Questions tagged [equinox]
Questions about the moment when the Sun's declination is zero. A less strict definition is the day when the day and night are the same length.
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The lowest position of the sun at the equinox and during the whole year
I actually have a follow-up question (because my first question was answered in such a surprising and simple way and I have studied the details of the formula for the highest position of the sun a) at ...
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How do we derive the sun's declination using right ascension?
It appears that there are 2 formulas to derive the sun's declination.
One is: $declination \approx 23.5 \times sin(\alpha)$ from the answer here
and another which is similar $\delta=−23.45°×cos(\frac{...
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Does the terrain around the South Pole interrupt the circle the Sun makes on the equinox?
A recent answer stated that
if you stand at the poles you'll see the Sun hover eerily slightly above the horizon due to refraction and circle all the away around you 360°!
To which I commented that
...
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First Day of Spring 2025---Why weren't Sunrise and Sunset Exactly Twelve Hours Apart? [duplicate]
March 20, 2025 is the first day of Spring this year in the northern hemisphere.
Thus, on this day, night and day are both of equal length; and so, I would expect the times of sunrise and sunset to be (...
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How did error accumulate in the Julian calendar and we needed the corrections of the Gregorian one?
I was trying to understand the corrections introduced by the Gregorian calendar.
The sidereal year is 20 mins longer than the tropical year (my assumption is that this is a constant difference).
The ...
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Why on the March 20, 2025 equinox does the sun rise due east at the equator but increasingly northerly as an observer travels north?
My source is the Suncalc.org calculator. Assuming the calculator is correct, then during the equinox and at the equator, the sun rises and sets due east and due west respectively. When one moves north ...
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How was the tropical year determined for the Gregorian calendar?
The 1582 Inter Gravissimas Papal Bull of Pope Gregory XIII used Italian chronographer Aloysius Lilius' determination of the tropical year, to go from the Julian calendar to the Gregorian. So how did ...
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Can you determine Earth's precessional period without using the torque formula?
The Julian calendar was in use from 45 BC to 1582, so for 1626 years. The tropical year to 4 decimal places is 365.2422 days.
The slip rate of the vernal equinox through the Julian calendar is
Slip ...
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Why doesn't Greenwich Sidereal Time match up with Greenwich Mean time on the equinoxes?
I'm trying to calculate the exact time closest to the march and september equinoxes that 12h RA and 0h RA lines up with my local meridian.
The march equinox this year was on March 20 ~03:07 UTC. My ...
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Coordinates of equinoxes/solstices for Solar System planets
I'm trying to build an accurate model of the Solar System in Blender (a free 3D software). I relied on NASA-provided values so far for the orbits of Mercury, Venus, and Earth, but the question that ...
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Vernal equinox for 2550 BC - why is it on Apr 12 and not May 12th?
calculating exact date of vernal equinox in 2550BCE. A straight calc of 1 deg precession gives approx 45 days vernal equinox May 12 2550BCE ( from Mar 20 in 2024). other calc say Apr 12 2550BCE. ...
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What causes the short term variation in the length of a march-equinox year
By a "march-equinox year" I mean the time between successive march/vernal equinoxes. I understand that this is different from the mean tropical year, and I also understand why this would be ...
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Determining Vernal Equinox by observation
Medieval society determined the date of Easter (or Passover) relative to the Full (or New) Moon on or after the (day of the) Vernal Equinox, where the state of the Moon was observed rather than ...
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How can I build a gear-based mechanism to calculate solstices, equinoxes, and cross-quarter dates?
I realize there are boundless amounts of information as to the formulas to calculate solstices, equinoxes, and cross-quarter days, but I would like to design a gear-based mechanical solution for the ...
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Calculating Earth-Sun distance only using trigonometry and terrestrial measurements
I have an interest in mathematics and astronomy, and my curiosity was piqued by the methodologies employed in contemporary solar distance measurement. Current practices use sophisticated instruments ...
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