Mars at Closest, Mars at Opposition

This site: is typical - it says that Mars is closest to the Earth Oct 6, and at Opposition Oct 13.

Opposition is when the planet lines up exactly 180 degrees away from the sun. You would think that this would be the closest as well, but I can see with elliptical orbits this may not be so.

But that site also says “Next Tuesday, Oct. 13, Mars will officially reach opposition, and maximum brightness in the sky.” which I find weird since it is further away than it was the week before. Unless it has something to do with the sunlit disc we are seeing.

Your insights would be appreciated!

That’s exactly what it is.

On Oct 13th, it will only be slightly further away than it was on the 6th.

However, we will see the entirety of the disc of planet with the sun reflected as much as possible back at us.

For what it’s worth, this is also the time (or rather, part of the span of time) when a planet goes retrograde: It’ll appear to move “backwards” from its usual movement, because Earth is passing it.

Yeah, that annoyed ancient astronomers to no end.

We ended up with epicycles to “explain” the behavior.

Highjacking somewhat, what is the point in Venus path, as seen from Earth, where it’s brightest? It gets closer and closer…but also more and more crescent. When it’s at its very closest, it’s a “New Venus” and quite dark. There has to be a particular angle where it is brightest. I Googled the tar out of this and didn’t find an answer.

Seems as though it is when it is at about 50% illumination. 72 days after its closest approach.

That is when the lit Venus takes up the most area of the sky.

Hmm. It shouldn’t be a difficult calculation, but Wikipedia says

The brightest magnitude occurs during crescent phase about one month before or after inferior conjunction.

Thank you both! I’m happy my intuition was right, and happier to have an actual value! Yay! Highjack over!

Yes, you are absolutely correct. I have no idea why I doubled 36.

I saw it was 36, knew it was 36, but, and I have no idea what I was thinking at the time, chose to multiply it by 2 when I posted that.

If there was still a headsmack smiley, it would be appropriate right now.

It’s not just the entirety of the disc, there’s also a minimal shadow effect. At opposition, shadows of mountains and other features on Mars are minimized, so there’s more light reflected back. We see the same effect with the Moon for about an hour or so around the exact time of a full moon. It’s significantly brighter during that time compared with just before and after it. More than can be accounted for by the amount of disc that’s lit up.

A mission to Mars in the near future is real and this is thanks to Elon Musk who aims to be buried there.


@cannon_gray, I’m glad that you’re interested in the content here, but we prefer that posters not bump old threads unless they have some new information to add on the topic. A mission to Mars isn’t really relevant to the topic of how the planets look from Earth. In other threads, you seem to be bumping the thread to repeat information others have already provided. If you wish to discuss a mission to Mars, possibly involving Musk as a financier and/or payload, I invite you to start a new thread in the appropriate category (in this case, probably MPSIMS, unless you have some specific questions you’d like to ask).

ok :wink: