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A region of space with a gravitational field so strong that nothing, not even light, can escape from it. The boundary beyond which light cannot escape is known as the event horizon.

A luminous giant star that has a low to intermediate mass and is in a late phase of stellar evolution. Its outer layers expand and cool as it runs out of hydrogen fuel.

A sudden flash of increased brightness on the Sun, usually observed near its surface and in close proximity to a sunspot group. It is a result of the release of magnetic energy stored in the Sun's atmosphere.

A highly magnetized rotating neutron star that emits beams of electromagnetic radiation out of its magnetic poles. This radiation can be observed when the beam is pointing toward Earth, giving the appearance of pulsating light.

High-energy radiation, mainly originating outside the Solar System and even from distant galaxies. Upon impact with the Earth's atmosphere, cosmic rays can produce showers of secondary particles.

The increase in the wavelength of light emitted from an object due to its motion away from us. This is used as evidence for the expansion of the universe.

The decrease in the wavelength of light emitted from an object as it moves towards us. This is less common than redshift in the universe.

A form of matter that is thought to account for approximately 85% of the matter in the universe. It does not emit, absorb, or reflect light, making it invisible to current detection methods.

A small, dense star that is the leftover center after a low-to-intermediate mass star has shed its outer layers and ceased nuclear fusion.

A stellar explosion that occurs at the end of a star's life cycle, which can briefly outshine entire galaxies and radiates more energy than our sun will in its entire lifetime.

The thermal radiation left over from the time of recombination in Big Bang cosmology, which provides a snapshot of the universe when it was only 380,000 years old.

A mysterious force that is accelerating the expansion of the universe. It constitutes about 68% of the universe's total energy.

The region around a star where conditions may be just right for life to exist on planets. This zone is where planet surfaces can have liquid water, considered essential for life as we currently understand it.

The scientific theory describing the origin of the universe at a single point, from which it has been expanding and cooling over the last 13.8 billion years.

A planet outside of our solar system that orbits a star other than the Sun. Exoplanets are important for understanding planetary formation and the potential for extraterrestrial life.

A natural light display in Earth's sky, predominantly seen in high-latitude regions, caused by the collision of solar wind and magnetospheric charged particles with the high altitude atmosphere.

The collapsed core of a massive supergiant star which can result from a supernova. Neutron stars are incredibly dense and have strong magnetic fields.