Thinking Outside the Classroom: Astronomical phenomena you can see during the day
Keystone Science School volunteer
At Keystone Science School, we highlight and celebrate the celestial events that happen in our ever-changing night sky to teach about Earth and space science. We don’t just teach facts about the night sky but want you to experience it.
And did you know there are astronomical phenomena you can see during the day? Here are a few you very likely will see while you are basking in the Summit County summer sunshine.
Also called a mock sun, it is an optical phenomenon occurring in the atmosphere consisting of a subtly bright-colored spot or patch to one or both sides of the sun and are seen usually after sunrise and near sunset.
Sundogs are created when sunlight is refracted by horizontal ice crystals in the atmosphere. Think of the ice crystal having the shape of a dinner plate on a table. A sundog’s patch is at the same altitude as the sun, and as the sun move closer to the horizon, the patches move closer to the sun.
The moon and planets
How many of you were unaware the full moon can be seen in the daytime sky? In general, the moon is always below the horizon while the sun is above the horizon on the date of a full moon. Yet when the conditions are just right, you might be able to see a full moon very close to the horizon and directly opposite the sun during daylight. For the rest of the month, the best time to see a daytime moon is when it is at a 90-degree angle with the sun, and the moon is in its first or last quarter phase.
Another factor that makes the moon visible during the day is its brightness. As the moon reflects sunlight back to Earth, it appears brighter against the scattered blue light background of the sky. This is why you can see the planets of Venus and Jupiter and even exceptionally bright stars during day. Look for them, too.
Glories are formed when sunlight is scattered back to the observer (backscattering) because small water droplets, mist or clouds in the atmosphere are acting similar to a prism resulting in an optical phenomenon of concentric colored circles. (Think of a saint’s halo.)
Glories are always opposite the sun (antisolar) and below the horizon, expect at sunrise and sunset. For glories to happen, the sun must be directly behind the observer and might appear as a shadow around the head of the individual, a halo.
Glories are frequently seen by airplane passengers looking down at the airplane’s shadow below them. Here in Summit County, glories are most often seen standing at or near a mountain’s summit and on hillsides. Look for one during your next hike.
This phenomenon is said to be “a smile in the sky” with an observer’s first impression being that of an upside-down rainbow. Similar to sundogs, the arc is formed by the same plate-shaped hexagonal ice crystals acting as prisms and also when the sun is low near the horizon. When you see a sundog, it’s a safe bet there is a circumzenithal arc overhead.
To see the arc, you’ll want to look straight up to the point in the sky that is directly overhead. This point is called the zenith. The curved edge of the arc will be extending down toward the sun. When you find the arc, look to discriminate the variation in colors with violet on top and red at the bottom. Unlike rainbows, circumzenithal arc colors are purer with crisp definition because there is less overlap in their formation.
These rays appear as parallel shafts of light and are also called antisolar rays because they seem to converge at the point opposite the sun toward a vanishing point — just like a long, straight road appears to converge to the distance horizon. You will see these rays oftentimes just after sunrise or just before sunset. Be aware the cloud structure can influence whether the sunlight can be seen as beams.
Like glories, these anticrepuscular rays are caused by the same backscattering of light and are frequently seen during mountain hikes. The rays will appear triangular, no matter the shape of the mountain, with the peak of the mountain acting as the antisolar vanishing point.
Challenge yourself, your friends and family to find each of these daytime astronomical wonders while you while away the dog days of summer. So go outside, look up, be curious and wonder.
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