Caoimhín's Content

Today we are going to take a look at the solstice. It is June, which is the month of the solstice. The solstice on the 21st is one of the things that happens to the entire world. Here in the northern hemisphere it’s the summer solstice, so the Sun will reach its highest position in the sky. The Sun was lower in the sky just a few months ago, it’s coming up to its highest position now and will fall back down as we move in towards winter. It is the opposite in the southern hemisphere, it is the winter solstice there. The Sun will be at its lowest point in the sky, but it is still the solstice. Even at the equator it is the solstice, but of course it is a little bit different if you are very close to the equator, something that I’ve covered in a previous piece.

We’re going to take a look at the solstice from the Sun and from the Moon. I think the reason why we would look at it from the Sun is pretty obvious. We’re going to be looking at how the North Pole points towards the Sun for the summer solstice, if we’re taking a look at the Earth. From the Sun’s perspective, the Earth will be in the sky somewhere, so we can look at its daytime side. The Earth in Stellarium is an image and of course it’s not perfect, for example there are clouds so it can be difficult to make out certain details. The initial view is of South America pointing off down in to the south and North America up towards the top. If we move through time, we will see the Earth rotating. For me, the part of the Earth that I am most familiar with is Europe, so we’ll turn back until Europe is facing towards the Sun. With Europe in view we can also see the Arctic ice cap and roughly where the North Pole would be. We can’t see Antarctica at all, even though Antarctica is just south of South Africa, which is visible. We can’t see it because it is in nighttime, the Sun isn’t shining on it. Oppositely, looking at the Arctic, it is in daytime, the Sun is shining on it. If we go through a whole day, we’ll move through time until Europe is facing us yet again. The Arctic stays visible, the Antarctic stays invisible.

This shows us that it is summertime. The Northern Hemisphere is tilted towards the Sun, and if you are high enough on the Northern hemisphere, the Sun will stay up the entire time. If you are in the Southern hemisphere, you’re tilted away from the Sun. The South Pole is completely pointed away from the Sun, so the tilt here is pretty extreme. Looking at half of the planet like this, part of Australia is visible coming into daytime while we’re we’re still seeing Europe, even up as far as Norway and Sweden. Northern Europe is barely going to go into the nighttime side of the Earth as we turn through these dates. I have written before about how the atmosphere distorts light, how the atmosphere will refract the Sun so that it appears above the horizon when it should be under the horizon. That’s going to allow sunlight to creep even further around the edge of the planet than we can actually see. Of course, that’s true at the opposite edge as well, but Antarctica is pretty far down and pretty big as well.

It is summertime and on the date of the solstice, the North Pole is pretty much pointing towards the Sun the entire time. In fact, from the Sun there is a little boundary visible between the Arctic ice cap and the island of Greenland. As the Earth turns around, that line remains visible, even when it is on the opposite side of the North Pole. That portion of the Earth is being shone on by the Sun the entire time. It doesn’t actually go into nighttime because of the tilt of the Earth. Of course the opposite would be true from the opposite side of the planet, but we would be looking at darkness so it would be difficult for us to see anything. that is part of the reason why we are going to the Moon.

The Moon is going to be full on the 29th of of June, and so the Full Moon, is fairly close to the solstice. It’s close enough at least, but on the solstice the Moon is closer to a Half Moon, the First Quarter Moon. If we take a look at the Earth from the Moon, the side we’re seeing is illuminated 58.8% on the Solstice. If we go back a day, it goes to 60%, which means we’re going closer to the New Moon. If we go forward a day, it goes to 58%. In between it must have dropped to 50% for the exact moment of the Half Moon. It looks like we’re close enough having a Half Earth here. We’ll have to turn the Earth around until we’re looking at a view we’re familiar with. Everything on Earth looks upside down because we are a little bit in the Moon’s southern hemisphere. To make things more recognizable, we’ll go into the Northern hemisphere. That puts things the “right” way up with north at the top. From the Moon the angle of the terminator, the line of nighttime, is visible. That line of darkness is going across the Earth at an angle. The Arctic up north is the white patch, and it is staying pointing towards the Sun. The axis of the Earth’s rotation isn’t lining up with the line of the terminator. That is again showing how the Earth is tilted during the summer solstice. We will stop with a view of Europe, Western Europe at least, with eastern europe starting to head towards nighttime. Western Europe is very much in daytime, as is the west of Africa.

The Greenwich Prime Meridian is one of the lines of longitude that was used to define time zones. It runs through Greenwich in London, so it runs through England, all the way up to the Pole. It also comes down through Africa and out the other side. It doesn’t go through Spain but rather through France and down into West Africa. That line, the Prime Meridian, is running parallel to the Earth’s axis of rotation, almost. It is a curved line, it is on a sphere, so it isn’t exactly parallel, but close enough. Following that imaginary line, down through Africa, it doesn’t line up with the line of the terminator, the line between daytime and nighttime is at a very different angle. It’s nearly sunset for Europe, and it is sunrise really, for a lot of South America. The sun is shining on the part of Europe at the Prime Meridian runs through, but following that Prime Meridian down, we move into nighttime. Down in South Africa, it’s already nighttime, but the Sun is just setting at the same longitude in Europe.

If we look at a map of the Earth, we can see England and France one above the other. Following a line through them shows that the Prime Meridian would come down through West Africa, pretty close to the coast of Africa further south. However, the line of the shadow, the line of the terminator, was coming across Western Europe, across West Africa, and down towards South America. The Earth is really quite tilted when we are experiencing the solstice. That tilt doesn’t just mean that the North Pole is pointing towards the Sun and the South Pole is pointing away. It does mean that, but it also means the line of where nighttime meets daytime, the Terminator, is at an angle to the Earth’s axis. The terminator is still the division between the half of the Earth facing the Sun and the half of the Earth facing away, but when the Earth is tilted, the line of the Earth’s axis of rotation doesn’t line up with the line between daytime and nighttime. It would, or it would at least more closely align, on the equinox but we’ll need to wait until September before we take a look at that.

We’ll return to our default location in Ireland and we’ll take a closer look at the Moon. It is pretty close to half, and that’s what I was hoping for. The Half Moon, or Quarter Moon, puts us in a position where from the Moon, we’re looking at the Earth’s terminator. Thankfully, the Moon was in the right position to provide that view on the date of the solstice, which doesn’t always happen. I hope that you enjoyed this description of how the Earth look son the solstice. If you did, please do like this piece and if you enjoy this kind of content, then please subscribe to this website and my YouTube channel. Thank you very much for reading and hopefully I’ll see you back here next time.