The appearance of stars as a ball with a line through them when observed through a telescope is likely due to the optical effects caused by the telescope itself. There are a few factors that could contribute to this observation:
Diffraction: When light passes through the aperture of a telescope, it encounters the phenomenon of diffraction, which causes light waves to bend and spread out. This can result in a star appearing as a small, round disk surrounded by rings or spikes. The central disk is known as the Airy disk, and the spikes or rings are caused by the interaction of light with the telescope's aperture and its support structures.
Telescope optics: The design and quality of the telescope's optics can also affect the appearance of stars. Imperfections or aberrations in the telescope's lenses or mirrors can introduce distortions in the star's image, resulting in irregular shapes.
Atmospheric conditions: The Earth's atmosphere can also contribute to the observed appearance of stars. Turbulence and variations in air density can cause the light from stars to undergo refraction, leading to fluctuations in their apparent position and shape. This effect, known as atmospheric seeing, can cause stars to appear as twinkling or shimmering objects.
It's worth noting that the apparent shape of stars observed through a telescope can vary depending on the telescope's design, its optical quality, and the observing conditions. Higher-quality telescopes with well-corrected optics and larger apertures can provide sharper and more detailed views of stars, reducing some of the optical effects mentioned above.
If you are observing stars through a telescope and notice a ball with a line through them, it is likely a combination of diffraction, telescope optics, and atmospheric conditions affecting the star's appearance.