<p>Yes, for a direction with <span class="math-container">$α = 18 \mathrm{hr}$</span>, or <span class="math-container">$270^◦$</span> and <span class="math-container">$δ = 30^◦$</span> it is correct to have a term in the dot product with <span class="math-container">$\cos 270$</span>.  It is merely a coincidence that that is zero.</p>
<p>The true value of the direction isn't exactly 270<sup>◦</sup>, so you can easily adjust the formula to a more accurate value later. A more precise value is 277<sup>◦</sup> or 18hr 28min.</p>

CC BY-SA 4.0
2022-02-16T08:32:21.610Z
Hi james me again - yes from Denmark. 
I already have been trying to put in 271 and so on - but I felt it was not the right thing to do. And it dident make mutch chance in result. Sorry for my typing error. again thank you james
john sommer
CC BY-SA 4.0
2022-02-16T08:38:59.063Z
If this solves your problem, you may mark it as accepted by clicking on the green "tick".
James K
CC BY-SA 4.0
2022-02-21T22:16:46.313Z
Where do I find the green tick?
john sommer
CC BY-SA 4.0
2022-02-15T21:15:35.473Z
2022-02-15T21:15:35.473Z
James K
<p>I am working radioastronomy and have a formula for sun/earth calculation.</p>
<p>The formula for sun begin with <span class="math-container">$20(\cos270 \cos 30 \ldots\ldots+$</span></p>
<p>Question:</p>
<p>The first part is <span class="math-container">$\cos270=0$</span> and is that correct in the formulas attached.</p>
<p><a href="https://advlabwiki.johnshopkins.edu/images/Vlsr.pdf" rel="nofollow noreferrer">https://advlabwiki.johnshopkins.edu/images/Vlsr.pdf</a></p>
<p>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)</p>

CC BY-SA 4.0
2022-02-20T01:25:18.183Z
@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
CC BY-SA 4.0
2022-02-21T12:16:42.750Z
[This question](https://astronomy.stackexchange.com/questions/41196/looking-for-a-routine-to-correct-for-local-standard-of-rest-lsr) might be related or useful :-)
nuwe
CC BY-SA 4.0
2022-02-21T22:36:31.067Z
I know the formula and james have the answer  - thank you :-)
john sommer
<radio-astronomy><radio>
Can it be that the formula for calc vlsr for sun have a part beginning with cos270 for Calculate sun/VLSR.cos 270=0?
john sommer
# Can it be that the formula for calc vlsr for sun have a part beginning with cos270 for Calculate sun/VLSR.cos 270=0?

(Asked by: username_0 on 2022-02-15)

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.

<https://advlabwiki.johnshopkins.edu/images/Vlsr.pdf>

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)

**Tags:** radio-astronomy, radio

> **Comments:**
> **username_1**: @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.  
> **username_2**: [This question](https://astronomy.stackexchange.com/questions/41196/looking-for-a-routine-to-correct-for-local-standard-of-rest-lsr) might be related or useful :-)  
> **username_0**: I know the formula and james have the answer  - thank you :-)  

---

## 1 answers

### Answer by username_3 on 2022-02-15. Score: 3

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.

The true value of the direction isn't exactly 270◦, so you can easily adjust the formula to a more accurate value later. A more precise value is 277◦ or 18hr 28min.

> **Comments:**
> **username_0**: Hi james me again - yes from Denmark.  I already have been trying to put in 271 and so on - but I felt it was not the right thing to do. And it dident make mutch chance in result. Sorry for my typing error. again thank you james  
> **username_3**: If this solves your problem, you may mark it as accepted by clicking on the green "tick".  
> **username_0**: Where do I find the green tick?  

---

