Science & Technology

Ian, I'm in the dark. Can you shed some light on this...?

"If the sky is clear on the night of March the 3rd we will be able to witness the first total eclipse of the Moon visible from the United Kingdom for three years and the best since January 2001. With the Moon's colour ranging from dark coppery-brown to bright orange it can be a most beautiful sight. The red colour is why it's also known as a 'blood moon.'

So what's actually happening up there?

"A total eclipse of the Moon occurs when the Earth lies precisely between the Moon and the Sun, and can thus only happen at full Moon. As there is a full Moon every 29 and a half days one might wonder why there is not an eclipse each month. This doesn't happen because the Moon's orbit is inclined at 5 degrees to the Earth's orbit around the Sun and the Earths shadow usually passes above or below the Moon."

If the moon's in shadow, won't it be just black?

"If the Earth had no atmosphere the Moon would be invisible in the Earth's shadow. However, light refracted and filtered through the atmosphere can still illuminate the Moon a little. Its appearance depends on the amount of dust in the atmosphere: following the eruption of Mount Pinatubo in 1992, the eclipsed Moon was nearly invisible. But as the Earth has not had a major eruption for some years we can expect an impressive sight!"

Lunar eclipse

So why does a 'blood moon' go red?

"As blue light is scattered by the atmosphere more than red light (which is why our skies are blue) the light that remains is predominately red and orange  - the colour of the Sun when close to the horizon. If there were astronauts on the surface of the Moon looking back towards the Earth during a total lunar eclipse they would see a black disc surrounded by a bright red ring. It is the light from this ring that we see reflected by the Moon's surface."

When can I see it?

A partial eclipse will start at 20:16 on Saturday night (03 March) but the effects will be difficult to see. Only when part of the Moon's disc enter the full shadow region, the umbra, will the eclipse become obvious. The Moon will enter the umbra at 21:30 and be fully immersed in the Earth's shadow by 22:44. Mid-eclipse is at 23:21 and the Moon will begin to emerge from the umbral region at 23:58.  The eclipse will be finally over at 02:25."

Where's the best place to observe the lunar eclipse?

"The eclipse can be observed anywhere, even in the centre of a large town, but dark skies will enable it to be seen at its best.  The Moon will be seen in the south at an elevation of 44 degrees.  Binoculars would be a useful aid, but are not needed."