In celebration of the birthday of its most diligent watcher, the Sun has let loose an unusual and quick-fire series of eruptions during the past week. Saturday was the 5th anniversary of SOHO's launch into space, on 2 December 1995.

A mass ejection from the sun on November 26 as seen by SOHO. Photo: ESA

As observed by SOHO itself, the eruptions began on 23 November. A succession of five big solar flares was accompanied by mass ejections blasted in the direction of the Earth. More flares and mass ejections occurred every day up to 27 November.

By that time the earlier mass ejections had already hit and jolted the Earth's protective magnetosphere, provoking displays of the Northern Lights (aurora borealis) from 26 November onwards. People living at high latitudes could see the results of solar fireworks with their own eyes. The last of that series of mass ejections is due to arrive in our vicinity today (30 November) but activity seems to be subsiding.

The Atlas rocket launches SOHO from Cape Canaveral in 1995. Photo: ILS

SOHO is a project of international collaboration between ESA and NASA, and when ESA had built the spacecraft, NASA launched it from Cape Canaveral. Lifting off at 03:08 Florida time or 09:08 Paris time, the two-stage Atlas 2AS (Atlas-Centaur) launcher performed flawlessly.

The subsequent journey to SOHO's special vantage point 1.5 million kilometres out in space, on the sunward side of the Earth, also went very smoothly and left the spacecraft with ample reserves of propellant. These were to prove valuable in 1998, when SOHO had to be recovered after going out of control -- and disappearing for a while!

In April 2001, SOHO's scientists will mark the 5th anniversary of the end of the commissioning phase, when the mission engineers handed the spacecraft over to them. They have plenty to celebrate. With twelve sets of instruments from European and American teams, they have revolutionized the study of the Sun, from its deep interior, through its stormy atmosphere, and outwards with the solar wind into interplanetary space.