Solar cycle 25

• Longer nights during the fall and winter also favour seeing more auroras, but the show is best outside of light-polluted cities.
• Impressive auroral events allowed bright auroras to be seen as far south as the United States recently.
• The number of auroras is increasing as the sun’s activity becomes stronger, approaching a solar maximum.

Night visions

• The Earth, in the sun’s outer atmosphere, is surrounded by hot magnetic plasma which rushes past us at speeds of several hundred kilometres per second in a flow called the solar wind.
• Earth has a magnetic field, which protects us from the solar onslaught, but is pushed back by it as well.

• This explains why auroras are seen at night: not only is it dark, but the sun’s energy takes an indirect route by first being stored in the magnetotail.
• If the magnetic fields change rapidly, they can affect large regions of the Earth, building up to cause problems for power networks.

Solar cycles

• About 300 years later, American astronomer George Hale showed that sunspots had intense magnetic fields, several thousand times stronger than Earth’s.
• In the 400 years since Galileo’s observations, we have found that the number of sunspots varies dramatically over an 11-year long cycle.

Energy storage

• Magnetic fields store energy, and sometimes, as in Earth’s magnetotail or near sunspots, this energy can be changed to other forms.
• In the strong fields of sunspots, it can be released as X-rays in rapid, unpredictable flares.
• Sunspots and flares are near the surface or light-emitting layer of the sun, but material can escape from the sun’s strong gravity field.

Space weather forecasts

• However, in this, the following solar cycle, we have already exceeded predicted numbers of sunspots and had large magnetic storms, so predictions may need to be revised upward.
• Although direct measurement of incoming disturbances by satellites in the solar wind gives us only about an hour’s warning of stormy space weather, we can also predict a bit further in advance by watching sunspots rotate into view as the sun turns.

Rare storms

• The strongest flare of Solar Cycle 25 so far occurred on Dec. 14, and was the most powerful eruption the sun has produced since the great storms of September 2017.
• Large solar storms are rare, but we must calmly prepare for possible space weather impacts that should maximize in a few years.

Martin Gerard Connors receives funding from Canada's NSERC.