From the May 2018 issue

Satellite ‘fake out’

In honor of NFL training camps starting in July, let’s compare an Earth-orbiting satellite to a running back.
By | Published: May 31, 2018
A common trick in American football is for a ball carrier to take a quick step forward in one direction — making it appear he’s heading that way — only to change direction at high speed, thereby confusing the defender to avoid being tackled. It’s called a “fake out,” and it not only works on the playing field, but also in the night sky with some pretty shifty satellites.

A visual trickster
It doesn’t matter how skilled we are as observers, satellites have no shortage of visual tricks to confuse our brain as they sail across the playing field of the night sky. While satellites look like “stars” that move at a steady clip in one direction, it’s common for them to appear to gently weave among the other stars like a running back heading for the end zone.

The slight weaving is a well-known optical illusion that results from our eye-brain system. This complex mass of receptors and nerves has difficulty fixing on a moving point of light (satellite) at night, especially when seen against a jumble of other points of light (stars) whose orientations change with the turn of the head.

The author added the colored dots, lines, and numbers to this photograph. The red dots show where the flashes appeared to him. The white lines give the expected direction of motion. The yellow dots show the expected location of the next event for each object.
Both illustrations: Stephen James O’Meara
Now imagine the difficulty the brain has in trying to keep track of the path of a flashing or tumbling satellite, which we only intermittently see as the highly reflective metallic surfaces of these objects send glints of sunlight to our eyes. Spinning satellites (which create rhythmic flashes as the craft rotates) are much easier to follow than tumbling satellites (such as rocket boosters and space junk), which can flash erratically as they topple out of control in a decaying orbit.

Sometimes, the flashes are so erratic in both magnitude and frequency that tracking their path requires a keen knowledge of the night sky. And therein lies the story of my “running back” satellite.

A series of flashes
I have to applaud the rocket booster or fragment of space junk I saw recently because it stopped me in my tracks with its seemingly impossible movements. Had I not persisted in watching it with a critical eye, I may have walked back in the house scratching my head.

It started with a prolonged, elongated flash lasting long enough for me to detect its direction (along the major axis of the flash). Scanning my eyes in the direction of motion, I waited for the next event. To my surprise, it occurred well below and to the right of the first flash, causing me to believe it was a different object.

This illustration shows the true path of the satellite (the red line) through the stars. Although the events seemed disjointed to the author, the appearance of each flash (the red dots in the above image) proves the object was moving in a straight line.
The second flash also was elongated, and appeared to travel perpendicular to the first satellite. So, now I had two satellites to follow. A third elongated flash occurred in an unexpected location in the sky, followed by a fourth seemingly unrelated flash.

The first photo-illustration (above, top) shows the location of the flash (red), the direction of elongation (white), and the expected location of the next event (yellow) for each object. After the fourth flash, however, it became clear that the satellite was, in fact, moving as it should: on a straight and steady course, but tumbling in a way so that its rotation axis was not aligned with its principal axis.

If the object itself were elongated, like a rocket body, this could explain the “fake out,” as sunlight slid along the length of the body. The second photo-illustration (above, bottom) shows that if you connect the red dots, the satellite is indeed moving along a straight line.

What’s interesting, however, is that if you try to connect the red dots with your eyes alone in the first image, the red dots seem to wiggle a bit. Perhaps, as they say, it’s all in your head (and mine!). As always, send your thoughts to