In most the field of astronomy, the periodic table is far simpler than the one you had to learn about in school. There are only three elements: hydrogen, helium, and metals. This does not mean that all of the other elements you know aren’t real, but because there is so much hydrogen and helium in our universe, they completely dwarf all of these other elements on large scales. In our entire solar system, the Sun comprises 99.86% of its total mass, and of that mass, about 98% of it is hydrogen and helium. Jupiter and Saturn alone make up 90% of what is left, and they too are made up of mostly hydrogen and helium. Virtually all of the other elements that make up basically everything you know are present in only trace amounts. The image below shows the relative abundances of all of the elements, and as you can see, most elements are too comparatively rare to even appear on the diagram.