Something has perplexed me to the longest time now. There were 5 of our presently 9 known planets that the ancients knew about: Mercury, Venus, Mars, Jupiter, and Saturn (I’m leaving earth out, since many of the ancients just assumed the earth was flat). The following cite gives the information (for those of you who like cites :)):
[emphasis mine.]
Anyways, I chose that cite because it is typical. The only thing is, all these 5 planets just look like ordinary stars in the sky. I remember, a long while back (so I don’t have the cite–sorry ), on PBS, Bill Nye the Science Guy explained the reason for that is that proportionately-speaking, if the planets are the size of peas, they are something like a football stadium in distance apart (sorry, I forget the exact distance–but from what I recall, that is pretty close).
So if they just look like stars, and they ancients didn’t invent the telescope yet, how the heck did they know these five pinpricks of light were something more than just ordinary stars–i.e., what we today call planets ?
Also planets don’t look just like stars; they tend to twinkle a whole lot less, vary in brightness quite a bit over time (though there are stars that do this as well), all are found in a straight line (the plane of ecliptic), and send hordes of invading aliens from time to time.
Uranus would have been visible to the ancients. It is visible to the unaided eye (more so if you’re in the backwoods of Montana than the sidewalks of New York, mind you, but that means the ancients had a better shot at seeing it). And like the others, it does wander.
As far as I’ve ever heard, though, no pre-telescope society was aware of it. They simply missed it. It’s far dimmer and moves far slower than Saturn and the others, so it would be easy to miss.
To elaborate on bughunter’s answer for those who didn’t catch the drift:
If you look up and find the Big Dipper ('cause, frankly, darned few people can find all of Ursa Major with all the light pollution) or the Southern Cross, you will find the same seven (or five) stars in the same shape every night that you can find them. As the Earth swings around the Sun, they will appear in a slightly different place each evening and move together across the sky, but the individual stars will always be the same distance from each other, and the constellations will always be the same distance and relative direction from any other constellation (such as Cassiopeia or Centaurus).
The planets, however, “wander” around the sky, moving from one constellation to another as they and the Earth orbit the Sun, causing their positions relative to the background of the distant stars to constantly shift.
These were the only five objects other than the Sun and moon that behaved in that way, so they stood out quite starkly to the peoples who spent much of their nights watching the sky, (Leno, Letterman, and your local syndicated re-run being unavailable at that time).
Further support: The term “planet” is Greek for “wanderer”. I guess it’s time for PBS to repeat Cosmos. But, Sagan’s series “Cosmos” did snuff out the spark of interest for many would be stargazers, or novice amateur astronomers.
BTW, they also knew certain planets exhibit reverse (retro) moton.
> . . . I’m leaving earth out, since many of the ancients just assumed the earth
> was flat . . .
Perhaps you know this, but just in case, any society with at least the sophistication of the ancient Greeks knew that the Earth wasn’t flat. In particular, everyone in Europe from the time of the ancient Greeks forward knew that the Earth was round, and they had a good estimate of the size of the Earth. By 300 A.D., they also knew the approximate size and distance of the moon.
The reason that they didn’t consider the Earth to be a planet was that they thought it was the center of the universe and didn’t move, either in rotation or in revolution.
It would be more correct to say “every educated person in Europe…knew that the Earth was round.” Your average illiterate mud-dwelling peasant, by far the largest demographic for several millenia, usually didn’t spend too much time contemplating the shapes of celestial bodies.
C.S. Lewis has quite a bit on this in his The Discarded Image, a description of the cosmology and natural sciences viewpoint of the Middle Ages. Even a collection of folk tales put together in South England in the 14th Century evinces popular knowledge that the world was round. In fact, contrary to the popular conception, the reason Columbus had problems with the scholars at the Spanish court was not that he thought the world round and they thought it flat, but that he had an erroneous conception that the world had only 60% of its actual circumference, making a cross-ocean voyage to the East make sense, while the scholars were operating on a 2,000-year-old demonstration on trigonometric principles based on propertie of the Sun and Earth that the earth’s circumference was within 1% of the actual modern figure.
When a modern observer says that Uranus is “barely visible to the naked eye under ideal conditions”, they are also helped enormously by knowing where to look. Without knowing that there was something to find in a particular spot, it was highly unlikely ancient observers were going to notice it.
Isaac Asimov once postulated that the number 7 was/is sacred in so many cultures because that was the number of planets* known to the ancients. I find the idea interesting, but cannot vouch for its accuracy. Is there anyone here who can?
The list of planets being different in antiquity because of the exclusion of the Earth and inclusion of the Sun and Moon.
One thing to note is that record keeping was essential to knowing how many planets there were. Illiterate cultures knew there were wanderers, but didn’t know, for example, that the morning star was the same object as the evening star (unless they learned this from a neighboring literate society). Only by recording Venus’ positions over a long period of time can it be established that they were the same object.
The same would be true of the other planets. They could follow an outer planet from night to night, but eventually it would not rise during the night and they would lose track of it.
This is an important point. Just because the ancient Greeks called them “planets” doesn’t mean they knew that they were giant round lumps of rock or gas. So, although they knew the planets were different from the stars in that they moved around, they still had no idea what they actually were.
I think your OP has been covered pretty good so far. The consensus being that they didn’t know they were planets in the sense that these heavenly bodies were “like the earth”. Some cultures viewed them as supreme beings that travelled in the heavens.
Anyway, I just wanted to kinda relate the other part of your OP.
**… will even all of those planets ever be lined up together? **
We had an oppostion just a few years ago IIRC. (May 5th 2000) Does that sound correct y’all?
All the major planets were in line on the opposite side of the sun from the earth. I forget the degrees in proximity but they could all be seen simultaneously and yet we suffered no major catastrophy as a result. Not yet anyway…
), on PBS, Bill Nye the Science Guy explained the reason for that is that proportionately-speaking, if the planets are the size of peas, they are something like a football stadium in distance apart (sorry, I forget the exact distance–but from what I recall, that is pretty close).
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