30

TL;DR: In a couple of weeks it might be possible to say precisely (within a second, perhaps a fraction of a second) when the summer solstice did occur. But until then, sub-minute estimates should be treated as fraudulent. The reason you are seeing different times for when the summer solstice will occur is that different websites use different models of the ...


13

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 ...


11

Not in any way, no. The December solstice is the moment when the Sun reaches its southernmost point in its daily path in the sky (the June solstice, when the Sun reaches its northernmost point). It only depends on the tilt of the Earth on its orbit and the Sun. On the other hand, Jupiter and Saturn being in conjunction is a phenomenon that doesn’t depend at ...


9

The other possibility is https://sunrise-sunset.org is inaccurate. An app that I use, LunaSolCal, show the length of day on Dec 20, 21, and 22 in Ashland OR are 9:05:45, 9:05:44, 9:05:49. The website https://www.timeanddate.com does not have Ashland OR in its database, so I used nearby Medford OR. The length of day on Dec 20, 21, and 22 are 9:04:50, 9:04:49,...


9

It is intrinsically hard to measure the exact time of solstice as, unlike the equinox, it occurs when the sun's declination is changing slowly. So, determining the exact time of solstice depends on models of nutation, etc. timeanddate.com has a user-created countdown time that uses 21:43:40 UTC for the exact time of solstice. I'm a little sceptical, as they ...


8

First, don't think that equinox is when the day and night are the same. It is the moment, when the sun's declination is zero, or when the sun is directly over the equator. Let me explain ... 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). As @...


6

Note that the Sun here is point-like and there is no refraction. What have I done wrong? Your supposition that the altitude of the Sun is directly related to the length of the day is wrong. Proof with counterexample: observe the altitude of the Sun on the equator and in the Moscow on the equinox; but still, the lengths are the same. And what is the correct ...


6

It depends how you define “conjunction.” For example, this year, Jupiter and Saturn will be at the same ecliptic longitude and the same right ascension within hours of each other on December 21, 2020. However, in 2000, they were at the same right ascension on May 30, but at the same ecliptic longitude on May 28, 2000. I have done calculations (using the ...


5

As Mike G said, the Sun's ecliptic longitude is ideal for this application. I see from your profile that you're a coder, with some knowledge of Python. Here's a short Python script that prints solar ecliptic longitudes for each day for any given year. (It actually prints 367 days, I figured an extra day or two may be useful). The code mostly avoids features ...


5

This can easily be tested using software such as Stellarium, where you can visualize the field of view with given focal length. If you have the software installed, click on "ocular view" (the most left button in the upper right corner). The following view is what you culd expect on December 21 with a 10mm eyepiece and a focal length of 1000mm: And ...


5

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 ...


5

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 ...


5

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

The diagram below illustrates the reason, which is that the earth moves at different speeds during it revolution around the sun and the distribution of those speeds is not equal because the solstices/equinoxes are not located at symmetrical points on the ellipse vis-a-vis the speed symmetries, which are centered on the aphelion and perihelion. Diagram by ...


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

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

What you need is the Sun's ecliptic longitude for a given date. As you expect, it increases faster near perihelion (1.02°/day in early January) and slower near aphelion (0.95°/day in early July). It is exactly 0° at the March equinox, 90° at the June solstice, 180° at the September equinox, and 270° at the December solstice. Wikipedia:Position of the Sun ...


4

Direct viewing through an eyepiece When looking through an eyepiece, there is an apparent field of view. This answer says: Because I was lazy, I used the default telescopes and eyepieces. which means that the circles shown are what one would see if one had an eyepiece with a field of view equal to the default eyepiece used in the Stellarium simulation. If ...


4

I was very surprised when I first heard this and it took a little while to understand it. The simple answer is to do with the M in GMT. This is "mean" in its sense of average. So, clock noon to the next clock noon is a fixed amount of time: the average day. If you used a sundial, then you would find that sundial noon to sundial noon was not ...


3

This is an interesting question which opens up wide vistas! Look up the Equation of Time on Wikipedia for a start. What is your source? I can't find the sunrise and sunset times in Ashland. The ESRL site for Ashland gives noon to the second but sunrise and sunset only to the minute. At present the days are 24 hours and 30 seconds long, so each noon is 30 ...


3

The fact that equinox and solstice dates don’t line up with the quadrants of the circle is due to the ellipticity and eccentricity of Earth’s orbit around the Sun. Let’s go back in history a little. Ancient Greeks thought all celestial movements were circular. This model was followed for approximately 2,000 years until Copernicus finally realized the Earth ...


2

By looking at https://en.wikipedia.org/wiki/Solstice, we find the dates for equinox and solstice in 2021 as March 20, June 21, Sep 22, and Dec 21. These correspond to days 79,172,265,355. That gives us differences of 89, 93, 93,and 90 days. Points need to be 90/89 degrees apart in the first quadrant, 90/93 degrees apart in the second quadrant, etc... Care ...


1

The earth is smoothly and constantly moving around the sun. At the moment of the equinox, a line from the center of the sun to the center of the earth passes through the equator. That only lasts an instant. Before that instant, the line is on one side of the tilted equator, and after that, it's on the other side. The day labeled "the equinox" is ...


1

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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