Starship Asterisk*

A Picturesque Equinox Sunset

Explanation: What's that at the end of the road? The Sun. Many towns have roads that run east - west, and on two days each year, the Sun rises and sets right down the middle. Today is one of those days: an equinox. Not only is today a day of equal night (("aequus"-"nox") and day time, but also a day when the sun rises precisely to the east and sets due west. Featured here is a picturesque road in northwest Illinois, USA that runs approximately east -west. The image was taken one year ago today, during the March Equinox of 2015, and shows the Sun down the road at sunset. In many cultures, this March equinox is taken to be the first day of a season, typically spring in Earth's northern hemisphere, and autumn in the south. Does your favorite street run east - west? Tonight at sunset, with a quick glance, you can actually find out.

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Arise my Druid Brothers and Sisters.... Muuuahhhahahahahaha...

Oh... Sorry.... um... not very scientific...OK...my bad...

Yes, another interesting APOD... strikingly done. Very Effective. Much Science... just a Scientific fact of where the Sun and Earth are in relationship to each other... and NO OTHER SIGNIFICANCE... Except of course the beginning of Spring Time as a Season, and getting out and cleaning the house, and preparing the yard... and VACATION!!!!!!! from College....WOO HOOOOO!!!

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I'm going to go out on a limb here...the pictured road? Forest Hills Road...perhaps somewhere near...11250 Forest Hills Road

Which by the way, is home of the best optics maker in the solar system, bar none.

" today [is] a day of equal night (("aequus"-"nox") and day time" - it is not. the correct line would be: 'today nowhere on earth are day and night of equal length, day being longer everywhere (on both poles there's 24 hrs daylight)". your statement would be true if 1) the sun had no diameter; 2) the earth had no atmosphere; 3) the earth were a perfect sphere. but the picture is beautiful and melancholy.

Forest Hills Rd is mostly North -South. There is a Forest Preserve with a East-West Rd nearby though. Not sure it really qualifies as norrwest IL. I'd call it northern Illinois

Curse the people who laid out the road grids of our cities! They lumbered us with NS, EW! As a result, we have sun in our eyes as we try to drive to or from work at times. If only they had decided on road grids tilted 45 degrees from that, we'd NEVER have the sun directly in our eyes as we drove --- and many people would be alive who are dead because of the folly of the road designers!

bjmb wrote:" today [is] a day of equal night (("aequus"-"nox") and day time" - it is not. the correct line would be: 'today nowhere on earth are day and night of equal length, day being longer everywhere (on both poles there's 24 hrs daylight)". your statement would be true if 1) the sun had no diameter; 2) the earth had no atmosphere; 3) the earth were a perfect sphere. but the picture is beautiful and melancholy.

Personally, I buy the explanation as reasonable given that "day" and "night" are loosely defined concepts to begin with, interpretable in many ways. This wording clearly expresses what's going on at the equinox in a nontechnical way that is accessible to most people.

A few years ago I taught an astronomy course, Since we live in the Midwest, we have lots of east-west roads. So I offered students extra credit if they could take a good picture of the sun rising or setting over one near the end of September. Many of them had no idea how to tell if a road ran east-west (look at a map) or how to get a picture with a digital camera. A sad tale of Nature Deficiency Syndrome.

heehaw wrote:Curse the people who laid out the road grids of our cities! They lumbered us with NS, EW! As a result, we have sun in our eyes as we try to drive to or from work at times. If only they had decided on road grids tilted 45 degrees from that, we'd NEVER have the sun directly in our eyes as we drove --- and many people would be alive who are dead because of the folly of the road designers!

Except that in the northern U.S. you'd have the problem near the solstices, when the sun rises in the NE or SE and sets in the NW or SW. My city (Green Bay) is laid out according to the French system where lots run perpendicular to the river, roughly WNW-ESE. We don't have a problem at the equinoxes, but we do in May and August near sunset.

You COULD park and wait until the Sun was in a better position.

Chris Peterson wrote:

bjmb wrote:" today [is] a day of equal night (("aequus"-"nox") and day time" - it is not. the correct line would be: 'today nowhere on earth are day and night of equal length, day being longer everywhere (on both poles there's 24 hrs daylight)". your statement would be true if 1) the sun had no diameter; 2) the earth had no atmosphere; 3) the earth were a perfect sphere. but the picture is beautiful and melancholy.

Personally, I buy the explanation as reasonable given that "day" and "night" are loosely defined concepts to begin with, interpretable in many ways. This wording clearly expresses what's going on at the equinox in a nontechnical way that is accessible to most people.

however 'loosely' one defines 'night' and 'day', there is no way you can define 24 hr sunlight at both poles as 'equal night and day'.

bjmb wrote:

Chris Peterson wrote:Personally, I buy the explanation as reasonable given that "day" and "night" are loosely defined concepts to begin with, interpretable in many ways. This wording clearly expresses what's going on at the equinox in a nontechnical way that is accessible to most people.

however 'loosely' one defines 'night' and 'day', there is no way you can define 24 hr sunlight at both poles as 'equal night and day'.

I'm not so sure. The exact poles are singularities, but even a fraction of an inch away from the poles the concept of equal day and night makes sense.

Chris Peterson wrote:

bjmb wrote:

Chris Peterson wrote:Personally, I buy the explanation as reasonable given that "day" and "night" are loosely defined concepts to begin with, interpretable in many ways. This wording clearly expresses what's going on at the equinox in a nontechnical way that is accessible to most people.

however 'loosely' one defines 'night' and 'day', there is no way you can define 24 hr sunlight at both poles as 'equal night and day'.

I'm not so sure. The exact poles are singularities, but even a fraction of an inch away from the poles the concept of equal day and night makes sense.

if only that were true - but it isn't. on the equinox, midnight sun begins some 111 km from the exact north pole (approx 1° from the pole) on the 0° meridian, and in the south midnight sun on the equinox extends some 55 km from the pole (on the greenwich meridian, approx. 0.5° from the pole). anyway, no 'equal night and day' by any stretch of the imagination. what you define is called 'equilux' and falls on a different date for (nearly) any place on earth, but never on the equinox.
is it such a chore to write 'on the equinoxes night and day are more or less the same length almost everywhere on earth'? it is nobody's fault that nature isn't as neat as we would want.

The equinox is defined as the day the sun crosses the equator. The time of the most recent crossing was 2016 March 20 04:30 UTC. This time is the same for all points on the Earth.

bystander wrote:The equinox is defined as the day the sun crosses the equator. The time of the most recent crossing was 2016 March 20 04:30 UTC. This time is the same for all points on the Earth.

and that is the exact definition, 'equal night and day' having no place in it.

bjmb wrote:

bystander wrote:The equinox is defined as the day the sun crosses the equator. The time of the most recent crossing was 2016 March 20 04:30 UTC. This time is the same for all points on the Earth.

and that is the exact definition, 'equal night and day' having no place in it.

Ok. We get it. Your point has been made.

Correct me if I'm wrong - an equinox occurs when the sun crosses the Equator. Thus, how can sunrise be due East (and sunset due West), as stated in the APOD description, at any point North or South of the Equator? Surely sunrise would be South East (for Northern denizens) and North-East for Southerners?

Narodul wrote:
Correct me if I'm wrong - an equinox occurs when the sun crosses the Equator. Thus, how can sunrise be due East (and sunset due West), as stated in the APOD description, at any point North or South of the Equator? Surely sunrise would be South East (for Northern denizens) and North-East for Southerners?

To the extent that the radius of the Earth is at all significant vis-a-vis the distance to the Sun you are correct.

Dear bjmb, in the 24 hour period that straddles the precise time the Sun crosses the celestial equator (i.e. the precise time of equinox), both hemispheres on Earth receive the same amount of incident radiation from the Sun (ignoring daily fluctuations in solar output). This only happens twice a year, around the equinoxes.

Indeed, the (more modern) definitions of the precise times of sunrise/sunset, based on the refracted light from the leading/trailing limbs of the Sun, relative to a perfect horizon, muck up the elegant literal translation of "equal night [and day]" that is otherwise seen as reasonable. But there are other ways of looking at what the term "equal night" can mean.

Narodul wrote:Correct me if I'm wrong - an equinox occurs when the sun crosses the Equator. Thus, how can sunrise be due East (and sunset due West), as stated in the APOD description, at any point North or South of the Equator? Surely sunrise would be South East (for Northern denizens) and North-East for Southerners?

If you think of the radius of Earth, relative to the Sun's (~109 times bigger), it can make it easier to visualize what a small difference it makes. The term "due east" is accurate enough for all but the most precise.

It is an interesting point, however. Another example is satellites orbiting Earth in geostationary, equatorial orbits. One might think that all observers on Earth could spot them on the celestial equator. But in fact, due to their relatively close proximity, an observer in the northern hemisphere will spot them south of the equator and vice-versa.

Nitpicker wrote:If you think of the radius of Earth, relative to the Sun's (~109 times bigger), it can make it easier to visualize what a small difference it makes. The term "due east" is accurate enough for all but the most precise.

It is an interesting point, however. Another example is satellites orbiting Earth in geostationary, equatorial orbits. One might think that all observers on Earth could spot them on the celestial equator. But in fact, due to their relatively close proximity, an observer in the northern hemisphere will spot them south of the equator and vice-versa.

I think the relevant ratio here is Earth's radius to the distance to the Sun- a factor of ~24,000.

heehaw wrote:Curse the people who laid out the road grids of our cities! They lumbered us with NS, EW! As a result, we have sun in our eyes as we try to drive to or from work at times. If only they had decided on road grids tilted 45 degrees from that, we'd NEVER have the sun directly in our eyes as we drove --- and many people would be alive who are dead because of the folly of the road designers!

Pfft. Just don't live to the west of your place of work.

Nitpicker wrote:

heehaw wrote:Curse the people who laid out the road grids of our cities! They lumbered us with NS, EW! As a result, we have sun in our eyes as we try to drive to or from work at times. If only they had decided on road grids tilted 45 degrees from that, we'd NEVER have the sun directly in our eyes as we drove --- and many people would be alive who are dead because of the folly of the road designers!

Pfft. Just don't live to the west of your place of work.

Unless you work the night shift.

Chris Peterson wrote:

Nitpicker wrote:If you think of the radius of Earth, relative to the Sun's (~109 times bigger), it can make it easier to visualize what a small difference it makes. The term "due east" is accurate enough for all but the most precise.

It is an interesting point, however. Another example is satellites orbiting Earth in geostationary, equatorial orbits. One might think that all observers on Earth could spot them on the celestial equator. But in fact, due to their relatively close proximity, an observer in the northern hemisphere will spot them south of the equator and vice-versa.

I think the relevant ratio here is Earth's radius to the distance to the Sun- a factor of ~24,000.

Yes, but I was only referring to a visualization aid. The size of the Earth projected onto the Sun, gives a good sense of the size of the error involved.

Chris Peterson wrote:

Nitpicker wrote:

heehaw wrote:Curse the people who laid out the road grids of our cities! They lumbered us with NS, EW! As a result, we have sun in our eyes as we try to drive to or from work at times. If only they had decided on road grids tilted 45 degrees from that, we'd NEVER have the sun directly in our eyes as we drove --- and many people would be alive who are dead because of the folly of the road designers!

Pfft. Just don't live to the west of your place of work.

Unless you work the night shift.

Touche.

I'll bite on this one. I notice that the picture taker's company is located in Laurel, MD. And living in the DC area, it seems that the trees look right for being in the area. However, our area generally is not laid out in a grid except in the cities. But that is not a city scene.

In any case, a look at Mapquest reveals a road called East-West Blvd located in Millersville, MD. And it does seem to run due east-west for a short while, before bending slightly to the south as the pictured road appear to as the road heads out of sight. In addition, that area is semi-rural and could easily be where the picture was taken.

I will admit this I cannot be 100% sure of this without going out there (and I am not about to), but what better-named road could that picture have been taken along?