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
    Re: Immutable firmament?
    From: Frank Reed
    Date: 2010 Dec 5, 22:42 -0800

    Gary, you wrote:
    "But even the ancients noticed that the sun had changed its position in relationship to the stars at the time of the solstices and equinoxes."

    Yes, Gary, but precession is a PURE ROTATION of the coordinate system. The point here is that it does not change the "immutability" of the firmament. For comparison, obviously when the stars change their altitudes and azimuths all during the night, we can still treat them as if they are fixed on a celestial sphere. Sirius climbs from 10 to 20 to 30 degrees, while Rigel rises from 30 to 37 to 40 degrees in the same period of time. The coordinates are changing, but the relative relationships of the stars on the "immutable firmament" of the celestial sphere does not change. Apart from refraction, the angles between the stars do not change during this daily rotation of the coordinates. While precession is drastically slower, it is exactly the same sort of thing. Over the course of 26,000 years, the celestial sphere rotates around the axis passing through the north and south ecliptic poles. And just like the daily rotation, this does not require us to drop the idea of an immutable celestial sphere. And sure enough, Hipparchus and Ptolemy did NOT abandon the celestial sphere even though Hipparchus had discovered precession.

    The "mutability" of the celestial sphere only comes about when we recognize that the stars are other individual celestial objects each with its own specific motion. And again, if you want to see evidence of this, look at the angular distance between Arcturus and Spica over the past couple of hundred years. Arcturus is a fast-moving star. It certainly isn't tied down to any "immutable" sphere of quintessence!

    Gary, you wrote:
    "I have always chuckled at astrology that assigns statuses to people born while the sun is in a particular constellation. The problem with this is that the dates given for the sun being in the birth constellation are incorrect and the sun is actually one and a half constellations removed from the stated constellation for those dates due to precession of the equinoxes over the time period since the astrologers set up their reckoning."

    I've got to warn you, Gary, that this isn't true AT ALL. Do you really suppose that astrologers would somehow have missed the news out of Greece 21 centuries ago informing the world of the existence of the precession of the equinoxes?? Professional or "real" astrologers are, in fact, well aware of this. The problem for people who know just enough astronomy to mock astrologers is that they don't understand what the zodiacal signs are (there are, by the way, plenty of excellent reasons to doubt astrology, but this is not one of them). The signs of the zodiac are indeed named after the constellations, but they are not the same as the constellations. The signs, from a mathematical perspective, can be considered nothing more than an extension of the sexagesimal system of degrees, minutes, and seconds. They are simply thirty-degree divisions of the circle. So, for example, I can express a position in a circle as 3s, 10d, 15', 59" where "3s" means "third sign". Depending on whether the numbering starts with zero or one, this "3s" would be equivalent to either 90 or 60 degrees. When applied to the ecliptic, these thirty-degree bands of ecliptic longitude are given names (corresponding to the constellations lined up with them thousands of years ago). So the first thirty-degree band is called Aries, the second Taurus, and so on. Thus the position of a planet could be given in quick shorthand as "Aries 12" or "Taurus 28" which, in modern terminology, would mean that the ecliptic longitude of that planet is 12 degrees or 58 degrees respectively. Is that easier? Is it perhaps easier to remember "Taurus 28"?? I would say that it depends on what you're used to. It rather reminds me of "Klondike 5-1234" being replaced by "555-1234" (see the PS if that is an unfamiliar reference for anyone following along).

    Now you might think that only superstitious astrologers would use such a weird system as attaching verbal labels to bands of ecliptic longitude or using names that do not reflect the current sky, but it's not so. As late as the early 19th century, professional astronomers still used the "S.D.M.S." (sign, degree, minute, second) system for listing ecliptic longitudes. I am attaching a page from the Nautical Almanac from 1820. And note that this is not back in the dark ages. This is over a century after Isaac Newton, decades after the discovery of the planet Uranus (known as the "Georgian" in Britain back then), and it's after the Enlightenment and the birth of real modern science. Nonetheless, they used the zodiac signs to specify the positions of the planets. In the attached almanac page, the geocentric longitude (meaning geocentric longitude in ecliptic coordinates) for Mercury on April 1, 1820 is listed under S.D.M. as 0.27.27. For us today, that's just 27d 27' ecliptic longitude. Meanwhile, at the bottom, the longitude of the Georgian is 8.28.48 which would be, as a modern angle, 268d 48' (268=8*30+28).

    And lest you still think you might mock astrologers for using such an old-fashioned, nearly two-hundred-years obsolete, system for naming positions along the ecliptic, bear in mind that a clever enough astrologer can turn the tables on you and point out that celestial navigators do EXACTLY the same thing in one special case, a vestige of that common usage from 200 years ago. The "GHA of Aries", so important in navigation, does not refer to the constellation Aries at all. It's almost as if celestial navigators are "too stupid to realize that precession exists" (so a debating astrologer might say). But no, this is just the old system for labeling the ecliptic. It's called Aries because that's the name for the first band of thirty degrees, the zero point of ecliptic longitude, starting from the point where the ecliptic crosses the celestial equator north-bound.

    By the way, there are some very intelligent people who post here who take a serious interest in astrology and do not consider it nonsense.

    ...Not me.

    PS: I said above that the change in the system for labeling points on the ecliptic "reminds me of Klondike 5-1234 being replaced by 555-1234". For those, especially outside the US, who are scratching their heads, this was the old system for listing phone number in the United States (and some other countries). A number in a local exchange has a three-digit exchange number followed by four digits for the specific number. Those local exchanges used to be known by letters which were then given mnemonic names like "Klondike". Until the early 1960s (so I have read), most phone numbers were listed with this mixed alphanumeric system and you can still here "Klondike" numbers in old movies and tv shows. More here: http://en.wikipedia.org/wiki/Telephone_number.

    NavList message boards and member settings: www.fer3.com/NavList
    Members may optionally receive posts by email.
    To cancel email delivery, send a message to NoMail[at]fer3.com


    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