Since that prognosticating groundhog, Punxsutawney Phil, has predicted six more weeks of winter weather (and he’s correct 50 percent of the time 😉), the atmosphere remains frigid overhead—at least here in the northeast United States. This can lead to beautiful optical effects. This week we’ll take a look at some meteorological optical phenomena.
I also want to highlight that Tuesday was International Day of Women and Girls in Science. To celebrate, AAPG and MicroSeismic have been showcasing interviews with women geoscientists. You can read my interview here (and I encourage you to read the interviews of the other women featured, too!). They are also hosting a special giveaway! Enter to win here before Friday!
Sharon Lyon
Editor, GeoLifestyle
Halos, Sun dogs, and Sun Pillars…Oh My!
Catherine Boivin/Shutterstock.com
A halo forms around the Sun or Moon when light undergoes two refractions as it passes through ice crystals in high-level clouds. Randomly oriented hexagonal ice crystals are responsible for the phenomenon.
A halo will have a 22-degree apparent diameter (from the observer) around the Sun or Moon.
The saying “Ring around the Moon means rain soon” has an element of truth to it. Halos are usually formed by cirrus clouds, which can precede the arrival of an advancing warm or cold front, so indeed, a halo can be a harbinger of rain. However, not all cirrus clouds form from a frontal approach.
Sun orMoon dogs are bright spots on one or both sides, and at the same altitude as, the Sun or Moon, within the 22-degree halo.
Sun or Moon dogs form when ice crystals with diameters larger than 20 micrometers lie flat on the broad end of the crystal. Orientation is important in causing these brighter spots within a halo. The refracting ice crystals are found in either high-level clouds or in “diamond dust,” an ice mist closer to the ground.
Sun pillars are vertical beams of light extending from the Sun around sunrise or sunset. Sunlight reflects (rather than refracts) off flat ice crystals falling through the air to cause this effect.
Sun pillars take on colors that reflect the sun and surrounding clouds and can range from white to shades of yellow, red, or purple.
Viewing tips: To see halos, sun dogs and pillars, look toward the sun when it’s low on the horizon, especially during sunrise and sunset. Halos and sun dogs are more common during frigid winter months and in the Northern hemisphere.
A message from AAPG and MicroSeismic
In continued celebration of the International Day of Women and Girls in Science, AAPG and MicroSeismic are showcasing interviews from women leaders. This week's featured leader is Layaan Al Kharusi, a technical advisor from Occidental Petroleum, Oman. Here is a sneak peek from her interview:
“Few geoscientists have worked on the deep stratigraphy of Oman. It’s so new, and I wanted to be at the forefront of it. Having geology without much knowledge and information might scare a lot of people away, but I took it as a challenge to come up with new ideas and look for greater prospectivity, and I did it.”
Rainbows, beautiful dispersions of sunlight, can form at any time of year.
Rainbows are produced by refraction and reflection of light within water droplets in the atmosphere. When sunlight enters a raindrop, it is refracted. It is then reflected off the inside surface of the drop. As the light exits the drop, it is refracted again into different angles, and therefore different colors.
Double the beauty: If light is reflected twice on the inside of the water droplet before leaving it, a double rainbow can form outside of the primary arc. The order of colors is reversed in the double rainbow.
Viewing tip: You can see the most luminous rainbows when it is still raining in one portion of the sky, and the Sun shines in another. Stand with the Sun at your back and look toward the rain.
Fun fact: Every rainbow is a circle, but when the viewer is standing at ground level, the bottom of the bow cannot be seen. The entire circle can sometimes be viewed from a high building or an airplane.
“At the Last Glimpse of Sunset, a Flash of Green Shoots Up into the Sky”—Pirates of the Caribbean III
David McManus/Shutterstock.com
I’ve always been fascinated by the green flash (popularized in the Pirates of the Carribean movie franchise). I have looked for it but never seen it. Have you?
The green flash is a green spot or streak above the rising or setting Sun (usually) or Moon (less commonly). It forms due to refraction of sunlight or moonlight through the increasingly thicker atmosphere.
The most common type of green flash is the inferior-mirage type, which appears as a green oval on the upper edge of the solar or lunar disc, lasting only one or two seconds. It occurs when the surface is warmer than the air above it, and is usually visible over the ocean.
Viewing tip: The green flash is most likely to be seen where the air is stable and pollution is minimal.
Fun fact: The longest observed green flash lasted 35 minutes, and it was seen by the Richard Byrd Antarctic Expedition in 1934.
The northern lights, Aurora Borealis, and the southern lights, Aurora Australis, are beautiful natural phenomena featuring multicolored curtains, rays, and arcs of light. I witnessed the aurora borealis at my home in Virginia last October.
Formation:
The sun ejects charged particles from its corona, creating the solar wind.
The solar wind travels through space until the electrons collide with the Earth’s magnetic field.
The field redirects and accelerates the particles toward the poles, where they transfer their energy to atoms and molecules within the upper atmosphere, exciting them to higher energy states.
When these atoms and molecules release their energy in the form of light, they return to their ground state. This process generates the lights of the auroras.
Shapes: During the early evening, rays can form arcs that stretch from horizon to horizon. Later in the evening, the arcs often begin to twist and sway. The peak comes when the light becomes brighter, moves rapidly, and expands to fill the entire sky.
Viewing tips:
The best place to observe auroras is above 60 degrees North and South latitudes. At these polar locales, the auroras can be observed more than half of the nights in a year. Skies must be dark, so during the summer months, the midnight sun prevents auroral observation at the highest latitudes.
The sun's emissions go through an approximately 11-year cycle, driven by the sun’s magnetic field. The frequency of sunspots is tied to this cycle. The current cycle—solar cycle 25—began as a minimum in December 2019 and reached its maximum in October 2024.
During the maximum, auroras are at their brightest and most frequent. The solar maximum can last up to one year, so auroras should be bright in 2025.
Dig deeper: You can view the forecast for aurora displays today and tomorrow at NOAA’s Aurora Dashboard.
Don’t forget the great evening alignment of Saturn, Mercury, Neptune, Venus, Uranus, Jupiter, and Mars on February 28—another reason to look up at the winter sky!
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