# Can it be that the formula for calc vlsr for sun have a part beginning with cos270 for Calculate sun/VLSR.cos 270=0?

I am working radioastronomy and have a formula for sun/earth calculation.

The formula for sun begin with $$20(\cos270 \cos 30 \ldots\ldots+$$

Question:

The first part is $$\cos270=0$$ and is that correct in the formulas attached.

Vr(sun) = 20.0 [cos 270° cos 30° cos α cos δ + sin 270° cos 30° sin α cos δ + sin 30° sin δ] (km/s)

• @GrapefruitIsAwesome it looks like JamesK has understood what the actual question is sufficiently to answer it, and I've added the expression in question back into the question itself.
– uhoh
Feb 20, 2022 at 1:25
• This question might be related or useful :-)
– nuwe
Feb 21, 2022 at 12:16
• I know the formula and james have the answer - thank you :-) Feb 21, 2022 at 22:36

Yes, for a direction with $$α = 18 \mathrm{hr}$$, or $$270^◦$$ and $$δ = 30^◦$$ it is correct to have a term in the dot product with $$\cos 270$$. It is merely a coincidence that that is zero.