My internal aurora detector went off last night when I stepped outside and noticed the bottom of the northern sky looking paler than usual. There was even a hint Irish green or so I imagined. Clouds roughhoused about the sky but left the far north alone. Once I got out to a nearby open field with horizon views all around, there was no doubt that northern pallor was a low arc of aurora. The time was shortly before 10 o’clock and the display – if you could call it that – lasted about a half hour. A half-dozen faint rays stretched lazily up from the horizon, each fading away within half a minute.
The modest show was precipitated by a gusty solar wind which interacted with out planet’s magnetic field to send high speed ions (electrons and protons) from the sun into the upper atmosphere where they pummeled atoms of nitrogen and oxygen into a state of excitation. As oxygen molecules return to their “rest” state, they shoot out green photons which give the aurora its characteristic color. The photos also record some pinkish-purple hues from excited nitrogen atoms doing the same, but these were too faint to see with the eye. There’s a chance for more auroras tonight, probably not a big display for the northern states, but maybe enough to whet your appetite for more.
Amateur astronomer Jon Dannehy commented last week that Jupiter would be ideal to point naked eye sky watchers to faint Uranus, which happens to be in nearly the same line of sight. Since the two planets are separated by only about a degree (your little finger held up against the sky), I told Jon that the glare caused by Jupiter’s proximity might overwhelm the faint planet and make it really tough to see without binoculars. He suggested it might not be as hard as that if we simply hid the planet behind something like the eave of a house or a power pole.
Last Saturday, Jon and I checked it out, and I’m happy to report we both saw Uranus in spite of the giant’s glow. We used the hiding technique as well as averted vision, a technique of looking around and to the side of Uranus rather than staring directly at the spot. This exposes a more sensitive part of your eye better at picking up faint objects. You can also prime your eye to know precisely where to look by first spotting the planet in a pair in binoculars.
Once we found Uranus by hiding the bright planet, we had no problem seeing it with Jupiter fully out in the open. One caveat: you’ll need dark skies. Don’t attempt this from downtown unless you’re into total frustration. Go out around 10:30 p.m. or 11 p.m., when Jupiter shines brilliantly in the southeastern sky, and use the photograph and binoculars to get oriented. Jon’s Challenge awaits – have at it my friends!