1. Hydrogen Envelope: This is the largest part of a comet. It's an enormous cloud of hydrogen gas that surrounds the entire comet, extending millions of kilometers into space.
2. Coma: The coma is the cloud of dust and gas that surrounds the nucleus of a comet. It's usually the second largest component, expanding as the comet gets closer to the Sun and heats up.
3. Nucleus: The nucleus is the solid core of the comet, made up of rock, dust, and frozen gases. It's typically the smallest part of the comet, often just a few kilometers across.
So, from largest to smallest, the components of a comet would be ranked:
Hydrogen Envelope > Coma > Nucleus