Query: There is no single continuous satellite measurement of Total Solar Irradiance (TSI).

Relevant passages:
Upper Atmosphere Research Satellite <=SEP=> The Upper Atmosphere Research Satellite ( UARS ) was a NASA-operated orbital observatory whose mission was to study the Earth 's atmosphere , particularly the protective ozone layer . The 5900 kg satellite was deployed from Space Shuttle Discovery during the STS-48 mission on 15 September 1991 . It entered Earth orbit at an operational altitude of 600 km , with an orbital inclination of 57 degrees .   The original mission duration was to be only three years , but was extended several times . When the mission finally ended in June 2005 due to funding cuts , 14 years after the satellite 's launch , six of its ten instruments were still operational . A final orbit-lowering burn was performed in early December 2005 to prepare the satellite for deorbit . On 26 October 2010 , the International Space Station performed a debris-avoidance maneuver in response to a conjunction with UARS .   The decommissioned satellite re-entered Earth 's atmosphere on 24 September 2011 . Considerable media attention surrounded the event , largely due to NASA 's predictions that substantial parts of the satellite might reach the ground , potentially endangering inhabited areas . However , the satellite ultimately impacted in a remote area of the Pacific Ocean .

Sunlight <=SEP=> Sunlight is a portion of the electromagnetic radiation given off by the Sun , in particular infrared , visible , and ultraviolet light . On Earth , sunlight is filtered through Earth 's atmosphere , and is obvious as daylight when the Sun is above the horizon . When the direct solar radiation is not blocked by clouds , it is experienced as sunshine , a combination of bright light and radiant heat . When it is blocked by clouds or reflects off other objects , it is experienced as diffused light . The World Meteorological Organization uses the term `` sunshine duration '' to mean the cumulative time during which an area receives direct irradiance from the Sun of at least 120 watts per square meter . Other sources indicate an `` Average over the entire earth '' of `` 164 Watts per square meter over a 24 hour day '' .   The ultraviolet radiation in sunlight has both positive and negative health effects , as it is both a principal source of vitamin D3 and a mutagen .   Sunlight takes about 8.3 minutes to reach Earth from the surface of the Sun . A photon starting at the center of the Sun and changing direction every time it encounters a charged particle would take between 10,000 and 170,000 years to get to the surface .   Sunlight is a key factor in photosynthesis , the process used by plants and other autotrophic organisms to convert light energy , normally from the Sun , into chemical energy that can be used to fuel the organisms ' activities .

Solar irradiance <=SEP=> Solar irradiance is the power per unit area received from the Sun in the form of electromagnetic radiation in the wavelength range of the measuring instrument . Irradiance may be measured in space or at the Earth 's surface after atmospheric absorption and scattering . It is measured perpendicular to the incoming sunlight . Total solar irradiance ( TSI ) , is a measure of the solar power over all wavelengths per unit area incident on the Earth 's upper atmosphere . The solar constant is a conventional measure of mean TSI at a distance of one astronomical Unit ( AU ) . Irradiance is a function of distance from the Sun , the solar cycle , and cross-cycle changes . Irradiance on Earth is also measured perpendicular to the incoming sunlight . Insolation is the power received on Earth per unit area on a horizontal surface . It depends on the height of the Sun above the horizon .