Caoimhín's Content

We are taking another look at exoplanets! There is so much to say about planets beyond our solar system that we are addressing them again here. You can go back on this website or my YouTube channel and check out my previous video and/or article on the topic. We will really be looking for and at other solar systems, with our eyes the star is the only part we can see. However, planets may exist without solar systems, as rogue planets, drifting through space with no star. Based on our current understanding of how planets from, rogue planets almost certainly form around stars, but somehow escape their solar system. They may be ejected due to planetary interactions or unstable orbits, or they might be able to escape their stars gravity as it falls apart at the end of its life. In any case, rogue planets are incredibly hard to spot, as it is usually variations in a stars brightness or position that we use to find exoplanets in the first place. With just our eyes, we would have no hope of spotting a rogue planet unless it was far too close for comfort.

Taking a look to the South in the evening, from a city location, even though only a few stars will be visible, at this time of year at least there are already a few visible with planets. We will look first at the constellation of Leo, which is nice and prominent to the South at the moment. The front of Leo is sometimes called the Sickle, and just where the curved hook-head of the Sickle joins the main body of Leo, there is a reasonably bright star. The star we can see with our eyes is bright enough to have a common name, Algieba, a name of Arabic origin. This star is roughly the third brightest, making it Gamma Leonis, but it is a variable star, its brightness changes over time. In reality, it is two stars Gamma 1 Leonis and Gamma 2 Leonis, with Gamma 1 Leonis being the host of a planetary system. AS far as we know, there is only one planet orbiting the star, but that is enough to make it a solar system and not just a star on its own, or a pair of stars in this case. Here, the more modern designation, although not as unique as the Arabic name, does provide extra information such as the constellation you can find it in, the fact that it is a binary and roughly how bright it is compared to other stars in the constellation.

Another star for a different solar system is Pollux one of the brightest stars in the sky, the brightest in the constellation Gemini. Despite being the brightest, it is designated as Beta Geminorum, as if it was the second brightest. This can occasionally lead to mix ups, but it is one of the rare occasions that the system is flawed. Although it is a reasonably prominent star, it can be trickier to spot Gemini, especially in the city. However, if you can find it, it is orbited by the planet Pollux b or Thestias, one of the lucky planets to be assigned a name as well as a designation. Thestias is a big planet, roughly twice the mass of Jupiter, with a period of a little over an Earth year. It is a massive planet orbiting quite close to its star, at least compared to our solar system, and this is a combination we commonly find. Aldebaran, the brightest star in the constellation Taurus, is a famous and often easy to see star that may also host a planet. Although the star will be leaving our sky soon, it is still visible at the moment and will of course pop up again in a month or so. Aldebaran is a very old star, and it may not have a planet, or it may have two, at the moment it still hasn’t been proved conclusively. The original observation suggesting a planet seems to suggest a planet almost 6 times bigger than Jupiter, orbiting the massive red star about as far as Mars orbits our Sun.

The constellations of Leo, Gemini and Taurus, and the stars they include, are only visible at certain times of the year. In the Northern Hemisphere, there are plenty of stars around the North Pole that are visible all year round. One of these stars, visible from Ireland, is even more reliably visible than the Plough or the Big Dipper. While the Plough dips close to the horizon, and further South it can disappear entirely, this star is closer to the Pole Star. In fact, it is the second brightest star in the constellation of Ursa Minor, sometimes called the Little Dipper. It accurately designated Beta Ursa Minoris, and it is comparable to Alpha Ursas Minoris, Polaris or the North Star. The Little Dipper or Ursa Minor is not quite as bright as the Plough or the main stars in Ursa Major., and in many cities the two brightest stars are the only two you will see. Often, the easiest way to find it is to first find the North Star using the Plough, and then look for the brightest star in its immediate area. A line drawn between them should be roughly parallel with the Plough. The Arabic name for this star is Kochab and it sits in the “bowl” of the Little Dipper, at the far end from the handle. However, in the city this Little Dipper shape my be impossible to see. Moving out to a darker sky is one way to mitigate this, and in darker skies the shape of Ursa Minor should mirror the Big Dipper in the sky. In very dark skies it can get tricky to figure out what star you are supposed to be looking at, but once you find the North Star and know what shape to look for from there, then you will be in with a good chance. In a dark countryside sky, with more stars visible, of course more solar systems become visible to the naked eye. Unfortunately, even with tens of thousands discovered, most are far beyond the realms of human vision. Of course, many of those become visible with a telescope, even if you are still limited to observing the star. Only with careful repeated measurements can it be determined if a star is hosting a planet.

Even as some stars set, new ones rise, and so at different times of the year and night we have an opportunity to see different stars, and hence different solar systems. Heading towards morning time at this time of the year, we can see that there are some planets in towards the core of our Milky Way, which is rising early in the morning at this time of the year. With exoplanets highlighted, a great number can be seen towards the core of the galaxy, but they continue to be found all along the arms, even out behind us towards the edge of the galactic disk. One host star is in the constellation Ophiuchus. The star listed as “v Ophiuchus” is Nu Ophiuchus, rather than Mu Ophiuchus as I say in the video, that would of course be “μ Ophiuchus”, but looking and sounding so similar I hope you will forgive my error. Ophiuchus is the 13th constellation in the zodiacal constellations, or the 13th sign of the zodiac in other terminology. The knee of Ophiuchus stretches down to the Milky Way’s core, between Scorpius and Sagittarius, while the top of the constellation rises high along the inner arms of the galaxy. If you would like, you can take a look back at my video about the ecliptic to learn more about the zodiacal constellations and why there are 13.

I generally stick to the Northern Hemisphere, but taking a quick look into the Southern sky reveals plenty of exoplanets there as well. Unfortunately, not quite as many as we have discovered here in the North. This is partly for various historical reasons, but also due to lees available land in the Southern Hemisphere. Thankfully, there are programs like the European Southern Observatories or ESO and the South African Large Telescope or SALT, which are contributing more and more discoveries from the Southern Hemisphere. I’ll remove the atmosphere for us here in the Northern Hemisphere, to reveal objects not visible to the naked eye and give a better idea of how many planets we have really found. A particularly dense patch of exoplanets was is visible where the Kepler Space Telescope pointed. I made a big deal about the Kepler Space Telescope in the previous video about exoplanets, as it is a big deal, and has single-handedly provide the data necessary to discover thousands of planets. The density of exoplanets we see in this region could probably be replicated all across the sky, if only the Kepler Space Telescope had observed other regions of the sky, or if many duplicate telescopes were created.

Rather than looking at the thousands of planets named Kepler after that telescope, instead we will look at a smaller group of exoplanets. The stars are named SOI-1 to SOI-8, with planets named SOI-1b, SOI-2b, SOI3b and so on. We can see by their name they were all discovered by the same telescope or group, part of an international research team’s sky survey. These stars are invisible to the naked eye, and so have no common name, but their designations still provide us with some information. These names can give you an idea of how many solar systems were discovered together and what telescope did the job. As well as common names, modern designations with Greek letters and names based on the observing telescope, stars that are invisible to the eye are also often known by their catalogue numbers in famous star catalogues, such as the Hipparcos catalogue. This can lead to one star having four or more possible way of being referred to, but luckily there is usually one most common name, or most appropriate name for a given setting.

It might seem strange then, that more names are sometimes requested. Particularly if a star only has a name based on the telescope that discovered it’s planet, the International Astronomical Union or IAU may elect to have that star given a more human name. This has happened before, and I will brifly mention for no doubt the umpteenth time, the star and planet that have been named characters from Irish mythology. It can be nice to have a star and a planet named in your language, especially if it’s not one of the big popular languages like English, Spanish, French and Arabic, or Hindi, Portuguese, Mandarin and Bengali (just to round out the list of top eight most spoken languages). Those languages are very popular and well known, Irish or Gaeilge is not quite as well known, so it is nice to have an official name that is part of the international science of astronomy. First we need to find Cor Caroli, the brightest star in the constellation Canes Venatici, just under the handle of The Plough or the Big Dipper. In a region that looks almost like empty space, between Cor Caroli and the point where the handle of the Plough meets the bowl, there is a star and planet now known as Tuiren and Bran. Tuiren is the new name for the star, formerly HAT-P-26, after the mother of the puppies, Bran is the name for the planet, formerly HAT-P26b after one of the puppies. According to Irish mythology there were two puppies, Bran and Sceolán, born of a human woman who had been shape-changed by a fairy. Hopefully we’ll get another planet discovered around Tuiren to name Sceolán in the future.

Brqan continues the trend of being a very large planet, much like Jupiter, but quite close its parent star. In this case, much closer than the other planets we looked at, Bran orbits its star in just 1.33 days. You need to be incredibly close to your parent star to orbit this quickly, even Mercury takes 88 days. This is great for astronomers here on Earth, if you have a big planet close to its parents star, it’s going to block out a load of light every time it passes in front of it, that’s going to make it much much easier for us to discover it. Even if the planet doesn’t block the light, it will cause the star to wobble much more, which is easier to notice than the tiny wobble a smaller planet that’s orbiting further from its parent star would create, and it would also black less light. This all means that it’s harder to discover a planet that is like Earth, small and rocky and pretty far from its parent star, in the habitable zone, it’s a lot easier to discover a big gassy planet like Jupiter that’s orbiting incredibly close to its star. Right now, it is easier for us to discover planets that are not like the Earth and would not be hospitable to life as we know it, much easier than it is to discover planets that might be capable of hosting life like our Earth. Thankfully, with tens of thousands discovered, we have discovered a few reasonably Earth-like planets and fingers crossed we’ll discover more in the future.

If you’d like to stay up to date about potential future discoveries make sure to subscribe to either this website or my YouTube channel. This is, I think, my first time revisiting a topic to look at it a little differently, and for any newcomers to my content, but it certainly won’t be the last. Now that we’re pressing on through April, soon it will be time to look ahead to the month of May and prepare you for what you can see. Hopefully I’ll see you back here for that.