The part of a star that extends millions of kilometers into space is its corona.

Here's why:

* Corona: The outermost layer of a star's atmosphere. It's incredibly hot (millions of degrees) and very thin, but it can extend millions of kilometers into space. The corona is visible during a total solar eclipse as a faint halo around the Sun.

* Photosphere: The visible surface of the star, where light is emitted. This layer is much denser than the corona.

* Chromosphere: A layer above the photosphere, where the temperature increases rapidly. It's not as extensive as the corona.

Let me know if you have any other questions!