The universe is made of different things, but much of it is made of things we can't see. The things we can see in solar systems and galaxies are made of atoms and molecules, plasma (hot gas of ions), and light. Atoms and molecules make gases -- like the air we breathe and the gases of Jupiter, solids -- like our Earth and many other planets in our solar system, liquids -- like water on Earth and the ammonia on Neptune, and living organisms; plasma makes up stars such as our sun; and light makes sunlight and starlight. Many of the things we can't see are called forces, which means that they affect us in ways we might be able to feel (such as gravity) or that we can measure them with special instruments, but we can't see these forces with our eyes. Some other things we can't see are also hard to measure, but help explain what we can see, and scientists have started calling these invisible and hard-to-measure things dark matter and dark energy.
Broadly speaking, based on what we currently understand, we can say that the universe is made of matter, dark matter, and dark energy, and we can see or measure everything in the category of matter, but not so much in the categories of dark matter and dark energy.
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