The sun has lost its spots: Here's what it means

A blemish-free sun indicates decreased solar activity known as a solar minimum. Photo / NASA

You may not have noticed but our sun has gone as blank as a cue ball. As in, it's lost its spots.

Meteorologist and sun-watcher Paul Dorian's latest report said the sun had gone "completely blank" for the second time in a month.

"The blank sun is a sign that the next solar minimum is approaching and there will be an increasing number of spotless days over the next few years.

"At first, the blankness will stretch for just a few days at a time, then it'll continue for weeks at a time, and finally it should last for months at a time when the sunspot cycle reaches its nadir. The next solar minimum phase is expected to take place around 2019 or 2020."

If you're confused about what a "blank" sun is, below is a picture of what it normally looks like, in all its solar flare-and-blemishes glory.

Solar flares and activity all over the place. Photo / NASA

According to Nasa, the sun goes through a natural solar cycle approximately every 11 years. The cycle is marked by the increase and decrease of sunspots - visible as dark blemishes on the sun's surface, or photosphere. The greatest number of sunspots in any given solar cycle is designated as "solar maximum." The lowest number is "solar minimum".

"During Solar Max, huge sunspots and intense solar flares are a daily occurrence. Auroras appear in Florida. Radiation storms knock out satellites. Radio blackouts frustrate CB radio as well. The last such episode took place in the years around 2000-2001," the space agency's website

"During solar minimum, the opposite occurs. Solar flares are almost non-existent while whole weeks go by without a single, tiny sunspot to break the monotony of the blank sun. This is what we are experiencing now."

Sunspot numbers for solar cycles 22, 23 and 24 which shows a clear weakening trend; courtesy Dr. David Hathaway, NASA/MSFC

There are consequences of a sun without spots, not least for astronauts who face the risk of having their DNA "shattered" by cosmic rays, whose potency surges during periods of solar weakness.

According to Mr Dorian, cosmic rays surge into the inner solar system "with relative ease" during periods of solar minimum.

"Solar wind decreases and sun's magnetic field weakens during solar minimums making it easier for cosmic rays to reach the Earth," he explains.

"This is a more dangerous time for astronauts as the increase in potent cosmic rays can easily shatter a strand of human DNA. Also, during years of lower sunspot number, the sun's extreme ultraviolet radiation (EUV) drops and the Earth's upper atmosphere cools and contracts.

"With sharply lower aerodynamic drag, satellites have less trouble staying in orbit - a good thing. On the other hand, space junk tends to accumulate, making the space around Earth a more dangerous place for astronauts."