IGY Bulletin, Number 4, October 1957 - Current Sunspot Numbers

We move on to the October 1957 issue of the IGY Bulletin. I have already posted this Bulletin along with that of September 1957 in a pdf downloaded from the AGU archive of the Transactions, American Geophysical Union, vol. 38, #5, October, 1957.

This issue is 16 pages, comprising four articles. The articles in this issue are listed below. The numbers in parentheses refer to the IGY sub-disciplines covered in the article, using numbers from a previous post.

1. Current Sunspot Numbers (#6)

2. The IGY Research Rocket Program (#11)

3. IGY Antarctic Weather Central (#2)

4. Arctic Program (#2, 4, 5, 6, 7, 9, 10, 12, 13)

I'll cover Current Sunspot Numbers in this post.

The Bulletin article points out that the IGY "year" from July 1957 to December 1958  was partly chosen to include the anticipated solar/sunspot maximum. The sunspot number had already reached a record high level in early 1957, as shown in the figure below, taken from the article.

Sunspot numbers from 1755 to the beginning of the IGY (from the Bulletin article)

Indeed, an update to the present day of the sunspot numbers shows that the maximum during the IGY remains the highest yet observed. That was a stroke of good luck!

World Data Center, Sunspot Index Long-term Solar Observations 

New programs for observing sunspots during the IGY were not particularly needed, since spots were already being systematically observed by solar astronomers. But related heliophysical phenomena were to be studied.

The Bulletin article is largely a review of the knowledge of sunspots at the time of the beginning of the IGY. Some of the major points are as follows:

• Galileo used his new telescope in 1612 to make the first detailed observations, concluding sunspots were on the sun's surface rather than shadows of other bodies.
• Sunspots have been observed regularly since 1749.
• In 1834, Swiss astronomer R. Wolf devised an equation to standardize the daily sunspot number, Rn = k(10g +s), where g is the number of sunspot groups, s is the number of individual spots, and k is a constant to normalize for the conditions of each observing station.
• Daily sunspot numbers fluctuate, so running averages are used to smooth the series.
• Sunspot cycles are about 11 years.
• The cycle maxima vary by about a factor of three.
• Sunspot sizes vary from 500-50,000 miles in diameter (the circumference of the Earth is about 24,000 miles).
• Sunspots concentrate at lower solar latitudes.
• Magnetic fields associated with sunspots are as high as 4,000 gauss (the Earth's magnetic field strength is about 0.5 gauss).
• Sunspots often occur in pairs of opposite magnetic polarity.
• Many other solar phenomena are associated with sunspots.

Today -- Oct. 18, 2021 -- the sunspot number is a big fat zero! There are no sunspot regions on the half of solar disc facing Earth.

Real time data from SpaceWeatherLive.com