Sunspots in History

Today's sunspot
number is

Courtesy National Oceanic and Atmospheric Administration
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Solar activity undulates on an 11 year cycle. At the "solar maximum" there are more solar flares, more sunspots, more sun quakes, more of everything that solar physicists love to study. But the solar cycle is not just for academics -- it affects everyday life on Earth, sometimes in unexpected ways. Northern lights have inspired art and poetry. A new science was born earlier this century thanks to the solar minimum. There's no evidence, but some people claim that even the length of mini-skirts and the performance of stocks are affected by sunspots.
This is your chance to draw your own conclusions. Using the plotter, below, you can graph the sunspot number around the time of any date you choose. A few historically interesting dates are listed in the sidebar, but you may enter any date you consider significant (even your birthday). If you find any interesting correlations let us know by emailing

Moments in History

1613 - Galileo discovers sunspots

1859 - Heinrich Schwabe announces discovery of the sunspot cycle

1859 - Richard Carrington discovers solar flares

1879 - Albert Einstein's birthday, March 14th

1895 - Marconi invents the radio

1897 - Amelia Earhart's birthday, July 24th

1911 - Roald Amundsen reaches the South Pole in December, one month before Scott

1927 - Charles Lindberg crosses the Atlantic by plane on May 20th

1929 - Stock market crash on Oct 24th precipitated the Great Depression

1939 - WWII begins

1942 - J.S. Hey discovers solar radio emission

1945 - end of World War II

1957 - The Soviet Union launches Sputnik, the first artificial satellite

1958 - "Score", the first communications satellite launched by the US

1969 - first manned mission to the moon

1980 - launch of the Solar Maximum Mission satellite

1981 - first flight of the space shuttle

1987 - Dow loses 508 points on Oct 29th, the worst percentage single day drop in history

1997 - Dow loses 554 points on Oct 27th, the worst total single day drop in history

For more information on current solar conditions visit
The Space Weather Bureau

Sunspot Plotter (Java support required)

Were you born during a solar maximum or minimum? Did the Great Depression occur during a dearth of sunspots? Was WWII waged under an active sun? Find out here. Using the pull-down menus below enter your birth date, or any other date that interests you, and hit "Refresh".

Sunspots and the Birth Of Radio Astronomy
Back in 1928 a young physicist named Karl Jansky was hired by Bell Labs to work on a new technology called "radio telephony". In those days radio telephone service was on the cutting edge, and there were many unsolved problems. Trans-Atlantic telephone connections suffered from myriad forms of interference including static from lightning and automobile engines, and a mysterious phonomenon called "magnetic storms" could disrupt service for days.

Jansky, who had very little experience in radio engineering, was nevertheless assigned the task of studying trans-Atlantic radio interference. In 1930 he began work on the antenna pictured right, and by 1931 Jansky was making regular observations of radio static at a frequency of 20.5 MHz. The "Jansky Antenna" doesn't look much like modern arials, i.e., TV antennas or satellite dishes, because it was designed to receive shortwave signals coming over the horizon.

A photo of Karl Jansky from a 1933 Bell Labs press release. He is pointing out radio emission contours on a celestial sky map.

By 1933 Jansky's studies of radio interference were well-advanced, and he noticed an extraordinary thing: some of the radio static he observed came from a fixed point in the sky, and it moved with the stars! Jansky was an amateur astronomer and he ultimately realized that the source of the cosmic radio noise was the Milky Way itself. It was the first time that anyone had observed the cosmos at wavelengths outside the optical window, and it marked the beginning of a new science, radio astronomy.

How do sunspots fit in to this story? This way: the earth's atmosphere has a layer called the "ionosphere" which is ionised by radiation from the sun. The ionosphere acts like a mirror. When a shortwave radio station transmits a signal, it reflects off the ionosphere rather than shooting off into space. Shortwaves can bounce many times and thus travel long distances around the globe. This is how ham radio operators can communicate over long distances.

During solar maximum the ionosphere is relatively dense 24 hrs a day. Shortwave radio signals from the cosmos reflect off the ionosphere back into space, and terrestrial radio stations and other sources of static are trapped inside the ionosphere and cause a great deal of interference. Radio astronomers who observe at shortwave frequencies can attest that it's nearly impossible to observe cosmic radio sources during the sunspot maximum, especially during the daytime when the ionosphere is particularly dense. Only during a sunspot minimum are conditions suitable for astronomical observations.

As fate would have it, Jansky's work was conducted during solar minimum. To see this, enter the date "01 Jan 1933" in the sunspot plotter above. His daytime observations of the Milky Way, conducted from 1932 through 1934, would likely have been impossible a few years earlier or later when solar activity was high. Thanks to Jansky's insight and the coincidence of the solar minimum a new window on the Universe was opened and radio astronomy was born.

This chart recording shows some of Jansky's observations of the Galactic Center (called "Sagitarius A" by astronomers). Jansky rotated his antenna 360 degrees around a circular track once every 20 minutes. When the antenna beam swung past the galactic center, which was low on the horizon at the time of these observations, a peak was recorded on the strip chart record. Note the times of day that the recordings were obtained -- in the late afternoon. Shortwave radio astronomy observations at that time of day, especially of an object low on the horizon, would normally be impossible. However, because the data were collected during a solar minimum, Earth's ionosphere was transparent, radio interference was low, and Jansky was able to make his historic observations.

Back to Sunspots and The Solar Cycle

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