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

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

Postby APOD Robot » Sun Jul 17, 2011 4:08 am

Image Lewins Challenge: 360 Degree Star Trails

Explanation: You could be the first person ever to take a real single-exposure image like this. The above image from Vienna, Austria is not real in the sense that the 360 degree star trails in the sky appear only because of a digital trick. Real star trails observed above Vienna could never go 360 degrees around because the Sun would rise at some time during the exposure and dominate the frame. Star trails of any length occur because as the Earth spins on its axis, the sky seems to rotate around us. This motion, called diurnal motion, produces the beautiful concentric arcs traced by stars during long time exposures. Towards the middle of the above digitally stretched picture is the North Celestial Pole (NCP), easily identified as the point in the sky at the center of all the star trail arcs. The star Polaris, commonly known as the North Star, made the very short bright circle near the NCP. Walter Lewin, though, has asked APOD to pose this as a challenge to astrophotographers: create a real single-exposure image of a clear night sky that features 360 degree star trails. Of course, such an image would only be possible near the poles of our fair planet, because only there could a nighttime run for more than 24 hours.

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Re: APOD: Lewins Challenge: 360 Degree Star Trails (2011 Jul

Postby Beyond » Sun Jul 17, 2011 4:55 am

Hmm... In other words, Lewins wants someone else to go to one of the poles and freeze their butts off, to make a real star trail picture like the one he did in his nice warm house. Cool! 8-) Butt - it won't be mine :!: :lol:
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Re: APOD: Lewins Challenge: 360 Degree Star Trails (2011 Jul

Postby owlice » Sun Jul 17, 2011 5:03 am

Lewin didn't create this APOD image; Peter Wienerroither did. (The image credit appears right under the image on the APOD page.)
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Re: APOD: Lewins Challenge: 360 Degree Star Trails (2011 Jul

Postby Beyond » Sun Jul 17, 2011 5:17 am

Hmm... In other words, Lewins wants someone to go to one of the poles and freeze their butts off to make a real star trail picture like the one that Peter Wienerroither did in his nice warm house. Cool! 8-) Butt - it won't be mine :!: :lol:

((This corrects my first post above. Somehow i missed the fact that Lewins didn't actually do the star trail picture.))
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Re: APOD: Lewins Challenge: 360 Degree Star Trails (2011 Jul

Postby Ann » Sun Jul 17, 2011 5:30 am

Peter Wienerroither could almost have taken that picture by spending 24 hours outside with his camera in December up where I was born:

Image

I was born in Luleå. You can see the Arctic Circle to the north of it. (Now I live in Malmö, in the far south of Sweden.)

Beyond wrote:

Cool! 8-) Butt - it won't be mine :!: :lol:


I'm sure glad that it isn't mine anymore, too. At the time of year when you got very few hours of daylight in Luleå, so that you could almost have taken Peter Wienerroither's picture "honestly", it sure was cold up there.

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Re: APOD: Lewins Challenge: 360 Degree Star Trails (2011 Jul

Postby owlice » Sun Jul 17, 2011 5:38 am

Beyond, there are people in Antarctica, and they probably know how to keep all their body parts warm. (I think they'd have to!)
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Re: APOD: Lewins Challenge: 360 Degree Star Trails (2011 Jul

Postby Beyond » Sun Jul 17, 2011 6:15 am

owlice wrote:Beyond, there are people in Antarctica, and they probably know how to keep all their body parts warm. (I think they'd have to!)

Yes, there are some people in Antartica, however, i'm needed where the grass grows. Someone has to cut it once in a while. My butt fits the ridemower a lot better than Antartica. :lol:
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Re: APOD: Lewins Challenge: 360 Degree Star Trails (2011 Jul

Postby Glenwar » Sun Jul 17, 2011 8:29 am

owlice wrote:Lewin didn't create this APOD image; Peter Wienerroither did. (The image credit appears right under the image on the APOD page.)

The data on the photo didn't say that Lewin created the image. It said that Lewin offered a challenge.
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Re: APOD: Lewins Challenge: 360 Degree Star Trails (2011 Jul

Postby Ann » Sun Jul 17, 2011 8:52 am

Ahhh! I'm stumped!

I've tried. Seriously, I've tried. I've tried to identify those circles and find out what stars made them.

What stars made the circles???

Well, I'm stumped. I've tried to judge the brightness of individual circles, the color of individual circles, and the relative position of each circle and then compare them with the position, apparent magnitude and B-V index of stars in the vicinity of Polaris with the help of my software. That way I hoped to identify the stars that made the individual circles.

This picture is centered on the absolute north of the sky, which would be +90.00 00.0 degrees.

There are five second magnitude stars within +90 00 00.0 and +55 00 00.0 degrees of the sky. Only five.

At the very, very least two of them have to show up in today's APOD, and possibly all of them are there. But if so, where are they? Remember that you are looking for five bright circles - or make that four, because you have already found one circle, the one made by Polaris. Where are the other four?

These are the five stars (Polaris, which we have found, and four others which we haven't):

    Polaris: Mag: 1.97 Dec +89 15 50.9
    Kochab: Mag: 2.07 Dec +74 09 19.7
    Dubhe: Mag: 1.81 Dec +61 45 04.0
    Mirak: Mag: 2.34 Dec +56 22 56.4
    Alioth: Mag: 1.76 Dec +55 57 35.4

Of these stars, Alioth and Mirak would make blue circles in today's APOD, and the other stars would make whitish circles.

Well? Can you find these stars here? Can you identify the circles? Neufer! Chris! This is my challenge for you, or for anyone else who might be interested. Where are these stars in today's APOD? Are Dubhe, Mirak and Alioth even part of today's APOD? Where is Kochab? And please, if Alioth and Mirak aren't part of the picture, what stars made the two bright blue outer circles here? Third-magnitude B2III star Beta Cephei (mag 3.23, dec +70 33 38.5)?

To help you with the identification, here is a picture of the Big Dipper and the Little Dipper:

Image

Polaris is the end star of the Little Dipper's handle. Kochab is the bottom star in the Little Dipper's bowl. Dubhe is the topmost star of the Big Dipper's pointer stars. Mirak is the bottom star of the Big Dipper's pointer stars. Alioth is the middle star of the "straight part" of the Big Dipper's handle.

Ann

EDIT: Nope! There aren't just five second-magnitude stars between 90 00 00.0 and 55 00 00.0. There are nine second-magnitude stars instead (and now I sure hope I haven't missed any others). The four that I missed are the following:

    Alderamin, Alpha Cep: Mag: 2.45 Dec: +62 35 07.8
    Gamma Cas: Mag: 2.15 Dec: +60 43 00.3
    Caph, Beta Cas: Mag: 2.28 Dec: +59 09 00.8
    Schedar, Alpha Cas: Mag: 2.24 Dec: +56 32 14.7

Thanks a billion to alter-ego for making me see my mistake!
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Re: APOD: Lewins Challenge: 360 Degree Star Trails (2011 Jul

Postby profe » Sun Jul 17, 2011 9:17 am

Place the camera on a well aligned equatorial mount, point it towards Polaris and change slowly the RA throug the 24 h scale. That's all.
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Re: APOD: Lewins Challenge: 360 Degree Star Trails (2011 Jul

Postby Ann » Sun Jul 17, 2011 9:56 am

profe wrote:Place the camera on a well aligned equatorial mount, point it towards Polaris and change slowly the RA throug the 24 h scale. That's all.


Thanks, profe! I'm sure that tells you all you need to know, assuming you have a camera and a well aligned equatorial mount. But for those of us who haven't, can you or anyone else please help? Can you identify the star circles? Anyone?

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Re: APOD: Lewins Challenge: 360 Degree Star Trails (2011 Jul

Postby rwb » Sun Jul 17, 2011 12:05 pm

Of course it could be done from a satellite. Why not ask someone on the ISS to set up a camera for the job?
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Re: APOD: Lewins Challenge: 360 Degree Star Trails (2011 Jul

Postby biddie67 » Sun Jul 17, 2011 12:43 pm

With the Earth's path on its orbit, wouldn't a camera setup near the North Pole and let run for several days come up with a picture of spirals? Or at least, some pattern that wouldn't be perfectly matching circles?
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Re: APOD: Lewins Challenge: 360 Degree Star Trails (2011 Jul

Postby orin stepanek » Sun Jul 17, 2011 12:50 pm

Why not put the camera on a turntable and keep it pointed toward Polaris? That way Beyond don't have to worry about frozen butts. :mrgreen:
owlice wrote:Beyond, there are people in Antarctica, and they probably know how to keep all their body parts warm. (I think they'd have to!)
Aww! I'll bet they are still pretty cold; any way I'm cold in the winter no matter how much I bundle up. :P
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Re: APOD: Lewins Challenge: 360 Degree Star Trails (2011 Jul

Postby biddie67 » Sun Jul 17, 2011 1:06 pm

orin stepanek wrote: ..... Aww! I'll bet they are still pretty cold; any way I'm cold in the winter no matter how much I bundle up. :P


When I lived up North, I used to be continuously cold for several months each year. That's why, after I retired, I found a place to live that still has seasonal changes but winter doesn't present such serious survival factors. However, summer is now presenting a problem - my annual "heat tolerance training" seems to be failing me and I spend more time in my A/C than I would like to admit ....
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Re: APOD: Lewins Challenge: 360 Degree Star Trails (2011 Jul

Postby owlice » Sun Jul 17, 2011 1:19 pm

Glenwar wrote:
owlice wrote:Lewin didn't create this APOD image; Peter Wienerroither did. (The image credit appears right under the image on the APOD page.)

The data on the photo didn't say that Lewin created the image. It said that Lewin offered a challenge.

Yes, I know that (obviously); I was responding to a previous post which was edited after I posted my quoted post above. The previous poster (who has now fixed the error) initially thought Lewin had created the image used in today's APOD. My post pointed out that he had not, and the preceding post was changed accordingly.

Orin and biddie, I'm not much of a fan of cold, either... unless there's snow. To me, the point of having cold weather is to have snow (which I love)!
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Re: APOD: Lewins Challenge: 360 Degree Star Trails (2011 Jul

Postby saturn2 » Sun Jul 17, 2011 1:44 pm

The image of the sky of Vienna is not real.
The stars look like go 360 degree around in the North Celestial Pole.
Here the image is true.
It´s necessary a long exposition of camera ( 24 hours )
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Re: APOD: Lewins Challenge: 360 Degree Star Trails (2011 Jul

Postby bystander » Sun Jul 17, 2011 1:45 pm

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Re: APOD: Lewins Challenge: 360 Degree Star Trails (2011 Jul

Postby neufer » Sun Jul 17, 2011 3:09 pm

rwb wrote:
Of course it could be done from a satellite.
Why not ask someone on the ISS to set up a camera for the job?

If it was done from a satellite it would have to be an equatorial (e.g., geostationary) satellite in order for the rotation to be around Polaris.

The ISS could has an orbital inclination of 51.64º and could do a nice photo
with Vega (Declination +38° 47′) or Shaula (Declination -37° 06′) as the Polar Star
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Re: APOD: Lewins Challenge: 360 Degree Star Trails (2011 Jul

Postby isoparix » Sun Jul 17, 2011 3:37 pm

Of course, if he would relax that 'single-exposure' constraint, I guess it could be done, by catching the trails across the seasons
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Re: APOD: Lewins Challenge: 360 Degree Star Trails (2011 Jul

Postby cosmictourist » Sun Jul 17, 2011 4:17 pm

Just put the camera on an equatorial mount and spin it to get the 360 effect !!!
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Re: APOD: Lewins Challenge: 360 Degree Star Trails (2011 Jul

Postby profe » Sun Jul 17, 2011 4:21 pm

Ann wrote:
profe wrote:Place the camera on a well aligned equatorial mount, point it towards Polaris and change slowly the RA through the 24 h scale. That's all.


Thanks, profe! I'm sure that tells you all you need to know, assuming you have a camera and a well aligned equatorial mount. But for those of us who haven't, can you or anyone else please help? Can you identify the star circles? Anyone?

Ann


Of course, without a suitable camera (able to take a long exposure) you won't be able to take a photo like this one.
The best thing after a well aligned equatorial mount is a poor aligned tripod with a tilted axis. I built one of such devices long ago, with quite satisfactory results:




In order to identify the star circles you can do the following:
  • use a star chart of Ursa minoris
  • resize it to the same scale of today's APOD (distance of Polaris to the pole (center) must be the same)
or
  • use a table of RA and declination of Ursa minoris main stars
  • order the stars for decreasing declination
  • the star of highest declination (i.e. Polaris) matches the inner circle, and so on

From Wikipedia:
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Re: APOD: Lewins Challenge: 360 Degree Star Trails (2011 Jul

Postby Wolf Kotenberg » Sun Jul 17, 2011 5:22 pm

Well, there is the moon with crater floors that have never seen the sun. It will take 28 days but ...............Pass me an ice cold one, pleqase !
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Re: APOD: Lewins Challenge: 360 Degree Star Trails (2011 Jul

Postby miguelozed@onemain.com » Sun Jul 17, 2011 6:11 pm

When I was at 77N in Greenland in 1962, our all-sky camera produced heaps of these, often with aurora.
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Re: APOD: Lewins Challenge: 360 Degree Star Trails (2011 Jul

Postby Ann » Sun Jul 17, 2011 6:22 pm

Thanks again, profe. The thing is, I don't own a telescope or a tripod of any sort. I used to have a telescope once, but I found it frustratingly difficult to use, and I thought that it didn't magnify things nearly as much as I wanted. So I gave it away, mount and all, to an eager young kid. Since then I haven't had any equipment. I'm frankly not good at finding my way around the sky with a telescope.

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.

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.

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