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0681: "Gravity Wells"

Posted: Mon Dec 28, 2009 6:21 am UTC
by Quicksilver
Image
alt text: "This doesn't take into account the energy imparted by orbital motion (or gravity assists or the Oberth effect), all of which can make it easier to reach outer planets."
http://xkcd.com/681_large/ credit to EcoReck20 for this.

Re: "Gravity Wells" Discussion

Posted: Mon Dec 28, 2009 6:25 am UTC
by MDark.Math
Wow, now he's just showing off

Re: "Gravity Wells" Discussion

Posted: Mon Dec 28, 2009 6:26 am UTC
by jspenguin
"A thrown baseball could escape Phobos"
"You could escape Deimos with a bike and a ramp"

And yet, in the original Doom, set on Phobos and Deimos, you couldn't jump out of a 4-foot pit. That BFG must be incredibly massive.

Re: "Gravity Wells" Discussion

Posted: Mon Dec 28, 2009 6:27 am UTC
by Blaze Krakaros
I don't see the burning cheese in this comic.

Re: "Gravity Wells" Discussion

Posted: Mon Dec 28, 2009 6:27 am UTC
by EcoReck20
MDark.Math wrote:Wow, now he's just showing off


You seem to have something against these large posters. :(

Re: "Gravity Wells" Discussion

Posted: Mon Dec 28, 2009 6:28 am UTC
by OneGyT
Wait, I'm confused. In uber-simple terms, is this basically displaying the amount of gravity necessary to escape orbit, adjusted for our smallminded earth-centric thinking?

Re: "Gravity Wells" Discussion

Posted: Mon Dec 28, 2009 6:30 am UTC
by IronyandParadox
There's...there's no Pluto. =(

Now, I know Pluto doesn't meet all the criteria for being a planet (clearing the neighborhood of its orbit? Ehhh...) and I know that classifying it as a dwarf planet makes things much neater and it satisfies my secret OCD side, but something about seeing this comic without it made a little part of me die inside.

On another note, I would *love* to have this as a poster.

Re: "Gravity Wells" Discussion

Posted: Mon Dec 28, 2009 6:31 am UTC
by EcoReck20
Why are the moons in the chart, but not Pluto? It seems pretty much everyone forgot about it and now its crying in loneliness. SHAME ON ALL OF YOU.

Re: "Gravity Wells" Discussion

Posted: Mon Dec 28, 2009 6:32 am UTC
by Quicksilver
Also, Randall, get out of my head! I was just looking for your mom in past comics, and all of a sudden, there's a new "your mom" joke!

Re: "Gravity Wells" Discussion

Posted: Mon Dec 28, 2009 6:33 am UTC
by Josephine
Randall seems to have seen the Sagan remix videos.(look at neptune guy)

Re: "Gravity Wells" Discussion

Posted: Mon Dec 28, 2009 6:35 am UTC
by Pit
This comic made me so glad that I took Astronomy 101. I wish he had put Ceres and Eris though... it would have been a good excuse to stick Pluto in.

Re: "Gravity Wells" Discussion

Posted: Mon Dec 28, 2009 6:36 am UTC
by Siguy
I feel like it would be possible to fit more jokes into this. I mean, there could be a lot more detail like in the other big comics (electromagnetic spectrum, etc). This was kind of bland. The well diagram is pretty interesting, though.

Also, not only is Pluto left out, Callisto is as well (we have Europa, Ganymede, and Io but not Callisto?)

Re: "Gravity Wells" Discussion

Posted: Mon Dec 28, 2009 6:38 am UTC
by HonoreDB
Should be "still more glorious dawn."

Re: "Gravity Wells" Discussion

Posted: Mon Dec 28, 2009 6:39 am UTC
by TheNextCaesar
HonoreDB wrote:Should be "A still more glorious dawn."

Sorry, it's the OCD in me.

Re: "Gravity Wells" Discussion

Posted: Mon Dec 28, 2009 6:40 am UTC
by wallacoloo
I forgot this forum supported smileys (don't worry, I edited them out!)

That was a bit of a disappointment. But Randall was probably in a hurry to not be even more late. The funniest part of this one was the your mom joke. No real punchline =(

But it's still better than I could do =D

Re: "Gravity Wells" Discussion

Posted: Mon Dec 28, 2009 6:40 am UTC
by khaighle
Came for the "STILL more glorious dawn."

Left without being disappointed.

Re: "Gravity Wells" Discussion

Posted: Mon Dec 28, 2009 6:42 am UTC
by Pit
Siguy wrote:I feel like it would be possible to fit more jokes into this. I mean, there could be a lot more detail like in the other big comics (electromagnetic spectrum, etc). This was kind of bland. The well diagram is pretty interesting, though.


@.@ I would have liked to have seen a nuclear fusion joke.

Re: "Gravity Wells" Discussion

Posted: Mon Dec 28, 2009 6:44 am UTC
by Omegaton
Well, looks like I'm off to Wikipedia to read about gravity wells!

Re: "Gravity Wells" Discussion

Posted: Mon Dec 28, 2009 6:45 am UTC
by ananab
Pluto? Where are you? :'(

Re: "Gravity Wells" Discussion

Posted: Mon Dec 28, 2009 6:46 am UTC
by Actaeus
I'm confused -- if the height difference between Earth and the plateau next to it represents energy needed to escape its gravity well, what does the steep slope just past the Moon mean? Each planet has its own local dimple, but there are also differences in height between the crests between planets.

Once you've escaped Earth's gravity, aren't you as 'free' as if you escaped Jupiter's? Is it because of distance from the Sun?


EDIT: Wait, I understand! It's because of the Sun; the jump between the Moon and Mars represents the potential energy difference because of the farther distance from the Sun. In effect, the whole thing is part of the Sun's own gravity well, just as Jupiter's satellites are partway down its well.

Re: "Gravity Wells" Discussion

Posted: Mon Dec 28, 2009 6:46 am UTC
by morticae
At first I thought he missed a golden opportunity for a Pluto joke... then I realized that's the joke. We all know it. He knows we all know it. And he knows how craaaaaazy it makes us!

Re: "Gravity Wells" Discussion

Posted: Mon Dec 28, 2009 6:47 am UTC
by firestar27
Very interesting, but not very funny, and it was the just the idea of the drawing that was interesting, even though a lot more interesting ideas could have been put in. In summary: great idea, but not so great an execution. I hope he expands on this later. (Even editing this quietly later would be appreciated.)
And I miss Pluto. If you can have various moons, then you can have Pluto!

Re: "Gravity Wells" Discussion

Posted: Mon Dec 28, 2009 6:48 am UTC
by eMan2718281828
I feel like there was some writer's block going on and someone just decided to make a very elaborate "your mom" joke...

Re: "Gravity Wells" Discussion

Posted: Mon Dec 28, 2009 6:52 am UTC
by sje46
The things making noise on Titan...is that a Vonnegut reference?

Re: "Gravity Wells" Discussion

Posted: Mon Dec 28, 2009 6:53 am UTC
by arcticfox.sq
I don't know, I kind of liked this, because it wasn't really funny, not despite of it.

Re: "Gravity Wells" Discussion

Posted: Mon Dec 28, 2009 6:56 am UTC
by Actaeus
I love this type of comic -- very Tuftesque, as he mentioned with the LotR character map.

But I feel he could really have included more jokes or factoids. This is neat, but it doesn't live up to Height or Depth or (best of all) the Online Communities map.

[sips wine] It is a fine vintage, but not the most aromatic of its vineyard. Disappointing to the discerning tongue.

Re: "Gravity Wells" Discussion

Posted: Mon Dec 28, 2009 7:03 am UTC
by bakert
I much preferred the comic to this thread.

Re: "Gravity Wells" Discussion

Posted: Mon Dec 28, 2009 7:03 am UTC
by psychosomaticism
The autotuned Sagan music video reference was much appreciated.

Also, to some of the previous posters: why does it have to be funny. It's interesting and has a few silly things thrown in for good measure.

Re: "Gravity Wells" Discussion

Posted: Mon Dec 28, 2009 7:08 am UTC
by CorruptUser
So... how much force do I need to escape your mom?

Re: "Gravity Wells" Discussion

Posted: Mon Dec 28, 2009 7:12 am UTC
by Arancaytar
"Hey, you there on Neptune. Is... is that you Carl?"

Also, this shows what a bitch it would be to try to land on Mercury without landing on the sun instead. Decelerate just a tiny bit too slowly, or miss Mercury in its orbit by a hair, and it's over.

Re: "Gravity Wells" Discussion

Posted: Mon Dec 28, 2009 7:15 am UTC
by SolkaTruesilver
CorruptUser wrote:So... how much force do I need to escape your mom?


The jokeyard called.

They want their joke back.

Re: "Gravity Wells" Discussion

Posted: Mon Dec 28, 2009 7:19 am UTC
by freespace
Earth's gravity well depth has 3 different figures: 5478, 6000, 6379km. The last one should be the correct one.

(Incidentally it is equal to the radius of the Earth used in the calculation).

Re: "Gravity Wells" Discussion

Posted: Mon Dec 28, 2009 7:20 am UTC
by phillipsjk
jspenguin wrote:"A thrown baseball could escape Phobos"
"You could escape Deimos with a bike and a ramp"

And yet, in the original Doom, set on Phobos and Deimos, you couldn't jump out of a 4-foot pit. That BFG must be incredibly massive.


Well, the DOOM (and later Quake) guy also carries heavy armor, 100 shotgun shell, 200 bullets/nails, 200 cells, and 99 Rockets, Brass knuckles/axe, Single-barreled shotgun, Double-barreled shothgun, pistol/nailgun, chaingun/supernailgun, rocket launcher, lightning gun/BFG. If you assume each gun weighs 5kg, that adds up to 35kg. The ammo probably doubles that to 70kg. Since you don't want to carry more than about 30% of your weight on your back, DOOM/Quake guy must have a mass of about 233kg, or a(n earth) weight of over 500 pounds (mainly muscle)


I mainly wanted to point out that Earth's planetary status was revoked the same time Pluto's was by the IAU. Since the IAU is only concerned with "Celestial bodies," the planetary definition begins "A Celestial body that: . . ."

That said, Earth is not out of place in the chart because several moons are represented as well as a couple planetoids.

Re: "Gravity Wells" Discussion

Posted: Mon Dec 28, 2009 7:22 am UTC
by Vagrant
In the comic, Carl is saying "an even more glorious dawn awaits."

The actual quote is "a still more glorious dawn awaits."

http://public.youtranscript.com/zs/664.html
http://www.youtube.com/watch?v=zSgiXGELjbc
http://www.youtube.com/watch?v=qEXGyyoh_og#t=04m56s
Cosmos episode 9, "The Lives of Stars"

Re: "Gravity Wells" Discussion

Posted: Mon Dec 28, 2009 7:23 am UTC
by Ferahgo
sje46 wrote:The things making noise on Titan...is that a Vonnegut reference?


That was my thought also. If it is, then well done, as that's one of my favorite books ever.

Re: "Gravity Wells" Discussion

Posted: Mon Dec 28, 2009 7:25 am UTC
by KTC
I want Pluto!! :cry:

Re: "Gravity Wells" Discussion

Posted: Mon Dec 28, 2009 7:28 am UTC
by Nereid
phillipsjk wrote:I mainly wanted to point out that Earth's planetary status was revoked the same time Pluto's was by the IAU. Since the IAU is only concerned with "Celestial bodies," the planetary definition begins "A Celestial body that: . . ."

That said, Earth is not out of place in the chart because several moons are represented as well as a couple planetoids.


Earth is a celestial body, but not an astronomical body. http://en.wikipedia.org/wiki/Astronomical_object

Re: "Gravity Wells" Discussion

Posted: Mon Dec 28, 2009 7:30 am UTC
by skeptical scientist
For those who were disappointed, like me, that the Jupiter/Sun numbers were not listed, and all those complaining about Pluto:
  1. Jupiter: 181,000 kilometers
  2. Sun: 19,500,000 kilometers
  3. Pluto: 75 kilometers
Pluto is about one quarter as deep as the moon, or too shallow for its depth to really be visible without its own cutout.

Google makes calculating these things extremely easy.

Re: "Gravity Wells" Discussion

Posted: Mon Dec 28, 2009 7:30 am UTC
by chocolate.razorblades
I would love to have Randall as a physics teacher.

Re: "Gravity Wells" Discussion

Posted: Mon Dec 28, 2009 7:34 am UTC
by Arvedui
Wonderful, but more would have been nice. Too quick of a comic. But wonderfully interesting nonetheless!