Balfour Stewart - Stewart Super Flare

Stewart Super Flare

Balfour Stewart recorded a super flare on the evening of 28 August 1859 and the morning of 2 September 1859, at the Kew Observatory, and presented his findings in a paper presented to the Royal Society on 21 November 1861. He noted that while "magnetic disturbances of unusual violence and very wide extent" were recorded in various places around the world, the Kew Observatory had the benefit of self-recording magnetographs, which allowed "the means of obtaining a continuous photographic register of the state of the three elements of the earth’s magnetic force—namely, the declination, and the horizontal and vertical intensity."

Stewart went on the make the following observation.

I now proceed to notice some of the peculiarities of this magnetic storm.

It appears that we have two distinct well-marked disturbances, each commencing abruptly and ending gradually, the first of which began on the evening of August 28 and the second on the early morning of September 2. These two great disturbances correspond therefore in point of time to the two great auroral displays already alluded to.

The second disturbance is now known as the Carrington Super Flare, while the first disturbance is unnamed. As Stewart recorded and described this disturbance, this event will be referred to as the Stewart Super Flare in this discussion.

At the 11 November 1859 meeting of the Royal Astronomical Society, Richard Carrington presented a paper describing his observations of the super flare that occurred on 1 September, at 11:18 GMT and later named in his honor. In what appears to be an editorial addition made after the meeting the follow observation was appended in parenthesis.

(Mr. Carrington exhibited at the November Meeting of the Society a complete diagram of the disk of the sun at the time, and copies of the photographic records of the variations of the three magnetic elements, as obtained at Kew, and pointed out that a moderate but very marked disturbance took place at about 11h 20m ., Sept. 1st, of short duration; and that towards four hours after midnight there commenced a great magnetic storm, which subsequent accounts established to be considerable in the southern as in the northern hemisphere. While the contemporary occurrence may deserve noting, he would not have it supposed that he even leans towards hastily connecting them. “One swallow does not make a summer.”)

From this addendum, it is clear that Richard Carrington was not willing to commit professionally to connecting the magnetic disturbance with the event he had observed on the surface of the sun even though they occurred at nearly identical times. He had indeed displayed the magnetographs at the Royal Astronomical Society meeting. The time of 11:20 GMT is good agreement with other reports but the time of 4:00 GMT on 2 September 1859 for the commencement of the magnetic storm is an hour earlier than reported by Stewart.

Stewart also reported on the magnetic disturbance that occurred at the same time as the event observed by Richard Carrington.

But, beside these two remarkable disturbances into which it divided itself, this great storm comprehends a minor disturbance, not approaching these two in extent, but yet possessing an interest peculiar to itself, which entitles it to be mentioned. On September 1, a little before noon, Mr. R.C. Carrington happened to be observing, by means of a telescope, a large spot which might then be seen on the surface of our luminary, when a remarkable appearance presented itself, which he described in a communications to the Royal Astronomical Society. On calling at Kew Observatory a day or two afterwards, Mr. Carrington learned that at the very moment when he had observed this phenomena the three magnetic elements at Kew were simultaneously disturbed. If no connexion had been known to subsist between these two classes of phenomena, it would, perhaps, be wrong to consider this in any other light than a casual coincidence; but since General Sabine has proved that a relation subsists between magnetic disturbances and sun spots, it is not impossible to suppose that in this case our luminary was taken "in the act". This disturbance occurred as nearly as possible at 11h 15m Greenwich mean time, on September 1, 1859, affecting all the elements simultaneously, and commencing quite abruptly.

By citing the previous research of Edward Sabine, which established a correlation between sunspots and magnetic storms, Stewart was able to correctly advance the theory that the event observed by Richard Carrington and the magnetic disturbance that was recorded at the same time were in fact connected. The magnetic phenomena that occurred at about 11:18 GMT on 1 September 1859 are now known as a Solar Flare Effect (SFE) or a Magnetic Crochet, but the connection would not be proven for another 80 years. The SFE is a sudden ionosphere disturbances caused by soft X-rays and Extreme ultraviolet (EUV) driven enhancement of the ionosphere current vortices responsible for the regular daily variation observed on magnetometer traces. SFE are mostly observed in locations close to the sub-solar point (i.e. the point on earth when the sun is overhead) and can only be observed from stations in the sunlit hemisphere at the time of the solar flare. Using Stewart’s times, the magnetic storm associated with the Carrington Super Flare took 17 hours and 45 minutes to reach the Earth.

Stewart reported that the magnetic storm from the Stewart Super Flare, began at 22:30 GMT on the evening of 28 August 1859 as recorded by self-recording magnetographs at the Kew Observatory. Assuming that the transit time for the first super flare was the same as the second or 17 hours and 45 minutes, the Stewart Super Flare occurred at about 04:45 GMT on the morning of 28 August 1859. As the Solar Flare Effect can only be observed from the sunlit hemisphere the question becomes, what time was sunrise at the Kew Observatory on the morning of 28 August 1859?

The coordinates for Kew Observatory are (51°29'N, 0°17'W). Using the US Naval Observatory “Sun or Moon Rise/Set Table for One Year” calculator, sunrise on the morning of 28 August 1859 sunrise was 05:06GMT. The Kew Observatory was still 21 minutes from sunrise and the Solar Flare Effect would not have been registered by the self-recording magnetographs at the Kew Observatory.

Stewart did not publish the magnetograph records for the morning of 28 August 1859. While it is extremely unlikely, the original magnetograph records for that date should be inspected to determine if any disturbance was recorded because of the uncertainties in timings and the nearness of sunrise.

In the time zone at GMT+7 in would have been 15 minutes to high noon on 28 August. Any observatory situated at plus or minus two time zones would have been in an excellent position to observe the super flare and record the magnetic signature of Solar Flare Effect. Unfortunately in 1859 the Kew Observatory had the only self-recording magnetographs. Other magnetic observatories were manually operated and typically only took readings at hourly intervals unless there was a magnetic storm, in which case readings were taken at 15 minute intervals. One such magnetic observatory was the Colaba Observatory on the Island of Colaba which is now part of Mumbai (Bombay), India at GMT+5.5. In a 2003 paper the manually recorded magnetic readings from the Colaba Observatory for 1 September, through 2 September 1859 were recalibrated and evaluated. No mention is made in this paper of reading before 1 September or any visual observations of the sun. After 150 years it is very unlikely that any additional data will surface but any reports of strange events about noon Asian time on 28 August 1859 would be of interest.