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Observations under lockdown: the solar cycle

Garry Dalrymple, Sydney City Skywatchers historian, is an avid TROVE searcher, currently ‘mining’ the 1895 to 1930 articles from the Sydney Telegraph, looking for articles relating to amateur astronomy, astronomical events and members of the BAA NSW. In this article he is investigating the solar observations during the Spanish Flu in 1919.

Feeling the Sydney Covid 19 Lockdown Blues? How did our predecessors, the members of the BAA NSW Branch get on in 1919 during the Spanish Flu when they were under lockdown without daytime TV or the internet? Of course they got out their telescopes and solar observing appears to have been a source of daytime distraction available.

In 1919 there was a record run of sunspots to be seen. According to Monty Leventhal OAM who is our indefatiguable daily Sunspot observer, our closest star, the Sun, is not so active currently. Please read on, and who knows, with the right equipment, used safely, you just might get in on the ground floor of the very next Sunspot rush (predicted for 2025 by NASA). The image below is from the European Space Agency and it indicates the number of sunspots observed from 1900 to 2015. You can see the solar maximum that occurred around 1917 to 1920 and the article written in 1919 (below) illustrates the interest and excitement at this solar activity.

Daily Telegraph (Sydney, NSW: 1883-1930), Saturday 29 Nov. 1919, page 8



Sir — The recent outburst of energy in our central luminary has drawn much attention to the orb of day. Two remarkable groups of sunspots have been appearing lately. They first appeared in August, and Mr. Gale observed 19 members in one group and 25 in the other.This is now the third time they have reappeared, with, of course some modification in their shape, etc.

They appear to be preparing for a fourth reappearance. Observing this afternoon, the second group appears to have gained very much in energy. I counted no less than 30 members in the second group, several of them being double, through being bridged, the leader of the group being 20,000 miles in extent, and the whole group covering an area of 100,000 miles. One peculiarity about the leader was a faint bridge across the umbra or nucleus shooting from three sides of the spot and forming something like Y across. Through the screen glass I noticed at times of atmospheric steadiness the reddish brown color of the penumbra, or edging, of the spot, and on projecting the image for the purpose of measurement the color was confirmed. This persistency of the groups is a peculiar feature, and should be noted. Miss Clerke ("Problems in Astrophysics," page 88) draws attention to one that persisted for 21 revolutions of the sun, lasting, with, of course, certain modifications, from September, 1891, to March, 1893.

Father Cortie, of Stonyhurst, averages the life of a spot at two rotation periods. The cause of the outburst is still obscure. The computed maximum period, 11.1 years, places 1916 as the last period and 1922 as the next minimum period; but we had a gigantic, but short lived outburst in 1917, and another in 1918. Father Cortie's researches tend to show that his solar majesty does not, for some unknown reason, keep to schedule a time...

T. BRINDLEY, Hon. Sec.,

The British Astronomical Association,

New South Wales Branch.

The sunspot image below was taken by James Short at Red Hill Observatory (Observatory Park Pennant Hills) on 4th April 1914 and shows a sunspot group observed in the solar minimum of 1914. Image courtesy MAAS: collection, Sydney Observatory.HNSW. Here is ereere