In simple terms, what are the ascending and descending nodes?

[Shiv]

I've always figured ascending node was when you should ascend to your target (burn prograde) and descending node was just the opposite of that (perhaps where you'd end up if you hit the ascending node in orbit of the target you're going to?). The more I play though, the more that doesn't seem to be the case. I'll often 'ascend' on my ascending node and it'll completely miss the mark. For instance, I was just now going to the Mun and the ascending node put me on the opposite side of where the Mun would be once there was intersection. Most other times require a good bit of adjustment, but this time was the one that really drove home that the ascending node is not what I thought it was.

So clearly that's not what the ascending node represents. I read the wiki but the explanation didn't make sense. In simple terms, what are the nodes and should I pay attention to them?

Edited July 18, 2014 by Shiv

[xcorps]

The ascending/descending nodes are the points at which the plane of your orbit intersects with the plane of your targets orbit. At ascending node your orbit is going from below the target to above it. If you burn for an inclination change at a point other than AN or DN, you will have difficult getting the desired inclination.

Above and below being relative to an inclination of zero.

Only use the AN and DN for inclination changes. Only do inclination changes at AN or DN.

If you have a perfect ascent profile from launch and have a zero inclination to Kerbin, your AN and DN to the Mun will be zero.

Edited July 18, 2014 by xcorps

[Awaras]

The ascending/descending nodes show where the plane of your orbit intersects the plane of your target's orbit. I have selected the Mun as the target in this screenshot:

*ninja'd while uploading image, lol*

Edited July 18, 2014 by Awaras

[Master Tao]

Those nodes are where your ships and your target's orbits have the same latitude and longitude – altitude can still be different. The ascending node occurs when your ship's is rising northward to meet the target orbit and the descending node when falling southward. In other words, these are the points where you want to burn normal or antinormal to match the target's inclination (angle off an equatorial orbit). If you look on the maneuver node page, normal and antinormal are the pink triangular directions. If you take off from Kerbin heading east, normal points more northward than antinormal.

Yes, you should pay attention to them. They are often vital for rendevous and achieving intercepts with other celestial bodies.

[EtherDragon]

Hi Shiv,

Simply: Ascending and Descending nodes are the two points where two orbital planes cross each-other.

Whenever you compare two orbits around the same body (say Mun and Minmus around Kerbin) you can think of each orbit as a flat disk. However, no two orbits are exactly the same - one of them is "tilted" with respect to the other. So the two "disks" cross through one another - where the orbits cross is at the Ascending / Descending Nodes.

[mudkest]

Im sure others can explain better then me exactly what it is and such, but lets try. If you have a globe and draw a straight line over it from pole to pole and you have a1 space ship thats orbeting over the equator and another over that polar line(both at the same heigth) then theye will only cross paths at 2 points. if you want the equator spaceship to have the same orbit as the other one you have it butn "up" or "down" at these nodes to change your orbit so theye will overlap. hmm wich makes me wonder, if those 2 points are where the 2 orbits intersect, shouldnt I be burning at 90 degrees from them?

[Shiv]

Ah so it's more for inclination rather than a transfer window. I guess that makes sense. Thanks y'all.

[xcorps]

Yes, what you are describing in the OP, you need to point at the Apoapsis marker and burn prograde to extend your orbit.

If you were trying to go to Minmus, it would require be helpful that you adjust your inclination by making a burn to match inclination at the AN or DN. Under 2 degrees will usually suffice, but when you start doing rendezvous with ships, you really want to try to get it as close to 0 as you can manage.