# PlanetData “VelocityAroundSun” giving inconsistent answers

My goal is to create a ListPlot showing the Earth's orbital speed over the course of a year, with one datapoint per day. I'm seeing problems long before I even get to the point of plotting the data! For example, if I enter: PlanetData[PlanetData["Earth"], "VelocityAroundSun", "Date" ->DateObject[{2015, 1, 1}]]

I sometimes get a reasonable response though I don't think it's responding to the "Date" parameter: 65546.3mi/h

and sometimes get: PlanetData[Missing["UnknownEntity", {"Planet", "Earth"}], "VelocityAroundSun"] What's the problem?

• Did you really mean PlanetData["Earth"] inside the brackets, and not PlanetData["Earth", "VelocityAroundSun", "Date" ->DateObject[{2015, 1, 1}]] ? – barrycarter Jan 9 '16 at 0:19