A giant sunspot group called Active Region 1339 recently rotated into view around the Sun’s eastern limb and now directly faces Earth in perfect view. In this image from NASA’s Solar and Heliospheric Observatory, the spot (upper center) resolves into a complex smattering of blotches large and small. Its north-south width is about 40,000 km (25,000 miles), three times larger than Earth’s diameter, and as you can see it’s twice again as wide lengthwise.The spot is actually visible without a telescope. But don’t stare at the Sun without a filter: you can permanently damage your central vision. A No.14 rectangular arc-welder’s glass from the hardware store will provide enough protection for naked-eye viewing. Those with scopes can buy a white-light solar filter to go over the front and enjoy the sight.
Only minor flares have come from the Sun today — so far — but AR1339 let go an X-class flare on November 3rd that swept past Mercury and Venus. X-class flares are the strongest of the four solar flare categories; you can find a guide to flare rankings in
Spaceweather’s glossary. The most recent NOAA forecast (from November 7th) for an X-class flare in the next 48 hours is 10%, but it’s 70% for the next highest category, class M. With the spot currently aimed right at us, we’d be in line for any coronal mass ejections. These can create spectacular auroras at lower latitudes than where the phenomena are usually seen.
The Sun was quiet for a long time after the last solar activity cycle ended. In 2009 there were 260 spotless days, and this current cycle (Cycle 24) is considered the slowest to get started of the space age. But activity has certainly geared up, and this year only two days have been spotless. Cycle 24 should peak in late 2013 or early 2014.
For more about sunspots, visit NASA's sunspot cycle page.
For a real-time look at the Sun, visit the Solar Dynamics Observatory site.