About that Jupiter - Venus thing -- it's hard to picture the geometry

[HamdenRice]

I was never very good at astronomy, but whenever something like this Jupiter Venus alignment happens, I struggle to picture it.

Jupiter is very much farther from the sun than us. Venus is nearer to the sun than us -- although still very far from the sun.

I used to be better at visualizing spacial relations in my head than I am now. I can kind of imagine looking at Venus kind at a tangent to it's orbit and seeing Jupiter on the other side of the sun. Is that basically what's going on?

It would be nice to have a diagram because my brain hurts trying to imagine it.

[elleng]

1. Think of a Smiley Face,

Crescent Moon the Smile, Planets a bit below each end of Smile.

&cap=Look+to+the+southwest+after+sunset+on+Dec.+1+for+a+close+conjunction+between+three+bright+solar+system+objects%3A+the+Moon%2C+Venus%2C+and+Jupiter.+If+you+have+binoculars%2C+you+might+even+be+able+to+fit+all+three+of+them+in+the+field+of+view.+Between+now+and+then%2C+you+can+see+Jupiter+and+Venus+getting+closer+together+each+evening.+

Got it?

[HamdenRice]

2. I can picture it in the sky -- I mean the solar system perspective

I'm trying to picture how the planets appear aligned from the perspective of their orbits around the sun, seen from the earth -- how something so much closer to the sun and something so much further from the sun can appear aligned from our perspective "between" them.

[elleng]

3. I was LOUSY

at spatial relations!!!!

[qazplm]

4. use a clock

think of us at say the 9 oclock position, the sun in the center and Jupiter at say the one oclock position.

Then all you need to do is put Venus somewhere in an inner loop "northwest" or the sun and "northeast" of us aligned in such a way that an observer standing at nine oclock looking at one oclock would also see Venus on the inner track.

I have no idea if the clock angle reflects where the planets are now at this point in real life but that should help with visualization I think.

[HamdenRice]

5. That's kinda what I figgered, but it would be nice to see a diagram ...

But it means that Jupiter has to be kind of on the "other side" of the sun for it to align with an inner planet?

[qazplm]

6. well draw a picture

with the sun at the center and earth at nine oclock.

Once you do that you can put jupiter pretty much wherever you want to so long as it isnt blocked by the sun but probably not on the same half of the clock as wherever you've placed the Earth.

draw a second interior ring, much closer to the earth than the sun and place venus somewhere along that ring as long as it is on the same side of the sun as where the earth is.

you will find i think at that point that jupiter doesnt have to be completely opposite the sun for the alignment to work. I dont know where exactly it would be of course. I am sure the window is much narrower then I am depicting but this is simply to help visualize a very rought spot of how it would work.

Turns out I wasnt that far off on the clock angles, talk about blind luck!

[muriel_volestrangler]

7. I think your description sounds about right

but I can't find a diagram for it. Maybe think of it in clock terms, with the Sun at the centre:

Earth is at 6 o'clock, say;
Venus is at maybe 8 o'clock, but in a smaller orbit - as you say, the line from Earth to Venus will roughly be a tangent there;
Jupiter is at perhaps 10 o'clock, but in a much larger orbit (7 times further out than Venus).

Ah - try here:

http://blogs.discovery.com/whats_up_astronomy/2008/11/the-great-conju.html

Looks like my guess for the 'times' was fairly lucky.

[jimshoes]

8. here's the diagram

Hope this helps.

[daninthemoon]

9. very nice

[HamdenRice]

11. OK, here's the part that messes with my brain, even with the diagram

Thanks for the diagram.

If that's the alignment and Jupiter is on the other side of the sun, how come we see this in the "night" sky? It's also why I've always found it difficult to imagine seeing Mercury in the "night" sky.

I guess this is why we can only see it in the early evening because later at night we are looking in the other direction?

On edit: I know the answer to that question. It's that these diagrams are so far off scale. Venus and mercury are very, very far from the sun.

I remember once some article that tried to explain the scale and it involved apples at opposite ends of a football field or something like that. It's just hard to wrap my mind around to get a picture of it that all works.

[muriel_volestrangler]

12. They're not that far off scale for Venus and Mercury

Mercury semi-major axis (ie 'average' distance from the Sun) is 0.387 AU, ie 0.387 of the Earth-Sun distance. That looks about right in the diagram. It would also mean the maximum angle between Sun amd Mercury, from Earth, is about 23 degrees (since Mercury's orbit is quite elliptical, it will actually get a bit more than that). That's not much - 15 degrees is an hour's travel of the Sun through the sky, so Mercury will never rise of set more than about 90 minutes away from the Sun. With twilight keeping the sky somewhat bright even when the Sun is a bit below the horizon, it means we don't see Mercury often.

For Venus, it's 0.72 AU (again, that diagram looks quite good for that); that's a maximum angle of about 45 degrees, so we get 3 hours after sunset/before sunrise to see it - in which time is can get properly dark (and it's brighter anyway), so we see Venus a lot more.

What they have done is show Jupiter closer to the Sun than it really is. It should be 5.2 times further away than the Earth.

[caraher]

13. Well, it's not really about scale, though the drawing definitely is not to scale

At any time (ignoring clouds) you can "see" essentially half the sky. When the Sun is in that half of the sky it is daytime, and its light (scattered by the atmosphere) swamps pretty much everything else in the sky.

At night, the half of the sky you can (in principle) see no longer includes the Sun. In the illustration, when you can see Venus and Jupiter the Sun is barely out of your field of view, but those planets are still within that half of the sky. This does not last long; as Earth rotates Jupiter and Venus will soon drop below the horizon (maybe a better way of putting it is that the half of the sky you can see no longer includes them).

[Orsino]

21. And the Moon in its orbit is currently off to the left of the Venus-Jupiter line.

As the Earth rotates, the Sun sets first, followed by Venus and Jupiter, and the Moon sets last.

[Bill McBlueState]

18. This also indicates

that the view from a satellite of Jupiter would be kind of cool, too.

[indepat]

10. The Jupiter-Venus conjunction(?) was spectacular during our 200 mile drive west in the early evening

last Tuesday and I'm so looking forward to that drive again this evening. :D

[Ediacara]

14. I made this image with a program called Celestia

The big yarn ball is Jupiter. There is an option to turn the orbit lines of moons on and off, and I wanted it on for our Moon, and off for the others, but alas, no luck, and we get a mess where Jupiter goes.

[redqueen]

15. A mess of awesomeness.

Thanks for the pic. :)

[HamdenRice]

17. Pretty amazing!

It also shows how vast the orbits are compared to the bodies. I love the idea of Jupiter as a ball of yarn because of its many moons.

Gravity is amazing. How the sun's gravity can hold on to these bodies at those distances, remains one of life's mysteries despite our ability to describe it.

[Ediacara]

19. I think most of those far off orbits are some of the micromoons

The four major Jovian moons are in pretty regular and fairly tight orbits around Jupiter's equator.

[Canuckistanian]

16. Think of a line - Moon- Venus-Sun-Jupiter

Now remove the Sun from the picture. Considering that the Sun disappears from the sky every day - that leaves the other satellites in place.

[Sequoia]

20. Here's a photo of them above Hong Kong.

Hong Kong's smiley face: That's Venus on the left, Jupiter and, of course, the Cheshire Cat crescent moon in a rare celestial alignment.