Caoimhín's Content

Today, we are mostly going to take a look at some mistakes. Mistakes from the past can leave behind little quirks and inconsistencies in things we use today, and catching mistakes is often a good thing. Realizing that we were wrong about something can help us prevent similar mistakes in the future. This is inspired by the discovery that a star we believed to host an exoplanet, actually, probably, does not. Although we have learned that something isn’t there, that is still something learned, and mistakes like this can happen in any discipline. Even though astronomy, especially astronomical research, attracts some of the most talented and rigorous scientists, mistakes can and do still occur.

To find the star we are looking for, we’ll need to find the constellation first. We’re looking for a the constellation of Eridanus, which is not very visible from Ireland, certainly not at this time of the year. By looking at the daytime sky with the atmosphere removed, we can see the Sun at its highest along with the constellations that are currently hidden behind it. The Sun is almost at its very highest, as we so close to the summer solstice. Our view of the midsummer sky during the day parallels our view of the sky at midnight on midwinter. With the Sun at it’s daytime peak, we are also seeing the ecliptic at pretty much its highest arc through the sky. In winter time, when the Sun is at it’s daytime low, the arc of the ecliptic instead rises highest during the night. Given that midsummer and midwinter are separated by 6 months, or half the Earths orbit around the Sun, we will see the same constellations at midnight on midwinter as would be in the sky at midday in midsummer. If there was a midwinter Full Moon, the Moon would be at its highest in the South, just like the midsummer Sun during the day. Of course this means planets like Mercury, wouldn’t be visible, but other objects like Jupiter, Uranus, the Moon and Mars could be, depending on the year.

Ignoring the Sun, we can see some of the most famous constellations, the ones that are nice and high through the long winter nights, now Behind the Sun in summer. Orion of course is one of the most famous thanks to the belt, while Canis Major is quite famous thanks to the brightest star Sirius. Gemini is visible high in the sky just East of South. Taurus is truly in the center, partly hidden by the Sun, but we can see the Pleiades next to Jupiter and Mercury, just to the West of South. The constellation we’re looking for is a long, squiggly line, stretching from next to Orions feet, curving under Taurus and then reaching down under the horizon from here in Ireland. given that we can’t see the whole constellation even when the ecliptic is at its highest indicates that we never can, from here in Ireland at least. Closer to the equator the whole length of this squiggly line can be seen. In past posts I have highlighted how much imagination some of the constellations require, with the short and slightly wonky line next to Taurus in the sky being a good example, as it is supposed to be a ram, Aries the Ram. With constellations such as that, it can be hard to imagine what this long squiggly line is meant to be, but it’s meant to be a river and that I think makes a little bit of sense, flowing and curving through the sky. This is Eridanus the River. By removing the ground, the horizon stops being in the way, and we can follow the whole length of the river. It’s the 6 largest constellation out of the modern 88, which is a lot easier to tell when all of it is visible, with the river ending in the star Achernar or Alpha Eridani.

I do make the mistake of saying “Eridanus” rather than “Eridani” for the names of these stars. The difference is that Eridani is the genitive, meaning “of Eridanus”, so Alpha Eridani really means “Alpha of Eridanus”. It’s easy to forget, especially with Latin having so many conjugations. Orion becomes Orionid, Canes Venatici becomes Canum Venaticorum. Regardless of my mistakes, Alpha Eridani or Achernar is the brightest star in the constellation, and by following the river of stars backwards, we’ll come to other names featuring other Greek letters, such Phi Eridani and Iota Eridani. Some will have other names besides the Greek letters, and some combine Greek letters with numbers, such as Beemim, or Upsilon 3 Eridani. This is often written u3 Eridani or Upsilon³ Eridani. It also has a name based purely on a number, 43 Eridanus. There are a lot of different names for some of these stars, with slightly different origins and uses. Way at the other end of Eridanus the River, next to the feet of Orion, is Cursa or Beta Eridani. Beta Eridani is supposed to be the second brightest star in the constellation after Alpha Eridani, just like beta coming after alpha in the alphabet. In this case it is accurate, but this isn’t always the case. People make mistakes, and when these stars were being assigned designations, a lot of the comparisons were being done by eye, there wasn’t very precise optical measurements of the brightness. In the case of the Bayer designations, the ones with mostly Greek letters, a system of moving through the constellation from left to right and from top to bottom also had and effect.

A great example is the two brightest stars in Orion, Betelgeuse or Alpha Orionid and Rigel or Beta Orionid. Bayer, the astronomer that made these definitions, started from the top, the first brightest one was alpha and then the bottom brightest one was beta, even though Rigel is brighter than Betelgeuse. Rigel has a magnitude of about 0.15, where as Betelgeuse has a magnitude of 0.45. They are very close, but Rigel is brighter then Betelgeuse, and this makes it seem like their names are the wrong way around. There are some issues with the Bayer designations, and so other designations are alos used. If we look to Eridanus, there are several stars with numbers in their Bayer designation, such as o2 or Omicron² Eridani, also known as 40 Eridanus. The point of these designations is to make sure the stars we see can all be referred to individually and specifically without getting mixed up. The fact that this is an o2 Eridanus implies that there is an o1 Eridanus, and indeed there is. The earlier mentioned Beemim is one of three Upsilon Eridani, and stuff like that can get confusing. This is one of the reasons the names based on numbers exist, the Flamsteed designation. This is sometimes used instead of the Bayer designation in situations like this, turning o2 Eridani into 40 Eridani. There are also catalogue numbers like the numbers of the Hipparcos Catalogue, but they are harder to remember, being a string of digits with no constellation name attached. These strings of digits are more useful in digital cataloguing.

By highlighting the stars known to have exoplanets or candidate exoplanets, the star Keid or o2 Eridani or 40 Eridani is not highlighted. I am unsure if this is because Stellarium is up to date enough to have removed it or if it was never highlighted, being considered a potential planet too tenuously or for too short a time. It took me a little bit of searching to make sure I was looking at the star I intended, because I am not a Trekkie, so I am not as intimately familiar with the solar system that the Vulcans come from. The planet Vulcan is supposed to orbit a star in the constellation of Eridanus, specifically 40 Eridani. This star, whose common name as mentioned is Keid, is labeled as a double star, though in this case no matter how close we look the stars don’t seem to split out into their separate components. This is due to the smaller components of the system being incredibly small and faint, including one of the first white dwarfs to be discovered. This means that the star we are looking for has a slightly longer name again, 40 Eridani A, to distinguish it from the smaller star orbiting around it, 40 Eridani B. There is also a red dwarf component to the system, 40 Eridani C, making this a triple star system in total.

There was believed to be a planet going around 40 Eridanus, and according to Star Trek that is where the planet Vulcan orbited. It’s not just in Star Trek, there is a sci-fi book titled “Project Hail Mary” which features the Eridani people , or Eridani species of aliens, hailing from a plant orbiting 40 Eridani. This is even specified as being 40 Eridani A b, following the nami9ng convention for exoplanets. In Star Trek it has the common name Vulcan, and while it was believed that we had discovered a sign of 40 Eridani A b existing, it was informally referred to as Vulcan in many locations. Star Trek of course is set in the distant future, so even if it was an accurate portrayal it would not have happened yet. We also now know that any aliens we do discover probably wont look almost identical to us, except with pointier ears and a personality trending more towards logic than emotion, though this is of course a much easier option for any prop or costume department working on a TV show. The famous Vulcan Spock is described described this way and said to hail from the planet Vulcan in the 40 Eridani system. At first glance, to many unfamiliar with the show, Spock looks very human, but to many Trekkies, it was a nice coincidence that the famous alien’s homeworld might, in some way, actually exist.

Now however, it appears that what we believed to be indications of a planet were actually just the star itself and its behaviour. With exoplanets and potential exoplanets, some of them are known with greater certainty than others. Part of this comes down to the various methods there are to detect exoplanets. Direct observation of exoplanets is just starting to become possible, most detection methods look for something that indicates that there is a planet instead. The transit method of exoplanet detection looks for the little drop in a stars light caused by something getting in the way and blocking it out. If the same drop in light happens at regular intervals, there’s a very good chance that it is caused by a planet. Another method is the radial velocity method, which looks at how much the star wobbles or wiggles from side to side, a phenomenon often caused by the gravity of a planet orbiting the star. The radial velocity method was used in this case, and it seems to have generated a false positive. The rotation of the star itself seems to have given the impression that it was wobbling as it rotated, rather than the effect of an orbiting planet.

Mistakes like these can happen with other methods, and they can cause both false positives and false negatives. For example, if look towards Vega, to the part of the sky that the Kepler Space Telescope observed, some of the candidate exoplanets it discovered were flagged using a computer system. The Kepler Space Telescope generated graphs of starlight for thousands of stars, and this had to be searched for the kinds of graphs that indicated regular dips. This helped to eliminate stars that had no dips or where the dips were irregular, unlike what we’d expect from a planet. However, despite this, the data still had to be further analyzed by individuals. Human astronomers and other human scientists were needed to double check and not only weed out false positive but also pick up on some false negatives. By looking back at the Kepler Space Telescope’s data, it was found that some likely planets were missed, dismissed by the initial, software led, analysis.

This is, I believe, an important thing to mention. Firstly, it show that astronomy is capable of mistakes. Sometimes we can say, “oh, there’s a planet over here, isn’t that great” and upon further inspection, this turns out not to be the case. Being able to accept those mistakes and change what we understand to be the truth based on new evidence is one of the cornerstones of science. We need to be flexible and we also need to be aware that even when something looks certain at first glance, if we go back and check again it could simply be completely wrong, as seems to have been the case here. As well as discovering new exoplanets, sometimes we have discover flaws in our methods and other mistakes. Relying on a computer program to sort through these graphs, it can definitely help cut down the work, but humans do still need to be involved to double check, to look for both false negatives and false positives, if we want to be certain. The more data you have the harder it is for humans to handle it all, but if you have enough people and enough time, we can sort through quite a lot of data. Software is certainly helping, but it isn’t quite ready to do these things on its own. Hopefully one day it will get powerful enough, but until that day comes, we’re still going to have mistakes like this where we think we found something and it turns out not to be the case. Even if we do perfect artificial intelligence it will probably make some mistakes as well.

It is a little disappointing to learn, after the possibility looked so likely, that Vulcan probably does not exist. If you are a Trekkie, you can take solace in the fact that we could turn out to be wrong again, it could turn out that there is in fact a planet going around this star, it’s just not the planet we thought we had discovered when behaviour from the start itself indicated it. We can still hold out some hope that there may be a planet Vulcan, but it now looks less likely or at least what we believed was the planet Vulcan has now turned out not to be. Despite the loss of a potential exoplanet, I hope you will return for my next post, as they are normally about things we can be a little more certain of, and if you’d like to be more certain of catching those posts, you can subscribe to this website or to my YouTube channel. However you return, I hope I see you back here next time.