---------- Forwarded message --------- From: Michael Ossipoff <email9648...@gmail.com> Date: Thu, Feb 16, 2023 at 14:12 Subject: Re: equation of time on Earth To: Kevin Karney <kar...@me.com>
Yes, French hours (Local True Solar Time), Babylonian hours, Italian hours & can be gotten from a sundial directly, without referring to an EoT table, & unaffected by precession of the equinoxes. I claim that nowadays sundials are of interest for Local True Solar Time anyway. EoT is more likely to be used (along with longitude-correction) to get Local True Solar Time from a clock or watch. The obliquity is constantly changing, & that will eventually put some kinds of sundials off, & those will have to be remade. Altitude Dials, & Azimuth Dials, such as the Analemmatic-Dial, use Solar-declination, which will vary with obliquely. But sundials that directly measure Solar hour-angle won’t be affected. Those include the flat-dials, including the Horizontal-Dial. …& the Equatorial-Dial, & the dials whose measuring-scale is along a band, ring or cylinder that measures around a line parallel to the Earth’s axis (I believe that those are all often called Equatorial-Dials). On Wed, Feb 15, 2023 at 15:48 Kevin Karney via sundial <sundial@uni-koeln.de> wrote: > Diese Nachricht wurde eingewickelt um DMARC-kompatibel zu sein. Die > eigentliche Nachricht steht dadurch in einem Anhang. > > This message was wrapped to be DMARC compliant. The actual message > text is therefore in an attachment. > > > ---------- Forwarded message ---------- > From: Kevin Karney <kar...@me.com> > To: Sundial <sundial@uni-koeln.de> > Cc: > Bcc: > Date: Wed, 15 Feb 2023 23:47:58 +0000 > Subject: Re: equation of time on Earth > Hi Fabio, > > I found interesting how the eot changes over the millennia and I concluded > that not all sundial time systems will survive. > > See below... > > And of course sundials will survive - just differently. The 'Clock of the > Long Now’ (which is designed to last 10,000 years) has a 3-D cam encoding > the EoT. When the sun is shining at noon, the clock will read the Sun’s > presence through an aperture, this connects thermally to the 3-D cam (see > below), which will re-set the clock to mean time. Mind-blowing project! See > https://longnow.org/clock/ > > Best wishes > Kevin > Kevin Karney > Freedom Cottage, Llandogo, > Monmouth, NP25 4TP, Wales, UK > 51°44’44” N 2°41’5” W > > > > On 14 Feb 2023, at 17:12, Fabio Savian <fabio.sav...@nonvedolora.it> > wrote: > > Hi all > > a couple of weeks ago I sent you news about a new app (on Sundial Atlas, > app 53) to get the equation of time of Mars. > I haven't heard of any spaceships leaving so I thought you might be > interested in the one for terrestrial resident as well :-) > > There is no shortage of software to draw eot but this new app (app 29, > www.sundialatlas.net/atlas.php?ori=29) can draw the analemma starting > from the orbital parameters of the Earth: > - eccentricity of the orbit > - inclination of the ecliptic > - longitude of the perihelion > > The app doesn't calculate these parameters but you can digit any values to > get the resulting analemma. > I found a web page of NASA (Goddard Institute for Space Studies) where you > can get the Earth's orbital parameters for the past or for the future: > https://data.giss.nasa.gov/modelE/ar5plots/srorbpar.html > > I found interesting how the eot changes over the millennia and I concluded > that not all sundial time systems will survive. > Some sundials could become archaeological finds in a few centuries just as > we look at those of centuries, or millennia ago and the understandable time > systems in the future are: temporary, Babylonians, Italians and local Sun > time. > Not the analemma because eot changes over the millennia. > Not time-zone Sun time because the conventions change over the centuries. > Not mean time because leap seconds may be not updated over the decades. > > Watching your wrist watch could become a goofy experience, one hopes to be > able to look at a sundial and know the local Sun time. > Also a Martian. > > ciao Fabio > > PS in the app 29 you can also enter parameters of other planets. > Remember that the longitude of the perihelion is a local reference, ie it > is measured from the vernal point of the planet's orbit. > > > > > --------------------------------------------------- > https://lists.uni-koeln.de/mailman/listinfo/sundial > > > --------------------------------------------------- > https://lists.uni-koeln.de/mailman/listinfo/sundial > >
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