On Tap August 19 — Aurora Alert, the Frail Moon and 653 Starlinks

Live in the northern U.S. or Canada? Keep an eye on the lower half of the northern sky tonight (Aug. 19) starting around 10 p.m. CDT till dawn. A double-punch of particles from a modest coronal hole and long duration solar flare are...

Aurora March 30_2017 B_S
Another view of Thursday night's northern lights. Both the green and red colors are caused by solar wind electrons striking oxygen atoms in the upper atmosphere. Credit: Bob King

Aurora ray sharp March 15_2018 S
A modest aurora from March 2018 displays multiple, pale green arcs low in the northern sky and several rays including a bright one resembling a tall flame.Bob King

Live in the northern U.S. or Canada? Keep an eye on the lower half of the northern sky tonight (Aug. 19) starting around 10 p.m. CDT till dawn. A double-punch of particles from a modest coronal hole and long duration solar flare are expected to arrive during that time and fire up a minor display of northern lights. In this time of solar minimum, when the sun's activity dips low and auroras are scarce, beggars can't be choosers. Even a peck-on-the-cheek from the restless sun will do.

Solar flare small Aug 16 2020
A solar flare on August 16 kicked out a cloud of solar electrons and protons into space called a coronal mass ejection or CME. Although the CME isn't headed directly toward the Earth space weather forecasters predict a glancing blow that could produce auroras tonight. Mercury appears above the sun which is hidden behind a special mask.NASA / Spaceweather


Find a location with a dark sky and wide open view to the north. An auroral display often begins with a subtle, fuzzy glow along the northern horizon that intensifies into a greenish arc about a fist high. Sometimes that's as far as things go, but if we're lucky the arc might brighten and break up into parallel, moving rays like palpitating fingers. Rays are often seen to pierce the arc. They resemble searchlight beams (but fainter) that glow for a few seconds and then fade.

Although the sequence of events from quiet to active is often the same, every aurora is unique, something that should come as no surprise. The closer you look at any natural phenomenon the more individual it becomes.

If you suspect you're seeing the aurora tonight but aren't sure, take a picture. You'll need a stable platform for your camera like a tripod and a time exposure of 15-30 seconds. Set the sensitivity to ISO 800 or 1600 with the lens at its widest opening, typically f/2.8, f/3.5 or f/4.

Next, make sure both the camera and lens are set to manual (M) then carefully focus on a bright star or (much better) focus on a bright star using your camera's live view feature. Live view gives you a real-time view of your subject. Press the live view button, center the star and then press the magnifying glass button and manually focus it down to the tiniest possible point.

You're now ready to photograph the aurora. Check the back screen when your first exposure is complete and look for the aurora's telltale signature: a green or rose glow. Stick around a while. Auroras often "simmer" for a half-hour or more before blossoming into something you'll be glad you waited for.

Moon Aug 19 2020
The moon will be very low in the west-northwestern sky tonight (Weds.). It's so thin that only a part of the crescent will appear. In binoculars look for a broken appearance caused by shadows cast by crater walls knifing the length of the crescent. Stellarium


Tonight (Aug. 19) we'll also have an opportunity to see an extremely young crescent moon very low in the western sky. Before I forget, bring binoculars as the sky will be bright and the moon as thin as a razor blade. New moon occurred yesterday at 9:41 p.m. CDT. For East Coast observers the crescent will be just 22 hours old; 23 hours for the Midwest; 24 hours for the mountain states and 25 hours if you live on the West Coast.

Few get to see a sub-24 hour moon. You'll need a clear, haze-free sky and the ability to see to within a couple degrees of the western horizon. Start looking about 20 minutes after sunset a short distance above and a little left of the brightest glow on the horizon where the sun recently set. Sweep back and forth with your binoculars until you catch sight of the moon then look with your eyes alone. As always, make sure the binoculars are focused "at infinity" or maximum distance. If there's a cloud around focus on that. If not, try the distant horizon.

Starlink visorsat best SpaceX
SpaceX began including visors on all Starlink satellites starting with the Aug. 7 launch. SpaceX

SpaceX sent up another salvo of 58 Starlink satellites yesterday brin ging the total number launched into orbit to 653. This mission, the 11th, is called Starlink-10 because the first launch back in May 2019 started with Starlink-0. Since Aug. 7 all the satellites are now equipped with special visors to reduce sunlight reflecting from their shiny surfaces. This to placate astronomers who have complained that the large number of bright objects compromise astronomical observations.

A quick check showed that the latest bunch will be visible early tomorrow morning from the southern hemisphere, but they won't be bright, only reaching 4th magnitude. Satellites from Starlink-9, launched on Aug. 7, are currently making passes in northern hemisphere evening skies with some as bright as magnitude 3. My home city of Duluth has a nice set of multiple Starlink passes tonight (Aug. 19) that will skim near the bright star Altair in the bottom of the Summer Triangle figure. The parade begins around 9:15 p.m. local time and continues past 9:45 p.m.

To find out when you can see them, go to Heavens Above , select your city (upper right corner) and then click on the blue Starlink passes for all objects from a launch on the left side of the home page.You'll get a table of times, magnitudes, etc. Click on any line and a map pops up showing the path of the satellite and where to look. Once you spot one Starlink the rest follow similar paths so can keep looking at the same spot in the sky. Make sure that spot is where they'll reach their highest altitude — that's also where they're typically brightest.

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