Caoimhín's Content

Lately, we have been looking a lot at the planets. A few videos ago when I spoke about the parade of planets, we followed some of the planets through the constellations that they’re going to be in over the next couple of months. For planets that are closer to the Sun, like Venus and Mercury, they change what constellation they’re in front of quite quickly, where as for slower moving planets like Jupiter and Saturn, they can remain in the same constellation often for the entire year, only moving from one constellation to the next over longer time scales. Mars is further from the Sun than the Earth and as such it does have a longer year. However, the year on Mars is only twice as long as the Earth’s and as such it does noticeably move across the sky on smaller timescales.

When following a planet across the sky, there will often be a little bit of apparent wobbling from side to side, at least with certain mounts or perspectives. Despite this side to side wobbling, Mars is moving in to Gemini and will subsequently move out of Gemini and into the next constellation over the course of time. There is less wobbling if you go day by day. Coming back into early January when Mars was sort of behind Gemini, moving forward Mars will move into Gemini, stop, turn back and leave Gemini again! It will then continue to move across the sky a little slower than the stars appear to, all the way into Leo, until eventually it ends up going behind the Sun. This is the Earth essentially moving away from Mars, overtaking Mars, moving to the far side of the Sun from mars, and then catching up to Mars again. When we catch up to Mars, it will appear to stop, it will appear to move forward, then we’ll move past it and it will appear to move back. This happens regularly, this is the retrograde motion of Mars, this little loop that it does.

Coming back to this year, following mars brings us all the way forward to 2026 because of course this does happen roughly every year. When Mars is on the far side of the Sun from us, it’s almost directly in line, but you may notice that Mars appears to be a little under the Sun for the next passage behind it. That’s due to differences in our inclination with respect to the ecliptic and the Sun’s equator. Some representations of the planets the orbits trace out the little loop they make from the perspective of the Earth, unfortunately Stellarium does not do so. Seeing the little loop does make these things a lot easier to see and understand. Starting from early in the year, day by day Mars is moving in the direction that we’d sort of expect a planet to move across the sky, it’s following the path of the stars. Mars is actually moving faster than the stars across the sky, but we expect night by night that a star at a given time will appear further and further to the west as we move around the Sun. That’s exactly what’s happening with Mars here, even in the later part of January into February, we’re seeing Mars a little further west at a given time every single night, the normal prograde motion of a planet here. However, as we come up to roughly the 25th maybe of February, Mars turns around. From the 25th, Mars goes against the motion of the stars. Unfortunately, it’s not doing it quite fast enough, as we continue to move, we will get around to the opposite side of the Sun from Mars nonetheless.

All we need to remember here really is that Mars is also orbiting around the Sun, in the same direction that we are. However, we’re orbiting faster, or at least completing a smaller orbit. We’re orbiting so much faster that we eventually catch up to Mars, and that’s when it appears to move backwards. We lap Mars, to use the terminology. Well, the terminology that’s used in athletics anyway, I don’t know if we actually use “lap” in astronomy for these kinds of things. To lap something basically, we’ve made a complete orbit around the Sun and overtaken Mars while it continues to make its complete orbit around the Sun. This comes from races where multiple laps occur around a short track. If you get so far ahead of someone that you come up behind tham and overtake them, you’ve lapped them. Accidentally looking ahead to the year 99,997, all of the constellations are out of place, but Mars continues to move in the same way. Starting from the end of that retrograde loop, we’ll see Mars slow down, appear to change direction, appear to change direction again, and that’s us moving past Mars, catching up to it, and then moving ahead of it in space.

The retrograde motion of Mars and Mars at opposition more generally, it’s a very interesting thing to see. I find that it is a fun one to pull out if people are talking about astrology, simply because the retrograde motion of some planets like Venus and Mercury, is considered such a big deal, where as the retrograde motion of these other objects like Mars, like Jupiter, like Saturn, is not considered as important. This is despite the fact that it is a very similar phenomenon and an illusory phenomenon. Of course, these objects aren’t actually turning around, moving backwards, and then changing their mind and moving forwards again, it’s all an illusion caused by the relative positions and relative motions of the Earth and these planets. We are all moving around the Sun, and this is something that you can observe yourself, you don’t have to take my word for it, you can go out, take photographs, and see Mars changing position with respect to the stars in this way.

Mars has seasons. I was planning to take a closer look at Mars because of the retrograde motion at opposition, it’s something that I’ve mentioned before, and it is an interesting phenomenon that we see on Mars. Thanks to a subscriber, a commenter, the same commenter in fact who gave me the last idea that I decided to steal, I have decided to look at the seasons from the surface of Mars. If you check the comments of my YouTube videos, you’ll see who they are, and they can make themselves known if they so wish as well.

Mars does not have the blue daytime sky that we have, so after translocating ourselves to mars, I get rid of the atmosphere. Stellarium lets you change the ground to something a little more appropriate, we’ve got the surface of the Moon, as an option, as well as Mars. The surface of Mars is composed based on an image taken from a rover apparently, which is nice, you can see it in the image. I was not sure immediately which one, I find it hard to tell just by looking at the solar panels, but it seems to be the Spirit rover. We are on Mars during the day, the Sun is in the sky. Mars has a tilt very similar to the Earth, so it goes through seasons in a similar way to the Earth. With the Sun pretty much on the ecliptic, along with Saturn, Venus, and the other planets, we can watch it appear to rise higher and lower over the course of the year. We’ll face south on Mars, in the northern hemisphere, and if we move forward the Sun will climb, getting higher in the sky as we come through to Martian summer. As we do, Mercury and Venus looping around the Sun several times. The Earth is an inner planet from the perspective of Mars, swinging from one side of the Sun to the other just like Venus and Mercury appear to. The Earth looks pretty illuminated, so it’s probably on the far side of the Sun from Mars.

Pushing past the summer peak, the Sun will reach a lower and lower highest point as we cone into Martian winter. The Sun ends up nice and low, a very observable difference from the summer. The Sun then moved through its lowest and begins climbing higher in the sky again, just like it does for the Earth. Of course, the seasonal variation on Earth is complicated by many other factors, Mars certainly doesn’t have a monsoon season because there’s no water. Roughly speaking however, we’ve got the northern hemisphere being warmer while it’s tilted towards the Sun, leaving the southern hemisphere in its cold winter, and then the southern hemisphere being warmer while the southern hemisphere is tilted towards the Sun. Mars goes through seasons just like the Earth, and we can see the Sun going up and down, despite the fact that its year is twice as long, that just means the seasons last twice as long as well. Despite the length, they do operate under the same principles as our year here on Earth.

I removed the atmosphere simply because it makes all of this easier to see, of course. Mars does have an atmosphere, it is a thin atmosphere of carbon dioxide, but it seems sufficiently thick based on all of the images I’ve seen. Obviously I haven’t gone to Mars to check myself, but based on all of the images that I’ve seen, the carbon dioxide in the atmosphere of Mars is sufficient for some sort of scattering to take hold. I don’t know if it’s Rayleigh scattering, which operates here on Earth, though I presume it is. Regardless of the mechanism, Mars’s sky has a colour during the day and the light of the Sun being scattered through that coloured atmosphere blocks out the stars. If you were actually on Mars, you wouldn’t be able to see the Sun and the stars at the same time, unlike the Moon, which actually doesn’t have an atmosphere, and this would be visible.

What counts as an atmosphere varies. Some planets have an exosphere or transient atmosphere, where at nighttime or when they’re further from the Sun, the atmosphere freezes, where as during the day or when they’re closer to the Sun, it reverts to a gas. Not saying that daytinme and closest or night time and furthest are the same thing, rather at perihelion or daytime, whichever is sufficient to raise the temperature enough to cause gases that sublimed onto the surface to evaporate back into the atmosphere, the atmosphere reforms. Or the exosphere reforms, depending on the name you prefer. That’s something that happens, it sort of happens on Mars as well, with winter and summer sublimation of carbon dioxide at the poles. However, that is something I will get into in a future video where we look specifically at Mars.

If you saw my last piece, I discussed some smaller objects, Makemake in particular, and then some of the other Trans-Neptunian objects, especially candidate dwarf planets or de facto dwarf planets, whichever you prefer. I mentioned that I will be looking at the major planets like Mars, Mercury and Venus in more detail, talking about their specific features in the future. If you don’t want to wait for the future articles where I take a closer look at Mars and its individual features, all you need to do is go back through my older posts, because I have discussed the planets of our solar system, the non-dwarf planets, the actual planets of our solar system, in several pieces in the past. You’ll just have to go back on this website nto find them, but I will be doing more of those in the future. They will be covering slightly different content, so it might be nice to look at both of them. You can look back at the pieces about Mercury and Venus and Mars that I put out in the past and look forward to the future articles that I’m going to put out as well.

That brings us to the end. I hope that you did enjoy, if you did, please do like this piece. You can also subscribe to this website and YouTube channel to see more of my content in the future. Thank you for reading and hopefully I’ll see you back here next time.