title: understanding how elasticsearch stores dates internally
body: <p>I would like to understand how ES stores date values internally in its indexes. Does it convert to UTC?</p>
  
  <p>I have a field "t" of type date. Here's the mapping:</p>
  
  <pre><code>"t": { "type" : "date" },
  </code></pre>
  
  <p>Now when I insert/add a document to ES, how does it store in its indexes.</p>
  
  <ol>
  <li><p>"t" : "1427700477165" (milliseconds generated from Date.now() function). Does ES recognize its epoch time in UTC and stores as is?</p></li>
  <li><p>"t" : "2015-03-29T23:59:59" (i adjust mapping date format accordingly)- how does ES store this. If it converts to UTC, how does it know what time zone this date is and convert it to UTC? Does ES get the default time zone from the machine its running on?</p></li>
  </ol>
  
  <p>Thank you!</p>