We call this the "winter" solstice but it's more accurate to call it the southern solstice because the sun is going to stand still over the southern hemisphere. The word "solstice" describes the event: sol means sun and stice, from sistere, means to stand still.
You might be jealous of the southern hemisphere right now because they're in the midst of summer but take heart in this: their spring and summer are shorter than ours.
That's because the Earth doesn't move at a constant speed in its elliptical orbit. It takes the Earth 92.8 days to travel from the point of our vernal equinox to the location of the northern/summer solstice (March to June), 93.6 days from the summer solstice to the autumnal equinox (June to September), 89.8 days from the autumnal equinox to the winter solstice (September to December) and 89.0 days from winter solstice to vernal equinox (December to March). Thus the seasons aren't equal in length.
This means that in the northern hemisphere spring and summer together are 7.6 days longer than those seasons in the southern hemisphere. We have a week's more warmth than they do.
If this is confusing, check out the earth map and explanation at this link at timeanddate.com whose information I paraphrased above.
(photo of the sun setting over the Susquehanna at Wrightsville, PA by John Beatty)
This week I read about colonial nesting in Ornithology by Frank B. Gill. "About 13% of bird species, including most seabirds, nest in colonies. Colonial nesting evolves in response to a combination of two environmental conditions: (1) a shortage of nesting sites that are safe from predators and (2) abundant or unpredictable food that is distant from safe nest sites."
The book mentions king penguin colonies; sometimes they're huge. This one is on the Salisbury Plain of South Georgia, an island in a volcanic ridge that arcs from the southern tip of South America to the northern tip of Antarctica. (Click here to see where it is on Google Maps.)
There are lots of king penguins in the photo above, but zoom out below and the number is stunning. Half a million king penguins in one place!
Obviously the advantages of living like this outweigh the disadvantages of occasional social strife, epidemics, or the crash of the food supply.
Imagine being in a place where there are penguins as far as the eye can see!
(photos from Wikimedia Commons. Click on the images to see the originals. Today’s Tenth Page is inspired by page 330 of Ornithology by Frank B. Gill.)
Recent photos by Steve Valasek in New Mexico reminded me that western birds are often very similar to their eastern cousins. Unlike the ecologically equivalent birds who live on different continents but have similar habitat requirements, these live on the same continent but have different habitat requirements.
Here are two western birds that fit the bill.
This Steller's jay perched on a feeder in the Sandia Mountains is recognizably similar to our blue jay but he lives in evergreen forests in the mountainous West. The blue jay prefers oak forests because he loves acorns. Both jays like to visit bird feeders.
Below, the mountain chickadee also lives in dry evergreen forests in the Western mountains. He looks like a black-capped chickadee except for his white eyebrows. The black-capped chickadee is far less picky about habitat and can be found in deciduous and evergreen forests, residential neighborhoods, weedy fields and cattail marshes. Because of this the black-capped has a wider range.
And finally, a seed-eating generalist, this dark-eyed junco shows how different he looks in the West. He's different but the same.
Juncos breed in northern or mountain forests but can be found in a wide variety of habitats in winter.
When I first started birding juncos like this one were listed as a separate species, the Oregon junco. Since then evidence has shown that the slate-colored junco of the East, the Oregon junco of the West, and the "white-winged" and "gray-headed" juncos are different races of the same species, now called the dark-eyed junco.
Test your skill. Leave a comment with your answer.
(photos: top and middle footprint photos are from Wikimedia Commons. Last photo is from the Ode Street Tribune blog. Click on each image to see the original ... and it will give you the answer to the bird's identity.)
"The asteroid could possibly have been spun up if the pressure of sunlight exerted a torque on the body."
The pressure of sunlight?
Apparently small bodies in outer space -- from dust particles to 10km wide asteroids -- are affected by the relentless though tiny touch of photons. They reflect or absorb the photons' energy and emit what they don't retain. The emissions become a tiny propulsion force. However, dust and asteroids have irregular shapes and surfaces so they reflect, absorb and emit unevenly. This affects their rotation and flight path.
There's a lot of fancy physics that predicts what a small irregular body will do under the pressure of sunlight. I read about the Yarkovsky effect, the YORP effect and the Poynting-Robertson effect until I got confused. Then I googled for a simple description and found ...
The United Nations' Space Generation Advisory Council holds an annual contest to solve the problem of deflecting a killer asteroid on a collision course with Earth. In 2012 the winning solution of the Move an Asteroid Competition was to bombard it with white paintballs.
The reason this would work is due to the Yarkovsky effect (I think). A dirt-colored rotating asteroid absorbs photons and heats up on its daylight side, then releases energy when that side turns to night. In a steady state the asteroid would stay on course and hit the Earth but if it's painted white it will absorb less and emit less -- and this will alter its course.
All we need for deflecting a dangerous asteroid is a 20-year lead time, a rocket, a lot of white paintballs and very good aim.
During the snowy owl invasion two years ago, Rick Remington captured close-ups of a resident peregrine falcon strafing a snowy at Chicago's Montrose Harbor in late January 2012. The snowy defended itself by doing somersaults to present its talons to the peregrine!
Speaking of talons, take a peek at this photo by John Mattera of a peregrine and snowy at Jones Beach, Long Island during a fight in December 2009. Click here for the story and photos from New York DEC's newsletter.
The boat-billed heron (Cochlearius cochlearius) is a strange-looking bird from the mangrove swamps of Central and South America. Not only does he have an unusually fat bill but his head feathers resemble dark hair.
Charlie Hickey took this photo in Costa Rica and noticed immediately that the bird looks like he's wearing a bad toupee. Click here to read whose toupee Charlie's reminded of.
The practice of giving plum jobs to your relatives is widely frowned upon but nepotism is a very successful survival strategy -- so successful that some birds use it too.
Closely related to North America's gray jay, Siberian jays (Perisoreus infaustus) live in the boreal forest of Northern Europe. Like other corvids in limited habitats they breed cooperatively. Each breeding pair has a suite of relatives who help guard the nest and feed the young. Often the kids stay with their parents even though they're old enough to breed.
Studies in Sweden have shown that male Siberian jays who stay with their parents are much more successful than those who leave home because their fathers practice nepotism. The father jays protect their own sons and harass incoming males who try to join the group. The sons thrive and learn while they wait for a good territory to become available.
The exception proved the rule. Ekman and Griesser experimentally removed fathers and watched as they were replaced by despotic immigrant males who ejected the missing fathers' sons. If dad's not there to protect you, watch out!
Success through nepotism.
(photo of a banded Siberian jay from Wikimedia Commons. Click on the image to see the original.
Today’s Tenth Page is inspired by page 390 of Ornithology by Frank B. Gill.)
Amber is a rock that began as tree resin. When it was resin it collected pollen, flecks of dirt, plants, small creatures, and other debris as it flowed from the tree. The amber above contains a spider, air bubbles, dirt and an ant, all preserved when the resin hardened.
Scientists are fascinated by amber because everything inside it is as old as the rock. This year an international team led by Ralf Tappert of the University of Innsbruck analyzed carbon-12 and carbon-13 in present-day tree resin and amber dating all the way back to the Triassic period. They chose amber for their chemical analysis because, as Tappert explains, "Compared to other organic matter, amber has the advantage that it remains chemically and isotopically almost unchanged over long periods of geological time."
From 538 samples they calculated the concentration of oxygen in the atmosphere for 220 million years of the Earth's history. Surprisingly, they learned that the concentration in the early Cretaceous period was only 10-15% compared to 21% oxygen today. The dinosaurs had less oxygen to breathe than we do!
This finding tossed out at least one theory about the dinosaurs, namely that their size was possible because they had so much more oxygen to breathe. Oops! They had less.
Click here to read more about the study at ABC Science (Australia).
Ancient air tells the tale.
(photo from Wikimedia Commons. Click on the image to see the original)