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Continuing the theme set by last week’s video, where we looked at the transit of Mercury coming up in 2032 and the return of Halley’s Comet in 2061, we are going to look even further into the future this time. the next transit of Venus that will be visible from the Earth is almost 100 years away. The most recent one was just over a decade ago, so we will begin by looking at that one. This transit was best seen from the Pacific Ocean, just under the Kamchatka Peninsula and across from Taiwan. This is somewhere around the top of Micronesia, but there isn’t much land, the nearest is probably Wake Island, quite a bit West from Hawaii. This location, pretty much in the middle of the ocean, is where the eclipse looked its best back in 2012. Not quite as recent as the last transit of Mercury, but still just 12 years ago. We will also need to move up into summer time, as this transit occurred on June 6th. We will need to look at daytime, of course we only get to see transits during the day. If you were to look at the Sun (never look directly at the Sun), nothing would look different, but by taking a closer look, at first with the atmosphere removed, we get to see Venus outlined by the Sun.

Venus is only a small dot in comparison to the Sun, though still significantly larger than the dot we see for Mercury. Mercury is of course much smaller than Venus, but it is also further from us and closer to the Sun when it transits compared to Venus. The combination of Venus being much bigger than Mercury and closer to us during its transit makes the disc of Venus look much larger. It is really much smaller compared to the Sun than it appears. These transits take hours, much longer than an eclipse, with transits of Venus usually taking longer than transits of Mercury. This is due to Venus’s slower orbit, but this isn’t the only factor. This particular transit lasted from about 8:30 in to morning until 2:30 in the evening. The planet Venus didn’t transit right across the equator of the Sun, but rather cut a chord across the disc of the Sun pretty close to one of its poles. This gave it a shorter journey to make. Hypothetically, a given transit of Mercury, passing across close to the equator of the Sun, could last longer than a transit of Venus that cuts across close to the edge of the Sun’s disc. Usually however, Mercury’s quicker orbit of the Sun compared to Venus will make sure that a transit of Venus lasts longer, especially if both of the planets are transiting across the same latitude. Watching this eclipse so close to the equator causes the Sun to appear to rotate or flip as it moves across the sky close to the zenith, making it harder to tell that Venus is moving in a straight line. Given that this transit lasted for about 6 hours, parts of it at least were visible across a broad area, but at this location in the ocean, Venus is reaches the North-South axis of the Sun around midday. When the middle of the transit happens roughly in the middle of the day, that ensures that you get to see the whole transit, usually beginning and ending a bit above the horizon.

Observing transits like this gives scientists some practice when it comes to observing transiting exoplanets. Spotting planets moving in front of distant stars is one way to discover other solar systems. The 2012 transit of Venus occurred while the Sun was close to its 11-year maximum, the peak of the 11 year cycle of solar activity. This is a time when the Sun usually has the most of its sunspots and greater activity of coronal mass ejections and flares. By looking at Venus moving in front of the Sun while the Sun was active, scientists got a chance to see what observing a planet in front of such an active star would be like. Unfortunately, the transits of Venus, are far less regular than the transits of Mercury. For the next one we need to look all the way forward to the year 2117. Halley’s comet will be back in 2061, just 37 years, where as our next Venus transit is 93 years ahead of us. I am hopeful that I will be around for the return of 1P/Halley, but I am far less confident that I’ll be here for the next transit of Venus. Then again, medical technology is always advancing so who knows. Jumping slightly less than 100 years into the future, we will see Venus transiting the Sun here from the same location, still observing from the Pacific Ocean. However, the same location is no longer the ideal location, as the transit reaches its peak a little bit after midday. The difference is reasonably slight, roughly the same area still lets you see the entire length of the transit.

All through the above video, I say eclipse when I mean transit. This is partly due to the reasonably slight difference between the two. A transit doesn’t completely block out the Sun, while an eclipse usually does. Of course, an annular solar eclipse doesn’t block out all of the Sun, though it still blocks more than either of these transits. The planet Venus, despite being much much larger than our Moon, is not quite big enough to obscure enough of the Sun from so far away, the Moon an only manage it because it is so much closer. Despite the larger area blocked by Venus, it does still require specialized equipment to observe, a solar telescope that is designed for looking at the Sun would be the best option. The extra magnification is more important with transits of Mercury given that it presents such a small dot. There may be a chance that if you are taking a look at a transit of Venus with eclipse glasses or welders glass to protect your eyes, you might be able to see a little black dot with your naked eye. Unfortunately, I can’t confirm that, as I didn’t get to see the transit of Venus in 2012 and I probably won’t be here to see the transit of Venus in 2117. Even if I am, I will have to have to book tickets to Wake Island or some other part of Micronesia in order to be able to see it at all.

Speaking of eclipses, I’ve mentioned before that we get them here on Earth, but not every planet does. Even other planets with moons don’t necessarily get to see eclipses the way we do. On Mars for example, eclipses are way more frequent. Mars has two very small moons, Phobos and Deimos, orbiting quite close to the planet and orbiting quite quickly, similar to Low-Earth Orbit satellites. They pass in front of the Sun more often than our Moon does, but they don’t cause eclipses to the same degree. They never block out the whole Sun, and so these events may be called transits. We’re going to travel back in time again, even further back to 2004. Although these transits are far more common on Mars, predicting when they occur isn’t given as much focus as when our eclipses occur for us. Although it can be calculated, rather than trying to predict when one will occur, its best to use one that was observed on a known date. Of course, there isn’t anybody on Mars to see them, no humans at least. Thankfully, there are robots, the rovers that drive around, helping us to study Mars remotely. On March 10th 2004, the Opportunity Rover got to see the moon Phobos passing in front of the Sun, from the surface of Mars. These moons orbit incredibly incredibly quickly and as such, the eclipse or transit they create is quite brief compared to our eclipses on Earth. It’s not quite something that happens in the blink of an eye, but Phobos moves noticeably faster than our Moon during the event. Stopping time at the peak of the transit, it is clear that even though Phobos is much smaller than our Moon, it still blocks out a good portion of the Sun’s disc. The little moon is close enough to Mars that despite it’s very small size, it causes something comparable to an annular eclipse here on Earth. It certainly doesn’t cover as much an annular eclipse with our Moon and Sun. Despite being the same Sun, Maars is much further from it, making the Sun appear smaller as well, contributing to how much of it appears to get covered. In the video, all of the simulation is done as if there was no atmosphere, giving a much clearer view. Mars does have an atmosphere, and as well as being thin is is poor in oxygen. This means that the sky wouldn’t look blue. Even with the atmosphere, enough of the Sun is obscured that it would certainly be visible with out any magnification, just some protection. It may even be noticeable without looking at the Sun, but or a much briefer duration than our eclipses. It may not be as good as ours, but it is something similar at least, that can be witnessed from an other planet.

Having looked at the transit of Mercury last time, coming up in 2032, I though it would be appropriate to look forward to 2117 to see the next transit of Venus. The eclipse from Mars is certainly a more common occurrence, but you do have to get there first, which is probably less of a technological marvel than extending the human lifespan to watch the next transit of Venus. Even then, I would rather let some other people make the journey first, just to make sure that it is safe. If you would rather see these things from the comfort of your home, then you have found the right place. I will show you phenomena like this, and to catch when I do, you can subscribe to this website, my YouTube channel or both, you can also find me on Instagram under Caoimhín’s Content as well. You won’t have to wait until 2117 for the next post, so hopefully I’ll see you back here then.