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Re: Vernal Equinox Re: day 3000 of 3rd
by Brillig
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I just had a thought. What if there could be more than two equinoxes
in a year due to notation. Well, that is probably impossible because
nutation is so small compared to the movement of the sun northward or
southward. OK. So what about the solstices? Those take place when the
north/south movement of the sun is zero.
So, for example, if we define the summer solstice as a local northern
extreme of the sun's apparent position in the sky, it seems possible
to have two such local maxima if the amplitude of the nutation is
strong enough and in the opposite direction.
Victor
On 3/20/09, Irv Bromberg <irv.bromberg@...> wrote:
>
> On 2009.03.20, at 11:00 , HR-CALNDR-L wrote:
> The vernal equinox is defined only by the heliocentric ecliptic longitude of
> earth being zero. The ecliptic latitude, which is not always exacly zero, is
> completely ignored. Earth's nutation is also ignored, so the moment when the
> sun is exactly in the equatorial plane is usually not the very same moment
> as
> that of the vernal equinox.
>
> Irv replies: My comments concerned rather crude observation of the equinox.
>
> Definitions based on celestial mechanics can be much more precise, but then
> one runs into controversies as to exact definitions of the moment.
>
> Isn't the "heliocentric ecliptic longitude of earth being zero" undefined in
> isolation?
>
> There is no heliocentric longitude in space which points to a fixed zero,
> because of precession of the equinoxes.The only "nail to hang one's hat on"
> is the solar declination crossing zero, and at that moment one can define
> the ecliptic solar longitude as 0° at the northward equinox, corresponding
> to a heliocentric ecliptic longitude of Earth = 180°.
>
> If the equinox is the moment of solar declination zero, then how can that be
> distinguished from a zero ecliptic latitude?
> With respect to nutation in this context, it would be included in typical
> solar longitude calculations, but generally not in the solar declination
> calculation.
>
>
>
> -- Irv Bromberg, Toronto, Canada
>
> <http://www.sym454.org/seasons/>
in a year due to notation. Well, that is probably impossible because
nutation is so small compared to the movement of the sun northward or
southward. OK. So what about the solstices? Those take place when the
north/south movement of the sun is zero.
So, for example, if we define the summer solstice as a local northern
extreme of the sun's apparent position in the sky, it seems possible
to have two such local maxima if the amplitude of the nutation is
strong enough and in the opposite direction.
Victor
On 3/20/09, Irv Bromberg <irv.bromberg@...> wrote:
>
> On 2009.03.20, at 11:00 , HR-CALNDR-L wrote:
> The vernal equinox is defined only by the heliocentric ecliptic longitude of
> earth being zero. The ecliptic latitude, which is not always exacly zero, is
> completely ignored. Earth's nutation is also ignored, so the moment when the
> sun is exactly in the equatorial plane is usually not the very same moment
> as
> that of the vernal equinox.
>
> Irv replies: My comments concerned rather crude observation of the equinox.
>
> Definitions based on celestial mechanics can be much more precise, but then
> one runs into controversies as to exact definitions of the moment.
>
> Isn't the "heliocentric ecliptic longitude of earth being zero" undefined in
> isolation?
>
> There is no heliocentric longitude in space which points to a fixed zero,
> because of precession of the equinoxes.The only "nail to hang one's hat on"
> is the solar declination crossing zero, and at that moment one can define
> the ecliptic solar longitude as 0° at the northward equinox, corresponding
> to a heliocentric ecliptic longitude of Earth = 180°.
>
> If the equinox is the moment of solar declination zero, then how can that be
> distinguished from a zero ecliptic latitude?
> With respect to nutation in this context, it would be included in typical
> solar longitude calculations, but generally not in the solar declination
> calculation.
>
>
>
> -- Irv Bromberg, Toronto, Canada
>
> <http://www.sym454.org/seasons/>
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