# How can one determine the angle between the line of nodes and the major axis of the orbit of Mars?

Edit:

What I really was looking for, was the difference in longitude on the orbit of Mars between its aphelion and the point where the north pole axis of Mars would point towards the Sun (northern summer sostice).
I found out with this article of the Planetary Society that the solar longitude (Ls) is 90⁰ for northern summer solstice and Mars is at aphelion at Ls = 70⁰.

I know when northern summer is on Mars, the solar radiation on its surface has a minimum of 492 W/m², meaning that is also the time when Mars is furthest from the Sun.
So this would coincidence somewhat with the north pole of Mars pointing towards the Sun.

But what is exactly the angle between the line of nodes and the major axis of its orbit ?

• The first sentence of your question is a little confusing, you say you know when the northern hemisphere of Mars experiences summer, "meaning that is also the same when Mars is furthest from the Sun" as if the two events are connected. Seasons on Mars are determined the same as seasons on Earth, by the tilt of the planet's pole, not the distance from the Sun. Can you elaborate more on exactly what you're looking for since @notovny answered what the angle is between perihelion and the ascending node? – AstroShannon Aug 11 '20 at 18:20
• @AstroShannon I wrongly supposed that the line of nodes were perpendicular to the pole axis. As novotny commented the two have nothing to do with each other. I was looking instead for the angle between the pole axis and the major axis. – Cornelis Aug 11 '20 at 18:47
• I'll probably remove my answer; it seems that I'm not describing the angle you're looking for. – notovny Aug 11 '20 at 19:48
• @notovny For me, you don't have to. I will just ask a new question about the angle between the pole axis and the major axis. – Cornelis Aug 11 '20 at 21:40

The name for this angle is the Argument of Periapsis.

The Argument of Periapsis (or in this case, Perihelion, since Mars orbits the Sun) is the angle, in the plane of the orbit, measured in the direction of travel around the Orbit, from the Ascending Node, through the body being orbited, to the periapsis of the orbiting object.

Princeton's Planetary Systems page lists the Argument of Perihelion of Mars as $$286.5°$$ in 2006.

This would make the interior angle between the major axis of Mars and the line of nodes to be $$360°-286.5° = 73.5°$$, as of 2006.

• Fine, so that would mean the Sun is at its highest in northern summer before perihelion occurs , right ? Could it be calculated how many days there is between those two events ? – Cornelis Aug 11 '20 at 16:25
• @Cornelisinspace I think we're having a miscommunication of terminology here. Neither the major axis nor the line of nodes have anything to do with the way that Mars' poles point. I may have answered a question different from the one you were intending to ask. – notovny Aug 11 '20 at 16:30
• Sorry, I will not ask a new question about the pole axis of Mars. I already found at Planetary Society that solar longitude (Ls) is 90⁰ for northern summer solstice, and aphelion is at Ls = 70⁰. – Cornelis Aug 12 '20 at 12:31
• @Cornelisinspace I'd recommend posting that as an answer to your question, and unselecting this one as an answer. That's allowed by Stack Exchange, would help others who might be looking for the same info (because comments are ephemeral), and there might be another user who can provide helpful clarifications on it. – notovny Aug 12 '20 at 12:47
• Instead I made an edit with the info, so no need to unselect your answer ! – Cornelis Aug 12 '20 at 13:42