Multiple Exposures Of The Sun

Stormbringer_X1 writes "This image holds many first. Called an analemma (a figure 8 loop), it is a multiple exposure of the sun, where one observes the sun at the same time of day, over the period of a year. The patience and dedication to pull this off are emphasized by the fact that there are so few in existence (7 total including the first in 1979). It is the first analemma imaged in a single calendar year, the first on the southern meridian, and the first in Greece. The author has other images from 2002 that will be available soon. So stay tuned. Here is an image from NASA archives"

What I don't understand is

[fredrikj]

...what's so hard about it?

Re:What I don't understand is

[Atrahasis]

I tend to agree - in this age of webcams and always-on computers, why not just set up a cron job to take a snapshot at X o'clock each day? Who's going to notice the odd missing frame when the box is down because of the annual blackout?

Film

[Xner]

From the article:

Incredible as it may sound, only seven times has someone ever managed to successfully image the solar analemma as a multi-exposure on a single piece of film.

"Single piece of film" is apparently one of the requirements. You could do it with a digital camera, but then it wouldn't count...

Re:Film

[Atrahasis]

Aaaah. You see, in traditional slashdot style I was posting without reading the article. Still, computer control can be extended to a film-based camera as well, though I suppose the problem there is with reliability of the film/camera mechanism.

Re:Film

[Patrick13]

What I think is funny is that this is the first article I have ever seen on Slashdot that apparently has no danger of being slashdotted... when I just went to the site, his hit counter said "45".

Bah

[0x0d0a]

Bah, looks like 3 minute job with a white paintbrush in the GIMP. :-)

Seriously, though, at least some of this *has* to be a photo-manipulated composite, or else they never would have gotten that cloud in the background.

Re:Bah

[AndrewRUK]

Well of course it's a composite, that's what multiple exposures are. I imagine the cloud came from the foreground image they say they took. Personally, I think the apod one looks better, but that's just my opinion.

Re:Bah

[0x0d0a]

Oh. The possibility that they weren't just directly overlaid images never occurred to me. I figured they just slapped in some ratty-looking stock imagery. :-)

Re:Bah

[giel]

Huh!? The pattern on the image is not completely regular, as one would expect. Maybe the interval varied a little (due to end of month, end of year, DST, a severe hangover or something else), or it is fake...

Re:Bah

[PEdelman]

Look at the right below of the picture, where the following is stated:
Software:
Photoshop V6

Processing:
Cropping / Resizing
Layers
JPG Compression

I don't get it

[Kanasta]

How many images does he have to take to qualify?

why is it so difficult? If you have a home in an area not affected by earthquakes then surely you can't just leave a tripod set up and do an exposure every week or so

Re:I don't get it

[torpor]

You have to do it *every day* for a year, at exactly the same time.

So, you'd have to do something like this, every day:

1. Get up.
2. Wank.
3. Check clock.
4. At 10:41:32 am, take picture
5. Profit!!!

The shadow is not right

[MoobY]

If this is a single film photo, then there are a couple of things disturbingly wrong:

1. The shadow on the parthenon is no in line with the suns

2. the suns look like frightingly stupid white circles

3. the cloud in the lower left corner can only be on the picture if that particular cloud is there every time the film is exposed

The shadow knows

[tdemark]

There is nothing wrong with the image.

41 pictures were taken with a solar filter on - after which the negative was unexposed except for the 41 "dots" that are the sun.

The solar filter is then taken off. The photographer waits until the frame looks good and the negative is then exposed one more time to "add" the foreground. The cloud and the Parthenon are only exposed once.

Judging from the shadows and the fact that the suns are due south, the foreground shot was taken in the morning (lit from left, which is east).

- Tony

Solar photography

[Xner]

You have to understand that the sun is many many many times brighter than the parthenon. The exposures of the sun alone would appear as a completely black surface with a white spot.

My guess is that the exposure of the parthenon was taken either before or after the solar ones (most likely after) when the sun was not in the camera's FOV (i.e. at another time of day). This is the reason that the shadows on the partenon look wrong.

Since the sun is so bright, the rest of the film is still relatively unexposed, and the picture of the parthenon (inc. cloud) can be taken more or less as if it were a regular photograph.

Re:The shadow is not right

[Caractacus Potts]

I noticed the same thing.....until I read the article.
The solar filter explains the stupid white dots and the (1 foreground exposure) explains the cloud and stone building thingy.

What about the "wiggle"

[Optical Voodoo Man]

The clouds I understand. They either come from a single, unfiltered exposure or they were illuminated on any given exposure by the sun. The Parthenon superimposed I can see the same way. I think the big problem with this new image is the "wobble."

We go around the sun pretty smoothly, right? Shouldn't the path that the sun traces be a smooth one? On the image with the Parthenon, there is some time issues certainly, but the wiggle off of a "perfect" figure 8 shows that the camera wasn't always replaced exactly the same.

Nice try, nice image, but not as good as the second image pointed to in the article. That's why there are so few of these images around.

Re:What about the "wiggle"

[MoobY]

If you don't get your timing right, and you're off by one minute one a certain day, the sun has shifted position a bit to the east or west, which gives you your wiggle.

Re:What about the "wiggle"

[toybuilder]

For much of the last month or so, I've been studying techniques for accurately predicting the position (and some other parameters) of the sun at any given time of day and then setting up experiments to verify the results.

(It's not exactly fun work, especially having to get up at 5 am to prepare for the 6:30 sunrise measurements.)

The wobbles you see probably can be attributed to being off by a minute or so in taking each of the multiple exposures.

The diamter of the sun is about 0.5 degrees (31.48' according to the page accompanying the image). A one minute delay in taking the shot will mean the sun has moved (for example on 5-1-2002) about .3 degrees in azimuth, and .16 degrees in elevation. It's also possible that the camera itself was slightly mispointed (nudged? wind? who knows?)

There's 41 images taken between January 12 and December 21, all supposedly at 10:28:16.

The sun would start at (149.99,22.53) (azimuth, elevation), move upward and to the left in time until June 12 where it reaches (112.84, 60.88) and then starts to move downward until June 27, where it reaches (111.64, 60.47) and starts to swing back toward the right, until November 27 (152.86, 25.75), where it'll start swinging back to the left until his last position at (151.55, 22.72).

The sun would have reached it's "lowest" point in 2002 on 12-28 at (150.59, 22.48).

I originally thought the wobble might be due to atmospheric ("optical air mass") refraction variation due to tmperature and barometric pressure, but at those elevations, those effects turn out to be negligible.

This program from NREL [nrel.gov] will let you calculate the position of the sun and some of the properties that affect its perceived position. If you don't want to compile a program on your machine, you can check out the a href="ssd.jpl.nasa.gov/horizons">web-based "ephemeris" calculator from JPL.

Re:What about the "wiggle"

[oliverthered]

That's the 1 forground image, the rest would have been taken with a very dark filter on the camera.

Seven analemma?

[Anonymous Coward]

There are definitely more than just seven analemma exposures in existence. There was an issue of Sky & Telescope with six by amateur astronomers alone.

It only took me about three minutes

[Mordant]

to do this with the Gimp - you people need to work on your photomanipulation skillz, werd!

It's not an easy thing to do

[smartin]

My neighbour did one of these several years ago. It is here [analemma.de].
It took him a year to do and required a lot of engineering including:

• Fixing the film in his camera and hacking it to do multiple exposures.
  
• Using the right filter to black out every thing but the sun. The last exposure was taken without the filter.
  
• Fixing the camera to the rad in his office.
  
• Locking the cleaning staff out of his office for the entire year.
  
• Figuring out where and when to take the picture so that the sun will not be obscured by a building at the target time.
  
• Arranging to be free to take a picture at the same time of day every two weeks for a year.
  
• Dealing with days that were cloudy.
  

It is a facinating project and there have never been that many of these taken. The building in the picture is Bell Labs by the way.

wrong time

[crow]

For something like this, wouldn't you want to use true local time instead of the time in the given timezone? Remember that time zones with the absence of daylight savings time are set up so that the sun is in the highest point in the sky at noon somewhere roughly in the middle of the time zone. Before time zones were created, each town set their clocks so that noon was true noon.

So the first thing to do in something like this is use GPS to determine your longituted and thereby compute the exact +/- UTC for your location.

Re:wrong time

[perdu]

I dont think that matters so much so long as it's the same time, though it will be highest around the local noon. The exact time of local noon changes a bit from day to day as the earth is going a little faster when it's closer to the sun. That's why you get the figure 8 pattern - otherwise it would be a straight line up and down.

Slash for Astronomy at M57:The Ring [m57.org]

Data mine some webcam files

[bill_mcgonigle]

If you've got a year's worth of webcam files with a view in the right direction just pull out one a month from the same time of day and composite them.

Extreme photography.

[mnmn]

How about using ISO 25 speed film in a camera with an EXTREMELY tiny aperture so that the whole exposure takes 1 year?? How about using a field camera maybe 6x7" kodak pan film?

The result will be the sun painting the sky strip by strip. Now that should be a first.. with the trees superimposed throughout the year.

Come to think of it, we can aim the camera at a mall or busy street area. With the blurs, you could see where people stand most and what color clothes they wear. You can definitely make out the dots where homeless people sit. Sounds like a feasable project... hmmm..

Re:Extreme photography.

[mnmn]

Gee thanks. You saved me a year.

Links...

[onomatomania]

Here are some links if you're interested in more:

Qualitative and mathematical description of why the effect occurs. [analemma.com]

Gallery of analemma images, description of construction and implementation of making one. [analemma.de]

By the way, if you saw Cast Away, that was an analemma that Hanks' character used to keep track of the time he was stuck on the island. Hollywood took some liberty with the concept though, because it would have been impossible without an accurate timepiece of some kind.

What about the Moon?

[krishy]

So what about the Moon?. Does it cause any such stuff?.

Oops, my ignorance is out!