This thought came to me concerning the Star Wars universe.  On our planet (Earth) we have many different habitats (snowy wastelands, forests, cities); but in the Star Wars universe there only appears to be be one kind of environment per planet, e.g: Hoth is snowy, Endor is all forest and Coruscant is city.  Why is this?
The Earth in all of its varieties has wide ranging climates. At the top level it has tropical, dry, temperate, continental, and polar climates. And yet often the planets depicted in science fiction are often single climate planets.    The forest moon of Endor The desert planet of Dune The desert planet of Tatooine The desert planet of Vulcan The outer planets in Firefly all appeared to be mostly desert (supiciously like Calfornia desert).  The inner planets in Firefly were all temperate or tropical.  The icy Breen homeworld The icy Andorian homeworld The icy Frost Giant planet   I'm not suggesting there are no Earth-like planets in science fiction, but it feels like it is less common than it should be. Considering the only planet we have as an example is our own, it seems like planets should be just as varied in the cosmos.
Is there any rule for differentiating between the endings "th" and "ht"? Some words end in th (length, width), and others end in ht (height, fight, tonight, caught).    I sometimes have difficulties in spelling such words because I don't know which ending to choose. Is there any rule or pattern (even localized) in choosing one or the other? Subject-Verb Agreement 50 hertz sine wave in oscilloscope when I touch it I bought a new PicoScope USB oscilloscope and noticed that when I touch the tip of the probe with my hand I see a 50&nbsp;Hz signal of 2 volts on the screen. What is causing this? (Or rather, how is the mains 50 Hz sine wave getting through me to the scope?) A better answer was posted long after accepting another. Should I accept the new one? Why am I asked for a credit card number to download a free app? I  want to download free app in my iPod touch device and i have the following doubts.  Kindly resolve me doubts.   when i try to download it asks my credit card security number. since i am trying to download free app , why do i need to provide my credit card security code? Will i be debited for downloading the free app from app store?   I cant able to find any information regarding this on apple.  Please provide me some references about this from apple and please resolve my doubts.  Thanks a lot. I've always wondered why the number of protons in the Universe exactly matches the number of electrons. They are such different particles with totally different cross sections. So, first of all, is this true? And, secondly, how could it be that they have been produced in the same amount after the Big-Bang? Lorentz Invariant Integration Measure "In" and "on": How can I decide which one to use for vehicles? Examples:   In a car, van, etc. On a bus, boat, motorcycle, etc.   How can one decide which preposition to use? Is memorization the only way or is there a better way?  Note: People generally explain this by either distinguishing between open and closed vehicles or between large and small vehicles. However, the examples I've given defeat both explanations. MacTEX-2014, TeXShop 3.36.1 on Mac OS 10.9.5 -- when using hyperref I do not see the colored border that should appear around the hyperlinks in the pdf.  for example, when compiled with pdflatex, the code below should produce a pdf with a green border around the link on the right of "abc", but it does not. Any idea how to check where the problem is?  \documentclass{article} \usepackage{hyperref} \hypersetup{colorlinks=false,pdfborder=0 0 1,citebordercolor={0 1 0}} \begin{document}  abc \cite{123}  \begin{thebibliography}{99} \bibitem{123} efg \end{thebibliography} \end{document}    this is the list of files from the generated .log     File List   article.cls    2007/10/19 v1.4h Standard LaTeX document class   size10.clo    2007/10/19 v1.4h Standard LaTeX file (size option)   hyperref.sty    2012/11/06 v6.83m Hypertext links for LaTeX   hobsub-hyperref.sty    2012/05/28 v1.13 Bundle oberdiek, subset hyperref (HO)   hobsub-generic.sty    2012/05/28 v1.13 Bundle oberdiek, subset generic (HO)     hobsub.sty    2012/05/28 v1.13 Construct package bundles (HO)   infwarerr.sty    2010/04/08 v1.3 Providing info/warning/error messages (HO)    ltxcmds.sty    2011/11/09 v1.22 LaTeX kernel commands for general use (HO)   ifluatex.sty    2010/03/01 v1.3 Provides the ifluatex switch (HO)     ifvtex.sty    2010/03/01 v1.5 Detect VTeX and its facilities (HO)    intcalc.sty    2007/09/27 v1.1 Expandable calculations with integers (HO)      ifpdf.sty    2011/01/30 v2.3 Provides the ifpdf switch (HO)   etexcmds.sty    2011/02/16 v1.5 Avoid name clashes with e-TeX commands (HO)   kvsetkeys.sty    2012/04/25 v1.16 Key value parser (HO)   kvdefinekeys.sty    2011/04/07 v1.3 Define keys (HO)   pdftexcmds.sty    2011/11/29 v0.20 Utility functions of pdfTeX for LuaTeX (HO)   pdfescape.sty    2011/11/25 v1.13 Implements pdfTeX's escape features (HO)   bigintcalc.sty    2012/04/08 v1.3 Expandable calculations on big integers (HO)     bitset.sty    2011/01/30 v1.1 Handle bit-vector datatype (HO)   uniquecounter.sty    2011/01/30 v1.2 Provide unlimited unique counter (HO)   letltxmacro.sty    2010/09/02 v1.4 Let assignment for LaTeX macros (HO)    hopatch.sty    2012/05/28 v1.2 Wrapper for package hooks (HO)   xcolor-patch.sty    2011/01/30 xcolor patch   atveryend.sty    2011/06/30 v1.8 Hooks at the very end of document (HO)   atbegshi.sty    2011/10/05 v1.16 At begin shipout hook (HO)   refcount.sty    2011/10/16 v3.4 Data extraction from label references (HO)    hycolor.sty    2011/01/30 v1.7 Color options for hyperref/bookmark (HO)     keyval.sty    2014/05/08 v1.15 key=value parser (DPC)    ifxetex.sty    2010/09/12 v0.6 Provides ifxetex conditional    auxhook.sty    2011/03/04 v1.3 Hooks for auxiliary files (HO)   kvoptions.sty    2011/06/30 v3.11 Key value format for package options (HO)     pd1enc.def    2012/11/06 v6.83m Hyperref: PDFDocEncoding definition (HO)   hyperref.cfg    2002/06/06 v1.2 hyperref configuration of TeXLive        url.sty    2013/09/16  ver 3.4  Verb mode for urls, etc.    hpdftex.def    2012/11/06 v6.83m Hyperref driver for pdfTeX   rerunfilecheck.sty    2011/04/15 v1.7 Rerun checks for auxiliary files (HO)    nameref.sty    2012/10/27 v2.43 Cross-referencing by name of section   gettitlestring.sty    2010/12/03 v1.4 Cleanup title references (HO) Dates and times: "on", "in", "at"? I’m often confused when I speak about times and dates. What is the rule for using on, in, and at in the following sentences?   I will do it ___ Tuesday. We married ___ March. He returned ___ the same day. Every day ___ the same time, I walk the dog. I have a quick question about buttons that toggle between two states. (Think Play/Pause, or Shuffle/Regular Play.) As the title says, should the toggle show it's current state or the state to which it will transition?  I think people are used to the Play/Pause convention. But the Shuffle/Regular play might be more confusing if you show the transition state instead of current. For example, the built-in music player on the Xbox 360 does it this way: when it's in shuffle mode, it shows the icon for direct play and vice versa and it always confuses me (am I in shuffle mode or straight play).  I see it this way: Play/Pause is more like action as in begin playing or pause playing. Yes behind the scenes it is a state transition but to the user, there is an action. Whereas Shuffle/Straight Play is an option and it's best to show the current state (and possibly have only one icon and change button to show that the option is enabled/disabled). Thoughts? Here is my attempt to prove the Well-Ordering Principle, i.e. that any non-empty subset of $\Bbb N$, the set of natural numbers, has a minimum element.  Proof. Suppose there exists a non-empty subset $S$ of $\Bbb N$ such that $S$ has NO minimum element. Define $A = \left\{n\in \Bbb N : (\forall s\in S)(n \leq s)\right\}$. It is obvious that $1\in A$. Suppose $n\in A$, then for each $s \in S$, there exists $q \in N$ such that $n + q = s$. Since $q \ge 1$, $n+1 \leq s$, for all $s\in S$. By Principle of mathematical induction, $A = \Bbb N$. Take any $s_0 ∈ S$, then $(\forall s\in S)(s_0 \leq s)$. (This contradicts that $S$ has no minimum element).  How do I prove the statement without invoking Mathematical Induction? Also, I read that the proof of Principle of Mathematical Induction makes use of Well-Ordering. Can it be proven independently of Well-Ordering too? Recently I have installed an older version of Ubuntu on my old machine. Whenever I try to install any software, I get an error saying it couldn't be found:  $ sudo apt-get install vlc Reading package lists... Done                Building dependency tree        Reading state information... Done     E: Couldn't find package vlc Difference between Can/Could: "Can (could) you sell your old computer to me?" What is difference between  Could you sell your old computer to me, seeing (that) you have no use for it. Can you sell your old computer to me, seeing (that) you have no use for it.  Can I use either one of them? Which one is grammatically correct or if both are, what is the difference in meaning? How to configure a firewall that only allows a few webpages and dropbox and U1 services? Image with axis Show that $\arctan\frac{1}{2}+\arctan\frac{1}{3}=\frac{\pi}{4}$ Show that $\arctan\frac{1}{2}+\arctan\frac{1}{3}=\frac{\pi}{4}$.   Attempt:  I've tried proving it but it's not equating to $\frac{\pi}{4}$. Please someone should help try to prove it. Is anything wrong with the equation? If there is, please let me know. How can I check if /bin/x86_64/bin/ls is a directory in a bash shell script  Here is what I tried:  #!/bin/bash  if [ $# -eq 2 ]; then     if [[ "$1" = /* ]]     then     cd ./bin/x86_64/bin/ls         if [ -d "$1" ]; then             echo "ok"             i="$1"             echo $i         else             echo "error2"             exit         fi     else         echo "error"         exit     fi fi Running ERDAS Imagine and ArcGIS Desktop on same machine? Books for Condensed Matter after Ashcroft/Mermin What are some good condensed matter physics books that can fill the gap between Ashcroft &amp; Mermin and research papers? Suggestions for any specialized topics (such as superconductivity, CFT, topological insulators) are welcomed.