THE SOUTHERN SKIES

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Überall lag der Mondschein
mit seiner Natürlichkeit und Ruhe,
die keinem andern Licht gegeben ist.
Franz Kafka (1883-1924): Der Proceß (Ende)

On the southern hemisphere everything seems to be reversed. We have to be careful, though. Many aspects are relative. If you inverted everything, all would be back to normal. We mortals need a reference frame to consider phenomena. It is not difficult to make an unambiguous choice. The directions north, east, south and west are no different from those on the northern hemisphere. These directions also join smoothly and continuously with each other everywhere, with only two exceptions: on the north and south poles of the earth this concept collapses dramatically. But in those regions conveniences are scarce in many other respects.

Nor on the directions above and below there needs to be confusion; if only because these concepts have had a profound and permeating meaning within living memory. When we are tired we lie down and mother earth pulls us into her arms; afterwards, when we get up it is clear that this is above our previous position; we raise ourselves to a higher position; there can be no misunderstanding about it. However, because we all live on a sphere some complications arise even on this simple aspect. Imagine your thoughts are drifting away toward a loved one who at that moment is staying at the other side of the earth. Maybe that same instant she looks up toward the skies! Isn't it frustrating to reflect that – while looking up yourself – you look in a totally different direction? And – although on both sides of the earth you can bask in the gentle shining of Orion – on such an occasion, on top of the physical separation, you are also separated in time...

In discussing differences between the two hemispheres, much is to be said for a description in terms of left and right. These notions will be abundant henceforth. The difference between left and right is much less fundamental than between the archetypal above and below, and the directions north, east, south and west, which partly rest on human arrangements, but are also defined by geographical and astronomical principles. On the southern hemisphere you can navigate on the same compass. For ordinary men right and left are quite arbitrary. Some of us are lefthanded, and they are no different even though they are a minority.

For us the northern hemisphere is the "normal" one. If someone would be standing on the southern side of the earth, supposing that he is on "normal" side, what would be different? He could call "his" pole the north pole. He could map everything just as we northerners have done in the past, the only difference being that for him, everything would be revolving to the right instead of to the left; the earth around its axis; the moon around the earth; the earth around the sun. His sun would rise in the west. But his west is our east! That's why such a description is less practical. Let us therefore return to our own "northern" reference frame.

The Sun

Of course on the Southern Hemisphere they have seasons, just like we have them. Everybody will know that when we have our summer, they have a winter and vice versa. The path of the sun along the sky depends on these seasons. As an example, lets conside the southern summer in december: Around noon the sun culminates high up in the north; at the same time the intersections with the horizon, where the sun is rising in the morning and setting in the evening have shifted toward the south. That's why the sun has to travel a long way. Because the days are long and because the high altitude causes much heat, it is summer by definition. Spring and autumn have exchanged there position on the calander too. The reason now is not so much the altitude of the sun nor the length of the day nor the temperature. Change itself is the issue here. Spring is coming after winter by definition and is a forerunner of the summer. This is no different on the Southern Hemisphere. Rounding up: it is spring in september when with us the leafs are falling; and the southern autumn is in march.

The Moon

The new moon is never seen, for the simple reason that the moon is positioned in the direction of the sun. Before the sun that is; when she is standing right in front of the sun we have a solar eclipse. This doesn't happen very often though, because the moon follows a track along a plane slightly inclined with respect to the plane where the earth is revolving around the sun. And also because the earth is tremendously big. Even when there is a solar eclipse, then only along a narrow path somewhere on the earth.

The growing moon in our parts shows herself one or two days later, at the left side of the sun. She wanders to the left because, when we look from the northern perspective, she revolves around the earth in a counterclockwise direction. When we pay attention we can see her gossamer crescent in the early twilight, only a few degrees above the horizon. What we see is the tiny part that's beeing lit by the sun, which disappeared in the reddish dusk just a few moments earlier. This sunlit part is at the right side, below and behind the moon. The moon sets shortly after the sun. Day after day the moon sets later and later, until she looks approximately as shown in the picture at right. Again a few days later she is lit exactly half and we call this phase first quarter.

One week later we have full moon and she is enlightening the heavens all night long. She is now opposite the sun. Connected with this opposite position is the fact that in the summer the full moon is in the lowest position and her presence is limited to much less than twelve hours. In the winter however, she rises early in the evening in the northeast, ascends high and for a long time and sets only late in the morning in the northwest.

To be complete: in the spring the moon reaches her highest position in her first quarter, that is in the early evening. In the autumn, early in the morning, we can see the last quarter of the moon (the phase between full moon and new moon) high up in the south. In that season, when we see the crescent moon in the evening, she is in a very low position. Near the poles we won't see her at all. This seasonal behaviour can be understood rather easily when we remember that – looking down toward the northpole of the earth – all celestial bodies are revolving in a counterclockwise direction: the earth around her axis; the moon around the earth; the earth around the sun or (in a relative sense, taking the stars as a reference frame) the sun around the earth. If we look at it this way the moon is running faster, and ahead of the sun, along her track betwee the stars. So when she reaches het first quarter position, she is where the sun will be 3 months later. When we have the sunset in spring, she is at a position where the sun will be in the summer, that is high up in the south! And so on...

The crescent of the last quarter is of course the mirror image of the one belonging to the first quarter. There is a familiar aid to remember the two: from both crescents we can form the letter . First and last quarter match with the left and right parts of this .

Which differences are to be expected when we observe the moon from the southern hemisphere? It is straightforward that we can adopt the same terminology for the phases of the moon. Which part of the moon is being lit by the sun depends on time only, and not on our observing position. What changes is her position and posture, as we observe her standing against the sky. In particular the shapes of first and last quarter are interchanged. Let us perform an experiment, merely in our minds. The moon is in her first quarter. It's around 6 o'clock in the evening. The moon is in the south, with her flat side toward the left. Now we bring Time to a stand-still and we start to travel straight to the south. Let's hope we don't encounter too much water. The moon stays in the south but is rising and rising until, near the equator, she is directly overhead, in the position known as zenith, the center of the sky. When we travel even further we must incline our heads far backwards, to see her standing behind us. When we look at her from this position her flat side is still to the left. But of course it's now much more comfortable to turn around... And, there you are, the moon now is in the north with het flat side toward the right!

The Stars

Ho, Ho... Stop! Maybe now we are progressing too quickly! When the earth turns around her axis to the left, then certainly the stars, with respect to the earth turn to the right? Sure! But now we look up; more or less to the inside bottom of the celestial sphere. Looking at it that way the stars turn to the left. When we look to the south, we do see the stars moving to the right!

In addition to their daily course, the stars also move around the sky once every year. In winter we see totally different stars than in summer. We already know that the sun   relative to the stars   revolves around the earth counterclockwise for one cycle in each year. Looking toward the south, the sun moves to the left. The track he follows is called the ecliptic. The time of our clocks is connected with the position of the sun. So when we look at the stars each day at the same time, we see them (looking toward the south) gradually shifting to the right. Looking in the direction of the polestar we notice that the entire celestial sphere with all the stars on it makes one turn to the left (counterclockwise) in one year. Therefore the movement of the stars in a year equals the movement in one day in size and direction. To see the "next" part of the starry sky we can wait till later that night or we can look at the same time, but later in the year. As an example, one month later we can see the same stars, but two hours earlier! And so on.

On the southern hemisphere, again everything goes the otherway around: looking toward the south the stars turn to the right (clockwise) around the celestial pole; looking toward the north we see the stars moving to the left. In northerly directions we see the stars familiar from the northern hemisphere, where they were passing through the south. These constellations are standing, like the half-moon, upside down! In southerly directions we see constellations we have never seen before on the northern hemisphere. Worth mentioning are: the Southern Cross (Crux Australis), the Great Magellanic clouds (a kind of detached fragments of our own Milky Way), and the extremely bright stars Canopus, Achernar and Alpha-Centauri.

The stars in the south differ in yet two other ways from those in the northern hemisphere. First, there is no polar star. This makes it much more difficult to find your way with the stars as your guide. The simplest but not very accurate way is to draw a line from Achernar to a point between the Southern Cross and (Hadar and) Alpha-Centauri. Half-way on this line is the southern pole.A second difference is that the Milky Way is much brighter than on the northern hemisphere. It runs approximately from Sirius, Vela and the Southern Cross toward Scorpio, with the brilliant red star Scorpion's Heart or Antares.

The Tropics and the Poles

First the poles. The directions north, east, south and west loose their meaning. But apart from that, it is conceptually easy. It is like standing on a merry-go-round; looking down all is at rest; everything outside the carousel is revolving to the right: the sun, the moon and the stars. The seasons here come about by the appearance and disappearance of the sun each half year; the famous midsummernight sun and the cold darkness of the endlessly lasting winter. The moon too turns her cycles along the horizon; she appears and disappears once every month; in winter she culminates as full moon; in summer she can hardly be seen, because she is very low above the horizon or close to the sun. The phases between new and full moon look just like we are used to, the crescent always standing up neatly straight. Again on the south pole the revolving directions are the other way around just like the orientation of the crescent phases of the moon.

The special thing about the tropics is that all year round the sun and moon rise and set almost vertically and culminate very high up in the sky, near the central point called zenith. The seasons behave very differently: every season is warm; day and night have the same length; dawn and dusk are always short. To compensate this lack of change, new phenomena arise, like the monsoon. The half-moon isn't standing upright but is always lying on her back or on her belly. Another peculiarity of the starry sky is that in one night it passes along almost completely. A small part of the stars disappears in the twilight but can be seen again a month or so later. Only the stars near the celestial poles are never clearly seen. Very special also is the extreme darkness of the night, which at high latitudes occurs only in the winters.

The orientation of the moon, depending on latitude

It is not very difficult to understand these phenomena. Imagine yourself standing on the North Pole. Both the sun and the moon turn in circles around you, in the vicinity of the horizon. Now the moon is always approximately lit by the left or right side. Take as an example the first quarter of the moon, 7 days after new moon. When you stand and look in the direction of the moon, the sun is on your right side (remember that in those 7 days the moon turned by around 90 degrees to the left). Maybe, depending on the season, you won't see the sun because it is a bit below the horizon.

Now, how does someone see the moon in southern California or any place 30-35 degrees from the equator? Imagine that you go there (at the proper time and very fast! The proper time is of course when California is to your left) from your North Pole. Just move to the left, opposite the direction of the sun. Soon, at any season, you won't see the sun any more. It will become night. Also, you will arive at some time-zone. You will adjust your clock and it will be around midnight! (because you left the pole in the direction opposite the sun). Also, your compass is working again and north now is to your right and the moon is in the west in front of you! She will set there soon. If you went there a few hours earlier, you would have noticed that she goes straight down when you had gone all the way to the equator; a bit more from the south when you got stuck in southern California.

But why is she now lit from below or almost from below? Has she turned around her axis? No! You are the one that has turned around YOUR axis! You didn't walk sideways along a straight line but along a circle. Just like lying down on your left side. So now it seems to you that the moon has turned in a clockwise direction and now is lit from below instead of from the right side.

To demonstrate this with a picture: just look at the photograph of the waxing moon above. The picture has been taken at moderate latitude (around 45º) When you tilt your head to the right, you see the moon as it looks at high latitudes or near the North Pole. When you tilt your head to the left, you see her as you would see the moon at low latitudes or near the equator.

When the moon is very narrow (a few days before or after new moon) her orientation can deviate considerably from what I explained above. This comes about because the moons orbit makes a small angle (around 5º) with the ecliptic, the plane which contains the orbit of the earth around the sun. Therefore, the relative orientation of the sun with respect to the almost new moon can be much higher or lower than "normal". This deviation of 5º is important. Without it, we would see solar and lunar eclipses every month!

Rounding up

One can ask oneself if it is wise to visit the southern hemisphere when you are born and live as a Northerner. We will not enter this discussion as most people are curious and will go anyway when they feel like doing so. But when should you go, how long must you stay there and how will it be to return to your roots afterwards? We have seen that the differences are large. Some of these are hard to grasp and therefore may have grave and far-reaching consequences, not reaching our consciousness. What to think for instance of the earth magnetic field? We don't feel it but we know that other creatures are sensitive to these kind of forces. The Artic Tern (Sterna paradisaea) migrates every year all the way to Antactica but should we follow this tiny bird? Most of us are familiar with an "ordinary" yet-lag, a disturbance of our diurnal rhythm. Couldn't a similar disturbance exist in our seasonal pattern? Maybe it is wise to return so quickly that you can finish your "own season" before it has evolved in the next one.

Justification