I've been trying to figure out how to convert parallax information from SIMBAD's database into parsecs. Looking at Wikipedia as well as many other sources, parallax is calculated as follows:
distance in parsecs = 1 / parallax
Given the nature of reciprocals, we can inverse this relationship:
parallax = 1 / distance in parsecs
The thing is, all stars I've looked up in SIMBAD do not match other sources using these methods.
- Rigel, according to sky-map.org is 236.967 parsecs away (0.0042p | ~773 ly). Wikipedia places it at 260 parsecs. SIMBAD has nothing even close to these numbers.
- Betelgeuse, according to sky-map.org is 131.062 parsecs away (0.0076p | ~427 ly). Wikipedia places it at 168.1 parsecs. Again, SIMBAD has completely different numbers.
I've checked a few other stars from SIMBAD as well and the parallaxes seem to be following some other format. They have a description of measurement types page, but it does not seem to indicate how these values are to be interpreted.
How does one actually interpret SIMBAD parallaxes, and how can they be converted to distance in parsecs?