Missing distance for named stars
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3C 273 and Polis has missing dist data.
proper id dist
3C 273 1272569
Polis 1831728
In general, when distances were unknown or of poor quality (negative parallax or parallax indistinguishable from 0 based on typical measurement error), the distance was omitted. These two entries are a good example of the situation.
3C 273 is a quasar, too far away to have reliable distance data in Gaia or any of the HYG sources. Its distance is actually known reasonably precisely, but since it is not a star and its actual distance is so much larger than any other object in this catalog, it didn't make sense to make a special case out of it. In any event the distance can't be obtained from the data sources used for other objects in HYG or in AT-HYG.
Polis is Mu Sgr, which does not have an accurate distance in the data sources I used (HIPPARCOS has a parallax of 0.09 mas, far below the measurement uncertainty, so it is not included in HYG; Gaia DR3 does not contain this star, so it was not included in AT-HYG's distance data either).