13.11.2025

"Every single subframe I take (prior to stacking) now contains at least one, and usually more than one satellite streak."

A composite image of Comet Lemmon revealing where bright pixels were rejected by an image-stacking algorithm. (Image credit: Dan Bartlett)

Recent months have seen space fans revel in a wealth of spectacular astrophotography depicting the evolution of Comet Lemmon's glowing coma and twisting tail as it journeyed through a Northern Hemisphere night sky swarming with satellites.

While the vast majority of photographers opted to post sanitized views of Comet Lemmon, others intentionally compiled their images to reveal the incredible number of satellites that crossed the night sky over the course of multiple exposures.

In each instance, Comet Lemmon is shown surrounded by a crazed network of thin, web-like lines, each of which represents the path of an orbiting satellite over the course of a short camera exposure.

"Photographically, if someone is attempting to take a single image of a target and needs the image to be 'clean' — free of manmade objects — well, that image is nearly impossible to obtain," astrophotographer Dan Bartlett told Space.comin an email. "Every single subframe I take (prior to stacking) now contains at least one, and usually more than one satellite streak."

There are currently about 13,000 operational satellites orbiting Earth, of which about 8,900 are SpaceX Starlink craft. This number is set to exponentially increase, with SpaceX alone aiming to orbit up to 42,000 of its internet-beaming spacecraft, while competing companies aim to add thousands more satellites to their own "megaconstellations."

Thankfully, astrophotographers have access to powerful editing tools that allow them to remove the unsightly streaks with ease.

"Despite the enormous increase in satellite traffic over the past few years, eliminating the satellite trails in post processing is actually fairly simple using the right tools," explained Bartlett. "I certainly don't like seeing so many satellites everywhere I point my telescope or even a good pair of binoculars, but we're still not at the point where you can't enjoy the night sky (there can be a thrill seen visually when a satellite passes through your field of view)."

Astrophotographers combat satellite streaks by capturing a multitude of short exposures over the course of a single session. The images are then combined and subjected to an algorithm that determines a median value for each pixel before rejecting outlier pixels with values that exceed set parameters.

"If you take at least a dozen images to stack, then you can use a combine method called Sigma Rejection," said astrophotographer Chris Schur in an email to Space.com. "This is available in nearly all astronomical imaging processing software. A single shot to up to about 6 images, the sigma does not have enough data to reject all the trails. So that's why comet and deep-sky imagers take sets of at least a dozen images as a normal process, so that the stacking software has a good set to perform its algorithm."

The end result is a gorgeous composite image of an ancient solar system comet, which has been locked in an orbital dance around the sun since the creation of the planets over four billion years ago.

Stargazers looking to capture their own views of the night sky should check out our picks for the best cameras and lenses for astrophotography, along with our guide to observing and photographing comets.

Quelle: SC