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First off, I want to remind you that tonight (Sunday, May 15) there will be a total eclipse of the moon widely visible across the Americas, Europe and Africa. Below you'll find a table of the times when the different phases of the eclipse occur for five time zones.
While you're taking in the shadowy spectacle, Northern Hemisphere observers can also watch the International Space Station make multiple go-rounds. From my location, it will make four appearances Sunday night. The first occurs around 10:30 p.m. local time, with the others following in succession about an hour and a half apart. That's how long it takes the station to complete one orbit.
The station's orbit is tipped 51.6 degrees (a little more than a "45") to the Earth's equator. This steep angle ensures that anyone living within a band stretching from 60 degrees North latitude to 60 degrees South latitude — basically most of the inhabited planet — can see the ISS at one time or another.
During a typical viewing period, we get one full pass and maybe a second partial one each night for a few weeks, but this weekend into early next week you might view three, four or even five passes each night depending on your location. Those living in the northern half of the U.S. and southern Canada are favored.
Of course, flybys happen like clockwork all night, but we don't see them because once it gets dark, Earth's shadow fills the sky and blocks sunlight from reaching the space station. Without sunlight to reflect back to our eyes, it's invisible.
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But twice a year around the summer solstice — May to July in the Northern Hemisphere and November to January in the Southern Hemisphere — the ISS remains in full sunlight as it orbits the planet. NASA refers to these time as the high beta angle season. In the minute-long video time lapse (above), you'll see the sun slowly reach a low point but never set, then resume its upward path.
The season happens twice a year when the station's orbit and the Earth's day-night terminator — the border between day and night — nearly align. Think of it as adding the Earth's sunward tilt of 23.5 degrees to the station's 51.6 degrees, "pushing" it further into the sunlight. From its altitude of ~250 miles (400 kilometer), the ISS remains in constant sunlight throughout its orbit for a week or so.
Observers on the ground see it on every pass. For the astronauts on board, the sun shines all day long, much like the midnight sun does north of the Arctic Circle. Because constant sunlight can overheat the ISS, the crew will reposition the solar arrays to act as a sunshade during this time.
Watching the space station is fun and easy. It travels in the same direction as the Earth turns, from west to east. So it always "rises" in the west and "sets" in the east. When it flies overhead the ISS shines as bright as Venus. At lower altitude passes it's as bright as Jupiter.
For predictions, go to Heavens Above and select your city by clicking on the blue Change your observing location and other settings link. Then return to the home page and click on the blue ISS link to see a 10-day table of passes that includes time, direction, brightness and altitude. Ten degrees (10°) of altitude is equal to one fist held at arm's length against the sky.
The higher the negative number in the brightness column, the brighter the pass. Click on any pass time and a map will appear showing the station's path across the sky.
All times shown are local times on the 24-hour clock for your location, so 18:30 = 6:30 p.m. local time and 2:15 = 2:15 a.m. You can also get a list of customized passes and alerts by downloading the free ISS Spotter app for iPhone and ISS Detector for Android devices. Or you can sign up for alerts at NASA's Spotthestation site.
As you're watching the total lunar eclipse, remember that the astronauts will see it, too!
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"Astro" Bob King is a freelance writer for the Duluth News Tribune.