Greetings Frank, I'm sure you're right. This applies to all vertical dials, direct south or declining by an angle no greater than the maximum angle by which sunrise differs from due east. The sun only shines on the dial when it is both above the horizon and in front of the dial plane. The earliest time for this is when the sunrise bearing is parallel to the dial. In the summer, the sun rises earlier, but further north. The time when its bearing reaches the dial's is later than in the winter. In the winter, however, it is below the horizon when on this bearing. So, as you said, the earliest time it shines on the dial is when sunrise is on the bearing of the dial. Similarly for sunset, so, for your dial declining 10 deg east, the latest time it can show corresponds to the sun setting on a bearing of 260.
At 55 degrees north, you are not far from the latitude (55 deg 45') where the midwinter and midsummer sunrises and sunsets are at 045, 135, 225, 315 degrees. So declining dials at 45 degrees to N-S have extra magic. I wonder that Stonehenge wasn't built at this latitude. Chris 51.4N 1.3W ----- Original Message ----- From: "Frank Evans" <[email protected]> To: "Sundial" <[email protected]> Sent: Monday, April 27, 2009 3:18 PM Subject: sunrise > Greetings, fellow dialists, > Am I correct in thinking that the earliest that a declining dial can > begin to tell the time is when the sunrise amplitude lines up with the > amount by which the dial is declining, for instance, sunrise bearing 080 > deg., dial plate declining 10 deg east? It seems that with both greater > and lesser sunrise amplitudes the dial will start work at a later hour. > Am I right? > Frank 55N 1W > > > --------------------------------------------------- > https://lists.uni-koeln.de/mailman/listinfo/sundial > --------------------------------------------------- https://lists.uni-koeln.de/mailman/listinfo/sundial
