Caoimhín's Content

Winter may already feels like it’s been going on a while, but the coldest part should still be on the way as of the date of posting. The weather gets colder in winter, partly because of the angle at which the Sun’s rays are hitting us (it’s a much shallower angle, less direct), but also due to the shortness of the day, especially at higher latitudes. With a shorter day and a longer night, the surface of the Earth, water and solid ground, is warmed for or shorter length of time, with more time to cool in the longer nights. However, this cooling takes time, especially water. This causes a phenomenon called the Lag of Seasons or Seasonal Lag. This phenomenon causes the coldest part of the year to happen after the winter solstice, and the hottest part after the summer solstice. Different parts of the world experience different degrees of lag, from just a few weeks to a couple of months. As Ireland is surrounded by water, it experiences a fair bit of lag. This is one of the reasons that in different parts of the world, different months are often assigned to different seasons.

This is of course before even considering the inversion of the seasons on the other side of the planet. As the Northern Hemisphere is tilted away from the Sun for its winter, the Southern Hemisphere is tilted towards it, giving it summer while we have winter. The above video may not be able to bring the warmth, but it does provide a view of the sky from a few locations down South, Australia, South America and South Africa.

The video begins by giving a quick look at the sky from the Northern Hemisphere, partly to help emphasize the differences and commonalities. Jupiter is still nice and high in South, along with the Moon for the date being shown. Orion and Taurus are also in the South, including the Hyades and the Pleiades. Canis Major is also visible, just under and East of Orion, as we can see by the bright star Sirius. These constellations will remain visible once we change our view, albeit in a different direction, it’s the stars in the North that we’ll lose. This of course includes The Plough or the Big Dipper, the North Star and the Little Dipper attached to it. As we shift our view South, these stars will dip under the Northern horizon, as we move around the globe the curve of the Earth will come between us and them.

Conversely, what is the the southern part of the sky for us, those constellations such as Orion and Taurus, they will appear to rise, first to the middle of the sky and then down into the North. This causes the familiar constellations to appear upside down, one of the reasons that the southern sky looks so different. The other reason is the other half of the sky visible down South. As the constellations we’re familiar with shift up, they are replaced by stars from beyond the curve of the Earth, stars that are as invisible from the Northern Hemisphere as the North Star is in the Southern.

The first region of the Southern Hemisphere that we visit is Australia. The very northern most part of the continent is pretty close to the equator, and the sky at the equator, as well as the poles, will need to wait for a future video. Instead, we’re going a little bit lower, closer to the center, to ensure that the sky we see is southerly enough. As this shift also includes a significant sift in longitude, our view of an early evening Irish sky is replace with a view of the sky at almost sunrise. Adjusting for this, we look to the North early in the evening. A few recognizable shapes and stars might pop out, especially with the bright stars like Sirius conveniently labeled by Stellarium .

Turning around to the South is what shows us some new stars and constellations, with one of the most famous being the Southern Cross. This little constellation is pretty close to the Southern Hemisphere’s version of The Plough or the Big Dipper. It doesn’t mark the spot above the south pole, but it does point to it. Unfortunately, the Southern Cross doesn’t point at the South Star, as it doesn’t exist. There is no star directly above the south pole. The fact that we even have a North Star at all is a lucky coincidence, and as I’ve shown in a previous video, the North Star is subject to change.

Of course, some things are the same on both sides of the planet, you just need to find them on the opposite side of the sky. Looking North at the same time of year, you’ll see the same planets you’d see looking South in the Northern Hemisphere, in this case Jupiter and Saturn in the evening. The planets and the Moon still rise in the East and set in the West, though in this part of Australia they do take a high arc across the sky. Orion as well is much higher to the North this close to the equator, compared to our view of it low to the South in Ireland.

Bringing up the images of the constellations really shows how upside down they look. These constellations were drawn by the Ancient Greeks, who were in the Northern Hemisphere, and so of course, they drew them to look correct from that point of view. The new stars that we see if we turn around and look into the South, those constellations were created in the Southern Hemisphere, but usually by explorers or astronomers travelling with them. The inclusion of such things as a huge boat, sextants and compasses, fish and a clock gives an idea of what was important in the age of sail, compared to the myths and legends prioritized by the Ancient Greeks.

Looking South and speeding up the progress of time, we can see that the stars in the sky appear to rotate, spinning around the point over the South Pole, just like our northern sky appears to do. The stars in this part of the sky may be different but the principle is the same as, and those stars will stay up in the Southern Hemisphere all the time, all year long. From our position in Australia, the Southern Cross it gets quite low, passing briefly under the horizon. We are much closer to the equator here than Ireland, and even off the southern coast of Australia on the island of Tasmania, we still don’t get equally close to the pole. Another difference that this causes is clear in the morning. We see that Mars, Mercury and Venus come up at a little bit of an angle, but quite close to vertical, compared to the shallower angle we see them at from here in Ireland at this time of the year.

To get an even more Southerly view, we’re heading to the bottom of South America. The very bottom of the continent is Tierra del Fuego, which is about as close to the Antarctic circle as Ireland is to the Arctic circle, and in many places colder, thanks to altitude and air and water currents. From a point this far south, Orion and Canis Major sink lower into the North, more comparable to our view, though still upside down. We can see the same stars in the sky if we turn around into the South, and the Southern Cross will appear much higher in the sky, and stay up all night long, just like the Plough does for us. Just like the night in summer in Ireland, the night is going to be incredibly short down in Tierra del Fuego so close to midsummer.

The final location is in the southern portion of Africa, in the country of South Africa, more southerly than northern Australia, but not as far as the tip of South America. This gives us a chance to see and in between angle when we see Venus, Mars and Mercury in the morning. A similar angle will appear at a similar latitude in the North, but the difference between summer and winter makes a difference here as well, thanks to the position of sunrise on the horizon.

Despite half the sky being upside down and the other half being new and unfamiliar, once you get used to it the southern sky becomes as much of a joy to observe as our familiar northern. We still see Saturn and Jupiter, they still set in the West and rise in the East, just looking into the North to see them instead of looking in the South. The view South appears to spin just like our view north. All of that is just what we can easily see, from a city with our eyes in the summer. We’ll come back to the Southern Hemisphere in their winter, our summer, and possibly see what it looks like without light pollution.

It might not have provided as much warmth as an actual visit to the Southern Hemisphere, but I do hope that you’ve gotten some idea of what’s visible in the sky down under if you don’t get a chance to visit. I do hope you stick around to see more of the view and other details in future videos, including of course a return to our Northern sky next time.