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Sorry, if this is a 'stupid' question of a non-expert, but this question came recently up in family discussion of mine and I couldn't give a satisfactory answer:

I know we have good (?) estimates of how many galaxies, stars and some planets exist in our universe, and we have database to track other bodies, but how many actual "visible objects" ( - "light blips" on film, if you will - ) has humanity uniquely identified? (i.e are in some sort of database, I assume.)

Also, exclude objects of our solar system (i.e. all "small stuff")

In essence, the question arose by watching the night sky and taking "How many stars can you count" literally. How many individual outer-solar system "shiny objects" has humanity really "seen" so far - not just deduced indirectly. (I'm aware that "looking at the sky" would always only give you less than this number, due to just watching half the universe at best.)

I fully expect not getting an accurate single number, but I don't even know the answer in rough over-the-thumb terms.

Also, I'm by no means versed in Astronomy. And I could also need help with appropriately tagging or rephrasing this question.

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    $\begingroup$ The answer to this gets really complicated when you start talking about other galaxies, which could be counted as a single object or as many more or less distinct objects depending on magnification... $\endgroup$
    – Darth Pseudonym
    Commented May 31 at 13:36
  • $\begingroup$ Fantastic question! please definitely read up on GAIA, the greatest spacecraft ever built, you'll love it. $\endgroup$
    – Fattie
    Commented Jun 1 at 14:45
  • $\begingroup$ "I fully expect not getting an accurate single number" I disagree! Every single astronomical "thing" as you are defining it, is indeed, in a computer database such as mysql, mongo, or so on. (The absolutely tiny handful of "items" from the paper era, have been, fully incorporated in to, current-day databases.) Yes, it might be a little work to ensure that one has a conclusive list of every such database, but the answer to your question is an integer. Which is great! $\endgroup$
    – Fattie
    Commented Jun 1 at 14:51
  • $\begingroup$ @Fattie Off-topic, but it's not in mongo unless the IT guy doesn't know what he's doing. Superior RDBMSs exist, they should be used properly. $\endgroup$
    – David Tonhofer
    Commented Jun 3 at 12:07
  • $\begingroup$ LOL @DavidTonhofer $\endgroup$
    – Fattie
    Commented Jun 3 at 12:22

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The NASA extragalactic database (NED) contains data on 1.107 billion distinct extragalactic objects. (See here). This catalogue is assembled by merging the data from many other observational sources (2MASS, SDSS, Chandra, GALEX...). The vast majority of the sources in this catalogue are genuine extragalactic sources (i.e. galaxies and quasars).

For stellar catalogues, the Gaia DR3 database (the current incarnation of the catalogue from the Gaia astrometry satellite) contains positions for at least 1.46 billion separate sources. Most of these are stars in our own galaxy, with only some 10 million objects identified as extragalactic sources.

The sum of these two numbers ($\sim 2.56$ billion) is a reasonable number for the total catalogued astronomical objects.

There are a small fraction of objects in common between the two catalogues that would reduce this number, but on the other hand there are some specialist deep photometric catalogues of stars over limited regions of the sky that would increase it a little.

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  • $\begingroup$ Of course anything on the far side from the galactic core will never appear in this catalogue. This includes the stuff from the "Great Attractor" IIRC. $\endgroup$
    – David Tonhofer
    Commented Jun 2 at 7:23
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    $\begingroup$ @DavidTonhofer since the NED database I mention include infrared catalogues, then galaxies on the far side of the galactic centre are included to some extent. However, Gaia is certainly blind to more than a few magnitudes of dust extinction. $\endgroup$
    – ProfRob
    Commented Jun 2 at 7:45
  • $\begingroup$ Thank you. I guess the one thing I as a non-expert am/was uncertain of is, how many of the objects in the database represent first-hand measurements, and how many (if any) are the result of computational results when interpreting other measurements. (i.e you measure one light-source, but based on trajectories' etc. you deduce it must be more than one object - will it count as two in that catalogue?) But one way or the other: 1.107 billion is a hugely impressive number of "verified facts" ! $\endgroup$
    – BmyGuest
    Commented Jun 3 at 7:20

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