Current Events

  • Kansas Legislator Proposes Bill to Outlaw Sustainability Education
    A bill has been introduced in the Kansas legislature this week that would prohibit the promotion of ...Read more

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    Kansas Legislator Proposes Bill to Outlaw Sustainability Education

    A bill has been introduced in the Kansas legislature this week that would prohibit the promotion of sustainability. Here is a link to the one-page bill: http://www.kslegislature.org/li/b2013_14/measures/documents/hb2366_00_0000.pdf. See report on Bloomberg News.
  • Earth's Center Is 1,000 Degrees Hotter Than Previously Thought, Synchrotron X-Ray Experiment Shows
    Scientists have determined the temperature near the Earth’s center to be 6000 degrees Celsius, 1000 ...Read more

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    Earth's Center Is 1,000 Degrees Hotter Than Previously Thought, Synchrotron X-Ray Experiment Shows

    Scientists have determined the temperature near the Earth’s center to be 6000 degrees Celsius, 1000 degrees hotter than in a previous experiment run 20 years ago. These measurements confirm geophysical models that the temperature difference between the solid core and the mantle above, must be at least 1500 degrees to explain why the Earth has a magnetic field. For more information about this study, see the press release from the European Synchrotron Radiation Facility.
  • Ocean Volcanic Rocks Contain Samples of Recycled Crust
    Scientists have long believed that lava erupted from certain oceanic volcanoes contains materials fr...Read more

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    Ocean Volcanic Rocks Contain Samples of Recycled Crust

    Scientists have long believed that lava erupted from certain oceanic volcanoes contains materials from the early Earth’s crust. But decisive evidence for this phenomenon has proven elusive. New research from a team including Carnegie’s Erik Hauri demonstrates that oceanic volcanic rocks contain samples of recycled crust dating back to the Archean era 2.5 billion years ago. Their work is published in Nature. Oceanic crust sinks into the Earth’s mantle at so-called subduction zones, where two plates come together. Much of what happens to the crust during this journey is unknown. Model-dependent studies for how long subducted material can exist in the mantle are uncertain and evidence of very old crust returning to Earth’s surface via upwellings of magma has not been found until now. For more information about these results, see the press release from the Carnegie Institution.
A diagram of how the Sun moves through the sky on the winter solstice.
Click on image for full size

The Winter Solstice

Let's pretend, for the moment, that you're the person standing on the Earth in the picture to the left, living in Topeka, Kansas, around 40° N latitude. The picture on the left shows the view from the solar system (upper panel), and from on the surface of the earth (lower panel). Notice that some of the same features are labelled on each panel.

The upper panel shows that on the winter solstice (which occurs around December 21), the northern half of the Earth is tilted away from the Sun. Notice that the Sun is south of the equator. For you in Topeka, the altitude of the Sun at noon is 26.5°, which is pretty low in the sky. That is the lowest the Sun gets at that latitude. It has been getting lower and lower in the sky since the summer solstice and through the autumnal equinox. The bottom panel shows how the Sun moves through the sky for someone standing on the ground in Topeka.

So, on the winter solstice, the northern hemisphere is getting less direct sunlight than the southern hemisphere. This is winter for people in the northern hemisphere. During the winter, the Sun is also above the horizon for a shorter time than it is during the summer (the nights are long). The winter solstice is the shortest day of the year.

At this same time, the southern half of the Earth is tilted toward the Sun. If you were living in Valdivia, Chile (about -40° S latitude) you would be enjoying a nice warm summer.

How high the Sun get's in your sky, and how long it is above the horizon during the day, depend not only on the season, but also on your latitude.

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