Over on our sister site, the Old Weather team are digitising ship’s logs from first world war Royal Navy vessels in order to capture the valuable meteorological information that the fleet collected. These records also contain information that can be surprisingly useful for a whole host of other reasons.
One such example was identified by HebesDad and brought to our attention over at Solar Stormwatch by Caro.
In the log of H.M.S. Hilary on Saturday February 10th 1917, the observer wrote;
“at noon aTS observed spots near centre of sun like this [diagram] it appeared to be two with a narrow passage between them, I make this note, for although I have seen sun spots before, I have never seen such large ones”
This is an unusual sighting and, if observed with the naked eye, (something you should never try to do as you risk damaging your eyes) the spots must have been very large indeed.
I consulted my colleagues at the UK Solar System Data Centre at the Rutherford Appleton Laboratory and they were able to confirm that this observation was indeed correct. Photographs taken from the Dehra Dun observatory show quite clearly that on that day, and on the days leading up to the 10th, a large sunspot group was indeed observed almost exactly as the observer on H.M.S. Hilary described.
My colleague Dr David Willis, an expert on historical sunspot observations, informs me that the accepted limit above which sunspots can be seen with the naked eye is taken to be when a sunspot exceeds an area of 500 millionths of the Sun’s visible hemisphere. On my screen, the Sun has a diameter of 220mm while the spots are around 10 mm. Using the formula for the area of a circle (3.14 x [radius squared]), I estimate that the area of each of these spots is around 6195 millionths of the total area of the Sun. These sunspots are clearly above the threshold to be viewed with the naked eye!
David also provided information from the Greenwich observatory publication “Sunspots and Geomagnetic-Storm Data Derived From Greenwich Observations 1874-1954” (HM Stationary Office, 1955). In a list of the 55 greatest sunspots in the interval 1874-1954 this sunspot group (number 7977) recorded the 8th largest maximum area.
The reason we are so interested in observation of sunspots is that these regions are closely linked with solar mass ejections – vast eruptions of material from the Sun’s atmosphere. If one of these eruptions comes towards Earth, it can generate spectacular auroral displays, disturb the Earth’s magnetic field – leading to anomalous compass bearings, deplete the ionosphere (the electrically charged layers in the Earth’s upper atmosphere) – leading to disruption of radio communications, and cause surges of electricity along any long cables such as power and communications networks.
Matthew Wild at the UKSSDC generated a plot of the aa index for February 1917. The aa index is a measure of the variability in Earth’s magnetic field. This index compares the measurements made by two magnetic observatories on opposite sides of the World in the UK and Australia. Measurements started in 1868. Originally the UK measurements were made at Kew in London but they are now made at Hartland in the UK while the Australian measurements are made in Canberra. Large values of aa represent a disturbed magnetic field.
Looking at the aa index for February 1917 we can see that the values around the 10th were not particularly high but that on the 15th February, aa levels increased from around 20 to over 150! It is likely that this is a result of the Earth being hit by a solar storm launched from this enormous sunspot group. It is difficult to say how big or fast this storm was since we have no record of when it was launched but these storms travel at speeds between 400 and 2000 km per second, reaching Earth in 1-3 days. It would be interesting to see if any ships reported erratic compass bearings during this time as the cloud of solar material buffeted the Earth’s magnetic field in space. Variable magnetic fields set up electrical currents that heat the Earth’s upper atmosphere, depleting the ionisation there. As a consequence, wireless operators, using the ionosphere to reflect their wireless signals around the world, would also have noticed a weakened signal strengths in the days that followed the arrival of the solar storm at Earth. The Greenwich publication noted a ‘small’ geomagnetic storm on the 15th and rather curiously relates it to the much smaller sunspot group number 7990 though there seems to be no conclusive proof of this.
So, there you have it. A rare observation of a large sunspot group visible with the naked eye recorded with precision by a diligent observer who presumably knew the potential impact that such an observation could have to both the ship’s navigation and radio communication (if it was equipped with such modern technology).
If you are interested in finding out more about the Sun and solar storms feel free to join us over at solar stormwatch where you can even help predict the arrival of solar storms at Earth. Meanwhile please keep us posted on any sightings of aurora, sunspots, erratic compass needles or poor wireless reception. They are all clues about the activity of the Sun in a time long before spaceflight.
My thanks to Matthew, Sarah and David at the Rutherford Appleton Laboratory for helping to piece this story together. If you would like more information about the UK Solar System Data Centre and the records it contains, visit http://www.ukssdc.ac.uk. Solar images are under Crown Copyright.
Thanks to everyone who helped track the most recent bunch of solar storms. Several of them came by Earth but their magnetic fields were mostly the same polarity as Earth’s and when this happens, just like in the school experiment, the two magnetic fields just bounce off each other. I was amazed that we could track an Earth-directed storm at all from where the spacecraft are now, particularly with the gaps now appearing in the data coverage in incoming-traceit. You are really showing us what the limits are on our mission! Keep tracking the real-time events though. Even if we can’t track them to Earth very easily we can still test out our tracking skills by watching them go by other planets. We have spacecraft around all the inner planets at the moment:- Messenger at Mercury, Venus Express at Venus, the sister-craft to Mars Express which (amongst others) is orbiting Mars.
Thanks to your efforts we now have two publications that used your clicks to help track storms and dust. The next task we’re aiming to do is to analyse the huge amount of data you have processed in the trace-it archive. With this dataset we hope to track each storm in detail as it expands out into the solar wind. Experts like Solar Stormwatch’s own Neel Savani can turn your clicks into a comprehensive survey of all the storms we have seen. Not only will this analysis tell us how fast and how big each storm was, it should also reveal how much it was distorted by the solar wind into which it was expanding – vital information in tracking their progress towards our planet.
So, please keep clicking on trace-it archive data too. The real time stuff may be the most exciting but the careful consideration of the archived data will be an important part of the Solar Stormwatch legacy too.
And the fruitcake? Ah… I appear to have eaten the last photograph of one that Jules posted to the forum… sorry.
Thanks once again for all your enthusiasm, time and efforts. It really is a privilege working with you all.
Hi Stormwatchers! The science team may have been a bit quiet on the Stormwatch forum of late but that doesn’t mean we’re not still involved. You may have seen the announcement in the forum pages of our first Stormwatch related paper, published in the Monthly Notices of the Royal Astronomical Society. This focussed on the detection of interplanetary dust from particle trails seen in HI images. If you want to see how your efforts translated to real science, a preview of the paper can be found at; http://arxiv.org/abs/1111.4389 thanks to everyone who spent the time looking at dust! There is a second paper, this time using Stormwatch identifications of solar storms to remove them from the data so that we could look at the effects of high speed solar wind streams arriving at Earth. This paper has been submitted to the Space Weather journal and is currently under review (it is sent to fellow scientists for their comments to ensure that we’re not saying anything incorrect or outrageous). I’ll let you know when I hear more about this. So, we have two publications on the go, with real science informed by your efforts. Thank you so much, we really appreciate your time and efforts but it won’t stop there. Currently we have scientists lined up to take a look at the Stormwatch real-time forecasts generated by you in incoming! and incoming trace-it, and also someone who will be looking at the comet data. This is potentially really exciting as we’re hoping to use observations of the absorption of starlight as the tail drifts across distance starts to tell us something about the particle sizes in the comet tail. Comparing these with observations made in the infra-red by the Herschel spacecraft will hopefully provide some insight into the generation of the very material that we have seen hitting the STEREO spacecraft!
You may also have seen that there was an earth-directed storm that arrived at Earth today without us being able to make a prediction from your clicks. This may have been due to unfortunate gaps in the telemetry from the spacecraft or simply that the spacecraft are now sufficiently far from Earth that making such forecasts for our planet are becoming more challenging. Please keep clicking though, any storm tracked in the science and real-time data is providing us with valuable information on what we will need if we are to accurately predict these storms in future. There is plenty of information left to be mined from our data and we simply wouldn’t be able to do it without you all. Thank you once again for your enthusiasm, efforts and time. It’s such a privilege to be working with you all.
Last month I attended the Astronomy Photographer of the Year awards, held at the Royal Observatory Greenwich, with fellow Solar Stormwatch forum moderator ElisabethB (Els) and fellow Moon Zoo forum moderator Geoff. The overall winner was an amazing photo of Jupiter, Io and Ganymede by Damian Peach showing detail on the two moons – well worth pouring over in high resolution. Some solar astrophotos made the final list this year. In particular Dani Caxete’s photo of the ISS crossing the Sun was one of our favourites as this required nerves of steel to click the shutter at the precise moment.
Here are the solar related photos that made it through to the finals.
“Earth and Space” category runners up:
by Ole C. Salomonsen (Norway)
high resolution version
by Örvar Atli Þorgeirsson (Iceland)
high resolution version
“Our Solar System” category runners up:
|May 7th Hydrogen-Alpha Sun
by Peter Ward (Australia)
high resolution version
|ISS and Endeavour crossing the Sun
by Dani Caxete (Spain)
high resolution version
And here are some that didn’t make the final:
|Another ISS transit
by Thierry Legault
|Entitled “solar keyhole”
by Steven Christenson
|A different kind of transit
|A fabulous sunset
by Stefano De Rosa
|A sun halo
by Niki Giada
Thanks to everyone for their efforts in tracking our first real-time Earth-directed solar storm. We have been very impressed by the care with which you have all been analysing our data. So, what happened? Well, from your clicks, we predicted a storm would reach Earth around 07:00 on the 13th of December. Meantime the official spaceweather forecast issued by NOAA gave the following warning;
Space Weather Message Code: WARK04
Serial Number: 1681
Issue Time: 2010 Dec 12 1708 UTC
WARNING: Geomagnetic K-index of 4 expected
Valid From: 2010 Dec 12 1710 UTC
Valid To: 2010 Dec 13 0700 UTC
Warning Condition: Onset
The K-index is a measure of the amount of disturbance in the Earth’s magnetic field (as it is buffeted by the solar wind). A little later NOAA sent confirmation that the Earth’s field was indeed being affected;
Space Weather Message Code: ALTK04
Serial Number: 1488
Issue Time: 2010 Dec 12 1742 UTC
ALERT: Geomagnetic K-index of 4
Threshold Reached: 2010 Dec 12 1741 UTC
Synoptic Period: 1500-1800 UTC
Active Warning: Yes
(I’d encourage you to keep an eye on the professional forecast issued by NOAA at http://www.spaceweather.gov)
So, it seems that something arrived at Earth around 14 hours before our prediction. The effect wasn’t very big but was this disturbance caused by the same storm that we were tracking? I think so, and I’d like to talk you through why I think that.
It is true to say that not much happened at Earth as a result of this storm but just imagine standing in front of someone who was about to throw a baseball at you from a distance. The difference in angle that the pitcher would have to throw that ball between it sailing harmlessly by and alternatively hitting you on the nose is very small but the two scenarios would have dramatically different consequences! OK so this analogy breaks down when you consider that the storm expands as it travels out from the Sun and is very large by the time it reaches the distance of Earth but the principle stands. It doesn’t have to miss by much for it to have little or no effect at all. To stretch this analogy a bit further, I think this storm just brushed by our ear! It’s also difficult to tell ahead of time just how effective a storm will be (in my now horribly tortured analogy, we don’t know whether it’s a baseball or a beachball – OK, that poor analogy has suffered enough, I’ll stop hurting it now).
The reason I think our timing was out for this event was that we ask you to scale the middle of the features in the j-maps (keep doing this, it’s the best way!) so this would mean we are not tracking the absolute front of the storm (which would arrive at Earth a little earlier). Once we have a few predictions under our belt, we’ll know what this offset is (and 12 hours is not a bad estimate from the experience we have so far) and will compensate accordingly.
But how do we know that there wasn’t much of an effect at Earth? Well, one way is to look at data from the Advanced Composition Explorer (ACE) spacecraft. This sits about a million miles upstream from Earth in the solar wind and ‘tastes’ the wind as it goes by. A solar storm usually contains a giant bubble of magnetic field that sweeps up material ahead of it while material from the solar atmosphere expands into the void behind. ACE has many detectors but a useful summary of solar wind conditions over the last seven days can be found at;
This is a rolling summary of solar wind conditions just upstream of the Earth. These plots are a somewhat confusing collection of wiggly lines that, between them, can tell us if anything unusual is happening. The top panel contains the total magnetic field strength (Bt) and the size of the component that is aligned to the Earth’s magnetic field (Bz). If a magnetic bubble goes by, we’d expect Bt to go up and if Bz was negative at the time (southward) it would mean that the solar storm and Earth’s magnetic fields were aligned in opposite directions – ideal for the two fields to merge and let the solar wind into the Earth’s atmosphere to cause an aurora. On the afternoon of the 12th, the total field does indeed increase in strength but the Bz component is positive for the most part, meaning that the Earth and solar wind magnetic fields were aligned – remember that two aligned magnets repel each other while opposites attract. Not surprising then that there wasn’t much activity.
As a storm goes by ACE, we’d also expect a sudden increase in the solar wind speed and density as a storm front passes (two of the lower panels are marked speed and density). While the speed and density did increase, they didn’t go up by very much and there were no sudden jumps indicating that the storm was not travelling fast enough to generate a shock ahead of it.
Another way of investigating whether the Earth’s magnetic field was rattled by the event is to look at measurements by the aurorawatch team at;
Their page shows the current state of the Earth’s magnetic field over northern Europe. When a solar storm hits Earth, the very least it does is cause the Earth’s field to be compressed and wobble. This shows up on the ground by very small compass movements. The aurorawatch team run a series of sensitive magnetic field monitors (called magnetometers) and present their data as a series of graphs. Basically, a flat line means a quiet magnetic field and a wiggly line means that the Earth’s field is being buffeted by the solar wind. On the day of our prediction the aurorawatch plots showed little or no disturbance to the Earth’s magnetic field over Europe (in contrast to the activity seen in Boulder, Colorado).
So, while this was not exactly ‘the perfect storm’, I think it did enough to show that our techniques work and that you are all doing a fantastic job in your careful analysis of the STEREO HI data.
In my geekier moments (which occur far too often to be healthy) I like to think that the pioneering space-weather forecasters of today are not only helping us to protect our technological infrastructure here on Earth but are also blazing the trail for the future exploration of the solar-system. Your efforts with solar stormwatch are an important part of this, and I’m really grateful for your time, careful analysis and enthusiasm in helping us with our work.
Tin hats on everyone! Stormwatchers have been tracking a solar storm launched from the Sun on the 14th October. Analysis of your results shows that this storm, travelling at 244 km per second, will cross Earth’s orbit at 14:43 GMT on the 21st October just 37 degrees ahead of our planet. While this is not expected to be a direct hit, we may still suffer a glancing blow so look out for auroral displays around this time. Stormwatchers have enabled this forecast by participating in the ‘Incoming -Trace it’ activity and have been doing such a great job that we can now start to issue warnings ahead of their arrival at Earth. Thanks to everyone for your hard work and patience. The more people we have looking out for and tracking these storms, the better our forecasts will be, so tell your friends!
Thanks to Neel for his ‘life as a scientist’ piece. While Neel is busy writing up his results, Stormwatch is gearing up for the next release of activities with which we hope to be analysing each storm in much greater detail. As we accumulate data from all your dedicated analysis, we are starting to get some preliminary science results that, at some point, when we are confident that we are interpreting them correctly, we will want to share with you so that you can see the outcome of your hard work. the question is, how would you like us to do this? Obviously there is the blog and the forum but are there any other ways you would like us to communicate the science with you?
Meanwhile, Stormwatch continues to attract media attention. This month’s (June) Sky at Night magazine contains an article summarising several astronomy projects that rely on the input from many members such as Galaxy Zoo, Moon Zoo and Solar Stormwatch (the cover disk also contains the April edition of the TV programme which is all about the Sun).
Those of you who have been looking at the real-time data will know that the Sun appears to be waking up (slowly mind you!) and this means that it is becoming increasingly likely that a CME will occur. Keep up the good work, and look out for new activities in Solar Stormwatch soon.