The distances to planetary nebulae are generally poorly determined, but the Gaia mission is now measuring direct parallactic distances between their central stars and neighboring stars. It is also possible to determine distances to nearby planetary nebula by measuring their expansion rates. High resolution observations taken several years apart will show the expansion of the nebula perpendicular to the line of sight, while spectroscopic observations of the Doppler shift will reveal the velocity of expansion in the line of sight. Comparing the angular expansion with the derived velocity of expansion will reveal the distance to the nebula.
The distances to planetary nebulae are generally poorly determined but the Gaia mission is now measuring direct parallactic distances between their central stars and neighboring stars It is also possible to determine distances to nearby planetary nebula by measuring their expansion rates High resolution observations taken several years apart will show the expansion of the nebula perpendicular to the line of sight while spectroscopic observations of the Doppler shift will reveal the velocity of expansion in the line of sight Comparing the angular expansion with the derived velocity of expansion will reveal the distance to the nebula