But in October in the straights of Magellan, the days would be getting longer.
ETA: Ah. I see now that they stopped in March and then set out again in November. That would make sense.
The ancients who were familiar with the basic two-sphere cosmological model, with a spherical heaven revolving about a spherical earth, were fully aware of all its consequences for the southern hemisphere of the earth (reversed day/night, solstices, etc.). Even if their view of lands and people south of the equator was hypothetical or speculative, they understood that the phenomena those people would experience would be symmetrical with those in the northern hemisphere.
For instance, Plato in the Timaeus states:
In fact, many of the ancients thought that the spherical earth’s physical symmetry meant that southern inhabited regions balancing the known northern ones must exist. Aristotle speaks of there being two habitable circular zones of the earth between the poles and the tropics, one northern (known) and one southern (unknown). He thought that the equatorial and polar regions, between the tropics and equator and between the polar circles and poles respectively, were uninhabitable.
It wasn’t just Hellenistic scientists but others who adopted the Hellenistic spherical model, such as Indian and Islamic astronomers, who understood the equivalence of spatial orientation north and south of the equator. Around 500 CE the Indian astronomer Aryabhata described the earth as being like a (spherical) kadamba flower (Neolamarckia cadamba) “covered on all sides with creatures of the land and water”.
No scientifically educated person in antiquity or thereafter who understood the two-sphere astronomical/geographical model, as far as I’m aware, ever imagined that spatial orientation south of the equator was literally upside down so that people walked on their hands or trees grew with their roots in the air, etc. They all knew that the “down” direction was equally towards the center of the earth for, e.g., people at 25 degrees north latitude and people at 45 degrees south latitude, and they correctly inferred that “down” would be toward the center of the earth in just the same way anywhere else on the earth as well.
:dubious:
The main cause of seasons in Sydney is because it’s a thousand miles from the tropics and it gets cold in the winter and hot in the summer, just like everywhere else in temperate regions.
Even within the lower latitudes of the tropics there are pronounced seasons because of the tilt of the Earth. If you look at Alice Springs, which is so close to being on the Tropic that it makes no difference, you’ll see that the mean minimum temperature swings from 4C (39F) to 22C ( 72F) between winter and summer. That’s a variability of 18C, which is comparable to the variability for Carson City (16C) or Boise (20C).
These seasons have no more to do with fronts fronts or pressure systems than the seasons in Anchorage or Dundee. It’s cold in winter because the sun is lower in the sky and the days are shorter.
Not the Pole! 
After I discovered my anus, I named it “George” for similar reasons.
As a lifelong resident of Melbourne, I can assure you that we do indeed have real winters on the Australian mainland. We might not have snow in the cities, which tend to be close to sea level, but we do have snowy mountains and you might be surprised by the extent of skiing in Australia.
Nitpick: 1488.
Otherwise, great post – and great thread!
I just read about that in The Age of Wonder.
Why did his large telescope have two mirrors to be switched out?
You might want to ease off of the brew this late at night, Tom.
Alll the southern constellations were known to the ancient Greeks, since even the Southern Cross is visible from Upper Egypt.
This is incorrect. Upper Egypt is only about the latitude of the Tropic of Cancer, which means that the 20 degrees (approximately) of the sky closest to the South Pole won’t appear above the horizon. The Southern Cross, at around 60 degrees south, isn’t that close to the south pole of the sky. Twelve constellations composed of stars near the southern pole were not created by the Greeks, but by astronomers after 1500.
In “Stars and Planets”, Jay M. Pasachoff and Donald H. Menzel state that Crux was regarded by Ptolemy to be a part of the constellation Centaur.
I apologize for my error if I misrepresented Ptolemy’s source of his astronomical data.
Further inquiry reveals that the Southern Cross is visible from the Kalabsha Temple at Aswan.
That’s not in dispute. You said:
[QUOTE=jtur88]
Alll the southern constellations were known to the ancient Greeks,
[/QUOTE]
This is incorrect. The Southern Cross, or Crux, is not the southernmost constellation by a long shot. As I said, twelve of the modern constellations were not known to the Greeks because their stars are too far south to be visible even from the latitude of Aswan.
Which were made up in 1922 (albeit, based on some earlier reckonings; largely from the 16:th - 17:th centuries)
They weren’t “made up” in 1922, that’s just when the International Astronomical Union formalized them (both the classical and more recent constellations). The “non-classical” constellations, which included both the newly discovered stars of the south polar region and some that filled in the spaces between the classical constellations in the northern hemisphere, were all delineated between 1603 and 1763.
Are you sure of that? I may well be wrong; but the fact that the boundaries weren’t “formalized” until 1922 seems to convey to me the thought that all earlier astronomers hadn’t agreed upon them!
Actually, we know that this is true for more ancient civilizations. Gaius Julius Caesar cut the claws off the Scorpion to create his newly-inventioned constellation of the Scales.
And some damn idiot must have created the Cancer by mistake (let’s all irradiate it into oblivion; you can’t spot it in the night sky anyway!) If the Zodiac must fill a dozen, fill it with the Snake-bearer instead!
Both William and John Herschel’s large telescopes used the alloy speculum for the mirrors. While this was the best material known at the time, speculum has the problem that it tarnishes in air, so the mirrors have to be regularly repolished. Nor is that a matter of a rub-down with a bit of cloth; they essentially had to slightly regrind the mirror to produce a fresh surface. The practical system was thus to have multiple copies of the mirrors, so that tarnished ones could be being repolished by day in parallel with a recently polished one being used at night.
Herschel’s diaries from South Africa (see Herschel at the Cape, University of Texas, 1969, ed. by Evans et al) are riddled with references to the constant work of repolishing the mirrors.
[QUOTE=Ignotus]
Are you sure of that? I may well be wrong; but the fact that the boundaries weren’t “formalized” until 1922 seems to convey to me the thought that all earlier astronomers hadn’t agreed upon them!
[/QUOTE]
The significance of the 1922 date has more to do with the creation of the International Astronomical Union in 1919. Prior to that there really was no trans-national astronomical organisation that could have formally agreed such things. Setting about getting an agreement to officially recognise the existing conventions for what the constellations were was pretty much the first thing they did. Yes it took a couple of years, even though they were essentially just rubber-stamping what was already in use, but that’s international committee-work for you.
Being from Canada, I think of winter as meaning … winter. Snow, extended periods below zero (or 32F) need shelter, ponds freeze, leaves fall off trees, etc.
Mind you, I’ve been in Florida when it snowed, and last year there was snow in Jerusalem and various other middle eastern points. I’m not sure what “winter” means in Greece or Italy - I was in Italy in September one year, and in Venice it got quite brisk; you can see pictures of Venice carnival-goers in the snow in February.
Just saying that Greek travellers would not have encountered this sort of climate in reverse by going south, unless they really exceed where we think they roamed. (I vaguely recall something about snow occasionally in South Africa). Similarly, the earliest voyagers to experience this might have been those rounding the Cape of Good Hope, depending on the temperatures there. But, it would take a number of voyages or a longer term settlement to discover - “oh, the weather changes like our seasons, only backward.” Certainly by Magellan’s voyage, if not earlier, some Europeans discovered this fact.
Since AFAIK, the Chinese were not in the habit of cruising the south of Australia back then, they likely would not have been aware either.
Thanks, bonzer.
It might help to realize that the word “constellation” means something a bit different to an astronomer than to a layman. To a layman, a constellation consists of a few stars, possibly together with a stick-figure set of imaginary lines connecting them. To an astronomer, however, a constellation is the entire region of the sky containing those stars, but also containing a lot of other sky. Every square degree of the sky is part of some constellation or another. So, everyone has agreed since antiquity that, say, Betelgeuse is part of the constellation Orion. But what about a spot a degree to the left of Betelgeuse? Ten degrees left? At some point, you must leave Orion and enter some other constellation; precisely where is that? That’s what the IAU formally set in the 1920s.