A halo and circumscribed halo (upper bright saggy arc) around the sun this morning. Both are formed when light is bent or refracted through pencil-shaped hexagonal ice crystals. Photo: Bob King
Happy Earth Day! What a great planet to call home. Situated in our sun’s habitable zone and endowed with life and sweet pleasures, we know of no where else like it. I wouldn’t trade this blue gem for all the planets of Star Trek.
The sun photographed by NASA’s Solar Dynamics Observatory earlier this morning April 22. The large sunspot group at upper right can be glimpsed with the naked eye only through a safe solar filter. Click to enlarge. Credit: NASA
The sun broke through morning clouds today with two pleasant surprises – a colorful circumscribed halo caused by light refracted through billions of microscopic ice crystals in high cirrostratus clouds, and a pair of naked eye sunspots.
Through a safe solar filter, I spied two side-by-side black dots in the upper right (northwest) quarter of the sun.
High-resolution closeup of sunspot group 1726. Sunspots are cooler regions of concentrated magnetic energy on the sun’s surface. They usually have two parts – a dark, inner umbra enclosed by a lighter penumbra. Credit: NASA
They’re part of the large sunspot group 1726 that today spans more than a dozen Earth diameters (approx. 100,000 miles / 160,000 km). The group spawned a few flares, including a moderately strong M-class flare earlier this morning, and holds the potential for more.
Two cool snowpeople catch some April rays last week in Duluth, Minn. Photo: Bob King
In April the sun’s slant in the sky is the same as it is in mid-August, high enough to feel on your cheeks when you walk out the door. It brings welcome relief to some of us still mired in winter with several feet of snow piled up in the yard. The angle of the sun in the sky has much to do with the amount of heat our planet receives and the global climate.
The overhead sun covers a smaller area of ground with the maximum amount of energy (left). At right the sun is shown in winter when its lower angle spreads its light over a larger area with a loss of 100 watts of energy. Result? Colder weather. Credit: Randy Russell / windows2universe.org
If Earth were a gigantic flat disk instead of a sphere and had no atmosphere to filter sunlight, every square meter of ground would receive 1,368 watts of solar energy. Our planet’s spherical shape spreads the sun’s light out over a larger area, diluting the energy received to 342 watts. The atmosphere also filters out a small amount.
A different view of the sun’s angle in winter versus summer and its seasonal energy footprints. Credit: Nicholas M. Short
When the sun is nearly overhead, as it is during summer, we get the full wattage and really feel the heat just like you would standing next to a 342 watt light bulb. In winter, the sun shines on the planet at a lower angle and its light spreads out broadly across the ground.
Since the amount of energy it’s beaming our way is constant, if it’s spread over a larger area, it becomes less concentrated and weaker. That’s one big reason why winter’s so cold – a lower sun means the intensity (energy) of sunlight is reduced. Without the customary heat to warm air and ground, rain becomes snow and accumulates.
The atmosphere also plays a part. In winter, the low sun shines spends much of the day shining through the lower levels of the atmosphere, where the air is thicker and dustier. Some of that light gets absorbed and some reflected away from Earth, further cooling the season.
Today’s angle suits me just fine. When I walked outside I felt the sun right away and knew it would be good day to celebrate another day of life on the planet. Wishing the same for you.