<a href="https://en.wikipedia.org/wiki/Galileo_Galilei" id="mwMg" rel="mw:WikiLink" title="Galileo Galilei">Galileo Galilei</a> makes his first observation of the four <a href="https://en.wikipedia.org/wiki/Galilean_moons" id="mwMw" rel="mw:WikiLink" title="Galilean moons">Galilean moons</a>: <a href="https://en.wikipedia.org/wiki/Ganymede_(moon)" id="mwNA" rel="mw:WikiLink" title="Ganymede (moon)">Ganymede</a>, <a href="https://en.wikipedia.org/wiki/Callisto_(moon)" id="mwNQ" rel="mw:WikiLink" title="Callisto (moon)">Callisto</a>, <a href="https://en.wikipedia.org/wiki/Io_(moon)" id="mwNg" rel="mw:WikiLink" title="Io (moon)">Io</a> and <a href="https://en.wikipedia.org/wiki/Europa_(moon)" id="mwNw" rel="mw:WikiLink" title="Europa (moon)">Europa</a>, although he is not able to distinguish the last two until the following night.<sup about="#mwt37" class="mw-ref reference" data-mw='{"name":"ref","attrs":{},"body":{"id":"mw-reference-text-cite_note-5"}}' id="cite_ref-5" rel="dc:references" typeof="mw:Extension/ref"><a href="./January_7#cite_note-5" id="mwOA" style="counter-reset: mw-Ref 5;"><span class="mw-reflink-text" id="mwOQ">[5]</span></a></sup>
<span class="mw-reference-text" id="mw-reference-text-cite_note-5"><cite about="#mwt34" class="citation book cs1" id="CITEREFLeverington2003">Leverington, David (29 May 2003). <a class="external text" href="https://books.google.com/books?id=6Hpi202ybn8C&amp;pg=PA78" id="mwB7U" rel="mw:ExtLink nofollow"><i id="mwB7Y">Babylon to Voyager and Beyond: A History of Planetary Astronomy</i></a>. Cambridge University Press. p.<span id="mwB7c" typeof="mw:Entity"> </span>78. <a class="mw-redirect" href="./ISBN_(identifier)" id="mwB7g" rel="mw:WikiLink" title="ISBN (identifier)">ISBN</a><span id="mwB7k" typeof="mw:Entity"> </span><a href="./Special:BookSources/978-0-521-80840-8" id="mwB7o" rel="mw:WikiLink" title="Special:BookSources/978-0-521-80840-8"><bdi id="mwB7s">978-0-521-80840-8</bdi></a>.</cite><span about="#mwt34" class="Z3988" id="mwB7w" title="ctx_ver=Z39.88-2004&amp;rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&amp;rft.genre=book&amp;rft.btitle=Babylon+to+Voyager+and+Beyond%3A+A+History+of+Planetary+Astronomy&amp;rft.pages=78&amp;rft.pub=Cambridge+University+Press&amp;rft.date=2003-05-29&amp;rft.isbn=978-0-521-80840-8&amp;rft.aulast=Leverington&amp;rft.aufirst=David&amp;rft_id=https%3A%2F%2Fbooks.google.com%2Fbooks%3Fid%3D6Hpi202ybn8C%26pg%3DPA78&amp;rfr_id=info%3Asid%2Fen.wikipedia.org%3AJanuary+7"></span></span>