Angle of Sun at Equinox Baby Island Heights Wa

Where does the celestial equator intersect your horizon? No thing what you breadth is, it intersects your horizon at points eastward and due westward. Read more than about how an observer's breadth affects your visible sky.

The September 2017 equinox happens on September 22 at 20:02 UTC (three:02 p.m. CDT); translate to your time zone. So as you read this, the due-eastward equinox sunrise might have already have happened for y'all. But possibly it's not also late for you to catch the due-due west equinox sunset?

It'southward often said that – at each equinox – the sun rises due east and sets due west. And that's true, no affair where you live on the globe. But why? And how tin can you visualize it?

Lookout man for the young moon and Jupiter on this first twenty-four hours of autumn (spring)

Photos of last night's moon and Jupiter, on equinox eve

What is an equinox? An equinox happens when the ecliptic - or sun's path - intersects the angelic equator, the imaginary line above Earth'due south equator.

First you need to know this. An equinox occurs when the sunday crosses the celestial equator. No affair where y'all are on Earth, the angelic equator intersects your horizon at due e and west. See the diagram to a higher place to endeavor to visualize that.

At its highest point in your sky, the angelic equator appears loftier or low, depending on your latitude. The imaginary celestial equator is a nifty circle dividing the imaginary angelic sphere into its northern and southern hemispheres, so, from the equator, information technology's directly overhead, for instance, wrapping the heaven directly above Globe's equator.

For purposes of today'due south visualization, though, the tiptop of the angelic equator in your sky doesn't thing. What matters are these ii things. One, the dominicus is on the angelic equator at the equinox. Two, the celestial equator intersects your horizon at points due e and w.

Voila. The sun rises due eastward and sets due w on the twenty-four hour period of the equinox, as seen from around the globe.

Where does the angelic equator intersect your horizon? No matter where you are on Earth (unless you're at a pole), the celestial equator meets your horizon at points due e and due west.

Why does the sun rises due east and set west at the equinoxes? The blue line is the celestial equator (ever at your due east and due west points). The purple line is the ecliptic, or sunday'due south path. At the equinox, these two lines intersect. Illustration via JCCC Astronomy.

This fact – the dominicus rising and setting due east and west at every equinox – makes the solar day of an equinox a good day for finding due east and due west from your yard or other favorite site for watching the sky.

Just go outside around sunset or sunrise and notice the location of the sunday on the horizon with respect to familiar landmarks. If yous do this, you'll be able to use those landmarks to detect those cardinal directions in the weeks and months alee, long afterward Earth has moved on in its orbit effectually the sun, conveying the sunrise and sunset points southward or north.

Equatorial sundial by Tom Laidlaw. The n face of an equatorial sundial receives sunshine in spring and summer, and the south confront receives information technology in fall and winter. On the equinoxes, sunshine should hit neither side of the sundial, but only the edge.

Now permit'south think about what an equinox really is. Information technology's an consequence that happens on the imaginary dome of Earth'due south heaven, just each equinox also represents a existent bespeak on Earth's orbit. What happens at every equinox is very existent – as existent as the sun's passage beyond the sky each twenty-four hours and every bit real as the change of the seasons.

Our ancestors didn't sympathize the equinoxes every bit events that occur in the course of Earth'due south yearly orbit around the sun. But if they were observant – and many were very observant indeed – they surely marked today equally being midway between the sun'south everyman path across the sky in winter and highest path across the sky in summertime.

And that'due south where nosotros are, in orbit, at this equinox.

We're midway betwixt the two extremes of the sun's path in your sky.

The seasons result from the Earth's rotational axis tilting 23.5 degrees out of perpendicular to the ecliptic - or Earth's orbital plane.

An equatorial ring was used in ancient times in an attempt to decide the equinoxes. The ring airplane is fix parallel to the plane of the Globe's equator. If the equinox happened during the daylight hours, the inside of the ring was expected to exist completely in shade at the equinox. Prototype via Wikipedia

Bottom line: The 2017 September equinox comes on September 22 at 20:02 UTC – or 3:02 p.m. Central Daylight Fourth dimension for usa in the central U.South. At each equinox, the dominicus rises due east and sets westward. The diagrams and explanations in this post are meant to assistance you visualize that.

Watch for the immature moon and Jupiter on this first solar day of autumn (spring)

Photos of last night's moon and Jupiter, on equinox eve

Bruce McClure

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About the Author:

Bruce McClure served every bit lead writer for EarthSky's pop Tonight pages from 2004 to 2021, when he opted for a much-deserved retirement. He's a sundial aficionado, whose love for the heavens has taken him to Lake Titicaca in Bolivia and sailing in the North Atlantic, where he earned his angelic navigation certificate through the School of Ocean Sailing and Navigation. He also wrote and hosted public astronomy programs and planetarium programs in and effectually his home in upstate New York.

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Source: https://earthsky.org/tonight/sun-rises-due-east-and-sets-due-west-on-day-of-equinox/

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