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Maybe you stuck around after the recent full-moon rise to watch the space station go by. If you didn't there are still plenty of opportunities to do so. For the next couple weeks, northern hemisphere skywatchers will see up to several flybys each night starting at dusk and ending near dawn.
For example, Sunday night, July 17, from my city of Duluth, Minnesota (and region), the ISS will make appearances at 10:30 p.m., 12:07 a.m. and 1:44 a.m. Notice that each occurs about an hour and a half apart. That's the time it takes the station to make an orbit of the Earth traveling at more than 17,000 miles an hour (27,400 km/h). There's also a 3:21 a.m. pass Monday morning as the ship passes through Earth's shadow then. Cut off from sunlight, it crosses the sky under a "cloak of invisibility."
SpaceX recently launched a Dragon resupply ship to the station that arrived and docked autonomously on July 16. After spending about month there, the Dragon will depart and return to Earth with cargo and research data. Among the experiments that were delivered to the crew was a dust mapping instrument to measure the mineral composition of dust in Earth's deserts.
Windblown dust can travel widely and affect weather, vegetation and climate. In just one example, dark dust that settles on snow and ice can absorb sunlight and speed up melting. If you live in the southern U.S. you're already familiar with dust from the Sahara Desert. Winds lift an estimated 100 million tons each year of the stuff, a fair portion of which is carried across the Atlantic Ocean and arrives in the U.S. where it turns skies orange and lessens air quality. The investigation will collect images for a year to create maps of the mineral composition of Earth's dustiest locales, the better to forecast and understand its effects.
Lunar concrete?
Other experiments delivered include BeaverCube , an educational project designed to teach high school students how to build a CubeSat . As the name implies, a CubeSat is a cube-shaped satellite just 4-inches (10 cm) on a side that weighs about 3 pounds (1.4 kg). They're an affordable way to get a satellite into space and often used for educational scientific research.
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Still another experiment will focus on how to make concrete in near-zero gravity using an organic material mixed with lunar or Martian dust called biopolymer soil composite. When permanent colonies are established on the moon and Mars, future astronauts will need to learn to use local materials to build shelters to protect the from deadly solar radiation and dust-laden Martian winds.
As the experiments get underway 248 miles (400 km) up, you can watch the ISS breeze by in your leisure. It always rises in the western sky and moves eastward. Before it "sets," the station will often disappear, eclipsed by Earth's shadow. As it enters the shadow, you'll see it fade for about five seconds and then poof — gone! At the same time, astronauts looking out the window see the sun set, one of 16 sunrises and sunsets that zip by each day.
In mid-July, the ISS remains in sunlight during nearly every orbit for northern hemisphere viewers, the reason we see it several times a night. It's caused by a combination of the station's steeply inclined orbit (51.6°) and the fact that in July, Earth's north polar axis is angled toward the sun. This keeps the ISS in sunlight every time it loops back up over the northern hemisphere.
Viewing predictions
To find out when and where to see it, 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.
"Astro" Bob King is a freelance writer for the Duluth News Tribune.
