Your Questions / Answered
"We are on holiday in Skye 29 March to 5 April. Will we see the northern lights and when and where is best place to look?"
Tom, Surrey
The northern lights are a very beautiful sight, and well worth seeing if you get the chance, however they are impossible to predict more than a couple of days in advance. The problem is that at the UK's latitude they generally depend on eruptions from the Sun (called Coronal Mass Ejections, CMEs), and we never know exactly when these eruptions may happen. In addition, the eruption must come towards the Earth, otherwise it won’t interact with the atmosphere to create the aurora.
The frequency of these CMEs depend on the activity of the Sun which varies on an 11 year cycle. During the most active part of the cycle, 2-3 CMEs can erupt per day. In early 2008 we just starting to climb out of the most inactive part of the solar cycle, so CMEs are a lot rarer. At the moment the chances of seeing the northern lights in Britain are low. These chances will improve over the next 4-6 years however.
To make things harder, in order to have the Northern Lights visible in the south of England, you need a large CME to erupt from the Sun and interact with the Earth. These are much rarer, but your chances improve as you go further north towards and into Scotland.
The best time to view the Northern Lights is in the winter when the skies are much darker. You are unlikely to see much in the summer time as the skies are generally too light. In spring time, when there are still several hours of true darkness, it should still be possible to say any aurora that occur during the middle of the night. It is a good idea to find a darker viewing sight away from street lights and other sources of light pollution and look toward the northern horizon.
On a positive note though, it is possible for a large eruption to go off at anytime and come towards the Earth, so you may get lucky. To help, you can sign up to the AuroraWatch alert service run by the Lancaster University. More information about the AuroraWatch project can also be found on this website by clicking here.
"How long does it take for the Sun’s light to hit Pluto?"
Roger, New York
Pluto’s orbit means that it is located between about 30 to 49 Astronomical Units (4.4–7.4 billion km) from the Sun. Since light travels at just under 300,000 km per second, it takes between just over 4 hours to just under 7 hours, depending on it’s Pluto’s exact position.
Prof Róbert (Erdélyi) von Fáy-Siebenbürgen - Sheffield University
"How long does space go on for and does it ever stop?"
Emily, UK
Space is finite but unlimited. Imagine, you are a 2-dimensional flat ant living on the surface of a huge sphere. You can go around and around (unlimited) but you know that the sphere has a surface boundary (that is to say the surface is finite, provided you can see this from 3 dimensions). I know, it is tricky:)
Prof Róbert (Erdélyi) von Fáy-Siebenbürgen - Sheffield University
"One of my dearest ambitions is to see the Northern Lights. Can you tell me whether it is possible to see if from anywhere in England at any time? I will be in Scotland 1-6 July but will the sky will be too light then?"
Mary, Kent
The northern lights are a very beautiful sight, and well worth seeing if you get the chance, however they are impossible to predict more than a couple of days in advance. The problem is that at the UK's latitude they generally depend on eruptions from the Sun (called Coronal Mass Ejections, CMEs), and we never know exactly when these eruptions may happen. In addition, the eruption must come towards the Earth, otherwise it won’t interact with the atmosphere to create the aurora.
The frequency of these CMEs depend on the activity of the Sun which varies on an 11 year cycle. During the most active part of the cycle, 2-3 CMEs can erupt per day. Unfortunately, during 2007 we are in the most inactive part of the solar cycle, so CMEs are a lot rarer. At the moment the chances of seeing the northern lights in Britain are low. These chances will improve over the next 4-6 years however.
To make things harder, in order to have the Northern Lights visible in the south of England, you need a large CME to erupt from the Sun and interact with the Earth. These are much rarer, but your chances improve as you go further north towards and into Scotland.
There are also problems with the time of year. The best time to view the Northern Lights is in the winter when the skies are much darker. You are unlikely to see much in the summer time as the skies are generally too light. It is a good idea to find a darker viewing sight away from street lights and other sources of light pollution.
On a positive note though, it is possible for a large eruption to go off at anytime and come towards the Earth, so you may get lucky. To help, you can sign up to the AuroraWatch alert service run by the Lancaster University. More information about the AuroraWatch project can also be found on this website by clicking here.
Dr Daniel Brown - University of Wales Aberystwyth
"Why are the Sun’s magnetic fields twisted?"
Peter, London
The Sun is not a solid body at all. Equatorial regions rotate faster than polar regions. And to make things even more complicated, internal regions rotate with different rotation rate than surface regions. This is called differential rotation.
In general, differential rotation is seen when different parts of a rotating object move with different rates of rotation (different angular velocities).
This differential rotation spins up the dipole magnetic field lines that are generated about 200,000 km below the solar surface. This region is called the tachocline - in solar terms it is a very narrow layer.
Once the field lines are spun up, they slowly rise and emerge from the solar interior and will pop up through the visible solar surface, e.g. in the form of sunspots.
Prof Róbert (Erdélyi) von Fáy-Siebenbürgen - Sheffield University
"I have read that over time the Earth's magnetic field will become reversed. Could you tell me over what sort of time scale this event would take place and how would we notice it?"
Derek Silvester, Kendal Cumbria.
The last reversal was about 800,000 years ago and, since the average time between reversals is about 250,000 years, you could say one is overdue. Current estimates suggest it might be another thousand years or more before the next reversal may occur. Of course the last one was so long ago that we simply don’t know the details of what happened then or will happen next time.
Our scientific models of the process suggest a reversal takes a few thousand years to complete. That’s fast on a geological time scale. During this time the well-known “bar magnet” pattern of magnetic field lines will be distorted into much more complicated patterns.
In all likelihood there will be more than one north and one south magnetic pole, at least for a time. The overall strength of the magnetic field will decrease and may almost disappear for a time. Then the field will start to strengthen again and restore a single north and single south pole. At that time, however, magnetic “north” on the compass will actually point south.
Dr Alan Thomson
Seismology and Geomagnetism, British Geological Survey.
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