Caoimhín's Content

At the start of May, we looked ahead to the whole month, but now as we approach the end I think it’s worth a second look. Even though the weather is getting hotter, the Earth is actually approaching its furthest from the Sun in our elliptical orbit. How close we are to the Sun in our orbit doesn’t really make much difference to our temperature, the tilt of the Earth, our obliquity, is what causes our seasons. Given that the Earths orbit is pretty close to circular, it causes only very slight changes in how much solar intensity the Earth receives. However, the Earth’s exaggerated tilt, compared to many planets, does cause a big difference in how much Sun each hemisphere receives. Even though the Northern Hemisphere is tilted towards the Sun when we are close to our furthest away, it’s still much hotter than when we are at our closest to the Sun and tilted away from it. Other planets, with more eccentric orbits and less obliquity may work differently.

At our furthest from the Sun is also when we are at out slowest, we’ll be moving around the Sun at our fastest closer to January and December when we are closer. This means that the background of stars should be changing slowly as well, but it certainly doesn’t feel that way. Just a week or so ago, Leo stood prominently in the South as the sky darkened, where as now it will appear a bit to the west of south, replaced by Virgo due south. The reason for this is the shorter nights. The stars aren’t becoming clearly visible for us until much later, giving Leo the time to drift further to the West. This is a lot less noticeable closer to the equator, but makes a big difference in Northern latitudes. As we approach the end of May, for example on the on the 31st, even as late as 11:15 there is still a glow of sunlight in the sky from sunset. We are going to have to wait until incredibly incredibly late to see the kinds of stars that we would normally expect to see, as late as midnight just to get a good level of darkness. This is with daylight savings time in effect. Just as daylight savings calls midday 1’o clock, physical midnight is also closer to 1 o’clock in the morning.

The Moon is coming up to full at the end of the month, but that won’t make too much of a difference if you’re looking for the brighter stars in the sky. As the Sun sets, the brightest stars will appear first as always, but they will be different stars to the ones that we saw first just a few weeks ago. With Sirius, Betelgeuse and a many more famous stars having gone below the horizon, Arcturus will be among the first stars that we see, given its high position to the South. Vega will also appear quite early, but it is lower to the East. Deneb will appear soon after it and, by the time the sky is actually dark, Altair will be above the horizon as well. With all three corners of the Summer Triangle, we can be sure that we’re moving into summer. The Plough is almost directly overhead by the time the sky is dark, so we can clearly see the arc of the handle of the Big Dipper, letting you arc to Arcturus and spike on to Spica, which is lower to the South. With the brightest star in Virgo right in the middle, Virgo must be dominating a large portion of the sky in the evening, even if it is a little hard to tell.

Moving a bit closer to midnight, the bright re star Antares will be visible low to the southeast. As it is the brightest star in Scorpius, that means that the constellation of the Scorpion is rising into the sky before midnight. On the night of the upcoming Full Moon on the 24th, the Moon will be very close to Antares. From here in Ireland, the Moon won’t quite occult Antares, but they will be right next to each other through binoculars and low power telescopes, a great opportunity for some astrophotography, especially if you don’t have a very powerful telescope or have to deal with light pollution. As always, I’ll mention that Antares is Anti-Ares, the Enemy of God of War. The red planet Ares may be called Mars now, but Antares continues to be one of the only things in the sky that can challenge its vibrant redness.

Moving closer to morning time,, as the glow of sunrise in the sky, you may be able to make out the W-shape of Cassiopeia just over the Sun. I mistakenly call Cassiopeia “Capella”, the brightest star in Auriga, by accident at this point in the video. Looking at the constellations, we can see Ophiuchus stretching up into the South, covering a large portion of the sky. extending up from between Scorpius and Sagittarius. Being the 13th sign of the zodiac, it doesn’t get as much attention as the 12 zodiacal constellations. Also just above the sunrise we have Pegasus and Andromeda. Despite the Square of Pegasus being quite clear, the glow of the Sun will quickly obscure the Andromeda Galaxy. Then planet Saturn is finally far enough out from the Sun to be seen clearly even from the city. Mars is starting to be a viable target, but it’s still not going to be easy to see from a city even in late May. However, another month or so should bring Mars into a better position for morning observations. we’re really going to have to wait until next month. If you’re in the countryside, without any light pollution, Mars is going to be much clearer, visible as an orangey-red dot above the orange yellow glow of sunrise. Even with the glow of the Sun, a lack of light pollution will let you more stars more clearly, and that’s going to let us pick out the shapes of constellations a lot easier.

The Summer Triangle is nice and high to the South in the early morning sky, and it has a clear triangle shape. Within the triangle, the shape of Cygnus is also very clear, a cross shape sometimes called the Northern Cross. Extending out from Vega, Lyra is a sort of parallelogram shape, but it’s pretty small which makes it hard to spot in the sky. Moving back to a slightly darker part of the early morning, Sagittarius should be clear low in the South, with the whole teapot shape visible by 4:30. This isn’t the entirety of Sagittarius, but it certainly makes a clear recognisable shape. By this time, the sky is starting to brighten, but if you’re in the countryside it should still be visible, in the city you may need to go out even earlier. Looking at the sky on the night of the Full Moon, the extra light is going to block out a lot of the Milky Way. With both Scorpius and Sagittarius clearly visible low to the South, we know the Milky Way should be extending up from between them. A dark sky also makes it easier to see how bright and red Antares really is when it doesn’t have to compete with light pollution. Getting back to the early evening sky, Spica will be much easier to spot once the Moon has moved away into Scorpius. We can see the Moon moving from one side of Spica on the 20th to the other side on the 21st. Somewhere to the West of Ireland this should lead to something like an occultation or at least a very close conjunction between the 21st and the 20th, but we’re not going to get to see it here.

Once the sky is reasonably dark in the countryside after sunset, we’re definitely starting to see that kind of kite shape of Boötes, extending up from the bright star Arcturus. Despite being a little further to the West, we can definitely still see the shape of Leo, that trapezoidal shape of the Lion’s body is clear on its own, with the curved shape of the Sickle, the Lions Head and Mane, at the front. Low to the South, under Virgo, the clear diamond shape is the constellation of Corvus the Crow. Despite being small, and not particularly famous, the constellation does have a clear shape, making it easier to pick out from the surrounding stars, even in the countryside. Virgo on the other hand is a pretty abstract shape. Even ignoring the “limbs” stretching out from it, as I do when looking for Sagittarius by looking for the teapot at its core, it’s still tricky. The body of Virgo is a pretty irregular, abstract shape. It’s not quite a square, it’s not quite a trapezoid, it’s just this weird, rectilinear thing in the sky. This makes it harder to sort out from the noisy background of abstract shapes that present themselves in the sky. If you use your own imagination and connect together whatever stars you want, you can create all sorts of crazy constellations in the sky. This is one of the reasons that some are considered official, so we can all learn them and talk to each other about them more easily.

Turning around to the North early in the evening, still in the countryside, the Plough of course will be easy to spot, but we’re also definitely starting to see a shape of the Little Dipper or Ursa Minor. It’s especially easy to find once you find the North star, as the Rest of Ursa Minor are some of the brightest in its immediate vicinity. Below the North Star, roughly opposite the Plough, Cassiopeia (which I mistakenly call Capella for a second time in the video at this point) is also clear with its distinct W-shape, although being below the North Star it is quite low to the horizon and more likely to be blocked by the terrain around you. As we move through the night, the Plough will appear to move around the North Star as the Earth turns. The Plough won’t quite make it all the way to the other side of the North Star. Due to the stars being relatively fixed, the apparent movement of the Plough is mostly down to the Earths rotation. It takes the Earth 24 hours, roughly, to turn around, and so it takes a similar amount of time for the Plough to come back to the same position in the sky. With our nights now being definitely less than 12 hours, the Plough won’t quite make it halfway around its circular path in one night for the next couple of months. This is complicated by the Earths motion around the Sun, it takes a little longer for the Earth to turn until the same spot is facing the Sun, a solar day, than it takes for the same spot on the Earth to line up again with a distant star, a sidereal day. This is noticeable over the course of a year, but not so much over shorter timespans. As it is right now, the glow of sunrise will start to come up and block the Plough from view as early as 4:10 in the morning. With the fainter stars blocked out, the slightly brighter stars that make up the legs and the head of Ursa Major become a little easier to see. These stars are a little fainter than the ones that make up the Body and Tail of the Bear, known as the Plough or Big Dipper. They are also just a few bright stars, not in a row or a tight curve like Orion’s Belt or the Handle of the Plough, so they are trickier to spot than a clear shape or pattern, of which the Plough itself is such a good example. This is partly why the Plough or Big Dipper, an asterism rather than a true constellation, is so much more famous and recognisable than the full constellation of Ursa Minor in which it is contained. Turning back towards the Summer Triangle, a little diamond shape can be seen between Deneb and Altair, the constellation of Delphinus the Dolphin. It is a small diamond shape, and some of the fainter stars disappearing in the early glow of sunrise can help the main stars stand out, but it is another good example of a rather geometric portion of a constellation, but being even smaller than Corvus it is also one of less famous ones.

With the Full Moon occurring around the end of May, we’ll need to push into early June to ensure that we can see the glow of the Milky Way. At the very of May, the light of the Full Moon obscures the Milky Way, but a few days before and after the Full Moon, it still remains visible until very close to sunrise, or appears very close to sunset, thanks to the shortening nights. This means that if the glow of the Moon isn’t a factor, the glow of the Sun will be, making it even harder to spot the Milky Way at the end of the month.

Although the sky will only appear to change quite quickly over the next couple of months, mostly because the nights are going to be getting so short, you’ll still only have a comparatively short time to see these things before their positions will seem to change. Hopefully you are more prepared now for what you’ll get to see over the next weekend or two. Even if there is no comets or asteroids or meteor showers, there’re still constellations of bright stars out there to be seen. If you enjoyed this catch up with the night sky, you can stay up to date by subscribing to this website or my YouTube channel, as well as catching videos about other aspects of the night sky, so I hope you come back next time.