30
votes
Accepted
What will the PRECISE time of the Summer Solstice 2020 be?
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 ...
- 27k
13
votes
Why is the time between equinoxes different?
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 ...
- 4,280
11
votes
Accepted
Are the Jupiter-Saturn conjunctions and winter solstice related?
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 ...
- 4,272
9
votes
Accepted
Why is today the shortest day but the solstice is actually tomorrow?
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 ...
- 7,073
9
votes
What will the PRECISE time of the Summer Solstice 2020 be?
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 ...
- 87.4k
8
votes
Why is the equinoxes only 2 days and not more?
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 ...
- 2,660
6
votes
Accepted
Confusion when calculating the length of the day
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 ...
- 2,660
6
votes
When was the last time a great conjunction coincided with a solstice?
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. ...
- 4,272
5
votes
Accepted
Will I be able to see both Jupiter and Saturn at the same time in my Astromaster 114?
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" (...
- 959
5
votes
Why is the equinoxes only 2 days and not more?
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 ...
- 129
5
votes
Why is the equinoxes only 2 days and not more?
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 ...
- 51
5
votes
Accepted
Aligning the equinoxes to the cardinal points on a circular calendar
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 ...
- 8,862
5
votes
Earth's perihelion vs winter solstice
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 ...
- 87.4k
5
votes
Accepted
Aphelion and the solstice
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 ...
- 27k
4
votes
Accepted
Why is the time between equinoxes different?
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/...
- 815
4
votes
Accepted
Date of solstices pre-0 AD
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 ...
- 2,980
4
votes
Aligning the equinoxes to the cardinal points on a circular calendar
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 ...
- 16.5k
4
votes
Will I be able to see both Jupiter and Saturn at the same time in my Astromaster 114?
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 ...
- 31.6k
4
votes
Why is today the shortest day but the solstice is actually tomorrow?
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 ...
- 339
3
votes
Why is today the shortest day but the solstice is actually tomorrow?
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 ...
- 652
3
votes
Aligning the equinoxes to the cardinal points on a circular calendar
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. ...
- 4,272
2
votes
Aligning the equinoxes to the cardinal points on a circular calendar
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 ...
- 13.5k
1
vote
Why is the equinoxes only 2 days and not more?
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 ...
- 2,525
1
vote
Accepted
Solar azimuth for celtic fire festivals
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(...
- 7,073
Only top scored, non community-wiki answers of a minimum length are eligible