This section will eventually be a guide to how astronomers determine distances.
For now, here are a few notes on the distance estimate section of the Avedisova summary pages.
There are no distance estimates in the Avedisova catalog itself. I've taken these from many different sources that use many different distance estimation techniques. For this reason, they are unlikely to be consistent.
There are currently distance estimates available for objects in about half of the 3235 star formation regions in the Avedisova catalog. I'll be adding to this over time.
One challenge is identifying objects listed in the Avedisova catalog, which is a huge compilation of objects from 2441 different sources.
For some objects, notably optically visible nebulae, dust clouds, and the infrared objects from the IRAS catalog, the Avedisova catalog provides explicit object identifiers. If the object is clearly identified in the Avedisova catalog, or can be looked up in a source catalog using its IRAS number (eg. the WB89 objects) it is marked with an "I" in the note column.
In most cases, the Avedisova catalog object information contains only the name of the catalog the object appears in, an approximate position, and a number of velocity measures. It does not provide the object identifier used in the original source catalog. In these cases I usually list the closest catalog object with one of the listed velocities. In that case, the note is 'V'.
In some cases (because I didn't happen to have the original object velocity information), I have simply selected the object with the closest position in the given object catalog. In that case the note is "P". Over time, I will add more velocity matches.
If a source provides multiple distance estimates for an object, they are all listed. If the source lists one distance estimate as more likely than others, it is shown in bold.