THE SOUTHWORTH PLANETARIUM

207-780-4249   www.usm.maine.edu/planet

70 Falmouth Street   Portland, Maine 04103

43.6667° N                   70.2667° W 

Altitude:  10 feet below sea level

Founded January 1970

Julian date: 2458743.5

2019-2020:  XI

           "If you touch a wasp's nest, wasps will fly out of it."

                      -Ancient Chinese proverb

                               or

                     -Your Kindergarten teacher

THE DAILY ASTRONOMER

Tuesday, September 17, 2019

A Bright Evening ISS

The International Space Station orbits at an average altitude of 254 miles.

At that height, the ISS completes one orbit around Earth every 92  minutes.   While the space station will often "fly over" us a few times a day, it will only be visible in the early evening or during the pre-dawn, when the sky is dark and the station is aligned

in such a way so as to reflect sunlight toward Earth-bound observers.

Heavens above!

We haven't paid much attention to the International Space Station lately.  In our defense, the Universe is so abuzz with activity -even here in the outer galactic suburbs- that we have to carefully pick and choose the topics we discuss.  All the same, the International Space Station (ISS) can make such a spectacle of itself that we really should focus on it now and again.   

Such a spectacle will occur in the evening of September 20th.  The ISS will rise in the SW sky at 7:58 p.m.    By 8:00 p.m, the station will be 10 degrees above the horizon.   At 8:03 p.m, the ISS will attain its maximum altitude of 63 degrees and will also shine at its maximum brightness of -3.8, about as bright as Venus, which, alas, will not be present in the sky at that time.  The ISS will vanish at an altitude of 33 degrees at 8:05 p.m.   While observers will not discern any details in the ISS, it will still look like a brilliantly bright star moving across the heavens.

As we can see from the star map above, the station will slice across Scorpius, pass north of Jupiter (at which moment it will about as bright as the planet) and as it ascends will pass through the lower region of the Summer Triangle.   It will vanish from view just before it appears to reach the Andromeda Galaxy

When you observe the International Space Station on the evening of September 20th, take note of its speed.  The ISS certainly moves swiftly.  As we can see from the map above, when the ISS first appears at 7:58 p.m, it will actually be moving over the Carolinas.  When it attains its maximum altitude, it will be passing over the Atlantic well off shore of Portland.  By the time it disappears, the ISS will be moving directly over southern Newfoundland.  

While most of the celestial spectacles we behold each night seem -but aren't- stationary, the ISS shows rapid motion through the sky, which makes it a delight to watch.   On the evening of September 20th, we'll see this orbiting spacecraft blazing brighter than any night sky star as it passes off shore and then to distant points beyond. 

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