* Brightness: Stars do change in brightness over time. This can be due to:
* Intrinsic variability: Some stars are naturally variable, pulsating or erupting, causing changes in their light output. Examples include Cepheid variables, RR Lyrae stars, and flare stars.
* External factors: A star's brightness can be affected by eclipsing companions, dust clouds obscuring it, or even the rotation of the star itself.
* Position: While stars appear fixed in the sky from our perspective, they are constantly moving through space. Over long periods, these movements become noticeable, causing changes in their apparent positions relative to each other.
* Internal structure: Stars are constantly undergoing nuclear fusion, transforming hydrogen into helium and heavier elements. This process changes their internal structure, temperature, and size over their lifetime.
* Evolution: Stars go through various stages in their life cycle, from birth in nebulae to eventual death as white dwarfs, neutron stars, or black holes. These evolutionary stages involve significant changes in the star's appearance, size, and luminosity.
Therefore, when you say a star is not constant, you could be referring to its brightness, position, internal structure, or its evolutionary state. All of these factors contribute to the dynamic nature of stars, making them anything but static objects in the cosmos.
