Question: ScientificConstants names

I fail to see the logic of using short form symbols for the scientific constants and then not being able to use that short form.  One manually has to equate the two as I show below.  Anyone see a reason not to do that in the internal programming?  Just wondering. 

with(ScientificConstants):

GetConstant(M__Sun)             

One has to use the names associated with those short forms described by the command

GetConstant(mass_of_Sun)

I would much rather like to use MSun , so what one has to do is manually equate them

MSun:=mass_of_Sun:

GetConstant(MSun)

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