APOD: Antarctic Analemma (2015 Sep 23)

[APOD Robot]

Antarctic Analemma

Explanation: Does the Sun return to the same spot on the sky every day? No. A better and more visual answer to that question is an analemma, a composite image taken from the same spot at the same time over the course of a year. The featured weekly analemma was taken despite cold temperatures and high winds near the Concordia Station in Antarctica. The position of the Sun at 4 pm was captured on multiple days in the digital composite image, believed to be the first analemma constructed from Antarctica. The reason the image only shows the Sun from September to March is because the Sun was below the horizon for much of the rest of the year. In fact, today being an equinox, the Sun rises today at the South Pole after a six month absence and won't set again until the next equinox in March, baring large atmospheric refraction effects. Conversely, today the Sun sets at the North Pole after half a year of continuous daylight. For all of the Earth in between, though, the equinox means that today will have a nighttime and daytime that are both 12 hours long.

<< Previous APOD

This Day in APOD

Next APOD >>

[/b]

[HellCat]

So why does there seem to be some asymmetry here? Did the camera stand wobble because of global warming?

[Nitpicker]

Interesting. I guess that the "4 pm" is based on UT+8.

[Rdlm]

the equinox means that today will have a nighttime and daytime that are both 12 hours long.

WRONG
In Paris, France, we have to wait saturday to have a daytime less than 12h00!
Today the daytime is 12h09min and it's only saturday that it will be 11h59. Check this: http://www.timeanddate.com/astronomy/france/paris
As the Sun is larger than earth, it lights a little bit more than half of the earth...

[bjmb]

the equinox means that today will have a nighttime and daytime that are both 12 hours long.
***
not only is this plainly wrong - the equinox is not the equilux, and as pointed out, the earth is always more than half lit, it is also wrong to say that " In fact, today being an equinox, the Sun rises today at the South Pole after a six month absence " - it rose already on september 21, two days ago; nor is it right to say that " Conversely, today the Sun sets at the North Pole after half a year of continuous daylight." it will set only on september 25, two days from now - all due to the lifting of the sun through the atmosphere and the apparent size of the sun.

[bjmb]

and of course the flattening of the earth towards the poles

[JohnCarswell]

Why did they build a fence in Antartica? ...keep the penguins out?

[Indigo_Sunrise]

Why did they build a fence in Antartica? ...keep the penguins out?

I wondered that too!
I also wondered about the 'asymmetry' that another poster pointed out.
And doesn't the foreground portion of the image look a little strange with the shadows not 'right', in relation to the sun?

But definitely an interesting image!

[neufer]

---

Why did they build a fence in Antartica?
...keep the penguins out?

I wondered that too!

More like above ground wiring than fencing.

(A thousand kilometers of Antarctic Plateau
is sufficient to keep the penguins out.)

I also wondered about the 'asymmetry' that another poster pointed out.

"The featured weekly analemma was taken despite cold temperatures and high winds near the Concordia Station."

And doesn't the foreground portion of the image look a little strange with the shadows not 'right', in relation to the sun?

The foreground portion of an analemma
generally looks better if it is not back-lit:

• . http://apod.nasa.gov/apod/ap081221.html
  . http://apod.nasa.gov/apod/ap101231.html
  . http://apod.nasa.gov/apod/ap061223.html
  . http://apod.nasa.gov/apod/ap130922.html

[Rdlm]

Why did they build a fence in Antartica? ...keep the penguins out?

I think it's used as handrails in order to avoid being lost during storm when you can't even see your noze. Being lost there means Death!

[Joe Stieber]

... Conversely, today the Sun sets at the North Pole after half a year of continuous daylight." it will set only on september 25, two days from now - all due to the lifting of the sun through the atmosphere and the apparent size of the sun.

And don't forget, sunrise and sunset are defined as the points when the upper limb of the sun is at the apparent horizon, whereas the equinoxes occur when the center of the sun crosses the celestial equator. Here's what the U.S. Naval Observatory says...

Sunrise and sunset. For computational purposes, sunrise or sunset is defined to occur when the geometric zenith distance of 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).

See: http://aa.usno.navy.mil/faq/docs/RST_defs.php

[neufer]

Why did they build a fence in Antartica? ...keep the penguins out?

I think it's used as handrails in order to avoid being lost during storm when you can't even see your noze. Being lost there means Death!

---

• To each his sufferings: all are men,
  Condemn'd alike to groan—
  The tender for another's pain,
  Th' unfeeling for his own.
  Yet, ah! why should they know their fate,
  Since sorrow never comes too late,
  And happiness too swiftly flies?
  Thought would destroy their Paradise.
  No more;—where ignorance is bliss,
  'Tis folly to be wise. - Thomas Gray

---------------------------------------------------
Blizz lines
This week at Mawson: 11 May 2012

<<Blizz lines or blizzard lines are ropes connecting one building to another, which we use when we are walking around the station or in the field in blizzards. What is a blizzard (blizz)? A blizzard must satisfy 4 factors. The wind must be equal to or greater than 34 knots, the temperature must be below zero, the visibility must be less than 100m and all these factors must last for at least one hour. So a blizzard is a gale force wind with blowing snow reducing visibility. In these situations and remember it could be dark, we walk from one building to another, holding onto a blizz line.

Malcolm is the blizz line monitor and he has spent many hours over the last week installing new sections, improving others, digging steps over and down blizz tails (bank of snow deposited downwind from any obstruction as a building, large boulder etc) and generally maintaining and improving all the lines. The most used blizz line is the section from the EVS (Emergency Vehicle Shelter) to the Trades Workshop. Seven people use this line several times every day. An accident occurred on this line where it crosses a blizz tail, so after speaking to all the users of the line a plan of action was developed. As it was not sensible to totally remove the blizz tail after every blizzard, Malcolm and Ian set to realigning the entire blizz line, transferring the rope so that it is always on the right hand side as one walks south from the Workshop to the EVS. This involved removing many obstructions and installing 2 additional drums full of rocks into the line. This realignment then allowed us to tension the rope as it crosses the blizz tail. We also aligned the rope with a series of steps up the blizz tail, improving the safety for the users. It will be interesting to assess the improvements during our next blizzard.

In addition to the blizz lines, when we walk in a blizzard we also have a Field Travel Conditions Advice Sheet, which is known colloquially in Antarctica as “Traffic Lights” as it has 4 categories of Field Travel (Normal, Caution, Danger and Stop) each with its own colour code (green, yellow, red and black). Since our arrival, 3 blizzards have been recorded in the red category for travel. In these conditions we only travel outside when it is necessary and in addition to the blizz lines we travel in pairs when possible, carry a radio and tell others where we are going and then ring them when we arrive at our destination. We also dress appropriately for the conditions wearing warm and windproof clothes, goggles, gloves and most importantly balaclavas and wristlets.>>

[Zuben L. Genubi]

I hope we are "barring atmospheric effects" not "baring" them. I'm not sure I could handle seeing totally naked atmospheric effects! Whichever the case, we will be "bearing" them either way. Doubtless Vitus Bering, aka "Ivan", the Danish explorer, would have appreciated this polar view of long summer days, during which in 1925 he discovered the straits bearing his name, and after which he reported straight back to Peter the Great. Got it straight?

[neufer]

I hope we are "barring atmospheric effects" not "baring" them. I'm not sure I could handle seeing totally naked atmospheric effects! Whichever the case, we will be "bearing" them either way. Doubtless Vitus Bering, aka "Ivan", the Danish explorer, would have appreciated this polar view of long summer days, during which in 1925 he discovered the straits bearing his name, and after which he reported straight back to Peter the Great. Got it straight?

OVERBEARING, a., Haughty and dogmatical; disposed or tending to repress or subdue by insolence or effrontery.

[Zuben L. Genubi]

Over Bering: prepositional phrase. What Vitus, aka Ivan, sailed over trying to get to get to Alaska.

[BMAONE23]

What causes the Red Fire patches to the left of the Analemma?
It looks like LMC and SMC or Red Aurorae but ???

[Indigo_Sunrise]

What causes the Red Fire patches to the left of the Analemma?
It looks like LMC and SMC or Red Aurorae but ???

I thought they looked like sprites!

[Ron-Astro Pharmacist]

I don't suppose that's the most southern set of McArches is it? Leave it to a "Ronald" to notice them. Keeping the fries hot all the way home is tough enough here.

Ronald.jpg (24.23 KiB) Viewed 4356 times

C'est tout ce que j'aime.

[ta152h0]

what a coincidence. Just this morning, about a couple hours ago on NPR, they had a scientist, operating a microwave telescope, describe the visual of the sun rising slowly over the horizon in Antartica and without the moon, it is getting lighter and lighter everyday

[dennisma]

These shadows look all wrong. It looks like the sun farther right and behind the camera not right in front.

[BMAONE23]

I don't suppose that's the most southern set of McArches is it? Leave it to a "Ronald" to notice them. Keeping the fries hot all the way home is tough enough here.

Ronald.jpg

C'est tout ce que j'aime.

Just keeping the fries all the way home can be tough

[BMAONE23]

These shadows look all wrong. It looks like the sun farther right and behind the camera not right in front.

The shadows are in deed pointing to the left of the image indicating that the sun is off to the right at the time the image was taken. This is likely because the sun Was off to the right at the time the final background image was taken.
The reason for this is that the 23 sun images that have been combined to form the analemma were taken when the Sun was pointing at the camera lens, Probably through a filter so as not to over bake the CCD. The 24th image was taken with the Sun out of the field of view and without the filter so that the background could be exposed without an overexposed sun within the field of view.

[saturno2]

Interesting

[geckzilla]

I think it would be easier for most people to understand the image if they saw all the images (or at least a selection of them) that were combined to create the final composite.

[Mikado]

Why is the Sun different sizes? Sep 30 being the smallest.