[UPDATE: Oh for criminy's sake. I made a mistake here. The big sunspot group I describe below is actually AR 1515 which has been on the Sun for a while now. AR 1520 can be seen in the full Sun pic on the very left, on the Sun's edge! It's still huge, roughly the same size as 1515, and it's just now coming into view. Most everything I said below about the sunspot group is correct, except it's about 1515 and not 1520! I've corrected the details below. Sorry about the confusion, and thanks to zAmboni in the comments for pointing this out!]
The Sun is at it again:
Active Region 1520, a vast sunspot group, is currently blemishing the Sun's face. Active Region 1515, a vast sunspot group, has been blemishing the Sun's face for days, and is being joined by Active region 1520, another huge group just now coming around the Sun's edge.
This Solar Dynamics Observatory image shows AR 1515 on the lower right and AR 1520 on the lower left. A quick measurement shows both are about 200,000 kilometers (120,000 miles) across - fifteen times the width of the Earth! If one end were placed on Earth, it would stretch halfway to the Moon.
Having a hard time grasping that? Let me help: here's the sunspot cluster AR 1515 zoomed in a bit, with the Earth overlaid pretty much to the same scale:
Holy. Crap. The Sun never does anything small, does it?
In fact, this cluster is so flippin' big you can see it without a telescope! I just went outside and looked using certified eclipse glasses I got for the last solar eclipse. The sunspot cluster was obvious to my naked eye! It's even easier to see than Venus was during the transit in June.
[WARNING: Listen folks, never look at the Sun without adequate protection. While looking at the Sun won't necessarily cause permanent or total blindness, it's not a good idea, and you should NEVER look at the Sun through binoculars or a telescope unless they are outfitted properly. If you don't know what you're doing with astronomical equipment, the best bet is don't do it. If you don't have eclipse glasses or the right kind of filter, I suggest using binoculars to project the Sun's image on a piece of paper (noting this can still damage your binoculars). I have notes on viewing something like this safely on my Transit of Venus page. Read that first before trying anything!]
This cluster should be visible over the next ten days or so as the Sun rotates. While AR 1515 will rotate around to the Sun's far side in a few days, AR 1520 is coming into view now and will be visible for about two weeks. The magnetic field associated with them will be huge as well, so it wouldn't surprise me if we get some activity in the form of flares from these guys, too. Since I'll be at Comic Con for several days starting Thursday, I suggest checking SpaceWeather and Universe Today for updates on any solar activity this cluster might unleash. Maybe we'll get more aurorae!