Welcome to the NavList Message Boards.


A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

Compose Your Message

Add Images & Files
    Mercury is the closest planet, on average...
    From: Frank Reed
    Date: 2019 Mar 15, 15:09 -0700

    Here's some silliness:

    This falls in the category of "true, yes, quite so... but, er... useless". And more than a bit silly. The real silliness is the amount of effort that went into validating this trivial result and the fact that it was published. 

    Back in college I had a professor who pointed out that the semi-major axis of a planet's orbit is not the average distance of the planet from the Sun in any meaningful sense of a genuine average. It is, however, the simple arithmetic mean of the nearest and farthest distances of the planet in its orbit. True, yes, this isn't much of an average, but that's (almost) totally useless information.

    Actually in the orbital average distance case, there is one relevant case that is worth remembering: the average distance of a long-period comet from the Sun. On "average", how far is Halley's Comet from the Sun? If you average the aphelion and perihelion distances, you get the semi-major axis of the elliptical orbit, which is often called the average. But on "average" in a time-average sense, Halley's Comet spends most of its time way out there near aphelion.

    This is off-topic for navigation. But I think it's close enough to topical for a brief side-discussion. Yes?

    Frank Reed

    Browse Files

    Drop Files


    What is NavList?

    Join NavList

    (please, no nicknames or handles)
    Do you want to receive all group messages by email?
    Yes No

    You can also join by posting. Your first on-topic post automatically makes you a member.

    Posting Code

    Enter the email address associated with your NavList messages. Your posting code will be emailed to you immediately.

    Email Settings

    Posting Code:

    Custom Index

    Start date: (yyyymm dd)
    End date: (yyyymm dd)

    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site