Date: March 12, 2011

Title: Sunrise In Greenland

Podcaster: Rob Sparks

Organization: http:/halfastro.wordpress.com & http://twitter.com/#!/NOAONorth

Description: North of the arctic circle, winter can be a time of darkness 24 hours a day. The return of the Sun is celebrated. In the small town of Ilulissat, Greenland, the citizens were looking forward to the first sunrise on January 13th. Many people were surprised when the Sun rose on January 11th, two days early. What could have caused this strange phenomena? This podcast will investigate what happened with a little help from a high school physics teacher in Greenland.

Bio: Rob Sparks is a Science Education Specialist at the National Optical Astronomy Observatory. A lifelong astronomy enthusiast, he earned a B.A. in physics at Grinnell College and his M.S. at Michigan State University. He taught high school physics, math and astronomy for 11 years at schools on St. Croix, Florida and Wisconsin. He spent the 2001-2002 school year working on the Sloan Digital Sky Survey as a recipient of the Fermilab Teacher Fellowship. He spent the summer of 2003 at the National Radio Astronomy Observatory as part of the Research Experience for Teachers. He has been working as a NASA Astrophysics Ambassador since 2002. He was a member of the Galileoscope Working Group for the International Year of Astronomy. He also blogs at halfastro.wordpress.com.

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Transcript:

Hi, This is Rob Sparks from the Education and Public Outreach group at the National Optical Astronomy Observatory in Tucson, Arizona. Today’s podcast explores a mystery that started on January 11th of this year.
Many people know that if you are north of the arctic circle, you will experience 24 hours of darkness for at least part of the year. The farther north you go, the longer you experience that long winter night. At the north pole, you do not see a sunrise from the first day of fall to the first day of spring.

As you can imagine, people who live that far north look forward to the return of the Sun. Many communities have celebrations the first day the Sun pokes over the horizon. Such is the case in Illulissat, Greenland, a small town of about 4,000 people located north of the arctic circle on Greenland’s west coast. The people of Illulissat were looking forward to the Sun rising on January 13th. This year, however, things were a little bit different.
The Sun was observed to rise above the horizon on January 11th, two days earlier than usual. What could have caused such a strange phenomena?

As usual, the internet was eager to come up with a variety of explanations. I wasn’t buying most of the explanations so I blogged about it (halfastro.wordpress.com) discussing my ideas. Eventually, with the help of a physics teacher in Greenland, the mystery was solved.

First, let’s examine several of the candidates for what happened. A story published online in the Daily Mail quoted Thomas Posch of the Institute for Astronomy at the University of Vienna that a change in the local horizon could be the culprit. He guessed that melting glaciers due to global warming could have let the Sun peek above the horizon two days earlier.

Although I accept the science of global warming, I wasn’t ready to buy this explanation. The first thing I did was figure out where the Sun was at local Noon on January 11th. After typing the latitude and longitude of Illulissat into the NOAA Solar Position Calculator, it turned top of the Sun was 0.41 degrees below the horizon. It didn’t matter where the glaciers were. The Sun was below the horizon even if it was completely flat! You can’t go lower than a flat horizon no matter how many glaciers you melt.

Another possibility floated was due to the glaciers melting, the city had been uplifted. Uplift after glaciers pass is usually on the order of millimters to centimeters per year so that seemed unlikely. Just for fun, I used the small angle approximation and the 0.41 degrees the Sun was below the horizon to figure out how much uplift you would need. A flat horizon is about 2.9 miles away. Plowing through a little math show you would need an uplift (or glaciers melting) of about 32 meters, over 100 feet (in my original blog entry I guessed the horizon was six miles away since I couldn’t remember off the top of my head the distance to a flat horizon so I revised this downward somewhat). Since the town is on the coast, they would have easily noticed if they were suddenly 100 feet more above sea level! (and this could easily be verified by GPS as well)

So I don’t buy the melting glacier idea. Another idea floated by some sources is that a cloud of methane could have drifted by and increased the amount of refraction caused by Earth’s atmosphere causing the Sun to rise early. This idea has a global warming tie in as well in that the methane could come from thawing permafrost in Siberia. But again, I have some problems with this one.

First, any methane cloud from Siberia would have a LOT of time to dissipate before it got to Greenland. Second, the index of refraction of methane is 1.00044 and the index of refraction of air is 1.0003. It would take a VERY high concentration of methane to significantly change the index of refraction of Earths atmosphere and cause an additional four tenths of a degree of refraction needed to get the Sun above the horizon.

Then there is the scenario proposed by doomsday proponents that somehow Earth’s geographic poles are shifting and that is the cause of this phenomena. The problem here is that the evidence just doesn’t back it up. Any shift in Earth’s rotational axis would affect Sunsets worldwide, not just in one town in Greenland. Additionally, it would affect the positions the stars. We measure the positions of objects to sub-arc second accuracy every night. A shift of four tenths of a degree would jump out at professional and amateur astronomers around the world who would instantly know something is happening. Sunset and sunsrise times would change worldwide as well. Our observations show everything is exactly where it should be. It should be noted that this phenomena is part of the 2012 doomsday nonsense and has been discussed in other episodes of the 365 Days of Astronomy.

To me the most plausible idea was an atmospheric phenomena. My first thought was a Sun halo. Sun halos can occur in many sizes, some as small as four degrees. A small halo, especially if it was only a partial halo, could give an illusion of a sunrise a few days early. That’s where I put my bet.

But the story on the web left many questions unanswered.. What is the exact location of the observation? What does the southern horizon look like from there? Did the sunrise again on the 12th? Were there any pictures of this early sunrise?

So I posted my blog entry. It got a lot of hits from around the world. A couple of days later, I got a break. A physics teacher from Greenland who commented under the name of Tommy B left a comment that filled in lot of details. He was able to provide the exact GPS coordinates of the observation as well as an image taken from that location. There is a fjord directly to the south. Icebergs might occasionally drift by, but there are no large glaciers to the south. The Sun did NOT come up on the 12th. He also revealed that the Sun came up LATE on January 13th! These observations kill any melting glacier explanation (unless the glaciers magically reappeared on the 12th) or Earth’s rotational axis changing. An atmospheric phenomena was clearly the front runner at this point.

On January 25th, Tommy posted an answer he got from the Neils Bohr Institute. They said there was an atmospheric inversion layer that day. An atmospheric inversion layer occurs when the air near the ground is cooler than the air above it. One of the effects of a temperature inversion can be the production of what is called a superior mirage. A superior mirage produces an inverted image of the object above it. So the mirage of the Sun was above the horizon even though the Sun was below the horizon (this phenomena sometimes happens with ships beyond the horizon as well). So it appears I picked the wrong atmospheric phenomena at first, but was at least on the right track. On January 13th, the opposite phenomena occurred and there was less atmospheric refraction leading to a delayed sunrise.

Other commenters on the blog added more interesting information. Tom In Kodiak linked to a story from the Anchorage Daily News about a sunrise a full week early in Barrow, Alaska. The National Weather Service confirmed it was an illusion due to an inversion layer. A commenter named Nirwana posted a link to a story about the Sun rising one day early in Trosmo, Norway

After hearing about some of these other reports, I am beginning to suspect this is not a rare phenomena at very northern latitudes, although it may not be frequently observed due to low population densities north of the arctic circle. I am curious if this is observed in the Antarctic (a little research reveals that temperature inversions are common on polar plateaus, but there are very few people there to see it.) I would love to hear other reports. I suspect this story got some legs to travel around the internet due to the global warming angle as well as the doomsday prognosticators pushing their “pole shift” ideas.

But in the end, after tracking down some sources with help from other curious people on the internet, it turns out to be an interesting yet understood atmospheric phenomena. Thanks to all who pitched in on this one!
You can see the original blog post and discussion at http://halfastsro.wordpress.com. Thanks for listening to today’s 365 Days of Astronomy podcast.

End of podcast:

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