Magnitude Conversions
B. L. Gary, Last updated 2015.11.23

This web page is meant for use with typical stars and asteroids in converting between magnitude systems: BVRcIc and g'r'i'z'. There are four types of conversions: 1) within BVRcIc, 2) within g'r'i'z', 3) from BVRcIc to g'r'i'z' and 4) g'r'i'z' to BVRcIc. A few miscellaneous "mixed" conversions are of interest (e.g., BVr' to V) which are included.

Introduction 

This web page is possible because of two crucial publications, culminating in the heroic work by Arno Landolt and staff of the Flagstaff Station of the U. S. Naval Observatory: Landolt  (2009) and Smith et al (2002). The Landolt publication lists 598 stars with carefully measured BVRcIc mags. The Smith et al publication lists 158 stars with SDSS magnitudes (u'g'r'i'z'). I have identified "same stars" to produce a list of 94 stars with both BVRcIc and g'r'i'z' mags. The following graphs and conversion equations are based on these 94 stars. A few "outlier" stars can be seen in the graphs, and they have been omitted in creating the conversion equations. A related web page describes how to create a SED (Spectral Energy Distribution) from BVRcIC and g'r'i'z' and JHK mags: SED.   

Links on this web page 

    BVRcIc to BVRcIc
    g'r'i'z' to g'r'i'z'  
    BVRcIc to g'r'i'z'  
    g'r'i'z' to BVRcIc  
    References
    Related web pages
    Examples   

   
BVRcIc to BVRcIc





g'r'i'z' to g'r'i'z'  




BVRcIc to g'r'i'z'   











g'r'i'z' to BVRcIc   






Examples  

1) Suppose we've measured an asteroid's spectrum to resemble the solar spectrum, i.e., it has a gray color. How would we convert an r'-mag to V? In the "BVRcIc to g'r'i'z'" section above, there a graph plotting V - r' vs. B-V (repeated blow). The sun's B-V = 0.64, so from this graph we note that V - r' = 0.165 0.023. In other words, for a solar-like star or asteroid (with very small B-V color uncertainty): V = r' + 0.165 0.023. Consider a realistic B-V measurement, with an associated SE, such as B-V = +0.77 0.10. For this color the graph states that V = r' + 0.23 0.08 (where SE uncertainties for both B-V and the graphical relationship have been included). This illustrates how a measured B-V, with an associated SE, can be used to convert an r'-mag measurement to V-mag.

2)


References 

Landolt, Arlo U. and Alan K. Uomoto, AJ, 133, 768-790, 2007 March

Landolt, Arlo U., AJ, 137, #5, 2009 May

Smith, J. Allyn and 21 others, AJ, 123, 2121-2144, 2002 April

Related Web Pages

    SDSS Data Release 6 Transformations  
    SDSS III Transformation Between SDSS & Other Systems 
    Creating a SED
    B. Gary's master list of web pages & resume    


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WebMaster: B. GaryNothing on this web page is copyrighted. This site opened:  Nov 03, 2015