The brightest blue knots (superassociations) detected by composite U,B,V color photography in spiral and irregular galaxies have absolute magnitudes B₁ ranging from -10 to -15, which are from 3 to 5 magnitudes brighter than the brightest single stars. The absolute magnitude of the brightest blue knot M₁⁰ (corrected for galactic extinction) depends on the corrected color index (B-V)_T⁰ and luminosity index Λ_c of the galaxy, being brighter in the bluer and most luminous galaxies. In a first approximation a two-parameter solution gives

M₁⁰ = M₁^C + 2(Λ_c -1)+2.5 [(B-V)_T⁰-0.5]

where 1^C> = -13.4 ± 0.2 from a sample of 78 galaxies having known distance moduli 18.3 < μ₀ < 32.0. In a second approximation allowing for internal extinction a three parameter solution gives

M₁⁰ = M₁^* +2(Λ_c -0.8)+2.8 [(B-V)_T⁰ -0.5] +0.7 (log R₂₅ -0.2)

where R₂₅ is the isophotal axis ratio of the galaxy and 1^*> > = -13.0 ± 0.2. Distances derived from B₁ and M₁^C or M₁^* are in good systematic agreement with distances derived from primary, secondary and tertiary indicators, but with a rather large dispersion (σ ≅ 0.55 mag) due in part to errors in the preliminary photometry (σ ≅ 0.4 mag). With some refinements and better photometry this new distance indicator appears capable of providing distance moduli with mean errors ≲0.5 mag out to distances in excess of 100 megaparsecs.

#	Concept	H-Index	Publications	Citations
1	Engineering	1	1	30
2	Physics	1	1	30
3	Photometry	1	1	30
4	Cosmology	1	1	30
5	Observational Cosmology	1	1	30

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