APOD: Lewins Challenge: 360 Degree Star Trails (2011 Jul 17)

[Chris Peterson]

So perhaps the circles can't be identified.

I'm sure it's possible. The declination can be established with reasonable accuracy, and the brightness and color can be estimated. That should be enough.

It's just that neufer once told me that it isn't hard to identify star trails if you give it a try. I gave the circles of today's APOD several hours this morning, but I wasn't successful, so I just wondered if someone else could identify the circles for me.

But he was talking about normal star trail images, where you have arcs, not circles. That allows you to estimate the relative hour angle between stars, and from that the right ascension. Much easier than working with declination alone.

[profe]

So I was wondering if anyone else out there recognizes the circles and what stars they represent. Perhaps it can't be done. Perhaps the photo, which isn't a real photo, differs too much from reality, given the fact that this isn't a 24 hour exposure at all. The circles have been created from an incomplete picture of the night sky, at best perhaps a 15 hour exposure.
Ann

Much shorter, of course. I've not asked the author, but you can:
peter.wienerroither@univie.ac.at
I bet that a digital treatment has been applied (perhaps rotation of a short exposure or blending of circumpolar trails obtained at different seasons).
Ask him!

[MrsDK]

Were someone within the antarctic circle to put a pinhole camera out, aimed at the "south celestial pole", expose the film for 24 hours, then cover the pinhole and retrieve the camera, they could get a view of the southern celestial 360 degree star trails.

To get an arctic version, one would have to wait about six months or so before getting a view similar to that seen in today's APOD.

[GB]

I'm wondering... has anyone achieved the same effect at lower latitudes by stitching together a year's worth of circumpolar photos, based on, for example, two hour exposures on the first of every month for a year? Sure beats spending a long day's night in Thule. One could even meet the "single-exposure" criteria for Lewin's Challenge by dedicating a camera for a year, forcing the diaphragm open for the whole year, exposing it to the stars for the twelve two-hour nights, and exposing it to the inside of a light-proof bag the rest of the time.

[gv]

Let's see: astronomical twilight is when the sun is within eighteen degrees of the horizon. It's called astronomical twilight because there is still too much light for astrophotography. So, since the inclination of the earth's axis is 23.5 degrees, on the day of the solstice (the most favorable day) you still need to be no further than 23.5-18=5.5 degrees from the pole to take that picture. A quick check of the map shows that there is no landmass within 5.5 degrees of the north pole, which makes the task difficult at the north pole. Therefore, the only place on earth where you could "easily" take such a picture is the Amundsen-Scott base at the south pole. One of the few people that spend the winter there might do it, but I am told that it's so cold there in the winter that outdoor activity is severely limited and, I imagine, you might need a specially designed camera for picture taking at those temperatures.
I am sure that among the astronomers at the south pole there must be some APOD readers. It will be interesting to see if one of them takes on the challenge!

[Chris Peterson]

Let's see: astronomical twilight is when the sun is within eighteen degrees of the horizon. It's called astronomical twilight because there is still too much light for astrophotography. So, since the inclination of the earth's axis is 23.5 degrees, on the day of the solstice (the most favorable day) you still need to be no further than 23.5-18=5.5 degrees from the pole to take that picture.

You can certainly take astronomical images much earlier in twilight than the start of astronomical twilight. That just marks the point where the sky can be considered to be near its darkest. Of course, the effects of twilight are greatest near the horizon, and as you approach the poles the point you would be imaging gets higher and higher in the sky.

I think you could make a reasonable 24-hour star trail image anywhere within 15-20° of either pole, which leaves plenty of opportunities for northern locations.

[alter-ego]

So perhaps the circles can't be identified. Perhaps it isn't possible to say which of the bright inner circles was made by red giant Kochab. Perhaps it isn't possible to say which circle is third magnitude Pherkad's, Gamma Ursa Minoris, an interesting and rare A-type giant. Perhaps it isn't possible to say if third magnitude and very blue Beta Cephei, Alfirk, has made its own circle in this image. Perhaps itsn't at all possible to identify the brightest broad whitish circle in today's APOD or the two bright blue circles outside it.

It's just that neufer once told me that it isn't hard to identify star trails if you give it a try. I gave the circles of today's APOD several hours this morning, but I wasn't successful, so I just wondered if someone else could identify the circles for me.

Ann

This is about the best scale-correlation I can get. I did not try to make sense of all the colors, and I believe there is some difference in scale (projection related) between the picture and the constellation overlay. I'm pretty sure Dubhe likely forms the brightest circle as the declination of the circle and Dubhe agree very well, and it's the brightest star. Dubhe was anchored to the ring for the case when Polaris is near lower culmination. I think for the four stars you asked about are close to their rings, but I'm not not as sure as I'd like to be. At least it's something you can look at ☺

Approximate star circle identification - Polaris at lower culmination

[Ann]

Thanks a million, alter-ego!

Thanks in particular for pointing out that the main stars of Cassiopeia lie within a declination of 55 00 00.0. And Alpha, Beta and Gamma Cas are all second magnitude stars. I missed them, because my software presents a rectangular picture which cut Cassiopeia off when I tried to make sense of the neighborhood of Polaris yesterday, and I'm not good at rotating the image. Still, it was a stupid oversight. And - darn it! - I forgot Alderamin, Alpha Cephei, too!

Ann

[pitwi]

Hello to all!

Wow, I'm impressed that my photo is discussed so vividly. (Is it the right word?) It's the same as at the first APOD publication on 7/14/2005.

The original intention for the photo was to show children and interested people the movement of the sky within 1 day and so I had the idea to make a 24h startrail image. As I live in Austria and not behind the polar circles I thought of making a minimum of 3 photos over 1 year to get the full circle but you have to fix a camera very accurate, always use the same lens and always have the same weather conditions to get a good result. So I wasn't very successful and realized the photo much easier: I took one single 5 min. image (and some more over 1 night as reference) and rotated it with Photoshop. That's all. So as you can see, sometimes it's only a simple idea to make people think and be astonished.

Thanks to "alter-ego" for showing the stars that made the circles. I'll have a look at the original image tonight to confirm it.

Greetings from Autria
Peter Wienerroither
peter.wienerroither@univie.ac.at
http://homepage.univie.ac.at/~pw/
---

[profe]

Thanks a million, alter-ego!

Thanks in particular for pointing out that the main stars of Cassiopeia lie within a declination of 55 00 00.0. And Alpha, Beta and Gamma Cas are all second magnitude stars. I missed them, because my software presents a rectangular picture which cut Cassiopeia off when I tried to make sense of the neighborhood of Polaris yesterday, and I'm not good at rotating the image. Still, it was a stupid oversight. And - darn it! - I forgot Alderamin, Alpha Cephei, too!

Ann

If the photo was taken from Vienna, Polaris is only 48º above the horizon and Cassiopeia must be much farther from the Pole at this scale.

[DavidLeodis]

Why was a "digitally stretched" image used as the APOD . I think the image brought up when clicking on the APOD (or through the "above image" link) is a better one as it is not distorted looking.

[profe]

Hello to all!
Thanks to "alter-ego" for showing the stars that made the circles. I'll have a look at the original image tonight to confirm it.
---

I've checked with SkyMap haw looked the sky at midnight from Wien the day the original picture was taken. I've must admit that alter-ego was right, and that the trails are mainly produced by the stars of Ursa maior and Cassiopeia:

Click to view full size image

[Wolf Kotenberg]

and then Mr Murphy steps in and flashes the brightest meteor ever seen, just as the carefully planned " git up " is almost finished. Just thinking about that scenario requires an ice cold one to settle back down.

[Ayiomamitis]

I'm wondering... has anyone achieved the same effect at lower latitudes by stitching together a year's worth of circumpolar photos, based on, for example, two hour exposures on the first of every month for a year? Sure beats spending a long day's night in Thule. One could even meet the "single-exposure" criteria for Lewin's Challenge by dedicating a camera for a year, forcing the diaphragm open for the whole year, exposing it to the stars for the twelve two-hour nights, and exposing it to the inside of a light-proof bag the rest of the time.

This challenge is something which has crossed my mind a number of times and I believe it is much easier than it may seem.

The suggestion above was my first possible solution to such an image and I believe it would require three strategically selected and dedicated evenings. Let's not forget that winter is approximately twelve hours in duration at its peak which solves one-half of our problem. The balance SHOULD be doable around late spring and early fall.

For something like this to be really pulled off, an area with dark skies would be necessary and where a camera could be left in a permanent setting so that the three exposures I describe above could be pursued.

The more and more I think about this exercise, the more and more convinced I become to (finally) pursue it since fall is not too far away for one of the three desired evenings.

[bystander]

This challenge is something which has crossed my mind a number of times and I believe it is much easier than it may seem.

The suggestion above was my first possible solution to such an image and I believe it would require three strategically selected and dedicated evenings. Let's not forget that winter is approximately twelve hours in duration at its peak which solves one-half of our problem. The balance SHOULD be doable around late spring and early fall.

For something like this to be really pulled off, an area with dark skies would be necessary and where a camera could be left in a permanent setting so that the three exposures I describe above could be pursued.

The more and more I think about this exercise, the more and more convinced I become to (finally) pursue it since fall is not too far away for one of the three desired evenings.

But the challenge was:

create a real single-exposure image of a clear night sky that features 360 degree star trails.

[Ayiomamitis]

Bystander,

I am debating whether a SINGLE 24-hr exposure is physically possible.

I can easily bypass the issue of a dead battery by using an older mechanical camera (I have a number of these). However, would the optics survive the extremity of the frigid temperatures for a period of 24 hours inside the polar circle?

I do have older cameras and lenses which I would deem "dispensible" (and worthwhile) for such an exercise and, I guess, there is an easy way to confirm my apprehension about the optics themselves surviving such an exposure (excuse the pun).

[Wolf Kotenberg]

Ulysses most likely could

[neufer]

Ulysses most likely could

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[Rupert]

Not sure if some one has tried:

A "single" exposure... Solved by using film (to much noise digitally). Fix the camera pointing in a direction, and only open the shutter for 1/365 of 24hours every day or 1/52 of 24hours once a week. It is only "exposing" 1 frame

[owlice]

Would a simple pinhole camera with sensitive film work for this?

I have a couple of cameras which require no batteries...

[Ayiomamitis]

Owlice,

The two cameras in your photo are fine as are any of the older cameras which did not have batteries for normal operation. I still have my Argus Cosina STL 1000 from the early 70's (my first camera ) and which cost me $125 at the time. Since its operation is totally mechanical with no battery needed (aside for the through-the-lens metering), it would work just fine.

Reading the challenge ad verbatim, one would have to expose for 24 hrs continuously and which is possible quite north (or quite south) where one has continuous darkness for a portion of the year. Given the temperatures involved, my single concern would be the ability of the lens to withstand such extreme elements and especially for 24 hrs. I do not know if film emulsion has any sort of operating temperature but I suspect it may also respond in a non-orthodox manner in such a harsh environment and especially over the course of 24 hrs.

Although I am technically deviating from the challenge by suggesting three well-timed and executed extended exposures for the same result, I suspect it is the only means to such an end. In fact, it is something I plan to pursue!

Anthony.

[Ayiomamitis]

Not sure if some one has tried:

A "single" exposure... Solved by using film (to much noise digitally). Fix the camera pointing in a direction, and only open the shutter for 1/365 of 24hours every day or 1/52 of 24hours once a week. It is only "exposing" 1 frame

I would advise AGAINST such a scenario since the weather can easily kill such a sequence, thus leaving a gap. I am convinced the best way to approach this challenge is with a 12-hr exposure during winter when the long nights permit such a lengthy exposure as well as two timely exposures for the balance in the spring and fall.

Anthony.

[Chris Peterson]

Reading the challenge ad verbatim, one would have to expose for 24 hrs continuously and which is possible quite north (or quite south) where one has continuous darkness for a portion of the year. Given the temperatures involved, my single concern would be the ability of the lens to withstand such extreme elements and especially for 24 hrs.

Not an issue. Camera lenses operate just fine at extremely cold temperatures. Optics might have an issue with thermal shock, but not absolute temperatures. Likewise for cameras- people have been using ordinary unmodified DLSRs at both poles for decades. I have simple video cameras with ordinary camera lenses operating year-round near both poles. There are no serious reliability issues, especially with the lenses.

I do not know if film emulsion has any sort of operating temperature but I suspect it may also respond in a non-orthodox manner in such a harsh environment and especially over the course of 24 hrs.

Again, no problem. Film actually works better at very low temperatures, where reciprocity failure is reduced. Problems with film under cold conditions come with static discharge during winding, as well as mechanical substrate problems when winding. But for a single exposure, these should not be issues.

[Wolf Kotenberg]

Some time ago, quite possibly a few years, prof Lewin issued a challenge to APOD viewers to explain a light issue with a photograph, possibly taken by prof Lewin himself, that had a misterious light source location. I have been following APOD for many things and some of them I have in the back of my mind as " no answer ". Perhaps someone can enlighten the vast audience, namely me, as to the answer to that puzzle.. An ice cold one would be nice for a reward.

[Beyond]