Astronomical Strangeness

The older I get, the more I am affected by daylight and the length of the days.

I don't understand this, and I already know I'm not going to understand the explanation after somebody explains it, but, although December 21st is the shortest day of the year here in the Northern hemisphere, sunset starts getting later a couple of weeks earlier than that. Here in Western New York, in Rochester, the nearest city to me that I could find data for, the earliest sunset occurs on the 9th of December. By December 21st, the shortest day of the year, sunset is already three minutes later.

So if, like me, you get up when it's already starting to get light out, and you're more aware of sunset than sunrise, December 10th is the day that relief from the darkness of Winter effectively starts.

By January 15th, sunset in Rochester has "latened" from 4:35 to 5:00 p.m.

Sad?
By the way, if you get depressed in the Winter...my brother Scott worked for Dr. Norman Rosenthal of the National Institutes of Mental Health when they were working out the treatment for seasonal affective disorder (SAD), the name for seasonal depression. The cure is as elegant as cures get—light! Bright, full-spectrum light administered regularly. And it's very effective, too. Search Amazon or Google for "SAD lights" or "SAD therapy lights."

Sit next to the light for half an hour to two hours every morning—45 minutes is a good starting time—preferably in the minutes or hours before the sun comes up, to artificially lengthen the day. (You can be doing other things.) You should feel improvement within ten days. The degree of relief varies with individuals, but can make dramatic changes for sufferers. (And SAD can be bad. NIMH got the worst cases, and I still recall some of the stories my brother told.)

The light cure is called phototherapy. I could think of some other definitions for that term.

Mike
(Thanks to S. and S.)

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(To see all the comments, click on the "Comments" link below.)
Featured Comments from:

Michael Perini: "Re the Broader 'Phototherapy' definition, several years ago I bought two of the 10,000 Lux S.A.D. boxes from Full Spectrum Solutions to use as relatively inexpensive product photography / copy lights and they have worked wonderfully. In a pinch, bounce them off a white wall for a 'window light' portrait. Full spectrum and very high CRI lighting enhances almost everything from the way your food looks in the kitchen to the ability to read small print—it's more than just brightness.

"Interestingly, as the LED revolution comes into full swing we should pay particular attention to CRI. The LEDs you purchase in big box stores can be of horrible color. So it pays to look. (If CRI  or Color Rendering Index is not on the package and above 90, look elsewhere) We didn't have this problem with tungsten because even if its color temperature is low, it emits some spectral energy across the full spectrum—it's a 'black body emitter.' Ctein had a recommendation for high CRI LEDs used in his renovation which I don't remember at the moment. Neither fluorescents nor LEDs radiate a full spectrum of light natively so they require some engineering to do so. As I am sure many folks have already found fixing color from a discontinuous spectrum can be impossible in the worst cases.

"Spend some time under 5500k CRI93 light and you will miss it when you turn it off. 'Good Light is a Good Idea.'"

Bryce Lee: "My own physician some years ago suggested with the time change from Daylight Savings to Standard, to use such a light device. I usually turn it on whilst looking at my morning electronic mail and then when reading the on line National Post. It sits to one side; I change the side the lamp sits on the desk to the opposite side every other day. The lamp has two settings, normal, and really bright as well as two different lenses. I got mine refurbished at the local Habitat for Humanity outlet. Have no earthly idea if it helps however do notice it does seemingly raise my internal energies!"

[Note: See the comments section for some nice-sounding and possibly accurate descriptions of the Equation of Time. As foretold, I make neither head nor tail of 'em. —Mike the Untechnical Ed.]

Jim Hughes: "Now that we live in the same time zone, let's compare. On December 9th in Rochester, sunset is at 4:35 p.m., eastern standard time. In Camden, Maine, due to our being located farther east in the zone, sunset will officially be declared at 3:58 p.m. So look on the bright side. You will be benefitting from an additional 37 minutes of afternoon daylight in which to make photographs!"

Mike replies: I always used to like to take the ferry across Lake Michigan to visit my cousins. In so doing I went from the Eastern edge of the Central Time Zone to the Western edge of the Eastern Time Zone, and magically acquired a lovely extra hour of evening daylight.

Kenneth Wajda: "I use SAD lights for food photography and portraits and film work. Great daylight-balanced soft light in a freestanding box."

Comments

[Mike Scott]

If the Earth's orbit was perfectly circular, then solar noon would always be at the exact same time, and the earliest sunset and latest sunrise would both be on or around 21 December. But it's not circular, and we're close to the sun in winter than in summer, which means that we're moving faster in winter than in summer, which means that the solar day is a bit longer in winter than in summer. Since the solar day is longerm, solar noon gets a little bit later each day, and so both sunrise and sunset also tend to get a bit later, which exacerbates the fact that sunrise is getting later anyway, but counteracts sunset getting earlier, and reverses it a few days before the actual solstice.

[01af]

> ...but, although December 21st is the
> shortest day of the year here in the
> Northern hemisphere, sunset starts getting
> later a couple of weeks earlier than that.

It's called the 'equation of time.' Basically it simply is the fact that, due to the earth's orbit around the sun being an ellipse (as opposed to a circle) and the earth's axis being tilted, the time from one noon to the next, for a given point on the earth's surface, is not always the same through the year. Not only the time from sunrise to sunset varies with the seasons; so does the time from high noon to high noon.

[Bruce McL]

One way of looking a this is as a very complicated geometry problem.

On the other hand, you could set it up and watch. Shine a spotlight on a globe with a properly tilted stand in a darkened room. Mark a longitudinal line on the globe with a sharpie, then watch what happens at the light/dark boundary as you rotate the stand of the globe relative to the position of the light. The angle the sharpie line makes with the line of light and dark made by the spotlight will change.

Photo therapy indeed! :-)

[TBannor]

Well, here goes. The reason sunsets start getting earlier a couple weeks before northern hemisphere winter solstice is due to the differrence between a sidereal day and a solar day and the fact that the earth is approaching perihelion (closest approach to the sun) and therefore acelerating in its orbit. Perihelion is about two weeks after the solstice. A solar day, the time is takes for a point on earth to rotate from sunset to sunset, or noon to noon, etc, is longer than the time it takes to rotate exactly once on its axis because of the earth's orbital speed. It has to turn a bit further each day to bring the sun to the same point in the sky. As it approaches perihelion, it's orbital speed increases enough that it has to rotate even further than we usually experience, so it delays both sunrise and sunset more markedly.

Curiously, the same effect is huge on Mercury, which rotates 3 times for every two orbits. As Mercury approaches perihelion, the sun actually appears to stop, reverse and then proceed in its path across the sky.

[TBannor]

I should have added that Mercury has a much more eccentric orbit than earth and so the acceleration as it approaches perihelion is much greater. Its orbital speed increases so much that it's rotation doesn't turn fast enough to put the sun in the same place from noon to noon, etc.

[Kenneth Tanaka]

You're in good company. It's a good season to spend time under the hood of a full-spectrum color print viewing booth! (Or in the southern hemisphere.)

[david adam edelstein]

Do we have to call phototherapy with tungsten lights vs. LED lights analog vs. digital phototherapy?

Have you built a community of snarky commenters?

[Apparently at least one [g] --Snarky Ed.]

[VK]

tl;dr: the Equation of Time (https://en.wikipedia.org/wiki/Equation_of_time)

The shortest and longest days of the year are related to the tilt of the earth's axis to its orbit. The days that these happen are not when the Earth is at its farthest or nearest point in its orbit. This difference leads to a discrepancy in where the Sun is expected to be and where it actually is, called the Equation of Time. That is why latest sunrise times and earliest sunset times don't match up with shortest day.

[Phil]

I believe that the disconnect between the time at sunset and the day's length is due to the Earth's precession movement. Think of it as a top (of the other kind ;) wobbling a bit about its rotation axis...

As for phototherapy, I think it's also worthwhile to mention that it's basically free, energy-wise, if you live in latitudes where home heating is required. All that light will eventually end up in the form of heat!

[Bob Rosinsky]

I lived in Boston for 21 years. For me, SAD usually kicked in around Halloween. By mid-December, I was miserable. I spent $400+ on a full-spectrum light box (made in Alaska) and doubled up on SSRIs. The light helps a lot if one is: A) a morning person; B) willing to stick to a photo therapy regimen.

I have never been a morning person, and my schedule often varies from day to day.

In April Y2K + 3, we (wife, daughter, dog, and I) moved to Florida--the sunshine state. I no longer get bogged down with SAD.

Here in Sarasota, Florida, the grass isn't greener, rather it's just a different shade of green. ... I miss Boston for its abundant intellectual, cultural, culinary, and cosmopolitan attractions. I alos miss autumn and spring.

Summers are brutal in Sarasota (6 months). Despite high heat and humidity, I'll take sunshine and sweat over darkness and chill.

Sarasota is nice. There are a lot of sharp retirees and snowbirds, hobby shops, meetup groups, cultural venues, and mom and pop restaurants.

As a kid growing up in Nebraska, I never imagined forsaking seas of corn and wheat for the Atlantic Ocean and the Gulf of Mexico.

[John]

At least much of the USA, if not all of it, still has plenty of sunlight to go around during the winter. In Europe, I couldn't stand the long dreary days of fall and winter. Hence my plan to not live north of the Alps again, if/when I move back to Europe.

[Jonathan]

Similar experience to Bob Rosinsky's. I dreaded Winter and left the Midwest for FL as soon as I could. Wish I'd gone sooner.

If you're a SAD sufferer living at high latitude your neighbors will tend to be self-selected for indifference to darkness and may not understand your problem. You have to trust your gut and do whatever you need to do to get light.

[Dave in NM]

Relief from SADness was one of the biggest benefits I experienced when I moved from NY to NM. Good lighting is great, but you can't beat natural sunlight and a short walk outside to cure the winter blues.

[David Parsons]

Regarding phototherapy, I wonder if computer monitors might be a useful tool for treating SAD. We all stare at them way too much as it is, why not have them serve double duty.

You could even get a prescription and insurance coverage to cover the additional cost of specific models.

[Bob Gary]

Mike,
Just use +2 stops more when shooting in Dec....

[robert e]

It's good to know that phototherapy lights have photographic applications, though it does make sense.

Before diving in, people might want to read this page about light therapy for an overview about how it works with different kinds of depression, the slight risks involved for certain people, and alternatives. One approach, called a "dawn simulator", doesn't require a special light, has fewer risks, and may also be a more effective way to use a phototherapy light (for depression, not photography):

http://psycheducation.org/treatment/bipolar-disorder-light-and-darkness/light-therapies-for-depression/

[robert e]

Oh, and I can report that at least some users of phototherapy lights use the catchier nickname "happy lamps". (I wonder if there's an emoticon for that...)