[AlexandrKushnirtshuk (OP)]

Betelgeuse is estimated to be 642.5 light years away. Why is dynamics of brightness of Betelgeuse so closely aligned with the dynamics of solar activity?


Diagram source link: https://www.climate.gov/news-features/climate-qa/couldnt-sun-be-cause-global-warming


Diagram source link: https://skyandtelescope.org/observing/fainting-betelgeuse/

Moreover, in addition to the correlation with 10-13 years solar cycles on the Betelgeuse brightness graph, there are clear 1 year cycles of brightness fluctuations also visible.

Based on this fact, I assume that Betelgeuse, like all other "stars" and "galaxies", are located in the Oort Cloud and reflect sunlight. Here is a link to more arguments in support of this assumption: New model of the Universe.

[Kryptid]

A solar cycle lasts about 11 years.

The link you provided states that Betelgeuse pulsates on an approximately 425 day (1.16 year) cycle and that it undergoes a brightness change on both a 100-180 day (0.27-0.49 year) and a 5.9 year cycle. So I do not see the correlation that you speak of. What's more, think about just how many stars there are in the night sky. It wouldn't be surprising, due to probability alone, to find a few stars with cycles that match the Sun's anyway.

So if a star with the same cycle period as the Sun is evidence that the two are linked in some way, wouldn't stars that don't have the same cycle period as the Sun be evidence that they are not linked?

[Bored chemist]

Here is a link to more arguments in support of this assumption:

They don't support it; it is unsupportable.

[Bored chemist]

Based on this fact, I assume that Betelgeuse, like all other "stars" and "galaxies", are located in the Oort Cloud and reflect sunlight.

How come some of them are (at some wavelengths) brighter than the Sun?

[AlexandrKushnirtshuk (OP)]

Annual cyclicity of Betelgeuse brightness fluctuations.

The annual cyclical fluctuations in the brightness of Betelgeuse can be explained by the fact that in December the Sun is farther from it, and in June - is closer to it (given the rotation of the Earth and the Sun as in the animation below, the Earth is larger). Betelgeuse is located in the constellation Orion. Sun in Orion (Orion behind Sun) in June.

[Kryptid]

The annual cyclical fluctuations in the brightness of Betelgeuse

But Betelgeuse doesn't have annual brightness fluctuations.

[Bored chemist]

in December the Sun is farther from it, and in June - is closer to it

Well... yes it is.
By about the diameter of the Earth's orbit. That's something like 8 light minutes.
And the distance to Betelgeuse is about 642.5 light years.
So the change in distance is 1 part in about 42 million.
The corresponding change of brightness due to the Earth's orbit round the sun is about 1 part in 21 million.

So most of the change in brightness must be due to something else.
Also, if the cause of the variation was the season then Betelgeuse would be bright every June and dim every December.
But it isn't.

Incidentally, you seem to have forgotten to answer this

Based on this fact, I assume that Betelgeuse, like all other "stars" and "galaxies", are located in the Oort Cloud and reflect sunlight.

How come some of them are (at some wavelengths) brighter than the Sun?

Could you explain how there are things out there which shine brighter than the Sun?