This is because of the Earth's orbit around the Sun. As the Earth moves in its orbit, our perspective of the stars changes. This change in perspective causes the apparent position of the stars, including Arcturus, to shift slightly in the sky.
However, the changes in right ascension and declination of Arcturus are very small, and they are mostly due to the Earth's axial tilt (obliquity) rather than its orbital motion.
Here's why the changes are small:
* Arcturus is very far away: The distance to Arcturus is so vast that the change in Earth's position around the Sun has a negligible effect on its apparent position.
* The Earth's orbit is nearly circular: If the Earth's orbit was highly elliptical, the apparent positions of stars would change more noticeably throughout the year.
Therefore, while the right ascension and declination of Arcturus do change throughout the year, the changes are very subtle and not easily noticeable to the naked eye.
