Jupiter---King of the Planets, King of the Gods

Factual Questions
1

If that title doesn’t catch attention, I don’t know what will! :wink:

Anyway, the planet Jupiter is named after the Roman god who was king over the other gods in Mount Olympus. It only makes sense when you think about it, since Jupiter is by far the largest of the planets. Except for one thing----nobody in the Roman Empire could have realized how big Jupiter was at the time. So was there a reason the first five planets got their name, or were they named by 18th Century astronomers who did know how big the planets were?

(Speaking of which, how were they able to estimate the size of the planets? I can only assume they did so from the speed of their orbits. An unusually slow planet woul suggest a very heavy mass. Sure enough, Jupiter which is about 11 times bigger than the Earth circles the Sun in about 12 years.)

One more question. The days of the week are named–for the most part—after the Sun, Moon, and five planets. In English, the names of the Roman gods are switched for the Nordic gods. Mars becomes Tiu, the Norse god of war (Tuesday). Jupiter becaomes Thor, the Norse god of Thunder (Thursday). Venus becomes Freya, the Norse goddess of love (Friday). All these make sense, but how did Mercury get associated with Odin of all people? (Wednesday)

Eddie

2

Some of the planets have obvious reasons for their names:
[ul]
[li] Mercury, named for the swift messenger god, is the planet that moves fastest through the sky.[/li][li] Mars, named for the god of war, is blood-red[/li][li] Saturn, named for the god of time and old age, is the slowest planet known to the ancients.[/li][/ul]

Venus is a bit more esoteric, but lovely evening star, goddess of love and beauty, uh, kinda works. But since Venus is the brightest planet at -4.4 magnitudes, vs. Jupiter’s less impressive -2.9, it’s hard to see why Venus “won.” (Remember, magnitudes are “backwards”–more negative is brighter.) Maybe 'cause if you annoy Jupiter, you get a lightning bolt, or maybe they tie you to a mountain and an eagle eats your liver. You piss off Venus, you die alone and ugly.

Maybe Jupiter was named for the king because Venus is only visible in the morning or evening sky, while Jupiter can be up all night. Jupiter barely edges out the next brightest up-all-night planet, Mars (m=-2.8) in maximum brightness.

3

I’m sure someone more astronomically minded will be by sooner or later to tell you how they DO come up with the masses of planets, but I seem to recall that the only thing that determines how long a planet’s year is (at least to lowest order) is how far it is from the sun.

Remember Kepler’s law tells us that the year is proportional to the distance from the sun to the 3/2. On the other hand, if you know both the length of the year and the distance from the sun already, you can work out what the planet’s mass is.

4

Yes, g8rguy is correct. Orbital period depends on the size of the orbit and the mass of the body in the center. If you are talking about planets orbiting the sun, orbital period depends on the mass of the sun and the distance between the planet and the sun. It does NOT depend on the mass of the planet. If it did, you can cause a planet to go into a different orbit by merely splitting it in two but leaving them floating side by side.

However, most planets have moons orbiting them. And their orbital period depends on the mass of the central body, i.e. the planet. If you knew the distance from the planet to the moon and the moon’s orbital period, it’s trivial to calculate the mass.

Planets also have a small but detectable effect on the orbits of other planets. This will depend on their masses, so if you measure the orbits carefully, you can calculate the masses of all the planets. Except maybe Pluto which has a miniscule effect on other planets.

By the way, the above are approximations that work only if the central body is far more massive than the thing orbiting around it. If this approximation fails - e.g. two stars orbiting around each other - then the mass of both bodies matter.

5

As I understand it - Jupiter was the Father/King of the Gods, hence the name was given to the slowest (and therefore most dignified and regal) of the Planets, except that Saturn was the Father of Jupiter (amongst others), so HE had to be even slower and more dignified!!

Etiquette of the Gods - Who understands it?? :slight_smile:

6

Or in plainer language, Saturn is:

From this site.

7

Nope, Friday is named after Frigga (or Frigg or Frija), Odin’s wife, who, according to this site, is

8

So when characters on TV say something is a frigging such-and-such, they actually love it. :D:D

9

This is more or less correct as I understand it.

Also, Jupiter tends to consistently be the brightest of the planets in the night sky. Venus is brighter, but is only a brief presence in the night sky (being so close to the sun…sunrise/sunset). Mars is only brighter on rare occasion.

10

I know that Jupiter’s mass was estimated in the 18th century. They must have done that by observing the periods of the Galilean satellites, and/or observing the effect Jupiter had on other planet’s orbits.

Well, it looks like almost all of my questions except one have been answered. Why did the Norse honor the god Odin with Wednesday? I can see how Tiu, Thor, and Frigg might be the Norse equivilents of Mars, Jupiter, and Venus—but Odin certainly isn’t the messenger of the gods! Why pick Odin and not someone like Loki?

Eddie

11

OK, how did Odin get associated with Mercury?

Well, Mercury wasn’t just the “messenger” of the gods. Mercury/Hermes was associated with medicine, secret knowledge, mystery cults, and the Egyptian god Thoth. Odin wasn’t just the ruler of the Norse gods, he was also associated with poetry, runes, secrets, etc. He was a very differnt figure than Zeus.

12

Weighing in. . . .

Edward J Cunningham has it much closer than gr8guy and scr4. The thing to remember about small objects (like Jupiter) orbiting large objects (like Sol) is that the orbital period is 99.99999+% determined by the mass of the large object and the distance of the small object from it. If Jupiter were to orbit at Earth’s distance, it would take about 365.24+ days to go around the sun, much like Earth. It would go oh-so-slightly faster, but not a whole bunch; anyone with the figures care to back me up here?

So anyway, what the period of Jupiter’s orbit gives one is a pretty good idea of Sol’s mass. In order to figure out what Jupiter’s mass is, we have to find some smaller-still objects orbiting Jupiter (i.e., the Galilean satellites), and an accurate determination of how far away from Jupiter they are. In this manner, the masses of Mars, Jupiter and Saturn (and later Uranus and Neptune) were all quite accurately known early on in the history of telescopic astronomy.

What about our own fair planet? We have a satellite, right? Yes, but…you see, Luna isn’t that small an object (it turns out it has about 1/81 the mass of Terra), and when you have two objects that are comparable in mass, your mass estimates become somewhat less accurate. We had a fairly good idea of Terra’s mass, but only after 1957 when we* had launched some artificial satellites did we have a really firm grasp on the figure. (And again, Luna’s mass was pinned down much more accurately after we* sent some stuff out to its vicinity** in 1959.)

Venus and Mercury were in similar situations until probes were sent out to them. Pluto is still tricky, because we haven’t sent a probe to it, but luckily for us it happens to have a moon (Charon), and so we have quite a good idea now as to the total mass of the Pluto-Charon system; as to the components thereof, we’re still basically guessing (based on their relative brightnesses, I believe).

As for Odin vs. Mercury (the Enthralla in Valhalla!), the real Roman equivalent to Odin was Jupiter. They were both the rulers of the gods, and they were both mean sons-of-goddesses. Jupiter and Thor only really match up in the lightning-bolt category; find some guy with the mother of all hammers, and match him up with Thor. The Norse and Roman mythoses didn’t match up all that well. The closest thing I can think of to Mercury is Huginn and Muninn, Odin’s raven-companions who bring him the news of the world (like having CNN perched on your shoulder).

And if I’m wrong, please correct me; I have a son named Odin (it’s a family name, I have some Norse blood).

  • By ‘we’ I mean the human race. It so happened that both these items were launched by the Soviets.
    ** Nothing human-made actually orbited Luna until 1966, believe it or not. Until then, it was all fly-bys. Three years later, we were sending people there.
13

Err… isn’t that what we said?

and

14

This site http://www.friesian.com/week.htm has some info, but doesn’t directly answer the question. But it does point out that Jupiter got more attention for being the god of thunder than for being the ruler of the gods, which would explain why Jupiter’s day is associated with Thor’s day instead of Wodin’s day. And that Odin is also often described as the “god of wisdom,” which is somewhat analagous to Mercury’s role. As Lemur pointed out, the Greek and Roman king of the gods ruled by force & flash, not necessarily by wisdom.

But the one thing that becomes apparent when comparing the names in all the different languages is that romance languages still use the Latin-derived names (e.g. Wednesday is “mercredi” in French), while Germanic languages like English use the Anglo-Saxon names. It seems to me that it was never the case that “Mercury got associated with Odin,” but that the Anglo-Saxons just chose a different representation for that day of the week than the Romans.

Is it commonly accepted that the Anglo-Saxons based their days on the established Roman version? If that were the case, I’d say sure, they mapped the Roman gods to their own versions and were just left without any day to devote to their ruler of the gods, Odin. But it looks just as likely to me that they each came up with their own versions of the names based on the heavenly bodies, and that saying “Jupiter corresponds to Thor, Mars corresponds to Tiw, etc.” is just creative re-interpretation. This site: http://www2.gol.com/users/stever/calendar.htm shows how it all went down in Japan, by the way.

While googling around I also found this message: http://omega.cohums.ohio-state.edu/hyper-lists/classics-l/00-05-01/0093.html , which looks like it’s probably chock-full of information on the subject, but my eyes started to glaze over after a paragraph or so.