# Tag Info

Accepted

### Calculate how many days left for synodic period from particular planet

If you know the date of the last opposition, then the next one will be about 399 days later (ie a year, a month and a bit). That is just counting days. So if you know that there was an opposition on ...
• 87.6k

### Is there a Lagrange point between the earth and the moon?

Yes, the Earth-Moon system has Lagrange points, and Wikipedia has a short list of satellites that have (or will) orbited near L2, L4 or L5. Neither L1 nor L3 appear to be popular. The Moon's orbit ...
• 8,912

### What is the **actual** average distance of the Moon from Earth?

Lunar theory is complicated. ;) The Moon's orbit around the Earth is only approximately a constant Keplerian ellipse. As I mentioned here, the Moon's orbit around the Earth-Moon barycentre has an ...
• 8,912

### What is the **actual** average distance of the Moon from Earth?

Your guess on the requirement for calculus is correct. What you need to do is integrate the moon's distance over one orbit to find an average distance. Starting from the equation below, the Moon's (or ...
• 14.4k

### Is there a Lagrange point between the earth and the moon?

@JamesK's answer is good, but I'll address some of your points more specifically. Is there a Lagrange point between the Earth and Moon... Yes, it is called Earth-Moon L1 (to distinguish it from Sun-...
• 31.5k
Accepted

### What is the **actual** average distance of the Moon from Earth?

Mean distance averaged over time for any Keplerian orbit is $a(1+\frac{1}{2}e^2)$, where $a$ is the semi-major axis and $e$ is the eccentricity. Using your NASA fact sheet, I get about 384,979 km for ...
• 13.6k
Accepted

### Is there a Lagrange point between the earth and the moon?

Yes. The Earth-Moon system has a Lagrange point L1, positioned between the Earth and the Moon, It is about 85% of the distance to the moon (about 320000km compared to 380000km.) A body at L1 would ...
• 87.6k

### How time-symmetric is orbital mechanics?

It's hard to give a definitive answer to this question. For the spherical-cow, Physics 101 answer, the answer is yes, the dynamics of orbital mechanics are time-reversible. However, as I'll get into ...
• 14.4k