Largest-ever Solar Sail Will Be Visible Over London This Week: Here’s How To Watch

In April this year, the Advanced Composite Solar Sail System (ACS3), a satellite to experiment with using a large solar sail for spacecraft propulsion, was launched. This week, skywatchers in London will have a unique chance to spot this largest-ever solar sail flying over the city.

What Is The Solar Sail?

NASA developed the ACS3 satellite in collaboration with Rocket Lab. This solar sail uses the steady push of solar wind to move spacecraft, just like old sailing boats. In space, where there’s hardly any resistance, a solar sail can keep speeding up over a long time, eventually reaching very high speeds.

Just over a week ago, the solar sail-powered spacecraft unfolded its 9-meter-wide solar sail in space. Because the sail is so large and reflective, the satellite can be seen from the ground when it passes overhead at the right angle to catch and reflect sunlight.

When To Expect The Solar Sail Over London?

When it flies over the UK, the spacecraft travels roughly from north to south. If weather permits, you should be able to spot it as a fast-moving star in the evening sky.

According to N2YO, the satellite will be visible from London (and much of the UK) on the following dates:

• 9 September at 8:46 PM
• 10 September at 9:28 PM
• 13 September at 9:24 PM
• 16 September at 9:19 PM

The weather forecast for London is currently favourable for viewing on the 9, 13, and 16 September, so don’t miss your chance!

Tips For Watching The Largest-ever Solar Sail

To catch a glimpse of the satellite, head to a dark park or an area away from streetlights to minimize light pollution and better see the night sky. Arrive about 10 minutes before it’s due to pass by and focus on the northern horizon. Your eyes will adjust to the darkness, and you should eventually spot a bright object rising and moving quickly towards you.

However, the largest-ever solar sail might not always reflect sunlight as expected, depending on NASA’s experimental movements. However, if you do see it, you’ll be witnessing the reflection of the largest-ever solar sail created by humanity!