# Advanced QuestionLongitude of the Ascending Node on the ground vs final orbit

#### PaulG

##### New member
I'm trying to conceptually understand something.

Why is the LAN after achieving orbit drastically different than on the ground just prior to launch? What I can tell, the value is represented by the following "formula", which could very well be wrong, so please, I'd like to understand.

Let G = ascending node on the ground at launch
Let L = latitude of the base (e.g. 28.5)
Let d = directional multiplier, (+1 if going north, -1 if going south)
Let LAN = longitude of the ascending node in orbit. Give or take a little due to the time it takes to get to orbit.

LAN = G+d*(90-L)
So, if my ground latitude is 28.5 and the on ground LAN is 244, the my orbital LAN after launching any direction northward will be around 244+1(90-28.5) = 306.
If going south, it would be 244-1(90-28.5) = 183.

Thanks,
paul

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