Editing Maunder Minimum (section)

==Sunspot observations==

{{unsolved|astronomy|What caused the Maunder Minimum and other grand minima, and how does the solar cycle recover from a minimum state?}}
The Maunder Minimum occurred between 1645 and 1715 when very few sunspots were observed.<ref name=Usoskin>{{cite journal|last1=Usoskin|display-authors=etal|title=The Maunder minimum (1645–1715) was indeed a grand minimum: A reassessment of multiple datasets|journal=Astron. Astrophys.|date=2015|volume=581|page=A95|doi=10.1051/0004-6361/201526652|arxiv = 1507.05191 |bibcode = 2015A&A...581A..95U |s2cid=28101367}}</ref> That was not because of a lack of observations, as during the 17th century, [[Giovanni Domenico Cassini]] carried out a systematic program of solar observations at the [[Paris Observatory]], thanks to the astronomers [[Jean Picard]] and [[Philippe de La Hire]]. [[Johannes Hevelius]] also performed observations on his own. Here is the total of sunspots recorded, by example, in the decennial years (omitting [[Wolf number]]s):<ref name=Usoskin/>

{| class="wikitable"
! Year !! Sunspots
|-
| 1610 || 9
|-
| 1620 || 6
|-
| 1630 || 9
|-
| 1640 || 0
|-
| 1650 || 3
|-
|1660  || Some sunspots (<&nbsp;20) reported by [[Jan Heweliusz]] in ''Machina Coelestis''
|-
| 1670 || 0
|-
| 1680 || 1 huge sunspot observed by [[Giovanni Domenico Cassini]]
|}

During the Maunder Minimum enough sunspots were sighted that 11-year cycles could be determined from the count. The maxima occurred in 1676–1677, 1684, 1695, 1705 and 1718. Sunspot activity was then concentrated in the southern hemisphere of the Sun, except for the last cycle when the sunspots appeared in the northern hemisphere. According to [[Spörer's law]], spots appear at high latitudes at the start of a cycle, subsequently moving to lower latitudes until they average about latitude 15° at solar maximum. The average then continues to drift lower to about 7° and after that, while spots of the old cycle fade, new cycle spots start appearing again at high latitudes. The visibility of these spots is also affected by the velocity of the Sun's surface rotation at various latitudes:

{| class="wikitable"
! Solar [[latitude]] !! Rotation period<br />(days)
|-
| 0°  || 24.7
|-
| 35° || 26.7
|-
| 40° || 28.0
|-
| 75° || 33.0
|}

Visibility is somewhat affected by observations being done from the [[ecliptic]]. The ecliptic is inclined 7° from the plane of the Sun's equator (latitude 0°).