Planets: questions answered
The blogosphere is now filled with complaints about the new definition by people who don't seem to have read the actual proposal and are getting second-hand news reports from reporters who don't properly understand the implications ether. I would like to point out that most of the points that people raise (many of which are pretty good questions) were discussed (and resolved) in the voting session yesterday. I'll try to list a few of the contentious points here along with some answers. Add any other good questions to the comment section.
- It shouldn't be allowed; we can't change the definition of a planet! Yes we can. Is the Sun a planet? No, but it was until only a few hundred years ago. What about the Moon? Like the Sun it had its planet status removed. There are also a few examples of large asteroids being named planets and subsequently having their planet status removed when we found out how small they were. Ceres (discovered by an Italian) is a good example of that. We have to re-evalute things as we get more information.
- Why isn't Pluto a planet? Pluto is one of the largest objects that reside is a huge belt of similar icy/rocky objects named the Kuiper belt. As such it hasn't cleared its orbit and would have to be much bigger to do so. And remember, Pluto has less than one percent of the mass of the Earth.
- Ceres has cleared its neighbourhood so should be a planet rather than a dwarf planet. Ceres is in the asteroid belt and as such is together with untold millions of asteroids which it has little influence over. That does not constitute clearing its orbit
- Jupiter has not cleared its neighbourhood. This claim goes on the basis that there are two groups of asteroids sharing an orbit with Jupiter. However, these 'trojan' asteroids sit 60 degrees behind and ahead of Jupiter in its orbit at Lagrangian points (L4 and L5 if you are interested) that exist because of Jupiter. This means that they are dominated/controlled by Jupiter so Jupiter is a planet.
- Pluto crosses Neptune's orbit so doesn't that mean that Neptune hasn't cleared its orbit. Again, Pluto like many other objects is in a 3:2 resonance caused by Neptune so Neptune is dominating them. That makes Neptune a planet and perhaps Pluto is then an object that is dominated by Neptune (another reason not to be a planet).
- Planets with satellites do not qualify because they haven't cleared their neighbourhood. Again, the planet is the dominant object and controls the satellites (otherwise they would fly off into space and not be satellites!).
- If a satellite such as Titan was to leave Saturn and take its own orbit around the Sun it wouldn't be accepted as a planet. Firstly, that is incredibly unlikely to happen but if it did, and it was not dominated by another object then yes it would be a planet.
- What about Sedna, Quaoar etc? They are on the "watch-list" for dwarf planet status. It will depend on what we find out about their shape, size and how much they control their neighbourhood.
- Under these rules wouldn't Mercury be a dwarf planet? No. Mercury has hydrostatic equilibrium and dominates its neighbourhood so is a planet.
- Shouldn't a planet have an atmosphere? No. As examples think of. Mercury and the limited atmosphere on Mars. How much atmosphere would be enough?
- Extrasolar planets are no longer planets. This resolution was only concerned with "Objects in the Solar System" so doesn't declassify them. It was suggested that extrasolar planets would get their own resolution at some point in the future.
- Planets not orbiting a star are no longer planets. Again, the resolution only covers objects in our Solar System so says nothing about them.
- Isn't 'demoting' Pluto just international astronomers being spiteful to the only US discovered planet? No and Clyde Tombaugh would not be turning in his grave either. I should explain that politics isn't split in the same way amongst astronomers as it does amongst politicians. Many astronomers know each other and often collaborate on projects with astronomers in different countries. As individual countries only provide limited funds for projects, it is often necessary to make an international collaboration to get together enough funds. In some ways all astronomers are in a common battle against their own national funding councils so tend to be quite friendly towards each other. The 'anti-American' issue is just ridiculous as far as I can see.
- We now have to wait three years for the group of trans-neptunian objects (TNOs) which are dwarf planets like Pluto to get a name. I'm not sure about this. The name will now be chosen by a committee of astronomers (as the suggested name was voted against) but I'm not sure if the IAU membership have to ratify this.
Comments: Planets: questions answered
"This means that they are dominated/controlled by Jupiter so Jupiter is a planet."
The definition doesn't say anything about dominating or controlling the orbit. It says that the object "has cleared the neighborhood around its orbit".
Therefore because of the Trojans, Jupiter is not a planet under the new definition. Because of Cruithne, Earth is no longer a planet under the new definition. Because of Pluto, Neptune is not a planet under the new definition. In fact, the only planets that actually conform to the new definition are Mercury and Venus.
If the definition had actually stated something like "1(c) gravitationally dominates the neighborhood around its orbit", then Pluto would still be a planet, as would all the rest of the classical planets.
Posted by Ed Minchau on Friday 25th Aug 2006 (20:50 UTC)
You said
Pluto crosses Neptune's orbit so doesn't that mean that Neptune hasn't cleared its orbit.
As far as my knowledge this information is wrong. Pluto is not intersecting or crossing Neptune's orbit. This misconception came because of the 2D images in text books. Pluto's orbit around the sun is very elliptical, or egg-shaped. Neptune's orbit is more circular. Also, Pluto's orbit is tilted 17 degrees above Neptune's orbit. Because of the tilt, the narrow part of Pluto's orbit dips closer to the sun than Neptune. Check the net for details.
check the this link.
Posted by Shiju Alex on Saturday 26th Aug 2006 (13:40 UTC)
Thanks for this post Stuart, it really helps clear things up. I've put up an omnibus post on Pluto which includes this post of yours, the top 10 reasons Pluto is/isn't a planet and a link to the wonderful song "they've demoted Pluto".
Posted by Ian Musgrave on Sunday 27th Aug 2006 (12:15 UTC)
Ed, watch or listen to the entire session in which the vote took place. There was an implication that there would be an "intelligent application" of the exact wording. In my view, this is fine because I don't think it is at all sensible to have a totally exact definition for a planet as there will always be borderline cases.
Shiju, all the questions or statements (the bits in bold) are things I have seen written on various noticeboards/comments to blogs (so aren't my words). I was putting them up and giving some reasons why they aren't correct. You are right to remind everyone that the Solar System is 3D. We should do that more often.
Posted by Stuart on Monday 28th Aug 2006 (18:15 UTC)
Well written. But have you any thoughts about the (now officially publicly viewable) petition signed by a huge number of the planetary science community? I've posted about it on asymptotia, and I'm curious to hear what people think about it, either here or there.
See the post here
Cheers,
-cvj
Posted by cvj on Thursday 31st Aug 2006 (02:09 UTC)
No, I don't think so.
But I do think that it's more "Revisionist Philosophy"
We have revisionist history and now revisionist
Astronomy.
Who knows, next week it will be revisionist
America and our freedoms might wander away.
Posted by P. Edward Murray on Thursday 31st Aug 2006 (03:56 UTC)
First I would like to point out that part of science is to re-evaluate things once you have more evidence to see if your original conclusion was valid. You can label it 'revisionist' if you want but it is part of the process especially when original classifications were made without much data.
Pluto is a bit small and sits in the borderline area between 'large lump of rock/ice' and 'planet'. Arguing over where exactly that border is is a bit like defining an exact edge of a cloud (you could define this as the point where the density of water vapour is half the peak level, or perhaps the 1/e level or in several other ways) Frankly, I don't care either way if Pluto is or isn't a planet; it is still a very large trans-Neptunian object.
Really, we should treat the word planet with caution and not assume that there is some huge difference between planets and non-planets when you are looking at the small end of the scale. The objects in our solar system (and others presumably) seem to exist over a whole range of sizes, masses and compositions. I wish we weren't limited to strictly defined boxes of language and could reflect the fuzzy nature of reality.
Posted by Stuart on Thursday 31st Aug 2006 (10:50 UTC)
I was thinking of geting a tatto like the symbol that Jimmy Page used on Zepplelin 4. I think the Zoso thang = out to Z=capricorn sun sign. oso=jupiter his rising sings planet and the sqwigaly line thang=cancer his moon sign. I was woundering if you could help me find what my Page symbol would look like.I am a Aries with Mars but im not shure about my moon sign.
Posted by andrew on Friday 10th Nov 2006 (07:01 UTC)
I don't know much about astrological symbols, however the symbols for Mars and Aries can be found by following the links.
Posted by Stuart on Friday 10th Nov 2006 (14:33 UTC)
Since the gravitomagnetic force component Fg is not radial, it exerts a moment of force on the two-body system. This moment of force is negative during half cycle A and positive during half cycle B. This moment of force induces a negative rate of change of momentum known as torque during half cycle A and positive one during half cycle B. Thus an alternating torque, hence an alternating rate of change of angular momentum of the two-body system. There is no conservation of angular momentum as stated by the Newton law. The positive moment of force is always greater than the negative one. This explains the mercury perihelion advance. For more details see gravitational waves radiation www.gravitomagnetism.com
Posted by nduriri on Wednesday 29th Nov 2006 (08:48 UTC)
For my thoughts on Mr Nduriri's comment, see the other post on which he included this.
Posted by Stuart on Wednesday 29th Nov 2006 (10:27 UTC)
how do plants get their shape?
Posted by liza on Tuesday 05th Dec 2006 (01:53 UTC)
why is pluto not a planet anymore? why did they change the it now when we learned that there is 9 planets? why change it now?
Posted by katie on Tuesday 12th Dec 2006 (20:10 UTC)
come one, it shoud still be a planet. it makes me sad that it isnt a planet anymore. you guys are mean
Posted by katie on Tuesday 12th Dec 2006 (20:12 UTC)
Katie, defining what is and what isn't a planet is not as easy as it sounds because the Universe provides us with so much variety that we should realise that the term 'planet' is a fairly arbitrary label. A good book on the whole subject is "Is Pluto a Planet?" by David Weintraub. Anyway, many people know that "there are 9 planets" but in the last decade over 200 planets have been found orbiting stars other than the Sun. This "fact" (that there are 9 planets) isn't a fact but was a limit of what we could detect until recently.
Just because we were told something (especially when it comes to classification) does not mean it is totally true. Classifications are based on what we know at the time and in all areas of human endeavour these can change as we find more examples or exceptions. Really, we shouldn't stick to ideas irrespective of what the Universe is actually like.
By the way, not being a member of the IAU, I didn't get a vote on the status of the definition of a planet. In fact, I don't think any of the people that commented here are members of the IAU either.
Personally, I don't care if it is or isn't a planet. It is still Pluto and interesting in its own right. If we only care about things because somebody once said it was a planet I think that would be very sad.
Posted by Stuart on Thursday 14th Dec 2006 (10:16 UTC)
Sorry to say friends, but your all mistaken. Pluto is a planet. It's Mercury thats isn't a planet. It's Moon to Venus. Using mass as the main criteria for determining planetary status is insufficeient . I've been writing a paper that explains that in order for anybody orbiting the Sun to be considered a planet it must have one moon. Venus is an identical planet to Earth each with one almost identical moon.
Posted by toby on Thursday 28th Dec 2006 (13:01 UTC)
Toby, I don't think you've solved the problem, you've only shifted the problem to how you define a moon.
One basic requirement would be for it to orbit the 'planet'. Using this definition I don't see how you can count Mercury as a moon of Venus. There are other issues to be thought of. Is a small lump of rock orbiting a body good enough to be a moon? Do artificial satellites count? I'm sure there could very easily be a small rock orbiting both Mercury and Venus. You also seemed to imply that the relative sizes is important but in that case Mars:Phobos isn't too impressive and neither is Jupiter:Io.
Posted by Stuart on Friday 29th Dec 2006 (00:42 UTC)
Actually Stuart,
If you look closely you'll see that Mercury is indeed orbiting Venus. Well Mercury is co orbiting the Sun and Venus as the Moon co orbits the Sun and Earth.It just dosen't appear as though it is. Think, Mercury & Venus are one thing similar to the Moon & Earh which another thing. Mercury and Venus behave differently because they are closer to the Sun.
Posted by toby on Saturday 27th Jan 2007 (18:46 UTC)
Toby, that isn't a correct analogy. Mercury, Venus and the Sun are NOT like the Earth, Moon and Sun. The Moon and Earth move around their common centre of mass which lies within the surface of the Earth. The Earth-Moon system orbits the Sun with a centre of mass well within the Sun. The orbit of the Moon around the Earth and Earth around the Sun are not far off circular. Mercury-Venus-Sun are very different.
Mercury and Venus orbit the Sun (the centre of mass of the Mercury-Sun or Venus-Sun systems are well within the Sun). Although you can sort of squint and say that Mercury kinda circles Venus, this "orbit" is far from circular and is only because they are both orbiting the Sun. The separation of Mercury and Venus ranges from 0.3 - 1.1 AU. Plus, they only have a tiny effect on each other. You may as well say that the Earth orbits Jupiter.
I suspect that you are just being deliberately provocative.
Posted by Stuart on Sunday 28th Jan 2007 (01:42 UTC)
I have removed many inappropriate comments from this post. It is not appropriate to post things totally unrelated to astronomy or of explicit nature as this is a family friendly site. This behaviour is not acceptable and I suspect that one person is behind this. All dodgy comments will be removed and the links will not boost your Google rankings because they have appropriate code added to them. There are also very few people reading the comments to old entries. There really is no benefit to advertising your dodgy sites here. Please stop it.
Posted by Stuart on Thursday 01st Feb 2007 (11:24 UTC)
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Posted by ujwotefakta on Monday 19th Feb 2007 (08:06 UTC)
I have solved the problem of deflecting an asteroid,( in a nut shell,)" simply land a craft onto the asteroid, the craft having a computer and large retro jets, the nozzle blast and duration can be aimed by the computer and well there it is.
Camie Gionet, 03/07/07
Posted by Camie Gionet on Thursday 08th Mar 2007 (03:30 UTC)
Why can't an object in the Kuiper Belt that has achieved hydrostatic equilibrium be considered both a planet and a KBO? It would make much more sense to keep "planet" as a broad general category with multiple subcategories, one of which would be the ice dwarfs. I believe the IAU made a mistake with this decision. The process they used is also questionable, as only four percent of members voted; no Internet or absentee voting was allowed; and most of those who did vote are not planetary scientists. Also, the definition they created makes no linguistic sense in that it claims a "dwarf planet" is not a planet at all. Personally, I do not accept the IAU's definition and am reasonably confident it will be overturned.
Posted by Laurel Kornfeld on Tuesday 04th Sep 2007 (20:06 UTC)
Laurel, who are your comments directed to?
Posted by Stuart on Wednesday 05th Sep 2007 (08:11 UTC)
father of the pride Now lower the soldier barked drawing close. The.
Posted by fat on Friday 07th Sep 2007 (20:55 UTC)
muscular woman gallery All emotional guards down, but no one another.
Posted by gallery on Sunday 09th Sep 2007 (01:07 UTC)
why isnt pluto a planet please can you reply over the next theree days??
thanks
p.s. can you give me all the reoson that pluto isnt a planet!?
Posted by jake warner on Friday 28th Sep 2007 (16:44 UTC)
I like the instresting facts!
Posted by Rose on Wednesday 03rd Oct 2007 (23:53 UTC)
I like the instresting facts!
Posted by Rose on Wednesday 03rd Oct 2007 (23:53 UTC)
What year was Mercury found?
Posted by Sloan on Thursday 11th Oct 2007 (19:58 UTC)
What year was Mercury found?
Posted by Sloan on Thursday 11th Oct 2007 (19:58 UTC)
What year was Mercury found?
Posted by Sloan on Thursday 11th Oct 2007 (19:58 UTC)
I live in northern England.
Does anyone know the identity of a very bright star I see early in the morning.
It is in the east , if 90 degrees was directly above I would say it is at about 25 degree elevation.....not very high above the horizon.
I don`t know if it`s a star or a planet.
Thanks,
Mike
Posted by Michael Kershaw on Tuesday 30th Oct 2007 (15:39 UTC)
Mike, if you mean directly east at about 20 degrees you are looking at the star Arcturus which is in the constellation Bootes. However, it is more likely that you are actually looking towards the south-east as that is where the planet Venus is in the early morning. Venus is very bright at the moment.
Posted by Stuart on Tuesday 30th Oct 2007 (17:05 UTC)
Thanks Stuart,
Come to think of it,it is more south east so I guess it must be Venus.
Posted by Michael Kershaw on Wednesday 31st Oct 2007 (11:55 UTC)
Flying at 30,000 feet last night at midnight a bright object rose in the southeast. Close to the horizon it appeared to glisten green and red. It looked like a planet, but was off the lower left tip of orion, not close to where I could see mars. At first it was so bright we thought it was another aircraft. Any ideas?
Posted by liam mcguinness on Thursday 29th Nov 2007 (15:54 UTC)
Liam, if the three stars that make Orion's belt were roughly pointing at it, I think you were looking at Sirius. Sirius - the Dog Star - is the brightest star visible in the sky except for the Sun.
When stars are low down on the horizon the light from them has to pass through a lot of our atmosphere which causes it to twinkle wildly. The twinkling affects different colours differently, so Sirius (when low) can often appear to change colour just as you describe.
Posted by Stuart on Thursday 29th Nov 2007 (17:09 UTC)
Stuart,I have noticed another bright star in the morning sky and wondered if you could tell me what it is.
It is almost directly opposite to Venus (ie NW)but about twice as high and not as bright.I could be wrong but it seems to have an orangish or pinkish tint.
Posted by Michael Kershaw on Thursday 20th Dec 2007 (14:43 UTC)
Michael, that is probably planet Mars. You can see it over in the east after sunset and through the night it moves around through south and sets in the north west at around 8:40 am or so (as seen from the north of England). Just the other day Mars was at its closest approach to Earth of the year (the orbits are slightly elliptical) so it is looking quite large in a telescope and is a bit brighter.
By the way, it might be worth your while downloading Stellarium for your computer. It is an excellent (and free) planetarium program which will show you the view of the sky from where you live for any time of day. It points out stars and planets.
Posted by Stuart on Thursday 20th Dec 2007 (17:10 UTC)
Oops, here is the correct link to Stellarium.
Posted by Stuart on Thursday 20th Dec 2007 (17:11 UTC)
Thanks Stuart,
It definitely is Mars as you say.
Thanks a lot for the stellarium link it is brilliant..... perfect for my needs.
Posted by Michael Kershaw on Wednesday 02nd Jan 2008 (14:16 UTC)
Thanks Stuart,
It definitely is Mars as you say.
Thanks a lot for the stellarium link it is brilliant..... perfect for my needs.
Posted by Michael Kershaw on Wednesday 02nd Jan 2008 (14:17 UTC)
Thanks Stuart,
It definitely is Mars as you say.
Thanks a lot for the stellarium link it is brilliant..... perfect for my needs.
Posted by Michael Kershaw on Wednesday 02nd Jan 2008 (14:17 UTC)
Sorry about that triple posting.
Posted by Michael Kershaw on Wednesday 02nd Jan 2008 (14:19 UTC)
We are able to calculate the redshift/blueshift of galaxies, from this we can calculate their speed and in what direction they are moving. Surely from this, over a period of time, we can trace back predicted movements of a sample of galaxies, to see where they moved from, aka the centre of our universe. Possible?
Posted by Bowlzy on Thursday 13th Nov 2008 (09:39 UTC)
If you run everything backwards you find that all places (and hence galaxies) were in the same place at the beginning of time. So, in a sense, everywhere in the universe was at the centre. However the word 'centre' doesn't really make sense because we are talking about space itself.
Having said all that, you can do exactly what you said. We know that our local galaxy clusters (the scale of hundreds of millions of light years) are moving in the direction of the Great Attractor.
Posted by Stuart on Thursday 13th Nov 2008 (14:51 UTC)
I live in New Mexico and every night there is a very bright star or planet in the sky to the south east. It is very bright, doesn't twinkle, and hasn't moved much in the last month(today is January 12th). It seems to be all by itself because it is so bright. I am very courious what it is! Please e-mail the answer if you know. I think it is a planet and no one believes me.
Posted by Mark Lines on Tuesday 13th Jan 2009 (05:35 UTC)
E=mc²/2
2009 is the end of Einstein's space-jail of time and Fraud symbol E=mc² Joenahhas1958@yahoo.com
Time is not a structure like space to allow space-to time-back to space jumping claimed by Physicists regardless of what physicists have to say about it because Physics is a business and not necessarily science or scientific and like every business it comes with fraud and fraud is Einstein's space-time (x, y, z, it) continuum that led to fraud symbol E=mc² and yes I am saying that 109 years of Nobel prize winners physics and physicists are all wrong and space-time physics is based on scientific fraud. When "results" expected and "No" discovery, Physicists rigged Physics for grant money since the start of the industrial revolution. Physics today is at least 51 % fraud!
r ------------------>>Exp (ì w t) ---------->> S=r Exp (ì wt) Nahhas' Equation
Orbit-------->> Orbit light sensing------>> Visual Orbit; Exp = Exponential
Particle ---->> light sensing of moving objects------------ >> Wave
Newton--------->>light sensing---------->> Quantum
Quantum = Newton x Visual Effects
Quantum - Newton = Relativistic = Optical Illusions
E (Energy by definition) = mv²/2 = mc²/2; if v = c
m = mass; v= speed; c= light speed; w= angular velocity; t= time
S = r Exp (ì w t) = r [cos (wt) + ì sin (wt) Visual effects
P = visual velocity = change of visual location
P = d S/d t = v Exp (ì w t) + ì w r Exp (ì w t)
= (v + ì w r) Exp (ì w t) = v (1 + ì) Exp (ì w t) = visual speed; v = wr
E (visual energy= what you see in lab) = m p²/2; replace v by p in E = mv²/2
= m p²/2 = m v²/2 (1 + ì) ² Exp (2ì wt)
= mv²/2 (2ì) [cosine (2wt) + ì sine (2wt)
=ì mv² [1 - 2 sine² (wt) + 2 ì sine (wt) cosine (wt);v = speed; c = light speed
wt = Ã/2
E (visual) = ìmv² (1 - 2 + 0)
E (visual) = -ì mc² ââ°Â¡ mc² (absolute value;-ì = negative complex unit) If v = c
w t = Ã/4
E (visual) = imv² [1-1 +á»Ⱐ=-mc²; v = c
wt =-Ã/4+á»â°ln2/2; 2á»Ⱐwt=-á»â°Ã/2 - ln2
Exp (2i wt) = Exp [-á»â°Ã/2 Exp [ln(1/2)] = [-á»Ⱐ(1/2)]
E (visual) = imv² (-á»â°/2) =1/2mc² v = c
Conclusion: E = mc² is the visual Illusion of E = mc²/2 joenahhas1958@yahoo.com. All rights reserved.
PS: In case of E=mc² claims to be rest energy claims then
E=1/2m (m v + m' r) ² = (1/2m) (m' r) ²; v = 0
E = (1/2m) (mc) ²; m' r =mc
E=mc²/2
Posted by joe nahhas on Monday 26th Jan 2009 (14:12 UTC)
I'm sure you are convinced by your theories. If you want to convince others, please publish them somewhere more appropriate such as a peer reviewed journal. If you have read around the subject, addressed counter-arguments, agree with the existing data and predict some future observation, people will take it seriously.
Posted by Stuart on Wednesday 28th Jan 2009 (17:50 UTC)
Thaks for more information about planets.
Posted by jeff(techastronomy.com) on Thursday 29th Jan 2009 (10:19 UTC)
You should still be able to post comments but please don't let them look like spam otherwise they'll get automatically blocked.
Posted by Stuart on Friday 30th Jan 2009 (10:04 UTC)
Hi
Please can someone answer this question - When we look up and see the Milky Way, are we looking at one of the spiral arms of our Galaxy?
Posted by Rebecca on Monday 21st Mar 2011 (08:58 UTC)
What with the increasing harsh solar flare bursts and greater frequency on the sun, are we looking at a sun breaking down and in the near future are we likely to see a second big band?
Posted by William G Ireland on Tuesday 24th Jul 2012 (10:50 UTC)