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Look up: Perfect time for skywatchers to spot the ISS in the skies above

NASA astronaut Barry 'Butch' Wilmore, Commander on the International Space Station. (Reuters/NASA)
NASA astronaut Barry 'Butch' Wilmore, Commander on the International Space Station. (Reuters/NASA)

Look up on the next clear night and you have great chance to catch sight of the International Space Station (ISS) make not just one, but a series of bright flybys above your doorstep.

The next few weeks offers an amazing opportunity for space fans to glimpse the football field-sized orbiting laboratory glide across the starry skies as many as four times in one night.

These nightly multiple flybys are an annual attraction for sky-watchers around the world, as the ISS is bathed in nearly continuous sunlight this time of the year, as it orbits the Earth. Every year around mid-June, its 90-minute long loop around the planet closely traces the day-night border of Earth, allowing it to be seen from dusk til dawn.

Because its in near perpetual sunshine now, observers get a veritable station spotting marathon, where anyone with clear skies gets a chance to observe it three (sometimes even five) times in a single night. This makes for quite a sky show, especially compared to other times of the year when its orbit is such that it is sunlit only about 70 per cent of the time, offering observers a more modest one or two passes a night.

Cruising at an altitude of about 280 miles and travelling at 17,000 miles per hour, with a crew of six astronauts aboard, the station looks like a brilliant star to the naked eye. And observers find that it moves at a good trek, covering the entire overhead sky from eastern horizon to western horizon in just about two to four minutes. So you have to be quick when you are searching the skies. But, you cant mistake it for a passing plane because the satellite will shine with a white, unblinking light.

In general, dawn and dusk are usually the best time for hunting satellites. Thats because while Earth has cast its shadow locally on the ground, the sunlight still reflects off the satellites shiny metallic surface making it visible. Currently there are over 800 of these high-flying, functioning space birds that are buzzing around the Earth. And NORAD Space Command tracking stations have as many as 50,000 man-made objects in their sights, some as small as a screw or hammer that accidentally floated away from astronauts conducting spacewalks. Amazingly all these objects are constantly being monitored and their orbits tracked to make sure there is no chance of collisions.

In fact, this Monday the space station had to dodge orbiting debris by turning on the engines on the docked Russian Progress spacecraft. The burn lasted 5 minutes and shoved the station aside by just 100 feet or so to avoid any possibility of collision with an expended U.S. government rocket stage.

Sometimes however there is not enough time given to steer the ISS out of possible danger. This occurred in March 2009 when the crew was asked to close hatches and evacuate and seek safe haven inside a docked Russian Soyuz vehicles. Luckily the debris passed by without making impact and the crew entered back into the station after a tense 10-minute wait.

The International Space Station is seen in an undated NASA handout picture. (Reuters)
The International Space Station is seen in an undated NASA handout picture. (Reuters)

Many of these orbiting objects are so bright that they are easily visible from even light polluted cities. Satellites like the space station, with larger, reflective solar panels are, of course, highly visible.

Some of these are easy targets for the sky-watchers: some are known to monitor the environment or conduct surveillance, while others are simply space junk, like leftover rocket boosters that orbit our planet for years before getting dragged into the atmosphere where they burn up.

When under clear skies, expect the ISS to first become visible as a faint point of light appearing near the horizon. As it climbs higher in the sky it quickly brightens, until it enters the Earths shadow and disappears into the darkness of the night. When the angle between the station, Earth and the Sun are just right the ISS can even outshine every star and planet except the Sun, the Moon and possibly Venus. More often it looks like an ordinary star, eye-catching because it moves so fast as it zips by between the stars.

As an added sport in recent years, backyard telescope users have amazingly been able to track and photograph the orbiting laboratory. Through larger amateur telescopes that can track the quick movement of the ISS across the sky, people are now able to spot structural details like the individual modules and solar panels.

The best bet to know when and where to spot the ISS with your own eyes is to use online prediction services like heavens-above.com or http://spaceweather.com/flybys/ where just by entering your city name or postal code, a customized viewing table is generated that describes the direction, altitude, and specific flyby times.

For all of us Earth-bound wannabe space travelers watching the space station silently slip across the sky, we get to experience at least vicariously the adventure of space exploration.