Caoimhín's Content

Today we will be talking about light pollution. I am after talking about light pollution before on this YouTube channel and I will talk about light pollution again in the future. Nonetheless, I am going to talk about light pollution for this show as well.

Very quickly to begin, before talking about light pollution, we will discuss sunset on the 13/14th or March. We’ve still got quite a few planets, the planets that are left in the sky now that the Parade of Planets has ended. Mercury and Venus are very close together by the weekend, particularly the 14th day, just above the horizon as the Sun sets. Mercury and Venus are almost as close as they can get, right next to each other in the sky. It’s certainly as close as they are going to get this time, they could get closer together at other times in other years. Much higher in the sky than Mercury and Venus is Uranus. Uranus is up somewhere next to the Seven Sisters or the Pleiades, but not visible to the naked eye. Jupiter and Mars we will be able to see nice and high in the sky, along with the the Moon. For the Full Moon we need to go back to the 13th. The Full Moon will cross the horizon as the Sun sets, by about 7:30 it is already in view.

All of this is from a city similar to Cork City in terms of light pollution, what is considered a suburban sky, about Bortle class 5. The view is good enough, it is nice, and still there is a little bit of light coming into the sky from the sunset. If we were in a city a little bit bigger than Cork, the light pollution would get worse. At the same time, the light of the Sun is still coming into the sky. The Sun is under the horizon, but with son much orange glow it has barely set.

From a city much bigger than Cork City, still at 7:30 there’s still some parts of An Bodach or Orion to be seen here. The brightest star is visible here. Sirius is the brightest star, and the planet Venus is the brightest planet, both in the sky at the same time. In Irish, Venus is sometimes called the Little Witch of the Morning, although it’s the Little Witch of the Evening at the moment. A little witch is cailleachaín, so Venus is Cailleachín na Maidine or Cailleachín an Oíche right now. Venus is the brightest thing, the brightest object in the sky after the Moon and the Sun, followed by Jupiter and then Sirius. Mars is visible and Jupiter is visible, but there aren’t many stars visible. If we turn around to the north the Plough, the Big Dipper, Ursa Major, whatever name you call it, is missing. The seven stars that point out where the North Star, those seven stars aren’t visible, at this time from a city much bigger than Cork City. The North Star is sometimes called the Star of Knowledge in Irish, Réalta an Eolais. Bortle class get much worse, up to class 9, but a sky like that at leaves only the two brightest planets visible at 7:30. Even the brightest star is practically taken from the sky. Sirius is just about visible, but it looks way too small to me, Sirius doesn’t look like Sirius at all. Of course, that is the result of intense light pollution. Even the brightest star becomes very difficult to see, at just 7:30 from a city much much bigger than Cork City. In truth, that extreme isn’t very common. That’s the kind of sky that you have if you are standing in the middle of big sports stadium completely lit by flood lights.

Going to the other extreme is Bortle class 1. This is certainly out in the countryside, but this is perfect sky. I’m after going to a perfect sky, even though large area of the countryside all over the world are less perfect than this. Still at 7:30, the two brightest planets are of course planets are visible, but so are Mars, Mercury and Venus. Uranus is right on the edge of being visible, the glow of the Sun would still make it tricky to see through binoculars but its is potentially possible with a small telescope. There aren’t many skies like this left on Earth. Every single city is gives a far worse view. Many satellites are visible in perfect dark skies as well. The International Space Station is not only visible crossing the sky, it’s very bright from a sky as dark as Bortle class 1.

As I said, there aren’t many skies like this left on Earth, but there is one down in Kerry. the area around Ballinskelligs is the biggest dark sky park on this side of the planet, certainly the biggest in Ireland. It is one of the very few Gold Tier Dark Sky reserves, the only one in the western hemisphere. Every year there is a Dark Skies Festival in Kerry due to the perfectly unpolluted sky like this, the Skellig Coast Dark Skies Festival. This festival is coming up at the end of this month, the last weekend of March starting on Thursday he 27th. One of Irelands Gaeltachts, the Iveragh or South Kerry Gaeltacht, is also in this area. The Dark Sky reserve and the Gaeltacht are practically coterminous. The majority of the Gaeltacht is in the Dark Sky Park and the majority of the Dark Sky park covers an area that is a Gaeltacht, they are almost the same place. For that reason I am speaking about this in Irish and it is during Seachtain na Gaeilge as well. If you are down in a place as dark as this, you could see all of these planets when the Sun is setting. If that place is Ballinskelligs then it will be a Gaelteacht as well. The Dark Skies festival is coming and Seachtain na Gaeilge is still on going, so that is another reason that these two go together very well, a sky as dark as this and speaking the Irish language.

We are going to push a little bit later in the night without any light pollution. Usually when I record videos I turn the satellites off. They are nice for things like the ISS, which we could see this weekend. It’s not for sure, the Space Station can move and I am both writing and posting this at the beginning of the week. We are looking at the future, it’s only a couple of days but the ISS could move during those days, the space station is under human control and the people in charge of the ISS are able to move it. This can change when it is visible, if at all. To get a completely dark sky, we need to push ahead until Mercury and Venus are out of the sky. Those two planets are low above the setting Sun and the sky won’t be dark with light from the Sun, so until those two planets are gone the sky isn’t dark. In the middle of the month the Full Moon is up as well. The sky will be a lot darker when the sky is completely clear of light sources. This reveals that there really are are a lot of satellites here, very visible if we are in a completely dark sky. You can see the dots moving around. Even if you are in a dark sky, without any light pollution from the ground, there is still pollution in the sky, you can see these spots dancing around. They are a very new type of pollution, and not even the worst out there. Satellites at least serve a function, the real pollution is the rubbish out side of the atmosphere. There is rubbish and satellites there and usually the vast majority of what we are able to see are satellites. There is real rubbish, broken satellites, parts of rockets, failed tests and at least one bag of tools, floating through space around the Earth. So far, not too many things have collided, but impacts from paint chips and similar artificial micrometeorites may be common.

Bringing back a little bit of the light pollution puts us in a very good sky. Bortle class 3 isn’t as dark as the Kerry Dark Sky Reserve, but it is a nice dark place. You can see a little of the Milky Way, but it would be hard to see with the naked eye. That’s partly due to the time of year, we are looking at the fainter outer arm of the galaxy at this time. To get the most out of the dark sky, you have to wait a while. They say 20 minutes, but I recommend half an hour to ensure that your eyes comfortable with the darkness. You need to give your eyes adapt to be prepared for the darkness. The fantastic view that I regularly describe and show in my videos, you have to wait 30 minutes until that becomes visible, you can’t see all of it as soon as you get out of your car or your house or where ever you are. Any light source can undo this adaption. If you cast your eyes on any light, you lose that extra sensitivity. Human eyes are able to see a lot in the night sky when they are prepared, when they have adjusted, but you have to give that 30 minutes without even looking at your mobile phone or anything like that. If you look at anything bright, you have to sort of start again counting down the 30 minutes all over again.

Coming down a little more brings us to a sky that’s still pretty good, better than Cork City, but not great. We can see a couple of the Pleiades, but certainly here there aren’t Seven Sisters, there’s maybe 4 or 5, but there isn’t 7. There is only a spot for Orion’s Sword rather than a line, but we can still see the majority of things. If we turn around, we can certainly see the Plough and, importantly , all 7 stars. You can see the 7 stars without a bother, without any problems. If we come back the whole way to a city like Cork, we are going to lose a little of the Plough. We’re left with the Plough with one star missing. The star is Megrez, the “elbow” between the handle and the body of the the pot. We can still see the North Star, but this is a common view. It is very hard now to see any of the Seven Sisters, there’s nothing there besides a sort of spot, there are no individual sisters there at all. The majority of Orion’s Sword is gone as well, even if we remove the Moon. This of course isn’t even as bad as it can get.

If we push the whole way back to Bortle class 9, it almost looks like daytime. Jupiter is barely visible, as is Sirius, and nothing else. Again, this is the sort of view you could get if you are in a stadium with all the flood lights on. There aren’t many places that are like that all over, walking a normal city it wouldn’t all be like that. You could be in a city that’s as bad as Bortle class 7 or so all over, with areas of 8 or 9. I am happy enough to be living in a city like Cork City with a sky at around Bortle class 5, even though could easily be improved. Even with skies as dark as the various dark sky parks and reserves, I am happy at least that the city of Cork city isn’t as terrible as it could be.

However, a perfect dark sky is certainly satisfying to see. It is well worth it to travel down to South Kerry, or up to Mayo to the dark sky parks in Ireland, or where ever your local one is, in order to see a perfect dark sky. There aren’t many places in the world where you can do that as easily as you can here in Ireland.

That’s my piece on dark skies, the light pollution, the different levels, what you can see and what you can’t see. If you enjoyed it make sure to like this piece and make sure that you subscribe to this website and my YouTube channel. Hopefully, I’ll see you back here next time.