Glossary of Radio Astronomy Terms
P
Pulsar:
A neutron star that emits regular pulses of light towards Earth.
![Pulsar](https://public.nrao.edu/wp-content/uploads/2017/03/NRAOPulsar-150x150.jpg)
Protoplanetary Disk:
The swirling disk of dust and gas that collapsed from a much larger cloud of material that will eventually evolve into a fully fledged planetary system. Features in the disk may already herald the presence of young planets.
Parallax:
The apparent change in an object’s location due to the change in position of the observer. Astronomical parallax is measured in seconds of arc.
![Parallax](https://public.nrao.edu/wp-content/uploads/2017/07/256px-Parallax_Example.svg-150x150.png)
Parsec:
A unit of length that looks at the distance between earth and objects outside of our solar system. One parsec is equivalent to 3.26 light-years, or nineteen trillion miles.
Peculiar Galaxy:
A galaxy that has distorted features and does not fit completely into a normal galaxy category.
![Peculiar Galaxy](https://public.nrao.edu/wp-content/uploads/2017/07/Merging_galaxies_NGC_4676_captured_by_the_Hubble_Space_Telescope-150x150.jpg)