How to ID STARLINK trains

On September 22, 2023 around 8:28 pm local time (MDT) – it was a clear night sky in Boulder. I was just getting home after dinner and looked up toward the stars. To my surprise I saw a line of bright lights streaking across the zenith. Immediately I knew these were the recently launched STARLINK satellites. I grabbed my phone and started recording the video and counting the number of “dots” (satellites) that were moving in unison in a single line across the sky. Here’s the video I shot from my phone (recommended video resolution: 1080p).

Just the week before I had heard a similar story from a group of friends that were camping in Rocky Mountain National Park that spotted a streak of twinkling dots moving in linear fashion. It was the first time I was seeing the STARLINK train with my own eyes and I was truly mesmerized by this. My curiosity was off the charts and I wanted to find out everything about these satellites.

Starting with some basic assumptions that can be leveraged to correctly identify the satellites that I saw on that night:

• STARLINK trains are typically seen soon after they have been deployed after a rocket launch.
• TLEs from recent launches can be found on CelesTrak: http://celestrak.org/NORAD/elements/table.php?GROUP=last-30-days&FORMAT=tle
• Using these TLEs, one can compute transits / ground tracks for these satellites over a given location and within a specific time range to cross-check ground observations with tracking data.
• Finally, after the specific STARLINK satellites are verified to be transiting over Boulder within the same time range I saw them, I can use a simple Google Search to find out more information like launch date, site, how many satellites, etc.

So the hunt begins…

Let’s start by downloading TLEs for the last 30-days of launch. This file will contain closed-form information about all satellites that were launched in the last 30 days. This close-form format is known as a TLE. Find out more in Wiki. Using a python library and some cool plotting tools this file can be read, parsed and each TLE propagated to get transits for a certain location. Here’s the TLE file that was downloaded from CelesTrak:

Now that we have the TLEs for the satellites launched in the last 30 days, we can use the following tool to compute and plot the transits over Boulder during the time period I saw the satellites.

The tool reported 22 transits from 22 satellites over Boulder between 09/22 7:00 pm and 09/22 9:00 pm MDT. Each colored line in the map shown shows a different satellite passing over Boulder (60 degree elevation). Even though the satellites are visually seen traveling in a single line in the sky, when ground tracks are plotted – due to the rotation of Earth underneath, these lines shift a little – resulting in the “swath-like” ground track pattern.

Additionally, we can see that the transits are starting from an azimuth of around 233 degrees, denoting the satellites would be seen going from west to east. This is in agreement with the my observations on that day as the mountains are in the western part of Boulder, and I was directly looking above the mountains when the satellites started to be seen.

We have verified that there are indeed satellites that passed Boulder during the time when I observed them on the ground, so now let’s find out when they were launched and other details about them. I simply Google searched: “2023-146L STARLINK-30472 satellite” and navigated to the first result: https://www.n2yo.com/satellite/?s=57901

Found out the following information about the satellites that I saw:
– There were 22 satellites launched on September 20, 2023 from Eastern Range (Cape Canaveral Space Force Station)
– Looking for the International Designator “2023-146” in CelesTrak database for Starlink Satellites, also resulted in 22 satellites. The international designator is a tag that describe the year of launch and the launch number resulting in “2023-146”.

So now when someone asks me which Starlink train you saw, I can share a link to this page.