People standing across a great swathe of the Earth’s surface will see the Moon take a big bite out of the Sun. Tuesday will see the first partial solar eclipse of 2011.
For north Africa and much of Europe, the event starts at sunrise, whereas in central Russia and north-west China, the spectacle occurs at sunset.
North-east Sweden should get the best experience. At 0850 GMT, near the city of Skelleftea, the Moon will cover almost 90% of the Sun’s diameter.
Skywatchers will have to have a high vantage point, however, as both celestial bodies will be skirting the horizon at that time.
As is always the case for solar eclipses, the public is being warned to take great care.
Viewing the Sun’s harsh light should only be done through protective equipment – proper solar glasses and solar telescopes, or through a pinhole projection system.
Partial solar eclipses occur when the Sun and Moon do not quite align in the sky as viewed from Earth, and the deep shadow cast by the smaller body passing across the bigger one just misses the planet.
Nonetheless, the phenomenon will result in a dip in light, depending on how big a chunk of the solar disc the Moon can obscure. This effect will vary from place to place and in time.
Northern Algeria was the first location to witness the phenomenon at 0640 GMT. In European cities like London and Paris, the eclipse will already be under way as the Sun rises, with the Moon covering up almost 70% of our star by 0812 GMT in the British capital, and 65% of the solar disc by 0809 GMT in the French capital.
The further east the event tracks, the closer it gets to local sunset. Central Russia, Kazakhstan, Mongolia and north-west China will all observe an eclipsed Sun dive over the horizon.
Although there are three more partial solar eclipses this year, for Europeans in particular Tuesday’s event is the key one. They will not get another chance to see so much of the Sun being covered up by the Moon until 20 March 2015.
The next total solar eclipse is in November 2013 over the South Pacific.
Jonathan Amos is Science Correspondent, BBC News
*Information courtesy of SkyandTelescope.com