Arcseconds

[KvickFlygarn87]

I am planning a Mun base, and I would like to use MJ's autoland, but to land close enough but not on the base, I need to now: How far is one arcsecond on the mun? Or rather, how would I calculate the length of one arcsecond?

Edited November 5, 2013 by KvickFlygarn87
Answered

[Geschosskopf]

Well, it depends on your latitude. If you're not on the equator, the distance on the ground per unit of angle is smaller. So this adds an extra step.

To find an arcsecond on the equator, go to the wiki and look up Mun's circumference. Multiply that number by 1 / (360 * 60 * 60) and you have the ground length of an arcsecond on the equator.

If you're not on the equator, you need to multiple this by a fraction based on your latitude. This fraction is the circumference around the line of your latitude divided by the equatorial circumference. So now you have to find the circumference at your latitude, which involves simple trig. I bet you can figure that out on your own .

[KvickFlygarn87]

Okay, thanks.

[Sirrobert]

You could use Mechjeb to to the main landing, and than take over for the final touchdown, to perfect your landing spot

[Mesons]

Unfortunately, it depends on the latitude. At the equator, you can just convert to degrees (one arc-second is 1/3600 of one degree) and convert to radians (one degree is pi/180 radians). The arc length is the angle in radians times the radius. I calculate one arc-second to be about 4.85E-6 radians, so for the munar radius of 200km, an arc-second at the equator is around 0.97 meters. This distance will scale with the cosine of the latitude for East-West measurement, but remain the same for North-South measurement all the way to the poles.

Condensed, approximate version:

Latitude: 1 arc-second = 1 meter

Longitude: 1 arc-second = cos(Latitude) * 1 meter