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.
As another year of stormwatching draws to a close I thought I’d summarise some of the things we have achieved and talked about. So rather than go on at length here’s a word cloud taken from the blog topics over the last year. The larger the text, the more that word featured. Enjoy!
Thanks to all stormwatchers for your sterling efforts in 2011. Here’s to 2012 and another busy year of watching and monitoring our nearest star.
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
Every four hours we pull all the data from incoming trace-it from the database, this give us a massive file with lines looking like.
This is broken down as follows:-
- 20110601_014721_hiB_jmap_999 – the name of the jmap – identifies the latest data in the jmap, the camera and in this case that the data is for the ecliptic plane.
- 99437 – the code number for the user
- 2455712.838797814 the date [as a julian date] here 2011/05/31 08:7:52 GMT
- 43.66942148760331 the elongation angle measured from the image
These last two fields repeat as a pair for the entire profile.
The first process is some simple housekeeping where the result set in each profile is ordered in time and where people have clicked on two traces the line is split into two separate entries; there is a potential pitfall here if two profiles overlap in time and contributors are discouraged from doing this but this process at least allows this data to go forward.
The profiles are then collected into sets arranged by the earliest time in the profile, if from less that 10 degrees elongation, rounded to the nearest hour and split by spacecraft ahead or behind.
The next process counts the number of profiles in each of these bins, but also introduces the concept of a “good” profile that must have a least 3 points and span an elongation range of at least 5 degrees. A 7 hour running window is then computed over the count of good assets. Intervals are then identified where there are more than 10 profiles and the largest value in that range is then identified as an event.
For each event all results meeting the “good” criteria in a 7 hour running window are gathered together into a single file for the fitting process.
The plot shows for August 2010 in red the total number of profiles, in green the total number of “good” profiles and in blue the running total and shows three distinct events on the behind spacecraft and two on ahead.
In my next post I will discuss taking the clicks for a single profile and producing speeds and directions.
Now that you have been analysing the data for some time, we can now start to look at the results that are coming out from your anayses. First off, thank you all for your efforts. I’m genuinely humbled that so many of you have taken time to click on our data.
We have been using the information you have provided via the spot! videos to identify storms and give preliminary values of the their speeds and directions where we can. Jackie has used these numbers to identify the start-times of storms in the jmaps we show you in trace-it (this tells us where to put that pesky blue bar on the jmap to show you which line we are interested in!).
Recently, I’ve been looking at your clicks from Trace-it and thought you’d like to see the preliminary results.
First off is a plot showing the speeds of storms from HI-A;
Here N is the number we see at each speed, so the taller the column, the more storms we see with that particular speed. This distribution certainly is a picture of a quiet solar wind! Most storms are travelling with speeds around 350 km/s but there are a few faster ones…
If we look at the distribution of speeds of storms seen in HI-B we see much the same picture;
Again, most with a relatively slow velocity (350 km/s) while a few have much faster velocities (for comparison, the famous Carrington storm of 1859 travelled at around 2,500 km/s reaching Earth in 17 hours).
So, what do your results tell us? Well, for one thing, it certainly is true that storms can occur at any time of the solar activity cycle. We were amazed to see so many with STEREO at a period when the Sun was quieter than at any time in the last century! The fact that storms still occur means that there are still changes occuring in the Sun’s magnetic cycle. Some scientists think that solar storms are the mechanism by which the magnetic field continues to evolve on the Sun. Even if the field is so weak on the solar disk that there are no obvious sun-spots. The fact that we can see storm activity during this period of extreme quiet is interesting evidence for this continued evolution. The fact that most were no faster than the solar wind would have meant that without spacecraft like STEREO and ACE they would probably have gone largely undetected.
I also plotted out the angles of the storm trajectories with respect to the Earth for HI-A;
We have seem storms over a wide variety of angles, as we’d expect (they should be emitted in random directions as the Sun doesn’t pick on the Earth out of spite!). The fact that the distribution peaks at an angle of zero (headed Earthward) is likely to be due to the evolving geometry of the mission as the spacecraft head away from Earth. The distribution for HI-B looks similar;
So, what do these first results tell us? Well, for starters it confirms that you are doing a fantastic job! It also confirms that there have been few spectacularly fast storms. Our next steps will be to compare the data from both spacecraft to see if they agree with each other (!) and update the speed and directions for the storms you have already identified in ‘Spot’ but for which we couldn’t estimate the speed. Then we can pick out (say) the Earth-directed ones and take a look at them in more detail.
We could still use your help in trace-it though so please keep looking at our data. The more clicks we have, the more accurately we can determine each storm’s characteristics. Eventually we hope to learn how fast each storm expands into space in all directions, how it is slowed or accelerated by the solar wind and how we can use these corrections to better predict the arrival of such storms at Earth.
Thanks again for all your time, effort and enthusiasm. Without you we would not be learning as much as we are nor learning it as fast.