned moving stars against the sky.
The most impressive phenomenon remains the "train" of satellites. If these trains are particularly spectacular in the days following a launch (when the satellites are not yet dispersed), we can also observe bright lines in operational phase. Indeed, satellites in the same orbital plane can appear in a tight convoy depending on the observation angle, creating this string of bright pearls moving in single file.
Observing Starlink satellites requires no optical instrument, just a clear sky. There are two types of passes:
However, to avoid scanning the sky at random, it is essential to know the passing times, which vary depending on your geographical location. To know exactly the time of the next pass over your location, the use of digital tools is essential. Several applications and websites, using data from TLE elements, allow predicting passes with an accuracy of a few seconds.
| Generation / Phase | Altitude (km) | Inclination (°) | Visibility to the Naked Eye | Observation Particularity |
|---|---|---|---|---|
| Post-launch Train | ~ 300 - 350 | Variable (53°) | Very easy | Spectacular single file for 3 to 5 days. |
| V1.0 (Operational) | ~ 550 | 53° - 70° | Possible | Reduced brightness compared to trains, but visible. |
| V1.5 (VisorSat) | ~ 550 | 53° - 97.6° | Difficult | Equipped with anti-reflective visors to reduce light pollution for astronomers. |
| V2 Mini | ~ 550 - 560 | 43° - 53° | Possible | Larger, but better optimized to reduce light reflection. |
It is estimated that the number of satellites in low orbit could exceed 100,000 by 2030. For professional astronomers, this represents a major challenge. Long exposures from telescopes are systematically streaked by the passage of these objects. In response, SpaceX is experimenting with anti-reflective coatings (such as "DarkSat" and "VisorSat") and attitude adjustments to minimize their albedo.
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