Caoimhín's Content

Today we are going to be looking at a couple of different things, but generally at the angle of things from the horizon. To start with, we’re looking at the sky for pretty much the middle of May. We’re looking at 1:30 here in Ireland, which should put the Sun at its highest in the sky. With daylight savings time and the width of time zones, physical midday is much later than midday on the clock.

We can double check the height of the Sun with various grids that come by default in Stellarium. Starting with the alt-azimuth or azimuthal grid, if we move a few days into the future, we’ll see the Sun gets higher because we are still moving closer and closer to summertime. If we move through time here, we can see that the Sun is lower at 1 and 2 o’clock than at 1:30, so this seems to be at its highest, we can see it moving down a little bit to either side as we go back and forth in time. The alt-azimuth grid simply provides some lines to help highlight the position of the Sun. Using the equatorial grid could demonstrate that a little bit better, as this grid is immobile compared to the Sun, it is fixed at our zenith. The other grid is connected to the North Star, and with the North Pole it rotates with the Earth. This lets us see if the Sun is exactly due South. With one line of the grid crossing the Sun, we can see that it is only making a short chord across the bottom of the Sun at just about 1:30.

We can use these grids to check the height of the Sun in the sky. The grid has tick-marks or gradations along the side, which we can use to figure out how many degrees up in the sky the Sun is. However, the grid is broken up in increments, and the Sun may be between the lines. The azimuthal grid lets tell how many degrees up in the sky it is as well, just from a slightly different frame of reference. If we want to get an exact measurement from the ground, we can use the angle measure tool found in a Stellarium plugin. You might remember it from a previous piece where I discussed the angle measure tool and measuring angles in the sky. This tool will let us measure how high in the sky an object is as, by clicking on the ground and dragging up to the Sun. It’s providing 55 degrees for mid May, that is how high in the sky the Sun is getting, roughly. As we move through days, the drawn angle moves with the sky. that can be useful in the case that you need to measure things across various dates or over the course of the night. It moves in a similar way day by day, sort of drifting across the sky there. Even as it moves, it definitely shows us the Sun is getting higher, it’s getting higher than the line at the top of the measured angle. If we draw another line, aday or so in the future, it’s gone up to 56 degrees. If we move through more dates, we can see that the measured line stays the same, but the height of the Sun changes. As we move forward into the future, the Sun gets higher and higher.

That change is because of the Earth’s tilt with regard the Sun, not the more distant stars. We will move into nighttime, now just looking forward to the end of the month so nothing will be extremely different, and turn around to the North. This way we can measure the angle from the North Star. The North Star is easy to spot, but we’ll double check just to be safe. We’ll find the Plough, or the Big Dipper, pointing down to the North Star, and follow it to directly over north, It doesn’t hurt to double check just in case. We will drag our angle down, and it’s showing just about 52 degrees. This is the angle of the North Star up in the sky from our location, and it is also the location of our current latitude on the Earth, 52 degrees if we’re observing from Cork. This is how far away from the North Pole we are, in degrees around the spherical Earth. We can very quickly test that by hopping up to the North Pole. With the location window of Stellarium we can see the exact coordinates of our location, and it shows us at 51 degrees, 53 minutes and a few seconds of arc. That is less than I expected, but I was off by only a part of a degree. The minutes, and seconds, the subunits of degrees of arc, are base 60. 53 arcminutes there isn’t halfway from 51 to 52 degrees, it’s most of the way to 52 degrees. Just a few more arcminutes and the degree will go up. Once it reaches 59, the degrees tick over because it’s a base 60 system. This is just like the hours, minutes and seconds of time. Minutes and seconds come in sixties, while hours have 24 a day and degrees have 360 in a circle.

Either way, we don’t need to worry too much about the smaller units. If we go all the way up to the top, we’ll hit 90 degrees and that is the North Pole. The equator is 0 degrees, and the South Pole is 90 degrees south, or negative 90 degree. The longitude east and west no longer matters. If you’re standing on the North Pole, your longitude isn’t going to matter at all because you’re centered, at zero or something like zero. Up at the North Pole at the moment it is summertime. We’re not going to get a night where the any stars are visible at all. The Sun doesn’t even seem to be get lower over the course of the day, so by the end of May we’re definitely getting the midnight Sun at the North Pole. Of course, that makes sense, the midnight Sun lasts for months once we’re up at the North Pole, not just on midsummer. If we get rid of the atmosphere and bring back the North Star into the sky we’ll be able to measure. The Plough, or Big Dipper, is there, but the North Star is even easier to find, it is the star at the zenith. We can use the angle tool and go straight across the sky. From star to horizon, really it shows 89 degrees, but maybe I didn’t click exactly on the North Star or perfectly align with the horizon. Of course, the North Star isn’t exactly, exactly dead center itself, it is a little bit off, but in the end it is pretty much 90 degrees up in the sky from the North Pole.

We can do this for any location on Earth, any latitude, of course, it’s going to be easier when we start going closer to the equator because we won’t have to worry about the Sun staying in the sky the entire time. For example, just grab a location down by North Africa and Southern Europe. The latitude is 34 degrees. Wecan turn the atmosphere back on. We don’t need it to be off anymore because we can make it nighttime. We’ll turn around to the north, and we’ll use the Plough or the Big Dipper to double check. We happen to be looking close to morning time, so the Plough or the Big Dipper is very low in the sky. Moving closer to Sun set brings it up, letting us double check that we are looking at the North Star. It’s immediately clear that the North Star is lower in the sky here than it was for us in Ireland, it’s visibly lower. If we actually measure it, we get 34 degrees. Again, this is give or take a few minutes, this software tool isn’t the most accurate thing in the world, I’m probably a little off the North Star, I may be a little off the horizon, but 34 degrees roughly.

If you were measuring it very accurately in the real sky, you would probably get a clearer answer. If you had a very accurate angle measure or something like a sextant, which is a tool that was used for measuring the angles of things in the skies for navigational purposes, you could test this for yourself. Within Stellarium I can show a sextant, as it is immortalized in the constellation Sextans. We can see that the angle of the North Star above the horizon, it matches the latitude on the Earth. If we move through dates, the sky and the measuring line rotate, but the north star stays at the same height. We’ll come all the way back to the middle of winter and confirm this. In the middle of winter the Sun would be very low in the sky, but the North Star remains at the same height, just about 34 degrees up in the sky. It is a little bit tricky getting the software tool to be very accurate, but we can see that the principle pretty much holds. The North Star stays at the same height in the sky over the course of the year, whereas the Sun and the Moon will change height in the sky over the course of the year.

We’ll hop back to the default location of Cork, because I know that the constellation of Sextans is up at the moment. That means we’ll have to come back to the middle of May as well. travel back to the current moment, or at least close to it, that’s a little bit further ahead, yeah, around here should do. Of course, we’re very close to the Full Moon at the moment, so getting the Moon out of the sky is going to make things a little bit easier to see, which means early in the evening at the moment. Bringing up our images of the constellations, and there is Sextans just under the Sickle of Leo. Sextans the Sextant is a constellation based on a navigational tool, but mostly for its use in astronomy. This constellation is a newer one, newer at least than the traditional Greek constellations. Some constellations were added in the first printed star maps, or star atlases, by early astronomers to fill in the gaps. Sextans comes from a 1687 catalogue, along with Canes Venatici, Lacerta, Leo Minor, Lynx, Scutum, and Vulpecula, published by Johannes Hevelius. It is said that Sextans was included to commemorate a fire that had destroyed Hevelius’s, along with many of his notes. The ancient Greeks didn’t have sextants, or at least they didn’t have the kind of fancy brass one, with glass lenses in them, described by the constellation.

The constellation is seen at a bit of an awkward angle from the northern hemisphere in May, but the tool can still be imagined. Possibly the most important part is an arc, very similar to a protractor, and a hanging arm or weight attached to the centre of the flat side, or corner, of the arc. The weight will always hang down, pulled by gravity, when the tool is held vertically. By lining up an edge of the measuring tool with a distant point, the difference from level is indicated by the position of the string. Lenses or an eyepiece in on side of the tool make it easier to aim at objects in the sky. Modern sextants use special split mirrors and a level eyepiece. The eyepiece points at the horizon, and a pair of split mirrors allow you to see a portion of the sky level with the horizon. By tilting the mirror until the right star is visible, the angle can be measured by measuring how tilted the mirror is. regardless of the form of the sextant, they could be used to measure changing angles to assist navigation. For example, if you were traveling north and you wanted to make sure you had gone the right amount north, firstly you would use some part of the sextant to mark out what angle you want to see the North Star at. Then as you look through, as you move further and further north and that angle increases and increases, eventually things would line up and you’d see that you are as far north as you want to be. Then you could head towards land or whatever your plans might be.

That’s just a little bit of the use of the angle tool. I will come back to the height of the Moon in summer compared to the height of the Moon in winter at some point in the future. Hopefully this served as a demonstration of the usefulness of the angle tool and how it relates to the North Star at least. I hope you enjoyed this little piece about measuring angles in the sky. Another piece about measuring angles of the sky now that I have the tool handy. Of course, I encourage you to head back and look at the past article where I measured angles related to the galactic equator as well, it was an interesting video, in my humble opinion.

I hope that you enjoyed this piece, if you did, please do like it. If you enjoy this kind of content, then you can subscribe to this website and my YouTube channel. Thank you very much for reading and hopefully I’ll see you back here next time.