APOD: Sunrise, Moonrise (2011 Jan 06)

APOD Robot · Post by **APOD Robot** » Thu Jan 06, 2011 5:06 am

Sunrise, Moonrise

Explanation: For many Europeans, the Sun and New Moon rose together on January 4 in a partial solar eclipse. Arriving close on the heels of the new year, it was the first of a series of four(!) partial solar eclipses due in 2011. This composite image documents the graceful celestial event in colorful morning skies over Graz, Austria. Beginning before sunrise, frames were taken to record the position and progress of the eclipse every 15 minutes. As Sun and Moon rose above the eastern horizon, the town of Graz is seen bathed in warming sunlight only partially blocked by the New Moon, spreading beneath the town's landmark clock tower.

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mikero2107 · Post by **mikero2107** » Thu Jan 06, 2011 5:23 am

Why does it look like the moon is moving slower than Sun?

neufer · Post by **neufer** » Thu Jan 06, 2011 5:42 am

mikero2107 wrote:Why does it look like the moon is moving slower than Sun?

The moon is orbiting the earth and thus going through all its phases once a month.

You are observing the moon orbit from its final waning phase to its starting waxing phase in just a few hours.

neufer · Post by **neufer** » Thu Jan 06, 2011 5:57 am

Grazer Schloßberg (Castle mountain) with "Uhrturm" (clock tower)

http://en.wikipedia.org/wiki/Grazer_Schlo%C3%9Fberg wrote:
<<Graz is the second-largest city in Austria after Vienna. Graz has a long tradition as a student city: its six universities have more than 44,000 students. Graz was also a city that famous astronomer Johannes Kepler lived in for a short part of his life. There, he worked as a math teacher, but found time to study astronomy.

Kepler left Graz to go to Prague when Lutheran people were banned from the city.

Among Graz's most famous tourist attractions is the castle Grazer Schloßberg which was never occupied until its partial demolition by Napoleonic forces under the Peace of Schönbrunn of 1809, was once a place of refuge for Graz's residents. It was turned into a public park in 1839. The word "Schloßberg" literally means "castle mountain", which describes it exactly. It is a hill topped by a castle, in the centre of the city of Graz, Austria.

The Schloßberg contains an "Uhrturm" (clock tower), which functions as a recognisable icon for the city. There is also a Turkish Well that was built by Turkish slaves that was used to get water during times when Schlossberg was under siege. The water was routed from the nearby River Mur.>>

http://findarticles.com/p/articles/mi_m0268/is_9_41/ai_101779176/ wrote:
<<Graz paid homage to two of its most famous 19th-century residents,
Leopold von Sacher-Masoch and
Richard Freiherr von Krafft-Ebing,
with a summerlong salute to perversity in 2003 called:

"Phantom der Lust:
Visions of Masochism in Art" at the Neue Galerie.>>

Chris Peterson · Post by **Chris Peterson** » Thu Jan 06, 2011 6:00 am

mikero2107 wrote:Why does it look like the moon is moving slower than Sun?

Because it is.

ChiefChuckalucky · Post by **ChiefChuckalucky** » Thu Jan 06, 2011 7:25 am

This is another example of the Sun appearing slightly larger near the horizon than at altitude. Measuring it on my screen, the first complete image has the Sun at 1/4 (4/16th) of an inch in diameter. The Sun's image highest in the sky has a 3.5/16 diameter. This is due to the denser atmosphere near the horizon which distorts the image... in this case enlarging it slightly.

ChiefChuckalucky · Post by **ChiefChuckalucky** » Thu Jan 06, 2011 7:36 am

mikero2107 wrote:
Why does it look like the moon is moving slower than Sun?

In a 24 hour period, the Sun will be at approximately the same place in the sky. The Moon's orbit in 24 hours is approximately 15 degrees shorter. Therefore the Sun's apparent movement is faster.

neufer · Post by **neufer** » Thu Jan 06, 2011 1:31 pm

Click to play embedded YouTube video.

Hickory Dickory Dox
Asternauts resolve another apparent paradox

ChiefChuckalucky wrote:
This is another example of the Sun appearing slightly larger near the horizon than at altitude. Measuring it on my screen, the first complete image has the Sun at 1/4 (4/16th) of an inch in diameter. The Sun's image highest in the sky has a 3.5/16 diameter. This is due to the denser atmosphere near the horizon which distorts the image... in this case enlarging it slightly.

Isn't the sun/moon the smallest in the middle

A denser atmosphere near the horizon often distorts the image by squashing it vertically but it seldom enlarges it in any direction.

verkle2 · Post by **verkle2** » Thu Jan 06, 2011 1:33 pm

I was always taught that the sun and moon looking larger on the horizon is only due to perception, and it really wasn't so.
But my PC shows that the sun size on the horizon is 37-38 pixels wide, while the one high in the air is only 33 pixels wide, which would make the one on the horizon about 30% larger in area.
Is this really the case, or is there another reason why the sun is smaller? (Zoom and/or other camera settings, etc.)

Confused...

Chris Peterson · Post by **Chris Peterson** » Thu Jan 06, 2011 3:34 pm

verkle2 wrote:I was always taught that the sun and moon looking larger on the horizon is only due to perception, and it really wasn't so.
But my PC shows that the sun size on the horizon is 37-38 pixels wide, while the one high in the air is only 33 pixels wide, which would make the one on the horizon about 30% larger in area.
Is this really the case, or is there another reason why the sun is smaller? (Zoom and/or other camera settings, etc.)

Confused...

It is confusing. Optically, there's no good mechanism to explain this. When the Sun or Moon are near the horizon, we see them through a vertical density gradient, which refracts light and compresses the apparent size of the object vertically. There is no horizontal gradient, and the horizontal size of the body shouldn't be affected. The atmosphere definitely does not act to magnify objects near the horizon in any way.

I believe we are seeing something that happened in the camera or in processing, not something that was physically present in the sky.

biddie67 · Post by **biddie67** » Thu Jan 06, 2011 4:03 pm

Wonderful photograph - the beauty and gracefulness of it make you almost forget about the workmanship behind the camera.

ChiefChuckalucky · Post by **ChiefChuckalucky** » Thu Jan 06, 2011 10:10 pm

Something in the camera or processing? No. I was a pro photographer for 20+ years, and this is NOT a camera trick.
The Sun gets smaller as it rises.
This is due to the amount of atmosphere and particles in the air that the light travels through.
It does not happen every sunrise or sunset, but I have seen HUGE Suns and Moons from time to time as they rise.

neufer · Post by **neufer** » Thu Jan 06, 2011 11:23 pm

Click to play embedded YouTube video.

ChiefChuckalucky wrote:
Something in the camera or processing? No. I was a pro photographer for 20+ years, and this is NOT a camera trick.

The Sun gets smaller as it rises.

This is due to the amount of atmosphere and particles in the air that the light travels through.

It does not happen every sunrise or sunset, but I have seen HUGE Suns and Moons from time to time as they rise.

You may have "seen" them but you have not photographed them.

http://antwrp.gsfc.nasa.gov/apod/ap031011.html
http://antwrp.gsfc.nasa.gov/apod/ap070607.html
http://antwrp.gsfc.nasa.gov/apod/ap090616.html

sheila365 · Post by **sheila365** » Thu Jan 06, 2011 11:25 pm

beautiful. but odd that the clock tower and the smoke from the various smokestacks doen't change in the timelapse... maybe the eclipse images are superimposed over a still image of the town...?

Chris Peterson · Post by **Chris Peterson** » Fri Jan 07, 2011 1:33 am

ChiefChuckalucky wrote:Something in the camera or processing? No. I was a pro photographer for 20+ years, and this is NOT a camera trick.
The Sun gets smaller as it rises.
This is due to the amount of atmosphere and particles in the air that the light travels through.
It does not happen every sunrise or sunset, but I have seen HUGE Suns and Moons from time to time as they rise.

The Sun does not get smaller as it rises. It is never larger near the horizon- in fact, it is always smaller near the horizon, because it gets compressed vertically. Since you're a photographer, you can easily test this by taking some images over the course of a day and comparing them. It would be best to use a fixed focal length lens to avoid any instrumental errors possible with a zoom lens.

Interestingly, the Moon gets measurably larger when it is high in the sky, because it is closer to you. (The Sun is closer, too, but not enough so compared with its difference to be easily detected.)

When you see a huge Sun or Moon on the horizon, you are always seeing an optical illusion.

neufer · Post by **neufer** » Fri Jan 07, 2011 2:58 am

Chris Peterson wrote:
The Sun does not get smaller as it rises.

It is never larger near the horizon- in fact, it is always smaller near the horizon,
because it gets compressed vertically..

: Click to view full size image

owlice · Post by **owlice** » Fri Jan 07, 2011 4:02 am

I have a sudden desire for candy corn.

Chris Peterson · Post by **Chris Peterson** » Fri Jan 07, 2011 4:10 am

neufer wrote:
Chris Peterson wrote:
The Sun does not get smaller as it rises.

It is never larger near the horizon- in fact, it is always smaller near the horizon,
because it gets compressed vertically..

Click to view full size image

Alright, it is almost always smaller near the horizon. <g>

It can clearly get distorted (vertically) in some pretty extreme ways on occasion, when it is essentially touching the horizon. Of course, in this APOD, there is little or no distortion in the larger Sun images.

eaglekepr · Post by **eaglekepr** » Fri Jan 07, 2011 6:20 am

sheila365 wrote:beautiful. but odd that the clock tower and the smoke from the various smokestacks doen't change in the timelapse... maybe the eclipse images are superimposed over a still image of the town...?

The whole of the background image was taken at sunrise (which is why the lighting is warm/orange-ish). Each stage of the sun afterward is a very short exposure, around 1/4000 or a second or (maybe even faster), otherwise there would be too much light and the sun would flare as it did in the last stage (which would have been a relatively "long" exposure). With those very short exposures for the sun, the rest of the town and the tower would be nearly black from under exposure. Each stage of the eclipse is then stacked on top of the sunrise background photo in Photoshop or similar.

For others, the reason the sun is a different size HERE has nothing to do with optical illusions. The photographer's web page gives the answer. The background image was taken at 18mm focal length and the images of the sun were taken at 55mm.

http://translate.google.com/translate?j ... %26hit%3D1

verkle2 · Post by **verkle2** » Fri Jan 07, 2011 6:23 am

OK. If it is an optical illusion, then WHY is the sun 30% smaller higher in the sky?
My measurements of pixels holds for both horizontal and vertical directions, so this "vertical compression" things doesn't hold much water....

verkle2 · Post by **verkle2** » Fri Jan 07, 2011 6:27 am

eaglekepr wrote:For others, the reason the sun is a different size HERE has nothing to do with optical illusions. The photographer's web page gives the answer. The background image was taken at 18mm focal length and the images of the sun were taken at 55mm.

-> Doesn't make sense. If the images of the sun were all taken at 55mm, shouldn't make a difference!

Chris Peterson · Post by **Chris Peterson** » Fri Jan 07, 2011 6:33 am

verkle2 wrote:OK. If it is an optical illusion, then WHY is the sun 30% smaller higher in the sky?
My measurements of pixels holds for both horizontal and vertical directions, so this "vertical compression" things doesn't hold much water....

As noted, the reason must be related to the photographic equipment or the compositing procedure. It is well understood that the Sun does not change size with position in the sky (outside the "size" effect of distortion- largely vertical- when the Sun is within a degree or so of the horizon).

Chris Peterson · Post by **Chris Peterson** » Fri Jan 07, 2011 6:37 am

eaglekepr wrote:For others, the reason the sun is a different size HERE has nothing to do with optical illusions. The photographer's web page gives the answer. The background image was taken at 18mm focal length and the images of the sun were taken at 55mm.

That explains why the rising Sun is a significantly different size from the eclipsed Suns. It doesn't explain why all the eclipsed Suns are different sizes, however.

I suspect that the zoom lens shifted (or was misadjusted) slightly between exposures, resulting in the actual Sun images being made at something other than exactly the same focal lengths.

sheila365 · Post by **sheila365** » Fri Jan 07, 2011 10:09 am

eaglekepr wrote:
sheila365 wrote:beautiful. but odd that the clock tower and the smoke from the various smokestacks doen't change in the timelapse... maybe the eclipse images are superimposed over a still image of the town...?
The whole of the background image was taken at sunrise (which is why the lighting is warm/orange-ish)....

thanks!

NoelC · Post by **NoelC** » Sat Jan 08, 2011 2:52 pm

Chris Peterson wrote:Alright, it is almost always smaller near the horizon. <g>

-Noel

Starship Asterisk*

APOD: Sunrise, Moonrise (2011 Jan 06)

APOD: Sunrise, Moonrise (2011 Jan 06)

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Grazer Schloßberg Uhrturm

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