Astronomy questions from sixth graders, part 3

By Phil Plait | May 21, 2008 8:41 am

Note: There is a special note to teachers at the bottom of this post. If you’re a teacher, please be sure to check it out!

My friend Tina is a teacher at the Saegert Sixth Grade Center in Austin, Texas. She asked her sixth grade students to send me questions they had about astronomy, and I answer them on camera. There were so many I had to split this into five parts! I’ll be posting one part every day, first thing in the morning. To catch you up, check out Part 1 and Part 2. Below is Part 3.

The questions asked in Part 3 are:

1) How do planets form?

2) Does Mars have polar ice caps?

3) What’s a meteoroid?

4) How do we measure temperatures on distant planets?

5) How large is the asteroid belt?

6) What happened to "Planet X"?

7) Can the Earth blow up?

SPECIAL NOTE TO TEACHERS: Many schools block access to YouTube. There is another video hosting platform called TeacherTube, which is designed to be used in schools. I’ve uploaded this video (Part 3) to my channel there, where you can access it in your school (note: the video is in higher-resolution on YouTube). If you do, please let me know! I’d love to know what the students thought of the video — warts and all.

CATEGORIZED UNDER: Astronomy, Science, Video Blog

Comments (26)

  1. fos

    Thank you for the TeacherTube access! I intend to use your videos during the Earth / Space Science sections next year.


  2. jrkeller


    You are wrong about the Earth exploding. If you go to this website,

    you’ll see that it can happen (add a lot of sarcasm here)

    Actually, I’ve had a small running feud with Thomas Chalko, the author on the exploding Earth article, on this topic. Even though he has a Ph.D., he doesn’t know how to solve a differential equation.

  3. Eric

    Just wondering, who picks the names for planets? And why are planets named after greek mythology figures? Great videos btw.

  4. Brent

    Would you consider uploading individual segments as well as the set of questions? This could allow teachers to mix and match your fantastic Q&A’s

  5. Todd W.

    Wait. They put dry ice in ice cream cakes? No wonder I get brain freeze! :-)

  6. overstroming

    The ability to destroy a planet is insignificant next to the power of the force!
    I find your lack of faith disturbing.

  7. Eric

    Just wondering, who picks the names for planets? And why are planets named after greek mythology figures? Great videos btw.

    The International Astronomical Union has the final authority to pick names. (By weight of the fact that pretty much all astronomers will follow their conventions, and they care more than anyone else.)

    The major planets are all named for Roman gods, except Uranus which is Greek for some reason. (And Earth, whose name varies with language for obvious reasons.)

    For moons of planets, there are pre-defined schemes for names you can use. Similar rules hold for KBOs and features on bodies. Comets are named for their discover(s) and asteroids… well, that’s been sort of sub-contracted out. They’re named after pretty much anyone who knows people. When it comes to picking the actual names, usually the discover(s) get to put forward a name (which much follow the rules) and the IAU committee on nomenclature can either accept or deny the suggestion. In my experience, they generally accept it.

  8. To destroy the Earth, use your imagination with the parameters here: 😉

    You can have an idea of how much energy do you need to blow it up by playing a bit. But be careful, it can be addictive (based on my experience).

    Great video, Phil. Looking forward to the next ones. You’re very good explaining things in an easy to understand, but rigurous way.

  9. @John Weiss: “The major planets are all named for Roman gods, except Uranus which is Greek for some reason.”

    They couldn’t think of any puerile jokes about, “Caelus”?

  10. Mark Martin

    John Weiss said:

    “The International Astronomical Union has the final authority to pick names.”

    More correctly, the IAU is allowed to arbitrate such things by the prevailing community of astronomers, who then accept it for the purpose of standardizing nomenclature and getting on with more important things. The IAU has no more real authority in such things than do English language scholars to dictate grammar to hillbillies. It’s all a matter of convention (often very useful convention). Anyone can attach any words to any objects at will.

  11. Maugrim

    Marvellous videos, Phil – I’m really enjoying them.

    One slightly cheeky request – when you’re using hand gestures to make your point, would it be possible to do them slightly off to one side so they don’t cover your face? I’m deaf so I’m pretty much relying on lip reading to follow what you’re saying.

    I realise I’m not your target audience but hey, not obstructing the view of your face is good practice for TV anyway :)

  12. I’ve never gotten an ice cream cake before – is that how they do it, huh?

  13. Annoyed

    A huge thank you, Phil, for the CORRECT pronunciation of Uranus.

  14. Reverend J

    250 million km = 150 miles?

    Me thinks some astronomer need to learn more conversions :)

    (j/k know you meant 150 million miles, but I can still poke fun at you)

  15. Jorde

    Wasn’t there a story a few months ago about the possibility of a planet x? It was about how there is a massive dropoff in the kupier belt at some point. Has this been discredited, or under serious consideration?

  16. Mark Martin

    There are several statistical gaps in the Kuiper Belt which are traced to resonances with Neptune. There’s a rather sharp decline in density after a certain distance. It could be the absolute edge of the belt, or there’s some speculation that it represents a resonance with another body with mass close to that of Earth.

  17. Buzz Parsec

    I for one welcome our new planet-destroying overlords.

    The names of Mercury, Venus, Earth, Mars, Jupiter and Saturn date from antiquity. I don’t think the IAU existed when Uranus (aka George’s Star) and Neptune were discovered and named. More a matter of informal consensus among astronomer’s. English astronomers might be happy to name a planet after George III, but I don’t think the French were too keen on the idea. The Germans were probably down with it, though.

  18. Mark Hansen

    Wasn’t Planet X destroyed by Duck Dodgers and Marvin the Martian in the 24th and a half century? Or should that be, will be destroyed?

  19. wright

    This is such a magnificent series, Phil. It’s great to see some respondents planning to use these mini-lectures as supplements to their teaching.

    Given that there’s so much misinformation online, material like this is all the more vital. Yeah, you messed up on Titan’s atmosphere, but you owned up to it, as you have your other mistakes. That’s more than a lot of folks who make mistakes are willing to do, especially online.

  20. Sili

    I really liked the explanation of the real Planet X (or should that be IX now?). I didnt’ quite know/remember that.

    Silly little complaint – I know you’re excited and stuff, but could you perhaps consider cutting back on the “actually”s a bit?

  21. StevoR

    The Bad Astronomer I’m sure its great but on dial-up with a really slow old computer and no sound … Well all I can do is aks for a transcript please. I’m surely not the only one who can’t get U-tube, etc ..

    Any chance of that, please?

    Anyway it sounds like fun – & regulars here will know I need to try & practice brevity – so I’ve decided to have a go myself :


    The questions asked in Part 3 are:

    1) How do planets form?

    Me : Over a very long time & with great difficulty but a little like how the (liquid metal T-1000) terminator re-forms in terminator II … Or how a snowball forms or a really huge ball of bluetack or .. (But hey I’m trying to be brief so no more ..) 😉

    2) Does Mars have polar ice caps?

    me : Yes. 😉

    3) What’s a meteoroid?

    me : A “shooting star” before it becomes a shooting star – that is a meteor -not Isaac Asimov’s ‘Shooting Star which was ‘Lucky Starr’s’ spaceship & .. Uh-oh, here we go again ! 😉

    4) How do we measure temperatures on distant planets?

    me : Very, very lo-oong thermometors! 😉

    (Okay, sorry no, I think its RADAR or spectroscopy of materials followed by thermal calculations or summin’ so just listen to the Bad Astronomer on this one folks! 😉 )

    5) How large is the asteroid belt?

    me : Depends how you count it .. Very to staggeringly to unbeleiveable to well.. from just outside Mars to just inside Jupiter’s orbits. I think.

    6) What happened to “Planet X”?

    It made the astronomical cricket XI as a superb spin bowler! 😉

    (Hmm… The Yanks’ll have no idea on that one – but the Brits and my fellow Aussies will know exactly what I mean! 😉 )

    Actually ‘Planet X’ or planet 10 is the ‘ice dwarf’ class planet Eris formerly nicknamed “Xena” and comes right after the ninth planet : Pluto!

    & the IAU and other anti-American, orbitally-mechanically-blinded chumps can take a lo-oong walk off a short pier! Pluto is too a planet! 😉

    7) Can the Earth blow up?

    me : Just wait until they turn the Large Hadron super-Collider atom-smasher & (Higgs Boson & Earth smasher too?) on & then we’ll find out … ! :-O :-(

    So where are questions 8 , 9 & 10 this time???


    Yes, I know, I’m not giving up my day job .. But if anyone did find this mildly amusing then I’ve also commented on the other sets of questions linked here too if anyone wants to read & hopefully enjoy those too .. 😉

    Just in case there’s a smart arr … donkey .. answer shortage! 😉

  22. StevoR

    Oh well only a slight italics stuff-up this time .. :-(

    IRONMANAustralia on 21 May 2008 at 11:14 am @John Weiss:

    “The major planets are all named for Roman gods, except Uranus which is Greek for some reason.”

    They couldn’t think of any puerile jokes about, “Caelus”?

    Actually, the proper spelling & pronunciation of that Greek God is Ouranos – “Oo- RAh-Noss” – which should be adopted now to
    end all those asinine bits of humour. 8)

    Well, its better than re-naming it Urectum as suggested in Futurama! 😉

  23. I have watched all 4 installments so far, and my only quibble is with your answer to “How do we measure temperatures on distant planets?” – you say that light can split into colours, and that we can learn a lot from that, but the explanation sounds almost magical or at least certainly not tangible. It wouldn’t have cost much time to add that the composition of colours is because different atoms emit different colours, and then punt on the rest of the explanation, just to give the kids a feel that there is a clear and tangible connection and that the process for deriving all this information from light is not at all mysterious.

    This is my only criticism in terms of didactic value; you handled all the other questions beautifully, and the series would certainly be plenty educational not just for kids, but for many an adult as well. Keep it up. :-)


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