Measuring circumference of Gas Giants vs. rocky planets

[jefs999]

In comparing the circumference of planets, I was wondering:<br />Even though it's suspected that the gas giants have cores of some nature, the measurements are made from the cloudtops. Is that correct?<br /><br />But don't we measure the Earth from the rocky surface. Shouldn't we also measure the Earth from the cloudtops? Or is it that we only measure the parts of the planet that have significant mass?<br /><br />Thanks for shedding any light on this.

 

[MeteorWayne]

Well actually there is no standard way to measure the diameter (or circumference) of planets. The source I use (RASC) gives that at 1 bar atmospheric pressure. For the earth that is by definition the rocky/watery surface.<br /><br />For the gas planets, it's at some point in the atmosphere. The metal/rock cores are only estimated based on the few gravity measurements we have.<br /><br />Measuring the earth at the cloudtops would only add about 20 miles to the diameter, an inconsequential amount. <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[Boris_Badenov]

<font color="yellow"> Measuring the earth at the cloudtops would only add about 20 miles to the diameter, an inconsequential amount. </font><br /><br /> Unless you are jumping from an airplane <img src="/images/icons/laugh.gif" /> <div class="Discussion_UserSignature"> <font color="#993300"><span class="body"><font size="2" color="#3366ff"><div align="center">. </div><div align="center">Never roll in the mud with a pig. You'll both get dirty & the pig likes it.</div></font></span></font> </div>

 

[vandivx]

<blockquote><font class="small">In reply to:</font><hr /><p>It is better to remain silent and be thought a fool than to open one's mouth and remove all doubt. <p><hr /></p></p></blockquote><br /><br /><img src="/images/icons/laugh.gif" /><br /><br />vanDivX <div class="Discussion_UserSignature"> </div>