Herschel's orbit

The Herschel spacecraft was at a point in space about 1.5 million km away from the Earth in the opposite direction to the Sun; that’s about 4 times as far away as the distance to the Moon.

Instead of circling the Earth in a conventional orbit, like most artificial satellites do, Herschel kept the Earth between itself and the Sun. This special point in space is called the second Lagrangian point of the Sun-Earth system (or 'L2') and is one of 5 similar places in the Solar System where a small object, like a spacecraft or an asteroid, can orbit the Sun at the same speed as the Earth does.

 

One of the most important reasons for going to L2 is to get it as far away from the Earth and Moon as possible. The Earth and Moon are powerful sources of infrared light that would heat the body of the telescope if it were too close. Another reason is that conditions at this location are very stable. The environment is very similar all day, every-day of the year which makes it ideal for observing. Above we show an animation of Herschel cruising to L2 - see how small the Earth looks!