<p>I looked for a source without luck, so I'll just post cause I've read this answer before.   The diameter is the solid surface, not the atmosphere for rocky planets.   For gas giants it's the atmosphere up to 1 bar.   </p>

<p>To determine Venus' angular diameter, you'd need to add something for it's atmosphere.   It's difficult to say how high it's atmosphere stops being reflective (and if anyone knows the details, please answer), but I would guess about 50 km where <a href="https://en.wikipedia.org/wiki/Atmosphere_of_Venus#Troposphere" rel="nofollow noreferrer">it's clouds reach to</a> on it's sunny side.   You'd need to add more if you look at it through infra-red.   But I think it would be an error to add the full 250 km listed as the thickness of it's atmosphere and it's reflectivity probably trails off well before then.  </p>

<p>A curious sidebar, <a href="https://www.quora.com/Which-moon-is-bigger-Titan-or-Ganymede" rel="nofollow noreferrer">Ganymede is listed as the largest moon by diameter</a>, but because of it's atmosphere, Titan appears larger.  It's visibly larger on accurate moon charts.   Because of ice in it's upper atmosphere and low gravity, Titan's atmosphere remains reflective for a significant distance.</p>

CC BY-SA 3.0
2017-04-28T05:59:42.790Z
2017-04-28T05:59:42.790Z
userLTK
<p>In NASA fact sheets, such as <a href="https://nssdc.gsfc.nasa.gov/planetary/factsheet/venusfact.html" rel="nofollow noreferrer">this one for Venus</a>, a radius of the planet is given.</p>

<p>Is that radius the radius of the surface of the planet, or of the envelope of atmosphere?</p>

<p>Put another way, if calculating the angular diameter of a planet/moon from a location, do I only have to look up this radius, or do I have to look up this radius along with the atmosphere height to determine the angular diameter?</p>

CC BY-SA 3.0
2017-04-28T05:38:55.710Z
Related question here:   https://astronomy.stackexchange.com/questions/8410/how-is-the-diameter-of-a-gas-giant-calculated
userLTK
<planetary-atmosphere><angular-diameter><mathematics>
Does the given radius of a planet/moon include its atmosphere?
Kate Bertelsen
# Does the given radius of a planet/moon include its atmosphere?

(Asked by: username_0 on 2017-04-27)

In NASA fact sheets, such as [this one for Venus](https://nssdc.gsfc.nasa.gov/planetary/factsheet/venusfact.html), a radius of the planet is given.

Is that radius the radius of the surface of the planet, or of the envelope of atmosphere?

Put another way, if calculating the angular diameter of a planet/moon from a location, do I only have to look up this radius, or do I have to look up this radius along with the atmosphere height to determine the angular diameter?

**Tags:** planetary-atmosphere, angular-diameter, mathematics

> **Comments:**
> **username_1**: Related question here:   https://astronomy.stackexchange.com/questions/8410/how-is-the-diameter-of-a-gas-giant-calculated  

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## 1 answers

### Answer by username_1 on 2017-04-28. Score: 3 | Accepted answer

I looked for a source without luck, so I'll just post cause I've read this answer before. The diameter is the solid surface, not the atmosphere for rocky planets. For gas giants it's the atmosphere up to 1 bar.

To determine Venus' angular diameter, you'd need to add something for it's atmosphere. It's difficult to say how high it's atmosphere stops being reflective (and if anyone knows the details, please answer), but I would guess about 50 km where [it's clouds reach to](https://en.wikipedia.org/wiki/Atmosphere_of_Venus#Troposphere) on it's sunny side. You'd need to add more if you look at it through infra-red. But I think it would be an error to add the full 250 km listed as the thickness of it's atmosphere and it's reflectivity probably trails off well before then.

A curious sidebar, [Ganymede is listed as the largest moon by diameter](https://www.quora.com/Which-moon-is-bigger-Titan-or-Ganymede), but because of it's atmosphere, Titan appears larger. It's visibly larger on accurate moon charts. Because of ice in it's upper atmosphere and low gravity, Titan's atmosphere remains reflective for a significant distance.


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