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# Size comparisons-planets

What is a real world comparison, size wise, between Neptune and Earth? I get that Neptune is bigger and all that, but HOW much bigger?

If earth is a ping pong ball then Neptune is what? A basketball? a beach ball? what are the size differences?

I've been playing D&D for almost a year now (not that long I know). The friends I game with told me that they're going to start teaching me how to DM. I'm trying to create my own world and want it to be the size of Neptune. Now i just need a real world something I can manipulate so I can figure out land masses and all that.

Or would it just be easier to go buy a cheap beach ball and call it good?

Asked by Rosehawk at 2:18 PM on May. 28, 2013 in Hobbies & Crafts

Level 40 (116,569 Credits)
• Good picture and comparison at enchanted learning website

http://www.enchantedlearning.com/subjects/astronomy/planets/neptune/

•  Earth and Neptune, So if Eath is a Ping Pong Ball, then Neptune would be a Basketbll

Answer by cassie_kellison at 2:23 PM on May. 28, 2013

• 4 Earths fit inside Neptune

Answer by okmanders at 2:24 PM on May. 28, 2013

• My stepson recently did an activity in his astronomy class using various balls to show the size of the different planets, and he used a ping-pong ball for Earth and a baseball for Neptune. I can't vouch for its scientific accuracy, but he got an A on the project.

• Neptune fits 60 earths inside of it.
Earth's diameter is 12,756km
Neptune's diameter is 49,528km
a ping pong ball is .00004km (or 4cm) in diameter
so setting up a relative equation

12,756km ............ 0.00004km
----------------- = ----------------------
49,528km ........ diameter equiv for neptune

49,528km x .00004km / 12,756km = .0001553km OR 15.53cm

there are 2.54cm in 1 inch

so 15.53cm / 2.54 cm per in = 6.11 inch diameter for a size equivalent Neptune compared to a ping-pong Earth

a child's size 3 soccer ball has about 23-24" circumference
circumference = pie x diameter SO diameter = circum / pie OR 23" / 3.14 = 7.3" which is about the closest I can think of to a 6" ball

a 6" diameter ball would have a circumference of 3.14 x 6" = 18.84" circumference

How's that for a bunch of math!

Answer by daylily888 at 2:46 PM on May. 28, 2013

• okmander's logic is on a 2 dimensional plane - on flat paper, Neptune is 4 x as big around as Earth, but in 3 dimensional logic (which is the accurate one here since these objects exist in 3 dimensions) you must consider VOLUME, not just circumference.

volume = 4/3 x pie x radius cubed

circumference = pie x diameter OR pie x 2 x radius

EARTH
radius = circum / (2 x pie)
R = 12,756km / (2 x 3.14)
R = 2031.12km
Volume = 4/3 x 3.14 x (2031.12 x 2031.12 x 2031.12)
Volume of Earth = 35,081,255,886 km3

NEPTUNE
radius = circum / (2 x pie)
R = 49,528km / (2 x 3.14)
R = 7886.62 km
Volume = 4/3 x 3.14 x (7886.62 x 7886.62 x 7886.62)
Volume of Neptune = 2,053,719,524,907 km3

How many earth's fit inside neptune?
Volume of Neptune / Volume of Earth
2,053,719,524,907 / 35,081,255,886 =
58.6 earths fit inside neptune to be almost exact!

Answer by daylily888 at 3:02 PM on May. 28, 2013

• daylily, after reading your answers about 500 times I can follow the math! (YAY!) That's saying a lot, I NEVER could figure this stuff out in high school.

Now my next question: What's the ratio of a beach ball to the actual size of Neptune?

I guess, in the long run it doesn't really matter, but if I'm going to create a world for D&D I want to be as accurate and consistent as possible.

Comment by Rosehawk (original poster) at 5:16 PM on May. 28, 2013

• what size is your beach ball? if you own it, blow it up and measure the circumference (the distance around the "equator" or the biggest/fattest middle part)

Answer by daylily888 at 1:43 PM on May. 29, 2013

• Don't have one yet. Mind if I pick your brain in a PM at some future date? I am mathematically dyslexic, so doing calculations on my own, I'm liable to get 2 + 2 = soup or something like that.

Comment by Rosehawk (original poster) at 2:20 PM on May. 29, 2013

• lol... PM me anytime. If you don't hear back from me within the day, that means I'm out camping or hiking or doing something adventurous!

Answer by daylily888 at 11:46 AM on May. 30, 2013

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