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OUT OF THIS WORLD | Earth, Space And The Stuff In Between - a daily journey through weather, space and science from meteorologist/science writer Scott Sutherland

Sticky shadows & balancing eggs: Debunking the fall season


Scott Sutherland
Meteorologist/Science Writer

Saturday, September 22, 2018, 8:28 AM - Summer's final curtain call. On Saturday, September 22, 2018 it's an official change in seasons as the Fall Equinox puts an end to summer. Here's a guide to the science behind this phenomenon, and one if its most colourful effects.

Standing here on Earth's surface, nothing may seem particularly out of the ordinary, but when you look at it from afar, our entire world is slightly off-kilter. As the Earth traces out its elliptical path around the Sun every year, the axis it rotates around each day is tilted with respect to that path, by roughly 23.4 degrees.

While we don't feel the tilt itself, we do see its effects, specifically in the changing of our seasons throughout the year. However, this 'tilt' doesn't translate into the planet 'wobbling' back and forth by 23.4 degrees during the year. Earth's tilt remains roughly the same all year long, with the planet's axis always pointing out of the North Pole towards a star named Polaris, and it's that consistent tilt, along with the motion of our planet around the Sun, that are the reasons for our seasons.

WATCH BELOW: This animation shows Earth's tilt throughout the year, which gives rise to our changing seasons.




As the video above shows, as Earth travels around the Sun, the angle of the planet's axis stays the same, and each hemisphere ends up pointed most towards the Sun during its summer solstice and pointed farthest from the Sun at its winter solstice. The panels on the right show how this affects the angle of the sunlight falling on Earth, with the bottom right showing the angle at the point where the stick figure is standing - roughly 44 degrees North latitude. In addition to the solstices, there are two brief moments during the year where both hemispheres are at exactly the same angle to the Sun. These are the equinoxes - Vernal in the spring and Autumnal in the fall.

Those two brief moments don't always happen at the same time and day every year though, due the way we tick off our minutes, days and years. 


The Myths of the Equinox

There are a few urban myths surrounding the equinoxes, that seem to make their rounds no matter how many times they're debunked.

1. Balancing act

Whenever the equinox is approaching, spring or fall, there are usually emails and social media posts that have people setting aside time that day to perform an amazing feat of egg balancing. Despite any implications that you can only perform this feat at the exact moment of the equinox, you can balance an egg on its narrow end at any time of the day, on any day of the year. The feat is not even easier on the equinox.

The reason for this? Firstly, the planet's tilt does not affect how gravity works, since Earth's gravitational force on us, and everything else on the surface of the planet, always points towards the centre of the planet.

Secondly, Earth's gravity completely overwhelms any other gravitational forces experienced here on the planet's surface. Even the Sun's gravity, which is the next strongest gravitational force on us here, is 1,600 times weaker than the 'pull' we feel from the Earth. The moon, the other planets and even the entire universe exert forces on us, but they're so weak that, next to the Earth's influence, they are completely negligible.

The only factors that matter in balancing eggs are the stability of the surface you are using, the 'bumpiness' of the eggs being balanced and the steadiness of your hands.

2. Those crazy days (and nights)

There are two days during the year when both night and day are roughly 12 hours long. However, despite expectations (and even the word equinox coming from the Latin for 'equal' and 'night') those two days do not fall on the equinoxes. Depending on what latitude you're at (for both northern and southern hemisphere), the date when day and night are roughly equal falls between 3 and 21 days before the spring equinox, and from 3 to 21 days after the fall equinox. The closer you are to the equator, the bigger the gap between those days and the equinox, and the equator actually never sees equal day and night.

That may seem strange, but in fact, we do this to ourselves by the way we track sunrise and sunset.

If we tracked sunrise and sunset based on when the sun was centred on the horizon, the dates would line up better. The way we actually track a day, however, is from the second that the sun's edge crests the eastern horizon, to the moment the sun's edge disappears below the western horizon. So, due to that, the day is always slightly longer than 12 hours on each equinox.

3. Shadows stick to us

Peter Pan may have lost his shadow, but it's very difficult for us to get away from ours.

There have been some claims that you can stand on the equator during the equinox and not cast a shadow. While that might seem credible at first glance, as long as it's a clear sunny day, you will still cast a shadow.

Even on the equator, with the equinox happening exactly at local noon - so the Sun was directly overhead - you would still look down to see the shadow of your head, shoulders and torso falling across and between your feet.

4. Leaves change colour in the fall

While not specifically about the equinox, this colourful trend does tend to take place after the equinox ushers in fall, and it's an interesting one - in that it's half true.

The leaves of deciduous trees do, indeed, change from green to various shades of yellow, orange and red during the fall. That much is true.

However, technically, the green didn't turn into those hues. The leaves simply lost the green, which let their natural colours - which were really there all along - finally show. So, why does this happen? I'll let my very learned colleague, meteorologist Jaclyn Whittal, take it from here:




Are there any other myths or claims you've heard about regarding the equinoxes? Any interesting facts you'd like to share? Leave your comments below.

RELATED VIDEO: Mars as big as the Moon? Zero-G Day? Balancing eggs on the equinox? Here's the science behind science hoaxes.




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