Ultraviolet image of the Sun; Credit: NASA |
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While many of us were huddled at home during last week’s snowstorm, some employees at NASA Goddard Space Flight Center in Greenbelt were preparing for a mission of cosmic proportions. On February 11th, the Atlas V launched from Cape Canaveral to send the Solar Dynamics Observatory (SDO) into space on its mission to better understand the sun. Although no shuttles or satellites are actually launched in Maryland, Goddard provides critical mission support for shuttle launches and missions like SDO from its Mission Operation Center and Network Integration Center. In the lead up to a mission, the center is staffed 24 hours a day as they prepare for a launch.
Layers of the Sun; Credit: NASA |
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Although it is the center of our solar system and our closest star, there is still much to learn about the Sun. We know the Sun is a ball of gas composed of the same elements found on Earth (mainly hydrogen and helium) that get denser as they move inward to the Sun’s core. We also know it is composed of distinct layers, but we can only observe the Sun’s outer layers directly. These include the deepest layer we can see, the photosphere, the next outer layer, the chromosphere, and the outermost region of the atmosphere, the corona, which can be viewed as a halo during an eclipse. Although temperature generally decreases as you move out from the core of the Sun, the chromosphere can reach temperatures higher than the photosphere, and the corona can reach millions of Kelvin. The corona is so hot that the majority of radiation is emitted at ultraviolet and X-ray wavelengths. (The atmosphere of the Earth can block most of this light, which is why we aren’t constantly sunburned.) We don’t yet understand why the corona is so hot. It may be because of the Sun’s magnetic field, but the mechanism is still unknown.
Most important to space weather (and therefore, Earth weather) is the Sun’s solar activity, which is measured by the amount of sunspots present on the Sun. Sunspots are cooler regions on the Sun’s photosphere and so appear to be darker than the photosphere. Although sunspots are locally cooler, their presence is associated with greater overall solar temperatures. They form in cycles of an average of 11.1 years, where at the maximum over 100 sunspots can be seen, and sometimes no spots are observed at the minima. The cycle of sunspots is closely related to the magnetism of the Sun and form in regions of intense magnetic activity. Solar flares and coronal mass ejections, large explosions in the Sun’s atmosphere, often occur in these magnetically intense areas. During extended periods of low solar activity, the Earth can experience cold temperatures (such as during the Little Ice Age in the 17th century).
The NASA Goddard-managed SDO will aid in understanding the Sun’s magnetic changes. The spacecraft is built to fly for five years but will probably outlast itself like previous satellites. SDO is the first satellite to launch under the Living With a Star program at NASA aimed to understand the relationship of the Sun to space weather. By measuring the properties of the Sun and solar activity, SDO plans to determine how the magnetic field is generated and structured and how the stored magnetic energy is released outward from the Sun into space. SDO data and analysis will be used to help predict the solar variations that influence life on Earth. Among other things, SDO will examine sunspots, solar flares, and coronal mass ejections like the one observed less than a month ago from another Goddard-associated satellite:
STEREO satellite movie from NASA
We could certainly use more of the Sun around Baltimore right now.
For more detailed explanations of the Sun and its properties, see NASA or Wikipedia.
