What Is Starlink? SpaceX's Satellite Internet Constellation Explained

If you have ever looked up on a clear night and seen a string of bright dots moving in formation across the sky, you likely witnessed a Starlink train. Starlink is SpaceX's satellite internet constellation, designed to deliver high-speed broadband to underserved and rural areas around the world by placing thousands of small satellites in low Earth orbit.

How Starlink Works

Traditional internet satellites sit in geostationary orbit about 36,000 kilometers above the equator, introducing noticeable latency. Starlink satellites orbit much closer to Earth, between 340 and 550 kilometers altitude, which reduces signal round-trip time to roughly 20 to 40 milliseconds. Each satellite uses phased-array antennas to create beams of coverage on the ground, and they communicate with one another using laser inter-satellite links so data can hop between satellites before reaching a ground station.

How Many Starlink Satellites Are in Orbit?

As of mid-2025, SpaceX has launched more than 6,000 Starlink satellites, making it the largest constellation ever deployed. The company has regulatory approval to operate up to 12,000 satellites and has filed applications for as many as 42,000 in the future. You can see all currently tracked Starlink objects on the Starlink category page within Track The Sky.

The Starlink Train Effect

After each Falcon 9 launch, a batch of roughly 60 satellites is deployed at a low initial altitude. During the first few days after deployment, these satellites fly in a closely spaced formation that appears as a dazzling line of lights moving across the sky. This phenomenon is known as a Starlink train. Over the following weeks, each satellite uses its ion thruster to climb to its operational orbit, gradually spreading apart until the train is no longer visible as a group.

Tracking Starlink on Track The Sky

Track The Sky includes a dedicated Starlink train detector that identifies recently launched batches still in the orbit-raising phase. Set your observer location, and the tracker calculates when the train will pass over your area, along with brightness estimates. You can also explore the entire constellation on the 3D globe to see how the network blankets the planet.

Impact on Astronomy

The brightness of Starlink satellites, especially during their early orbit-raising phase, has raised concerns among astronomers. SpaceX has responded by adding sunshade visors and darker coatings to reduce reflectivity. Later-generation satellites are significantly dimmer, though the sheer number of objects still presents challenges for wide-field telescope surveys. Understanding this issue is part of the broader conversation about responsible use of low Earth orbit.