Editing Sunlight (section)

===Solar intensity variation===
{{Further|Solar variation}}
Space-based observations of solar irradiance started in 1978. These measurements show that the solar constant is not constant. It varies on many time scales, including the 11-year sunspot solar cycle.<ref name="acrim"/> When going further back in time, one has to rely on irradiance reconstructions, using sunspots for the past 400&nbsp;years or cosmogenic radionuclides for going back&nbsp;10,000 years.
Such reconstructions have been done.<ref>{{cite journal | title = Modeling the Sun's Magnetic Field and Irradiance since 1713 | last1 = Wang | display-authors = etal   | date = 2005 | journal = The Astrophysical Journal | volume = 625 | issue = 1| pages = 522–538 | doi = 10.1086/429689 | bibcode=2005ApJ...625..522W| doi-access = free }}</ref><ref>{{cite journal | title = Total solar irradiance since 1996: is there a long-term variation unrelated to solar surface magnetic phenomena? | last1 = Steinhilber | display-authors = etal   | date = 2009 | url =https://www.dora.lib4ri.ch/eawag/islandora/object/eawag%3A6539/datastream/PDF/view | journal = Geophysical Research Letters | volume = 36 | page = L19704 | doi = 10.1051/0004-6361/200811446 | bibcode=2010A&A...523A..39S| doi-access = free }}</ref><ref>{{cite journal | title = Evolution of the solar irradiance during the Holocene | last1 = Vieira | display-authors = etal   | date = 2011 | journal = Astronomy & Astrophysics | volume = 531 | page = A6 | doi = 10.1051/0004-6361/201015843 | bibcode=2011A&A...531A...6V|arxiv = 1103.4958 | s2cid = 119190565 }}</ref><ref>{{cite journal | title = 9,400 years of cosmic radiation and solar activity from ice cores and tree rings | last1 = Steinhilber | display-authors = etal   | date = 2012 | journal = Proceedings of the National Academy of Sciences | volume = 109| issue = 16| pages = 5967–5971| doi = 10.1073/pnas.1118965109 |bibcode = 2012PNAS..109.5967S | pmid=22474348 | pmc=3341045| url = http://epic.awi.de/30297/1/PNAS-2012-Steinhilber-1118965109.pdf| doi-access = free }}</ref> These studies show that in addition to the solar irradiance variation with the solar cycle (the (Schwabe) cycle), the solar activity varies with longer cycles, such as the proposed 88 year (Gleisberg cycle), 208 year (DeVries cycle) and 1,000 year (Eddy cycle).