Caoimhín's Content

Having taken a look at Mars at opposition and how Mars enters into a strange, temporary, apparent retrograde motion during that time, we are going to take a look at the Earth doing the same. Of course, to see the Earth at opposition, we need to head to Venus or Mercury.

However, before that I want to take a look at the evening sky from here on Earth. Looking a little bit into the future, we’ve got Mars, Jupiter, Venus and Saturn visible in the sky. At the moment, we can see Saturn and Venus there being really close together, which of course looks very nice. I usually push out to the countryside in order to make fainter objects visible, but if we get rid of the atmosphere it would achieve the same result. Without the atmosphere to light up, fainter objects would be visible even with significant light pollution. Without the atmosphere, Uranus could be visible, and if we take a closer look with a telescope, Neptune is out there as well. Over the next couple of days, Venus will be passing right past Neptune just like it passed past Saturn, and of course, that looks great as well. That’s six planets Mars, Jupiter, Uranus, Neptune, Venus and Saturn, six planets all in the sky together. I’m not going to say that that’s not cool, I’m not going to say that that’s not a significant number of planets to see all at the same time.

However, just a month away, just over 30 days from the date of posting on the 25th or so of February, we will have seven planets in the sky. Mars and Jupiter are easy to spot, with Uranus nearby if you have exceptional conditions and eyesight. Venus is of course very easy to spot, with Neptune still out there somewhere, right in between Venus and Saturn. Just next to Saturn we have Mercury, with both of them quite close to the horizon. Even with the atmosphere back on we definitely can see Mercury. We will need to head out to the countryside to see Saturn shine through. With the right conditions and timing, even from Ireland, we’ve got Saturn, Mercury, Venus, Neptune, Uranus, Jupiter and Mars, all seven of them. If you just wait a month, we will have the full parade. There are various news sources, news sources that are widely considered to be trustworthy and reputable, saying that the parade of planets is peaking on the 20th or so, when we have Venus and Saturn close together, but this isn’t even the full parade. I don’t like the term parade of planets very much, but if you’re going to make a big deal out of the parade of planets, make a big deal out of all seven of them being in the sky.

A couple of the planets in this parade aren’t even visible to the naked eye. We can’t see Uranus, unless you are incredibly gifted and live in the absolute middle of nowhere, and none of us are seeing Neptune with our naked eye, However, we do have five planets visible to the naked eye, even if Mercury and Saturn are a little bit tough to spot. That is the peak, all five of the naked eye visible planets visible at the same time. If you do not have all five of the naked eye visible planets, the parade is not really at its peak, is it? The close conjunction looks great, but Saturn and Venus get next to each other at least once a year because of the way Saturn moves across our sky at roughly the same speed of the stars due to its slow orbit around the Sun. Therefore, you can see this any year, it looks great and I hope you got to see it, and I hope you get to see it again in years to come. However, with so many newspapers and publications saying that the conjunction is the peak of the parade of planets when the actual peak is yet to come, it’s disheartening to see.

We will now, finally, shift our perspective to Mercury and look out into space. Of course, a day on Mercury is a little bit strange which will complicate our observations. We will of course need to find the the Earth, and we will want to get to a position where the Earth is visible during the night for our location on Mercury. The Earth is nice and bright, quite easy to see from Mercury, but we may need to travel across the surface of Mercury to get into the right position. For opposition, we need the Earth and the Sun to be pretty much on opposite sides. Once we have the Earth roughly at opposition and we are on the right side of Mercury to see it, we will need to move through time. If we move through time day by day, just looking outwards, the stars in the background will appear to stay in the same place, but the Earth will vanish from view. We need to select the Earth and follow it across the sky. This is tricky because a day on Mercury lasts so long. As such, we don’t get to see the planets moving through opposition in the way that we’d expect, we can’t simply go out one night after another because the planets won’t just have moved just a little bit in that space of time, they will have jumped to the complete opposite side of the sky, all because Mercury’s day is so, so long. Mercury only gets through a couple of days per year, so trying to observe the Earth is a little bit difficult.

We’re going to do whatever it takes, including things that would be impossible in reality, to see Earth go through this retrograde motion. To make sure that we are seeing the Earth at opposition, we can check that it is 100% illuminated. From our location on Mercury, the Earth is just rising as it hits 100%, but once we remove the ground, where it is in the sky won’t matter. When jumping through time day by day on Mercury using Stellarium, the software uses a Mercurian day. For this reason, I’m jumping a full 59 Earth days, practically two Earth months, each time we go 1 “day” forward. Over the course of a Mercurian night, it will appear like the Earth has traveled quite far across the sky, and that’s just because the days on Mercury are so, so long, so yeah. We’ll have to go through quite a number of days before it will appear to stand in the right place for a given location. Watching the Earth from the right place, we can see it appearing to move in the normal direction. As Mercury just about catches up to it, the Earth does that same back-to-front little weird loop from Mercury that Mars does from the perspective of the Earth. Mars would, of course, go through retrograde motion form Mercury as well.

It would be very difficult to observe this, and I turned off the ground to ensure the Earth would not go out of view. I don’t know if this would be observable with the terrain of Mercury potentially getting in the way before the whole loop has occurred, simply because of how long this could take. Regardless, with all limitations removed, the Earth can be observed to slow down, turn the other way, and then turn back the other way, and proceed across the sky. Here on Earth, because we turn around so fast compared to our year, everywhere on Earth gets to see Mars go through its retrograde motion, because Mars goes through its retrograde motion on the scale of several days. The Earth also takes several Earth days to go through retrograde motion from Mercury, we need to speed through time pretty quickly to see this weird back to front looping happening in reasonable time frame. However, because Mercury is turning so slowly, even though we’re going through several Earth days at a time to watch this happen, we’re only going through a couple of Mercurian days, if that. This means if you wanted to see Earth do this strange side to side looping motion that Mars does, you’d most likely have to move around Mercury to keep the Earth in the right position for it to be visible.

I did commit, perhaps too much time, giving out about the parade of planets and how inaccurately it’s being described by lots of people, but we will now move to Venus. Venus also has an incredibly long day, but we will persist and start by finding the Earth in the sky, quite easy to do from Venus as well. At least, it would be from above Venus’s atmosphere. Moving to night time to see the Earth at opposition again. If we were to jump through days, it would have a very similar effect to what we saw on Mercury, so instead I will do what we did on Mercury. We’ll get rid of any extraneous details like the ground and we’ll move through time quickly, but while focused on the Earth. Venus also has a very interesting day length compared to its year length, with a year of 225 Earth days, while Venus turns around once every 243 Earth days. Thankfully, it turns backwards, or rotates in retrograde, to it only takes 117 Earth days to go from one sunrise to the next. Thanks to the strange day and night, we may not be able to see Earth doing its weird retrograde back to front from any fixed location on Venus for a given year. However, with no ground in the way, the Earth can be seen moving against the stars and doing that weird little loop. Starting from the Earth appearing to move in the normal way, it moves forward, grinds to a halt, moves against the stars for a short distance, and then moves forward again. That is Venus catching up to the Earth, drawing level with it and then moving past it as Earth appears to move backwards in the sky. Eventually, Earth’s apparent motion causes it to end up behind the Sun from Venus’s perspective. It must be behind the Sun, the Earth can never come between Venus and the Sun because it is further from the Sun than Venus is. From Venus, it appears that the Sun’s kind of catches up to the Earth from the East as Venus moves. We’re looking at this all from the southern hemisphere, but this is from the retrograde rotation. Mercury can also be seen doing a very, very similar behavior as to what we’d see from here on Earth, looping from side to side around the Sun.

I hope you enjoyed this quick look at the Earth doing the exact same thing that Mars does. All that really matters is our location, of course, but it is a bit more difficult to observe from the inner planets, not because they are inner planets, but because both of them have such weird days and rotations. Both turn very slowly, but Venus’s rotation is itself a retrograde rotation, and not just “apparent” like the retrograde motion of planets in the sky, Venus really spins the opposite way to all the other planets. I also hope you concur with my point regarding the parade of planets. Maybe you don’t, feel free to leave your own opinion in the comments if you’d like. Do like this article if you enjoyed it, and you can subscribe to this website and my YouTube channel if you’d like to see more of my content. Thank you for reading and hopefully I’ll see you back here next time.