Solar Stellar Comparison Experiment (SOLSTICE)
SOLSTICE will take spectral readings of the ultraviolet energy coming from the Sun. Light from the Sun will enter the instrument and shine on a diffraction grating, which is essentially just a series of very closely spaced slits—many thousands per inch. These slits spread the light into its spectral components much as a prism does. The ultraviolet light is directed towards two arrays of photodetectors similar to the way light from a projector is directed towards a movie screen. One photodetector array measures ultraviolet light in the range of 115 nm to 180 nm at 1-nm to 3-nm increments. The other array will pick up readings for ultraviolet light with near-visible wavelengths from 180 to 320 nm in increments from 0.1 to 2.2 nm. Each of these photodetectors is capable of switching jobs and of measuring the opposing range of wavelengths.

There are actually two independent SOLSTICE instruments onboard SORCE, referred to as SOLSTICE A, and SOLSTICE B, pictured here mounted at right angles to each other, above and below the optical flat, respectively. These can each measure both the F and G band of wavelengths, 115-180 nm and 180-300 nm, respectively, so that if either instrument fails, the other can take up its duties. (Image courtesy Solar Radiation and Climate Experiment Project)

This is not the first SOLSTICE in operation. The first was on the Upper Atmosphere Research Satellite (UARS), which was sent up to measure chemical and physical changes in the Earth’s upper atmosphere. The SOLSTICE on SORCE will continue to monitor ultraviolet radiation well after the UARS satellite is taken out of service next year. With SOLSTICE, scientists can observe to what degree solar cycles affect the ozone layer, the ozone hole, and the stratosphere. They can also see if changes in ultraviolet radiation correspond with atmospheric disturbances in the upper troposphere.

The calibration for this instrument is unique. As SORCE passes through the nighttime portion of its orbit, SOLSTICE will measure the ultraviolet radiation coming from certain blue stars. These stars emit spectra that have significant energy in the ultraviolet range measured by SOLSTICE, that are known to be constant in time. So if SOLSTICE’s measurements from these stars change over time, then scientists know that the instrument’s response has changed. They can then use the knowledge to make adjustments to their data.

next: Extreme Ultraviolet Photometer System (XPS)
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Solar Radiation and Climate Experiment (SORCE)
Introduction
Earth’s Energy Balance
Solar Variability
The Sun and Global Warming
Uncertainties in Solar Measurements

The SORCE Satellite
Total Irradiance Monitor (TIM)
Spectral Irradiance Monitor (SIM)
Solar Stellar Comparison Experiment (SOLSTICE)
Extreme Ultraviolet Photometer System (XPS)

Related Articles
SOLSTICE
Watching the Sun
ACRIMSAT
Sunspots and the Solar Max
Clouds and Radiation
Why isn’t Earth Hot as an Oven?

Related Datasets
Reflected Solar Radiation
Outgoing Heat Radiation