Land of the Long Twilights

The first (and only!) sunset1 this year at Amundsen–Scott South Pole Station in Antarctica occurs on March 22 at 0615 UTC (using “astronomer’s time” as time zone has no meaning so close to the South Pole).

The year’s first and only end of civil twilight (when the geometric center of the Sun lies 6° below the horizon) occurs on April 4 at 1153 UTC. That’s 13d05h38m after sunset.

The year’s first and only end of nautical twilight (when the geometric center of the Sun lies 12° below the horizon) occurs on April 21 at 0409 UTC. That’s 16d16h16m after the end of civil twilight.

The year’s first and only end of astronomical twilight (when the geometric center of the Sun lies 18° below the horizon) occurs on May 11 at 0521 UTC. That’s 20d01h12m after the end of nautical twilight, and 49d23h06m after sunset. That’s one heck of a long twilight!

Night lasts from May 11 at 0521 UTC until astronomical twilight begins on July 31 at 1916 UTC. A duration of 81d13h55m.

Nautical twilight begins on August 21 at 0024 UTC. That’s 20d05h08m after the beginning of astronomical twilight.

Civil twilight begins on September 6 at 2121 UTC. That’s 16d20h57m after the beginning of nautical twilight.

The first and only sunrise of the year occurs on September 20 at 0945 UTC. “Morning” twilight lasts a total of 50d14h29m.

The Sun remains above the horizon continuously until sunset on March 22, 2025 at 1100 UTC. Daylight “hours” last 183d01h15m.

Strange place!

1Sunrise and sunset. For computational purposes, sunrise or sunset is defined to occur when the geometric zenith distance of the center of the Sun is 90.8333 degrees. That is, the center of the Sun is geometrically 50 arcminutes below a horizontal plane. For an observer at sea level with a level, unobstructed horizon, under average atmospheric conditions, the upper limb of the Sun will then appear to be tangent to the horizon. The 50-arcminute geometric depression of the Sun’s center used for the computations is obtained by adding the average apparent radius of the Sun (16 arcminutes) to the average amount of atmospheric refraction at the horizon (34 arcminutes).
[Reference:, but see here:]

Note: SkySafari 6 Pro, Version 6.8.2 (6820) for MacOS was used to determine these dates and times. The location coordinates used for Amundsen–Scott South Pole Station were 89° 58′ 59.9″ S, 139° 16′ 01.2″ E, 2835 m.

Fun Fact: Did you know that there is a seismic station near the south pole, and that it has been operating since 1957?

Streetlighting Concerns

I submitted the following letter to the editor to the Dodgeville Chronicle this evening:

Dear Editor:

Have you noticed the gradual transformation of our streetlights in Dodgeville, Mineral Point, and other communities in SW Wisconsin?  The light source in our streetlights is changing.  High Pressure Sodium (HPS), which has been in use for decades and produces a orangish-white light, is being replaced by light emitting diodes (LEDs), producing a whiter light.

What’s not to like?  LED’s many advantages include: efficiency, longevity, instant-on and instant-off, and dimmability, to name a few.  But Alliant Energy is installing new streetlights that produce white light that is too blue, and the illumination levels are about 2.6 times as bright as the high pressure sodium streetlights they are replacing.

Lighting specialists use a term called “correlated color temperature” or CCT (in Kelvin) that allows us to compare the relative “warmness” (redder) or “coolness” (bluer) of  various light sources.   The illumination provided by candlelight has a CCT around 1500 K, HPS around 2000 K, an incandescent light bulb around 2800 K, sunrise/sunset around 3200 K, moonlight around 4700 K, and sunny noon daylight around 5500 K.  The higher the color temperature, the bluer the light.

Higher color temperature illumination is acceptable in workplace environments during the daylight hours, but lower color temperature lighting should be used during the evening and at night.  Blue-rich light at night interferes with our circadian rhythm by suppressing melatonin production, thus reducing sleep quality, and several medical studies have shown that blue light at night increases the risk of developing cancer, most notably breast cancer.  Even low levels of blue-rich light at night can cause harm.  While it is true that something as natural as moonlight is quite blue (4700K), even the light of a full moon provides an illumination level of just 0.01 foot-candle, far dimmer than street lighting, parking lot lighting, and indoor lighting we use at night.

LED streetlights are available in 2700K, 3000K, 4000K, and 5000K.  I believe that Alliant is installing 4000K streetlights in our area—I certainly hope they are not installing any 5000K.  What they should be installing is 2700K or 3000K.  These warmer color temperature lights are no more expensive than their blue-white counterparts, and the slightly higher efficiency of the blue-white LEDs is entirely nullified by over-illumination.

Even considering a modest lowering of light level with age (lumen and dirt depreciation), these new LED streetlights are considerably brighter than the HPS lights they are replacing.  Just take a look around town.  What is the justification for higher light levels in our residential areas, and when was there an opportunity for public input?  In comparison to older streetlights, the new LED streetlights direct more of their light toward the ground and less sideways or directly up into the night sky, and that is a good thing.  But now the illumination level is too high and needs to be reduced a little.

If you share my concerns about blue-rich lighting and illumination levels that are often higher than they need to be, I encourage you to contact me at oesper at mac dot com.  I operated an outdoor lighting sales & consulting business out of my home (Outdoor Lighting Associates, Inc.) from 1994-2005, and wrote the first draft of the Ames, Iowa Outdoor Lighting Code which was unanimously adopted by the city council in 1999, so I am eager to work with others in the Dodgeville area who are also interested in environmentally-friendly outdoor lighting.

David Oesper