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Dancing with Venus and Jupiter

Sky and Telescope - This Week's Sky at a Glance

Venus and Jupiter struck me hard this morning, bringing me out of the fantasy world of elections and into the real world with a sense of awe and thanksgiving. Suddenly all seemed right and I didn’t really care about today’s vote. What I cared about was this rapidly evolving – and unusual – close encounter of the celestial kind.

In just a few days – November 5, 2004 to be exact – Jupiter and Venus will be less than a degree apart – and that is really close. Then on each succeeding morning there will be more distance between them. This morning Venus was significantly higher than Jupiter. Less than a week the positions will be reversed.

And that’s why it is such an excellent learning opportunity. Anyone can see this – just look for the two brightest “stars” in the southeast before dawn. (Or if you happen to be in Australia, in the northeast, I think/) Watching this little dance in the morning sky and seeing the positions change each morning gives you a real sense of motion – the complex motions of Earth, Venus, and Jupiter and how these motions change our point of view. That to me is the real world, easily lost among our day-to-day concerns.

Yes, I’ll vote today. And yes I’ll watch the returns and probably stay up all night and feel lousy the rest of the week because of it no matter what the results. But as I walked the woodchip path around my yard in the cool, pre-dawn air I felt tremendously uplifted by these two bright planets and the even brighter quarter Moon that was high in the sky and gently lighting my way

You see, Venus is the brightest thing we see – besides the Sun and Moon, of course. Right now it is a “morning star.” And next to Venus, Jupiter is the brightest thing we usually see and it is, right now, next to Venus and moving closer to it with each day. (It’s actually below it.) Science, as my friend Don Douglas points out, is often counter-intuitive. So as I looked over the trees to the southeast and saw these two bright points of light only a few degrees apart, I paused and paid homage to them. Then I resumed my walk and began to think in two directions at once – first, what was I really seeing? And second, if I didn’t have modern scientific knowledge, what would I think of this spectacle? What would my intuition tell me was going on?

Neither question is that easy but I can be more certain about the answer to the first. To begin with, I know that neither of these planets is “rising” in our sky. To say they are “rising” implies that it’s their motion we detect – and it isn’t. What we are seeing as something rises, of course, is the result of our daily rotation. We’re on a merry-go-round and the universe is the backdrop. As our “horse” - in my case Westport, MA – turns towards the Sun, it appears to rise. So it is with Venus and Jupiter. As we turn towards them they appear to get higher in the sky.

This is not difficult to understand, but it is counterintuitive and we still speak regularly of the Sun or Moon “rising” or “setting.” We don’t feel the Earth move – in fact, quite the contrary, it seems rock steady. So even though we know better, the real events are not intuitive to us. So it is with Venus and Jupiter – but here we have to take two other motions into account – our annual revolving around the sun and theirs as well. And that’s what I pondered as I walked the path around my yard. Each time these two planets came into view in my circuits, I though about the larger motions of the solar systems and tried to picture the relationships. Where did I stand – and where were the planets in relation to me and the Sun?

I finally got it right when I came in and sat down at the breakfast table and moved little objects around that represented the Sun, Earth, Venus and Jupiter and Bren chipped in her two cents worth. It was easy enough to place them on the correct side of the Sun to have them come into view as we rotated. Since we are rotating counter-clockwise they had to be lined up to the right of the Sun for me to see them before I see the Sun each day.

Ah – but are they on the same side of the Sun as I am? That got a little trickier. You see Venus is getting lower in the sky each morning – that is, closer to the Sun – and Jupiter is getting higher in the sky each morning – that is, farther away from the Sun. So how do we explain that?

Well, it’s far easier to explain with a picture, than with words, so take a look.


Studying the graphic above a few things should be clear. First, Venus is closer to the sun than us and thus travels in a shorter orbit and so will run ahead of us. In fact, it has already turned a corner and is starting to head in the opposite direction we are heading – thus from our perspective it is getting closer to the Sun. In other words, coming into our view later and later each morning until it will at last be lost in the glare of the Sun.

Our own movement in orbit tends to counteract this somewhat, but we have a larger orbit and so cover a smaller percentage of the total orbit in a given number of days than Venus does. In terms of this week’s sky show, though, we will see Venus move closer to and eventually go past the lower Jupiter.

Although this diagram, taken from “Starry Night” software, shows only the orbits of the inner planets to scale, we do notice Jupiter off in the distance near the top and to the right of the Sun . At first glance it may look as if it’s to the right of Jupiter, but lay down a straight edge on the image connecting Earth and Venus and what you see is Jupiter is just a tad to the left of that line.

Which is exactly what we are observing in the morning sky. But Jupiter won’t get lower. It will get higher, primarily because we are moving around the Sun and as we do so Jupiter appears higher and higher in our sky each morning. Yes, Jupiter is moving as well, but just as Venus completes a larger portion of its orbit in a given length of time than we do, so we complete a much larger portion of our orbit in a given length of time than Jupiter completes of its orbit.

In fact, in a matter of months we will pass Jupiter and eventually it will be appearing in our eastern sky just as the sun disappears in our western sky.

Whew! Is that clear? If not, I suggest you get out some marbles or things and try representing the players on your table top, then see what happens as you move them in their orbits.

The bottom line for me is I can get these motions straight and as I watch Venus and Jupiter this week I will remind myself of this perspective so I can capture this reality in my head.

But what if we were living 1,000 years earlier? What then would we make of this?

To begin with, we would probably be much more conscious of it because the night sky would be a part of our livex. Today it is almost always drowned out by artificial lights and we are not aware of it. As recent as a century ago this wasn’t the case. Even when indoors, the light was usually so weak that we could easily see stars when we glanced out a window. Now if we glance towards a window in a lighted room we see nothing but reflections of the room light.

We also would be used to seeing these “wanderers” – these planets – moving each night. They simply didn’t stand still as the “fixed” stars did. And so as we saw Venus and Jupiter make this unusually close approach to one another we may imagine it was a heavenly sign – a sign of important things about to happen.

Hey – maybe that’s it! Maybe this means Kerry will win the election!

Oops. Now I’ve lost it. I’m back in the fantasy world of sound-bites and the electoral College. Oh well, Tomorrow will be different. The elections results can’t change the sky show.

Posted by Greg Stone at November 2, 2004 02:43 PM