Astronauts In Perpetual Twilight As Space Station Returns To View

This picture of the Earth's terminator, the fuzzy boundary between day and night, was taken from the window of the space station recently. The astronauts on board will spend a lot time in the coming week flying over this zone of perpetual twilight. Credit: NASA

Astronaut Don Pettit’s latest blog entry from his current stay aboard the International Space Station (ISS) is an interesting one. Pettit, a flight engineer, describes this time of year as one of perpetual twilight for him and his fellow astronauts. Twice a year around the time of the solstices, the orbit of the ISS nearly parallels the Earth’s terminator. In his own words:

“For a period of about a week, we live in what seems like perpetual twilight, being in neither full daylight nor full night. Our orbit follows the terminator, so that the space station is constantly sunlit. From this vantage I can see both day and night simply by swiveling my head from left to right. But the night is not really dark, and the day is lit by low-angle rays from the sun.”

It almost sounds like a description of our winter except for the 24 hours of sunlight part. Pettit describes other peculiarities:

How many layers of blue can you see in this photo taken from the ISS recently? Credit: NASA

“The Moon sets in a counterintuitive way. From this vantage it moves nearly parallel to the horizon. Once I saw it slowly set, only to reappear in a few minutes. The Moon was visible for nearly the whole orbit. The night side is equally fascinating. The atmosphere on edge glows with a vibrant electric blue. Did van Gogh paint this scene? I can see at least five, maybe six distinct layers of blue—perhaps a visual display of the classic atmospheric strata.”

We can imagine Don musing out the window during his down time, because the space station is making a new series of bright passes in the morning sky  The times listed below are for the Duluth, Minn. region. For your town, please click HERE and enter your zip code or log on to Heavens Above, which includes sky maps for every pass. The ISS moves from west to east and typically appears as bright as Jupiter. Its large orange-colored solar panels give the craft a yellow hue.

* Sunday morning Jan. 22 beginning at 6:16 a.m. across the northern sky. Very bright!
* Monday Jan. 23 at 6:54 a.m. similar to above
* Tuesday Jan. 24 at 6 a.m. Appears out of Earth’s shadow below and west of the North Star
* Wednesday Jan. 25 at 6:38 a.m. Another pass across the north
* Thursday Jan. 26 at 7:16 a.m. in twilight. A high,brilliant pass — peak magnitude -3.0!
* Friday Jan. 27 at 6:21 a.m. in the northern sky
* Saturday Jan. 28 at 6:59 a.m. straight across the top of the sky. Another brilliant appearance!

A very "old" crescent moon punctuates the twilight sky earlier this morning seen from Duluth. Photo: Bob King

I wish I could say you’ll have the company of the crescent moon when you’re out ISS-gazing, but by tomorrow it’ll be too low in the east before sunrise to see from Duluth. Floridians and others in the Sun Belt might still catch a glimpse of it. The following day the moon will be new and then coast back into the evening sky.

This morning was calm, cold and very clear. Saturn’s rings and moons and Mars’ north polar cap were stunning in the telescope. As the temperature sank to -14, I watched the star Altair finally clear the treeline in the east to complete the Summer Triangle. Yes, it’s back! Anytime you want to see what the starry future holds, just look up at dawn. It’s a whole different world up there.

6 Responses

  1. Great post, Bob! The terminator shots have always been so impressive to me (I have nearly all the “photos from space” books, starting with a classic old brown NASA publication), but I never imagined this annual treat for the ISS crew. So cool. And thanks for the pre-dawn look into the future; you’re a better man than I!

    1. astrobob

      Hey Jim, thanks. I don’t often think about the Earth’s terminator because we really don’t see it directly. More often I’m watching the moon’s terminator to see what’s coming next. I remember those old, heavy-bound NASA books. You’ll find more than a few in my library, too.

  2. Becky

    Hi Bob, I am new to the area. I hear that a solar flare happened on Thursday which will cause the Northern Lights to shine tonight. I saw your blog from August and drove out to the beach today to scope it out for tonight. What time do you think would be the best to see the lights, if at all? I am from Iowa and have never seen them in person… I worked at a planetarium for 4 years and am so excited! Thank you, Becky

    1. astrobob

      Hi Becky,
      Do you still live in Iowa now or are you in Minnesota? You’re right — there’s a chance for auroras in the northern U.S. and Canada, but the most recent forecast calls for a minor storm starting at around noon tomorrow the 22nd and continuing into Monday. I’ll keep an eye on it and alert via the blog tonight or tomorrow depending on whether anything happens. Thanks for writing and I hope you get to see the aurora soon!

      1. Becky

        I now live in Duluth, MN. Ok so maybe tonight wouldnt be a good night to venture out? Maybe Sunday night? Thanks for your help!

        1. astrobob

          Welcome to Duluth Becky even if I’m a little late. Both tonight and tomorrow night look bad because of the weather. Clouds and snow are in the forecast until late Monday. Yet another unfortunate clash between Earth and space forecasts!

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