The Real Horizon – Where Earth and Space Meet

Sunsets are amazing things. Beautiful, brilliant streaks of light dividing the sky from the depths of space. But where does the sky end and space begin?

According to the Canadian Space Agency and researchers from the University of Calgary, that would be 118KM above the Earth – that’s about 73 miles straight up.

To give you a – pardon the pun – bird’s eye view of just how high that is, your average commercial airliner cruises at about 7.3KM above the Earth – that’s about 4.5 miles, or in pilot lingo 24,000 feet.

Scientists at the University of Calgary placed their Supra-Thermal Ion Imager on NASA’s JOULE-II rocket, which was then launched from Alaska on January 19, 2007. The Supra-Thermal Ion Imager is a new invention from the scientists, which measures the flow of charged ion particles.

By measuring the movement of these ions in the atmosphere, the scientists were able to determine the border between our relatively calm winds, and the raw violence of space.

See, despite all the wild weather we get here on planet Earth, our atmosphere actually protects us from the dangers of open space. Where the average winds range from none to 50KM/hour here on Earth, due to gravitational forces in space, objects can reach speeds well over 1,000KM/hour.

Down here on Earth, storms with winds over 100KM/hour are classed as F1 tornadoes – the most powerful of which are F5, with wind speeds over 400KM/hour.

Ion particles were used to measure the distance between the Earth’s atmosphere and the icy depths of space due to the lack of wind in space. Scientists knew there is movement of objects in space, caused by the gravitational rotation of stars, planets, even asteroids and other large rocks can generate their own gravitational pull.

Using this information, the scientists were able to calculate the speed of the particles, and concluded that our sky ends at 118KM above sea level, and that’s where space begins.

Understanding where our atmosphere ends and space begins will help scientists studying our climate, global warming, and space travel. It gives scientists a “big picture” of how energy and matter change and react when they cross that boundary – be it solar energy from the sun beaming down on Earth, or the Space Shuttle rocketing through that boundary from the Earth to the International Space Station.

Knowing how energy and matter pass through the atmospheric boundary – called the ionosphere – may even help meteorologists make more accurate weather predictions. We know that the tides here on Earth are directly linked to the different phases of the moon, because the distance between the moon and the Earth changes the relative gravity between the two, which impacts tidal formations.

So next time you’re watching the sun go down over the horizon, you’ll know just how high up that horizon really is – 118KM!