Last night, as you can see in my video below, the International Space Station and the Space Shuttle Discovery were very close together in the night sky, having just undocked a few hours earlier. During their pass over Denver, the ISS was trailing 13 seconds “behind” the Shuttle, meaning it would take 13 seconds for the ISS to reach a point that the Shuttle had just crossed. They were even closer on their further-east flyovers: 6 seconds apart over the East Coast, 11 seconds apart over the Midwest and Great Plains. By the time of the night’s final continental flyover, visible from the Pacific Northwest, they were 18 seconds apart.
The Shuttle is moving steadily away from the Space Station, so by the time tonight’s flyovers roll around, they’ll be much further apart — 73 seconds, rather than 13, at the time of the Denver flyover. This will somewhat reduce the dramatic visual effect, which Kristy accurately described last night by saying, “It’s almost like [they’re] on a string,” being pulled along in unison by some unseen puppetmaster. (Adherents to cosmic string theory might say that this analogy is more accurate than meets the eye!)
But on the bright side — literally — they’ll be much brighter here in Denver at their peak tonight than last night.
First, the distance. According to Heavens-Above (where you can check your local flyover times), the Shuttle and ISS will be 5 1/2 times more distant from each other tonight than last night over Denver. Here’s an approximate look at their respective locations in the sky at 7:38:30 PM, which is 30 seconds after the Shuttle’s peak magnitude, and 43 seconds before the ISS’s peak:
The good news, for Denver specifically, is that the spacecrafts’ flyover path will actually be much closer to us tonight — taking them over Pueblo, rather than over central Utah and Wyoming — and, as a result, they’ll reach a much higher point in the sky (65° of altitude, rather than 37°), and will be much brighter at their visual peak.
According to Heavens-Above’s estimates of their visual magnitudes, the Shuttle will reach -1.4 magnitude tonight, compared to 0.1 last night, and the ISS will reach -3.4, instead of -1.9. (In magnitude, lower numbers are brighter. The full moon has a magnitude of -12.6; Venus is around -4; Jupiter is in the -2 range; the brightest star in the sky, Sirius, is -1.5.)
Going by the formula for apparent magnitude, this means both the ISS and Shuttle will be four times brighter tonight than last night, when they’re at their respective highest points in the sky. Another way of looking at it: tonight’s Shuttle will be almost as bright as last night’s ISS — just 1.6 times dimmer, whereas last night it was more than 6 times dimmer.
Again, to find out the exact time of your local flyover(s) and where in the sky you should look, via Heavens-Above, enter your location here and click “Search.” (If you’re outside of the U.S., you’ll first need to select your country here.) Then pick your location from the resulting list, and then click under “Satellites” where it says “ISS” and “STS-128.” Alternatively, you can use the Simple Satellite Tracker — just enter your ZIP code — but it’s been offline due to high volume, so Heavens-Above may be a better bet.
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