I’m not 100% on the science of this, but maybe this could be because you use your presumably dominant right hand more, use more force with it, etc. Using a lot of force calls for more blood flow to the area, and your veins might dilate and become more noticeable.
The body is capable of changing in response to the physical demands that an individual puts on it.
Star gazing has a reasonable answer, but there are a lot of other considerations that would have to be evaluated for a more definitive explanation in an individual case.
Here's more information:
www.quora.com/Why-are-my-veins-very-visible-on-my-hands-arms
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