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This is because the summer and winter solstices (approx. June 21st and December 21st) do not correspond to the aphelion and perihelion (approx. July 5th and January 4th). Therefore, the average distance from the Sun is longer in the period from the Summer Solstice to Winter Solstice than vice versa, so the Earth is moving slower (on average) and it takes ...


4

There is no connection between the date of the solstice and the perihelion. It is merely a minor coincidence that perihelion occurs close to the solstice. The relationship isn't fixed. Precession in the Earth's orbit (caused by gravitational perturbations of Jupiter and other planets) will change the relative time of perihelion and solstice over a period ...


4

The two coincided about 800 years ago. The December solstice and perihelion date coincided in 1246, 773 years ago. There are many different concepts of what qualifies as a "year". Three of them are the sidereal, tropical, and anomalistic years. The sidereal year measures how long it takes for the Earth to complete one orbit about the Sun with respect to the ...


4

Sounds like Julian Calendar slippage. The Gregorian Calendar, the one we use now, was created to fix a problem with the Julian Calendar: The fact that the Solar Year wasn't exactly 365.25 days. As a result, compared to the calendar year, the date of the Vernal Equinox (and more importantly at the time, Easter) was slipping forward. To remedy this, ten ...


4

The easiest graph to consider is the graph of day-length. If the day-length varies from 8 to 16 hours, there can only be two equinoxes: At the time of equinox, the day length changes at the fastest rate, by a few minutes in temperate regions, compared to the solstices, which change by a few seconds every day. So, the equinox doesn't exist perfectly, the ...


4

Earth is always rotating around the Sun, so declination of the Sun is always changing (except at the solstices when it stops for a minute and goes in the other way). An Equinox doesn't last for a day. It lasts for a moment when the Earth is totally aligned and straight. So equinoxes last for a moment.


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The azimuth of the sunrise (or sunset, or any object) is a function of the Sun's declination and observer's latitude. It can be calculated from the following forumla: $$\cos(\theta_R)=-\frac{\sin(declination)}{\cos(latitude)}$$ where $\theta_R$ is measured from due south to the location where the object rises or sets. For example, at 55 degrees north ...


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Two further points to make are that: (1) because of the way we define sunrise and sunset as being when the entire Sun is below the horizon not just the centre of the Sun. (2) When the Sun is close to the horizon the Sun’s ray are refracted (bent) by the Earth’s atmosphere so that the Sun appears to be slightly higher in the sky that it would be if the ...


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