File:Galilean moon Laplace resonance animation.gif

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Galilean_moon_Laplace_resonance_animation.gif （365 × 245 像素，檔案大小：351 KB，MIME 類型：image/gif、循環、288 畫格、5.8秒）

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摘要

描述	English: Animation of the 1:2:4 Laplace resonance between Io, Europa, and Ganymede. The labels indicate the ratios of orbital periods: Europa's is twice Io's, and Ganymede's is four times Io's. Warning: do not downsize the image below its original size of 365 × 245 when used in a Wikipedia article, as the animation won't move then (at least not for all users).
日期	2011年2月16日, 18:10 (UTC)
來源	based on earlier version of this file, avail. below
作者	User:Matma Rex
授權許可 (重用此檔案)	Public Domain
其他版本	Deutsch Latin English .SVG Français .SVG Edited version with conjunctions highlighted by color changes

授權條款

我，此作品的版權所有人，釋出此作品至公共領域。此授權條款在全世界均適用。
這可能在某些國家不合法，如果是的話：
我授予任何人有權利使用此作品於任何用途，除受法律約束外，不受任何限制。

Generation

This image has been generated by the following Ruby code and optimized in GIMP.

# author: Matma Rex
# code licensed under CC-BY-SA license

require 'rubygems'
require 'RMagick'
include Magick



step=5 # degrees by which Io will move in every frame


# Io, Europa, Ganymede
distances=[46, 72, 112]
speeds=[1, 0.5, 0.25]
shifts=[-90, 90, -90]

centerx=122
centery=122



list=ImageList.new

base=Image.new 365,245
base.ticks_per_second=1000
base.delay=5*step


gc=Draw.new

# lines
gc.stroke 'lightgrey'
gc.stroke_width 1.5
distances.each{|d| gc.line centerx, centery-d, 360, centery-d}
gc.line centerx, centery, 360, centery

# orbits
gc.stroke 'grey'
gc.fill 'none'
gc.stroke_width 2
distances.each{|d| gc.circle centerx, centery, centerx, centery+d}

# Jupiter
gc.stroke 'black'
gc.fill 'black'
gc.stroke_width 2
gc.circle  centerx, centery, centerx, centery+9

# labels
# gc.stroke_width 0
# gc.gravity EastGravity
# gc.font_family 'arial'
# gc.font_size 18
# gc.font_weight LighterWeight
# gc.text_align RightAlign
# gc.text_undercolor 'white'

# gc.text 360, centery-distances[0]+7, '"  Io 1:1"'.upcase
# gc.text 360, centery-distances[1]+7, '"  Europa 2:1"'.upcase
# gc.text 360, centery-distances[2]+7, '"  Ganymede 4:1"'.upcase

# gc.font_weight BoldWeight
# gc.text 360, centery+7, '"  Jupiter"'.upcase


gc.draw base

# ImageMagick sucks at text - load a predefined text img instead
base=base.composite Image.read('text.png')[0].transparent('cyan'), 0, 0, OverCompositeOp



(0..(4*360-1)).step(step) do |deg|
  img=base.clone
  gc=Draw.new

  0.upto(2) do |i|
    rad=(deg*speeds[i] + shifts[i]) * Math::PI / 180.0
  
    x=distances[i] * -Math.cos(rad)
    y=distances[i] * Math.sin(rad)

    gc.circle centerx+x, centery+y,  centerx+x, centery+y+4.5
  end

  gc.draw img
  
  list << img
end

list.write 'magick.gif'

檔案歷史

點選日期/時間以檢視該時間的檔案版本。

	日期/時間	尺寸	使用者	備⁠註
目前	2011年2月16日 (三) 18:08	365 × 245（351 KB）	Matma Rex	a much nicer version, even if somewhat larger
	2010年12月23日 (四) 18:33	365 × 245（21 KB）	Bark~commonswiki	Changed direction from clockwise to counter-clockwise to better represent the Jovian system with the view from above the north pole, the typical convention. The previous version accidentally implied retrograde motion in the system, which is not the case.
	2006年11月3日 (五) 08:17	365 × 245（32 KB）	Splarka	{{Information \|Description=Animation of the 4:2:1 Laplace resonance between Ganymede, Europa, and Io \|Source=created for Wikimedia \|Date=~~~~~ \|Author=User:Splarka \|Permission=Public Domain \|other_versions=This is the first }}