Field Notes: On watching the International Space Station pass overhead

[Listen to this post read by its author.]

"Where is it?" I looked again at my wristwatch with exasperation. I read 5:25 pm. "It should be well above the southwestern horizon by now." With sunset only 30 minutes earlier, dusk had not yet yielded to night. Could it be that the International Space Station (ISS) was washed out by residual daylight? "No. That cannot not be!" I was arguing with myself again.

In the clear sky, Venus and Jupiter were already visible, two points bright against a darkening indigo sky. This pair of planets hovered over the silhouettes of countless roofs and buildings marking the horizon. ISS ought be bright as well. With a predicted magnitude [1] of -3.5, it should rival Venus. Again, where was it?

That morning's Albuquerque Journal had briefly mentioned the ISS visit beneath the weather forecast. 5:26 pm -- another minute had passed on a watch I assiduously keep accurate. "Am I the only one in this city looking for it, and not seeing it?" Linus in the pumpkin patch on Halloween came to mind. He was waiting to witness the Great Pumpkin. It never appeared. Strange, isn't it, how childhood comic strip characters like Linus endure?

How close Venus and Jupiter were! Mating perhaps. Jupiter did have many women, goddesses and mortals alike. Extended at arm's length, my fist alone could cover both planets offering the Olympian pair some modesty. Here then was my consolation prize: seeing Venus and Jupiter nearly conjoined.

And, suddenly, there it was: a pinpoint of pure white light slowly, steadily ascending over the parental pair of planets.

Emerging from between
conjugal Venus and Jupiter
into nightfall.

Or, could it be something else, a false alarm, a plane for instance? But no vapor trail did I spot, no dull distant roar of a jet engine did I hear, nor any trace of a high flying aircraft's lights, flashing once or twice per second. This had to be it, the space station. In its predicted path, it would traverse the dome of the sky, passing directly overhead at its halfway point. Would it?

Saturday, 23 November 2019, promised a pass of the space station directly over my home of Albuquerque. Moving at 7.7 km / sec (17,200 mph) at an altitude of 410 km (255 miles), the ISS would rise in the southwest and set in the northeast. In its five minutes of visibility, ISS would travel from northern Mexico to southern Kansas. Though a mere speck seen in the sky, ISS is actually quite impressive, 51 by 109 meters in size and 420,000 kilograms in mass. Add to that the reflectivity of its solar panels and Venus, usually the brightest object in a moonless sky, now has serious competition.

Three or four minutes after I spotted it, the ISS bid me farewell and finally faded into invisibility above the Sandia Mountains.

Rising, soon receding,
rounding the world in just
ninety-three minutes.

I thought of the French author Jules Verne. Late in the 19th Century, he wrote a science fiction novel Around the World in 80 Days. Yes, eighty days. ISS does it in 93 minutes, again, and again, and again, freely moving without need for propulsion [2], kept aloft by balancing gravitational and centripetal forces.

This Linus -- me -- had, at long last, glimpsed his Great Pumpkin.

Footnotes

1. Magnitude is a measure of relative brightness as perceived by the human eye. A value of negative 3.5 for the ISS is very bright for night time, though not bright enough to be seen during the day. Location-specific predictions of the ISS's magnitude and flight path can be generated at the Heavens Above website.

2. Some propulsion is occasionally needed to correct for orbital decay (of about 2 km per month).

posted: 2019-12-01, last edited: 2019-12-01