Distance
At least two methods have been used to measure the distance to the Sombrero Galaxy.
The first method relies on comparing the measured fluxes from planetary nebulae in the Sombrero Galaxy to the known luminosities of planetary nebulae in the Milky Way. This method gave the distance to the Sombrero Galaxy as 29 ± 2 Mly (8.9 ± 0.6 Mpc).
The other method used is the surface brightness fluctuations method. This method uses the grainy appearance of the galaxy's bulge to estimate the distance to it. Nearby galaxy bulges will appear very grainy, while more distant bulges will appear smooth. Early measurements using this technique gave distances of 30.6 ± 1.3 Mly (9.4 ± 0.4 Mpc). Later, after some refinement of the technique, a distance of 32 ± 3 Mly (9.8 ± 0.8 Mpc) was measured. This was even further refined in 2003 to be 29.6 ± 2.5 Mly (9.1 ± 0.8 Mpc).
The average distance measured through these two techniques is 29.3 Mly (9.0 Mpc) with an uncertainty of 1.6 Mly (0.5 Mpc).
Read more about this topic: Sombrero Galaxy
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