päikesefaasidega

Päikesefaasidega refers to the different apparent shapes of the Sun as seen from Earth throughout its orbital period. While the Sun itself is a sphere, its apparent illumination and visibility can change due to various astronomical phenomena. The most common and well-known example of päikesefaasidega is the lunar phases, where the Moon's illuminated portion visible from Earth changes. However, the term can also be extended to discuss apparent changes in the Sun's disk.

The Sun's apparent size can vary slightly throughout the year because Earth's orbit is elliptical, not perfectly circular. At perihelion, closest to the Sun, Earth is about 3.3% closer than at aphelion, farthest away. This results in the Sun appearing slightly larger in early January and slightly smaller in early July. These variations are subtle and not typically described as "phases" in the same way as lunar phases.

Another consideration for apparent changes in the Sun involves phenomena like sunspots and solar eclipses. Sunspots are temporary phenomena on the Sun's photosphere that appear as dark spots compared to surrounding areas. Their appearance and movement across the Sun's disk can alter its perceived surface. Solar eclipses, both total and partial, significantly obscure parts of the Sun's disk, creating distinct and temporary changes in its visible form. While not a cyclical change in illumination like lunar phases, these events represent temporary päikesefaasidega.