Tag Archives: Autumnal Equinox

Equinox Does NOT Mean Equal Day and Night

20 Thursday Sep 2018

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The Myths of the Equinox

This Saturday at 6:54 pm PDT the Sun will be directly over the Equator. Geographically, the event will occur over the western Pacific Ocean, north of Papua New Guinea (≅149° east longitude.) It is the Autumnal Equinox and it is the moment that summer ends and winter begins…in the northern hemisphere. In the southern hemisphere, the equinox is the end of winter and beginning of spring.

Equinoxes are ripe with myths, but probably the most common myth is that an equinox is a date of an equal day (12 hours) and night (12 hours.) It is a myth established by those who live in the mid-latitudes because, on the day of the equinox, the day and night are approximately equal. Near the equator, the length of day and night are nearly the same year-round, so the equinox has no significance.

Equal Day/Night is About Location, Location, Location

Near the equator, day and night are almost equal the entire year; however, the closer one is to either pole, the length of the day increases to the point that there is no night on the equinox. Most locations away from the poles do have a date when day and night are approximately equal, but that rarely occurs on the equinox.

In Panama City, Panama, October 6, 2018, is the date when day and night are equal. In Reno, Nevada, USA, the date is September 25th. In New York City, NY, USA the date is September 26th. In São Paulo, Brasil it is September 17th. The date occurs near the equinox, but the exact date varies depending on location.

Finding East and West on the Equinox

What is true about the equinox? The equinox is the date that an observer can determine true east and true west from her or his location if she or he has an unobstructed view of the sunrise and sunset. Why this happens is complicated, but the point on the horizon where the Sun rises is true east and where it sets is true west.

Don’t get me started about balancing an egg. Eggs are for eating regardless of the date…and that’s about it.

Five ‘Facts’ About the Equinox?

24 Saturday Feb 2018

Posted by in Astronomy, Random, Science, solar, Space, United States

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At 9:15 am PDT on the 20th of March, we will reach the Spring Equinox, or more correctly, the Vernal Equinox. People in the northern hemisphere refer to this as the beginning of Spring. It is also referred to as:

  1. the date when day and night are equal
  2. the date when the Sun shines on both the North Pole and the South Pole
  3. the date when the Sun rises exactly East and sets exactly West at every location on the Earth
  4. the date you can balance an egg on its end
  5. the date you won’t cast a shadow.

Two of these ‘facts’ are false, one is “well, sort of,” fact, one is “mostly true,” and one is true.

Timelapse From Space:  Seasonal Progression of Sunlight on Earth

The Date of Equal Day and Night?

Nope. While the length of day and night are almost equal on the day of the Vernal Equinox, it’s not actually true unless you’re closer to the North or South Pole. At the poles and the farther away from the poles, the less this is true.

For example, in Longyearbyen, Svalbard, Norway, in the Arctic Circle, in 2018 the date that comes closest to being equal in day and night hours is the 19th of March (day = 11:58:51 hours long.) In Reno, Nevada, USA, the date day and night are almost equal  is the 16th of March (day = 11:59:28 hours long.) In Sydney, Austrailia that date is the 24th of March (day = 12:00:38 hours long.) In Bogata, Columbia it was the 21st of February (day = 11:59:59 hours long.) 

The Date the Sun Shines on Both Poles?

Yes, and on the North Pole, it spirals up from the horizon, around the viewer until the Summer Solstice when it begins to spiral downward, setting after the Autumnal Equinox in the Fall. The same is true for the South Pole, only the Sun rises at the Autumnal Equinox and sets after the Vernal Equinox.

South Pole sunrise

Sunrise on the South Pole

The Date the Sun Rises Dead East and Sets Dead West?

Mostly true. Its explanation makes my head hurt, but I’ve been able to use pencils on a globe on its axis with a single light source to prove it to myself. You can read multiple descriptions on the Internet but have pain reliever at the ready.

However, there’s a catch. The viewer has to have an unobstructed view of the horizon and be near or at sea level. The Sun’s trajectory is at an angle compared to the horizon and if the view of the true horizon is blocked the Sun will appear to rise or set at a location that is off from true East or West.  

The Date You Can Balance an Egg On Its End?

Long proven to be false…and stupid at the same time.

The Date of No Shadows?

Sort of true, but only if you’re on the equator at exactly high noon. Not many people want to do that…it’s hot at the equator. Who wants to stand out in the Sun at noon just to NOT see your shadow? Besides, the people who might want to do that are still trying to balance an egg on its end.