Yes, it does. And that’s true no matter where you live on Earth, because we all see the same sky.
Image credit: James Jordan
No matter where you are on Earth, you have a due east and due west point on your horizon. That point marks the intersection of your horizon with the celestial equator – the imaginary line above the true equator of the Earth.
At the equinoxes, the sun appears overhead at noon as seen from Earth’s equator. That’s the definition of an equinox: it’s when the sun crosses the celestial equator, as seen in Earth’s sky.
That’s why the sun rises due east and sets due west for all of us on the day of an equinox. The sun is on the celestial equator, and the celestial equator intersects all of our horizons at points due east and due west.
This fact makes the 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 sun on the horizon with respect to familiar landmarks.
Image credit: Dendroica curulea
If you do this, you’ll be able to use those landmarks to find those cardinal directions in the weeks and months ahead, long after Earth has moved on in its orbit around the sun, carrying the sunrise and sunset points southward.
I’ve been thinking about this for a while and I really dont understand this. If I am far in the northern hemisphere, lets say near the north pole, wouldn’t the sun generally have a southerly direction to it. It would seem that the Sun would intersect the horizion in a more southern place in the sky, than someone who is watching the sun from Antartica? I dont understand how we all (around the world see the same sky) when it is undoubtedly a different season elsewhere in the world.
Hi Charles.
At the north pole, all directions are south. At the south pole, all directions are north. There is no east or west at the poles. Therefore, at the poles on the day of an equinox, the sun does not rise or set, but sits on the horizon all day long. Elsewhere around the globe, the sun rises due east and sets due west. However, the sun’s path across the sky differs, depending on your latitude. At the equator (0 degrees latitude), the equinox sun crosses the zenith (or is straight overhead) at noon. At 30 degrees latitude, the equinox sun shines 30 degrees below your zenith point at noon. At 60 degrees latitude, the equinox sun sits 60 degrees below the zenith point at noon. At far northern or far southern latitudes, the sun still rises due east and sets due west on the equinox, yet the sun’s path across the sky is much closer to the horizon than at places that are closer to the equator.
Bruce
Also keep in mind that the sun is incredibly far away.
Could I offer this plain-language attempt at an explanation?
1. At equinox the North Pole is the same distance from the sun as is the South Pole.
2. Latitude is measured by an observer in relation to the North-South axis of the earth. If an object appears to be 90 degrees to the North-South axis it is due East or due West of the observer.
3. The sun illuminates half the earth’s surface.
4. Light from the sun to the earth forms a cone. The sun is at the apex. The cone is symmetrical. The base of the cone is bounded by the circumference of the earth.
5. At equinox the Poles are two points on the circumference of the base of this cone. The angle North Pole to centre of the circular base to sun is 90 degrees, the same as the angle South Pole to centre to sun.
6. From the point of view of the sun, the earth rotates from left to right.
7. The left side of the circumference of the base of the cone is sunrise for all points. The right side is sunset for all points. (Ignoring a small complication at the poles.)
8. Light from the sun travelling the shortest route to any point on the circumference strikes it at a right angle, because of the symmetry of the cone.
9. Therefore, at equinox, for all observers on the left side of the circumference, the sun is rising due East, as East is at right angles to the North-South axis. And for all observers on the right side of the circumference, the sun is setting due West, as West is at right angles to the North-South axis.
10. This cone analogy is appropriate for an observer who does not know how far away the sun is. Once the sides of the cone are hugely longer than the base it is more accurate to imagine light arriving on earth as a cylinder. But again, light meets the circumference of the base at right angles, and the same reasoning as for a cone applies.
At other times of the year, the Poles are not equidistant from the sun, and the base of the cone (or cylinder) of light does not include them. Light does not strike the circumference of the plane that contains the observer and the two Poles, at right angles, and at those times the sun does not rise due East or set due West.
Thank you for this article. I have used a compass and measured the sun rising at 90 degrees in the morning and setting at 270 degrees. My,husband, told me I was wrong! He did not do the measurement with me. He insisted that there would be a difference due to our latitude (about 34 degrees N). Our disagreement is settled!
Mary,
The sun rises due east and sets due west on the equinox. However, magnetic north may or may not agree with geographical north, depending on where you live. See more at http://www.thecompassstore.com/decvar.html
To be ridiculously precise the sun is only over the equator for an instant. (9/23/2011 09:05 UTC.) Therefore unless you sunrise/set is at 09:05 the sun will not be exactly east or west.
Of more importance is the terrain to the east and west. At my house due to Kittle Hill the I first see the sun about 1/2 hour after the published sunrise and it will be somewhat to the south of east. The hill to the west is closer and the sun “sets” almost 1.5 hours early.
To find the direction (azimuth) of the sunrise find distance (in degrees) of the sun’s position of on the ecliptic from the celestial equator (as in the sun is in Gemini) . On the summer solstice it is 23.4 degrees, so the sun rises 23.4 degrees north of east. Your latitude determines the angle from the vertical at which the sun rises (not the angle from which it rises along the horizontal -{north to south})— at least that’s my impression of how it works
Why is it called sunrise & sunset, when (supposedly) the sun isn’t moving & we have been taught for the last 600 years? that the earth is moving, although prior to that it was recognised that the earth is still & the sun moves around the earth (thus sunrise & sunset.
NASA supports a still earth by using still earth calculations with satellite usage & rocket launching.
Who would care to do some research & advise what is the truth, not just accept what someone with a small old telescope told us was the truth?
This question arose as I watched night after night Venus being in (what appeared to be) the same spot, hour after hour – if the earth is spinning, why didn’t Venus’ position move (as the sun does)?