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Eyes on the prize
Millions of people in the United States will turn their faces to the sky on Aug. 21 to watch the total solar eclipse as it sweeps from coast to coast. The event will also capture the attention of several spacecraft, as well as the six crewmembers currently aboard the International Space Station (ISS).
From their perches near Earth, orbiting the moon or in deep space, these spacecraft will track the behavior of the sun or how the moon's shadow passes across the Earth's surface.
Check out the planned activities of these spacecraft, as well as the ISS crew, in the following slideshow. [Total Solar Eclipse 2017: When, Where and How to See It (Safely)]
Solar Terrestrial Relations Observatory (NASA)Slide 2 of 20
Solar Terrestrial Relations Observatory (NASA)
The Solar Terrestrial Relations Observatory (STEREO) mission launched in 2006 with two spacecraft, each in an Earth-like orbit. One of those spacecraft orbited ahead of Earth (STEREO-Ahead/Stereo-A) and the other behind (STEREO-Behind/STEREO-B). The twin observatories showed how solar storms leave the sun and move through space, enhancing space weather predictions. NASA lost contact with STEREO-B in 2014, except for a brief period in 2016. The agency still is in contact with STEREO-A.
Because STEREO-A is behind the sun (from Earth's perspective), the spacecraft won't see the moon pass in front of the sun. However, STEREO-A's coronagraph will provide views of the corona from a totally different perspective than that of Earth. "The observations STEREO gathers during the eclipse can also be used to round out observations of the solar atmosphere taken from the ground and thus create a robust, more three-dimensional picture of the sun's dynamic corona," NASA stated.Slide 3 of 20
Solar Dynamics Observatory (NASA)Slide 4 of 20
Solar Dynamics Observatory (NASA)
The Solar Dynamics Observatory (SDO) has been in space since 2010, looking at the sun 24/7. This observatory views the sun in a few different wavelengths, each of which shows material from a different layer of the sun or from its corona.
SDO is in an inclined geosynchronous orbit, which means that, from the perspective of the Earth's surface, the spacecraft is almost motionless over one spot. From that perspective, SDO will see a partial eclipse on Aug. 21 from 3:27 p.m. to 3:55 p.m. EDT (1927 to 1955 GMT).
"Scientists will be able to compare SDO imagery of the corona to images captured from the ground," NASA stated. "During a total eclipse, the lower parts of the sun's atmosphere, or corona, can be seen in a way that cannot completely be replicated by current human-made instruments. The combination of space-based and ground-based observations together create[s] a more comprehensive picture than either can do alone."Slide 5 of 20
Interface Region Imaging Spectrograph (NASA)Slide 6 of 20
Interface Region Imaging Spectrograph (NASA)
The Interface Region Imaging Spectrograph (IRIS) spacecraft, which launched in 2013, studies how the solar atmosphere is energized. The spacecraft does this by capturing ultraviolet images of the chromosphere (the lower part of the sun's atmosphere) and the transition region between the sun's surface and its atmosphere, where temperatures jump dramatically.
IRIS is in a sun-synchronous orbit, which is a near-polar orbit. The spacecraft always passes over Earth at the same local solar time; in other words, IRIS is in constant sunlight. IRIS will see the moon pass in front of the sun several times during the solar eclipse, for about 15 minutes each pass. IRIS will calibrate its instruments during the transit, NASA officials said.
IRIS will focus especially on the lower atmosphere (the chromosphere) and loops of material projecting from the sun (prominences.) IRIS can view solar material at temperatures impossible to see from Earth's surface. It will also scan the entire limb of the sun in high resolution.
IRIS will also work in conjunction with observatories on the ground, NASA officials said.Slide 7 of 20
Solar and Heliospheric Observatory (European Space Agency/NASA)Slide 8 of 20