[X] My Assistant

[JRehling]

Probably some perfect "grand tour" type alignment, where each spacecraft-planet encounter is as close-in to the planet as possible for a departure trajectory that's approximately tangent to the planet's orbit or as close to tangent as possible.

Eris is also well off of the ecliptic at present (and for a long time coming). I doubt that keeping things in the ecliptic for three flybys then counting on Neptune to provide all of the work to acquire a high inclination is feasible. Maybe a Jupiter-Saturn combo could do it, assuming the rings weren't a problem.

That would actually be a scenario that would unfold fairly often.

Uranus is actually in a pretty good position right now for an assist to Eris, but it'll soon move out of that good position and not come back for 8 decades. Neptune, however, is moving into position, but again, Neptune can't bend the path down in very good proportion to Jupiter's bending it out.

In only 230 years or so, Eris will come within 40 AU of the Sun. Let's plan on an Eris Orbiter/Lander then. Start the buzz now.

[Alan Stern]

You probably already know about The Great Planet Debate meeting coming this week near DC, if not, see:
gpd.jhuapl.edu.

To register for Great Planet Debate conference web participation, click: http://tinyurl.com/6xcqec
Watch the talks and debate on line!

-Alan

[djellison]

I was worried this would turn into another 'define-a-body' argument, because we've really had enough of that here. But wow - we've got a new one, define-a-debate. Debating who can debate it is a nice new twist...I like it.

Doug

[JRehling]

The "authority" issue is a relevant one. If you like a particular kind of music, and a panel of experts convened and came out saying that the term you'd always used to describe it was invalid, would you stop using it? If there were a cartographical definition that discriminated between hills and mountains and you saw a protuberance whose height was unknown to you, would you pause mid-sentence out of uncertainty which term was correct?

Part of the issue here is the relationship between folk uses of terms and expert uses. Look up "star" in any dictionary and, besides the terms referring to actors, you find one astronomical definition denoting large gaseous spheroids heated by fusion and another denoting small, twinkling lights in the sky. By the latter definition, the percept Jupiter makes in the night sky is aptly labeled a "star".

One of the things that concerns me most is when a naive viewer of the night sky asks a question about a "star" and is told snippily that they just displayed their ignorance -- that what they are looking at is not a star. I don't think many people get very far in life without having some encounters like that, and the take-home lesson is that science equals pedantry and poor manners to boot. And I think the whole notion of the IAU defining "planet" gives that perception a giant shot in the arm.

When it comes right down to it, the "twinkling pointlike source of light" is *a* perfectly fine definition of the word "star" that doesn't supplant the scientific one, but exists for another context. And my perspective on that hypothetical encounter is that the pedant is actually the one displaying ignorance.

Cue the "planet" debate: While the lay-experience with planets is much less frequent than with stars, I'd say the folk experience (in schools, in backyards, watching science fiction movies) is still extensive enough to consider the term to have a folk sense. Meanwhile, it has absolutely no useful scientific sense. Saturn and Mars obviously have less in common than Pluto and Triton.

So I find the whole thing to be that backyard experience writ large: There's a kind of arrogance behind it, and it says to the world that pedantry is really what science is up to. If some jazz counsel had a vote on whether or not Miles Davis played jazz, I wouldn't care if the vote were 51-49 or if it were 100-0 -- I'd still keep calling it jazz. Far from caring about which side of which line Pluto is placed, I consider this a battle against pedantry, which, if won unbloodily, might mean more people who care about science.

[Greg Hullender]

One of the things that concerns me most is when a naive viewer of the night sky asks a question about a "star" and is told snippily that they just displayed their ignorance -- that what they are looking at is not a star. I don't think many people get very far in life without having some encounters like that, and the take-home lesson is that science equals pedantry and poor manners to boot. And I think the whole notion of the IAU defining "planet" gives that perception a giant shot in the arm.

I think we definitely need to restrict the debate to exclude people who can't tell the difference between planets and stars. I realize this will hurt their feelings, but I just don't think it can be helped.

--Greg :-)

[JRehling]

I think we definitely need to restrict the debate to exclude people who can't tell the difference between planets and stars.

It can be pretty hard to tell the difference between Saturn and Regulus in a lot of circumstances.

Through a car window in the growing light of dawn, when you're uncertain which way is due north, etc.

And try spotting Uranus without mechanical assistance and see if you're immediately sure which magnitude 5.8 object it is.

It can be pretty hard to come away from the context of looking at books and articles, but there is a real world of lights and sounds, and it's in that context where the "pointlike source of light" definition of star is perfectly useful. So you don't have to say things like, "There, in Capricorn, between the two pointlike sources of light which could be either stars or perhaps one of them is Uranus or even Vesta or a dim comet..." A word of one syllable comes in pretty handy.

[dvandorn]

It can be pretty hard to come away from the context of looking at books and articles, but there is a real world of lights and sounds, and it's in that context where the "pointlike source of light" definition of star is perfectly useful. So you don't have to say things like, "There, in Capricorn, between the two pointlike sources of light which could be either stars or perhaps one of them is Uranus or even Vesta or a dim comet..." A word of one syllable comes in pretty handy.

Which takes us back to the very origin of the word planet. Back in the days when the only way we could chart the seasons and predict celestial events was to examine the sky and the stars. Some of the most revered astronomers of the early ages spent lifetimes plotting the movements of the stars in the heavens. And while most stars moved in easily predictable patterns, some of them -- and indeed, some of the brightest of them -- moved in odd and eldritch fashions, passing through the static and unchanging constellations in non-intuitive, hard-to-predict patterns that repeated (with major variations) over the course of months in some cases, or over the course of decades in others.

These were the planetes, the wanderers.

So, the original meaning of the term had absolutely nothing to do with the physical characteristics of the bodies. It only referenced the different way in which they traversed our skies from all of the other stars.

As I said, as time goes on, context changes...

-the other Doug