Happy Fourth of July! I hope your day explodes with enjoyment.
Just don’t go to bed after the fireworks show before checking the northern sky. NOAA’s space weather prognosticators expect a small auroral storm to begin sometime tonight and continue through tomorrow night. There’s a 20% chance we’ll see action at mid-northern latitudes and a 60% chance at high latitudes, where one wonders if any auroras are seen to advantage this time of year. North of about 49 degrees north latitude, twilight lingers all night long during the summer months.
The forecasted northern lights are brought to you by a slower moving coronal mass ejection, a blast of particles from the sun usually caused by the explosive power of a solar flare.
We may not have to wait too long for the next eruption. Sunspot group 1785, which rotated onto the sun earlier this week, is a large, complicated magnetic mess and harbors the energy to kick out powerful M-class flares. The sun’s rotation will bring it forward to face Earth more directly in the days ahead increasing the chances for more auroras.
Not far behind, sunspot cluster 1787 put on its own fireworks show when it first rotated around the sun’s limb early Wednesday morning, greeting astronomers with a moderate M1.5 flare.
The big spot in 1785 is now large enough to see with the naked eye using a safe solar filter – I easily spotted it this morning as tiny dark fleck in the sun’s southeast quadrant. Sometimes we forget how big sunspots truly are. What looks like a tiny dot in a small telescope is about as big as the moon; Earth-sized spots are larger but ordinary by solar standards. This morning’s behemoth was easily thrice our planet’s diameter, and the group it belongs to spans some 8 Earth diameters.
A sunspot’s dark tone is deceiving. They only look that way because they’re 3,000 degrees cooler than the 11,000 degree photosphere, the glaring white “surface” of the sun. If we could remove the spots and see them alone against the black backdrop of outer space, they’d be much too bright to look at safely. Their size hints at the true vastness of the sun, an 863,700-mile-wide (1.4 million km) sphere of incandescent gas 4 times hotter than a handheld sparkler.