Help with the name of an astronomical phenomena please?

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danwiz
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Help with the name of an astronomical phenomena please?

Postby danwiz » Mon Nov 18, 2013 11:25 pm

I know that I have seen this explained somewhere on APOD, but a search brought up no results for me.
If you view the picture at http://danwiz.com/IndexPagePhotos/Aug09_028PSHDR_MtChokai_SunriseTimeRC.jpg
you'll see some anti-crepuscular rays and a shadow of the mountain we are standing upon. But - the problem is that the sun has not yet risen and won't rise for another 20 - 30 minutes. So, my question is - how can I see the shadow of the mountain? Is it a simple mirage or a Fata Morgana, or something else - what is it called and how can it be explained?
As this is my first post I am not sure if I can insert an image, but I'll try to insert the image linked above.
Image

The photo has been heavily manipulated to bring out the rays and to brighten the foreground.

Thanks in advance.

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Re: Help with the name of an astronomical phenomena please?

Postby Nitpicker » Mon Nov 18, 2013 11:39 pm

There may be a fancier name, but I would have thought a kind of "twilight" should cover it.

Image

See also:
http://en.wikipedia.org/wiki/Twilight

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neufer
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Re: Help with the name of an astronomical phenomena please?

Postby neufer » Mon Nov 18, 2013 11:42 pm

Art Neuendorffer

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Re: Help with the name of an astronomical phenomena please?

Postby Nitpicker » Mon Nov 18, 2013 11:47 pm

Oops, my previous post is not that valid. I was looking at the wrong shadow and assumed (incorrectly) the Sun would be soon rising in the field of view, rather than behind the camera.

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Re: Help with the name of an astronomical phenomena please?

Postby danwiz » Tue Nov 19, 2013 12:20 am

Thanks nitpicker - but you found your error. Yes, the sun will be rising behind the camera - and in another 30 minutes we were able to see the "real" shadow of the mountain!

neufer - I don't think that's the image I saw here several years ago and it does not seem to fit the situation I described - with a shadow being visible before the sun has risen.

Can we please keep trying? Thanks in advance.

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Re: Help with the name of an astronomical phenomena please?

Postby Nitpicker » Tue Nov 19, 2013 12:26 am

It is still a real shadow. It is the shadow of the Earth (which at this point includes a mountain) cast onto the atmosphere above the anti-solar horizon. Some refer to this general phenomenon as the Belt of Venus. The photo neufer linked to is the same thing, but also included the moon as an added bonus.

Edit reason: changed "projected" to "cast" -- poor choice of words.
Last edited by Nitpicker on Tue Nov 19, 2013 12:35 am, edited 1 time in total.

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Re: Help with the name of an astronomical phenomena please?

Postby Nitpicker » Tue Nov 19, 2013 12:30 am


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neufer
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Re: Help with the name of an astronomical phenomena please?

Postby neufer » Tue Nov 19, 2013 12:58 am

danwiz wrote:
neufer - I don't think that's the image I saw here several years ago and it does not seem to fit the situation I described - with a shadow being visible before the sun has risen.

Which is physically identical with after the sun has set:
http://apod.nasa.gov/apod/ap101205.html
Art Neuendorffer

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Re: Help with the name of an astronomical phenomena please?

Postby danwiz » Tue Nov 19, 2013 1:13 am

Thanks for your help with this guys, I appreciate it! Anybody else want to offer anything?

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geckzilla
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Re: Help with the name of an astronomical phenomena please?

Postby geckzilla » Tue Nov 19, 2013 1:19 am

If you are positive the sun is below the horizon then the only other place the light could be coming from is bouncing off the atmosphere and providing a secondary source of light which is illuminating the water and your camera is able to detect what I suppose could be a very elongated penumbra and antiumbra.
Just call me "geck" because "zilla" is like a last name.

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Re: Help with the name of an astronomical phenomena please?

Postby Nitpicker » Tue Nov 19, 2013 1:28 am

geckzilla wrote:If you are positive the sun is below the horizon then the only other place the light could be coming from is bouncing off the atmosphere and providing a secondary source of light which is illuminating the water and your camera is able to detect what I suppose could be a very elongated penumbra and antiumbra.


Water? I thought they were clouds.

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Re: Help with the name of an astronomical phenomena please?

Postby geckzilla » Tue Nov 19, 2013 2:03 am

Is it all a layer of cloud? Sorry, but my brain is programmed to interpret flat, blue planar surfaces as water.
Just call me "geck" because "zilla" is like a last name.

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Re: Help with the name of an astronomical phenomena please?

Postby danwiz » Tue Nov 19, 2013 5:43 am

What you are seeing is the Sea of Japan and a few clouds lying close to the water, looking from east to west. The time is 4:50 AM. Supposedly, the sunrise was at 4:47 AM on that date at this latitude and longitude (I just checked the navy's sunrise/sunset data), so I suppose technically it is after sunrise, but I am at the top of the mountain and cannot see the sun!!!! By 4:57 AM this shadow had totally disappeared and then at 5:01 a "real" shadow of the mountain appeared. If you want to see the series of photos I could post several in a sequence for you - but I am getting ready to leave for work right now, so those will have to come tomorrow. Here is a shot from 5:02 AM:
http://danwiz.com/DCResource/Aug09_043_MtChokai_SunriseTime_resize.jpg
and here is the photo.


If you want to see bigger images please click the actual links and then you can see them in separate browser windows.
Last edited by danwiz on Tue Nov 19, 2013 5:57 am, edited 1 time in total.

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Re: Help with the name of an astronomical phenomena please?

Postby Nitpicker » Tue Nov 19, 2013 5:53 am

It looks to be almost certainly the same shadow of the same mountain in both shots, albeit with the Sun at slightly different elevations. The fact that it disappeared in between could be explained by clouds in the East rolling past momentarily and blocking the Sun.

Edit: not to mention that the exact time of Sunrise/Sunset, though well defined, is different for different locations. It depends on date, latitude, longitude and elevation. At a high elevation, the Sun will appear to rise sooner.
Last edited by Nitpicker on Tue Nov 19, 2013 5:58 am, edited 1 time in total.

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Re: Help with the name of an astronomical phenomena please?

Postby geckzilla » Tue Nov 19, 2013 5:56 am

Given these new facts it sounds like you saw the shadow of the mountain appear as the sun rose behind it and disappear as it passed behind a cloud layer and then reappear as it rose above that cloud layer. Regardless of the circumstances, the name of the phenomenon is a shadow.

And Nitpicker just beat me.
Just call me "geck" because "zilla" is like a last name.

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Re: Help with the name of an astronomical phenomena please?

Postby danwiz » Tue Nov 19, 2013 6:02 am

Note please - that I just edited my previous post with the information that I was at the top of the mountain and could not see the sun until the 5:02 AM shot.

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Re: Help with the name of an astronomical phenomena please?

Postby Nitpicker » Tue Nov 19, 2013 6:20 am

The shadow appears higher in the first shot, relative to the foreground ridge. It is unclear where ocean and sky meet precisely, but the Earth can certainly cast a visible shadow on the anti-twilight arch just before sunrise and just after sunset. The more I look at it, the more it looks like the one that neufer posted, that is:
http://apod.nasa.gov/apod/ap101205.html

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Re: Help with the name of an astronomical phenomena please?

Postby danwiz » Tue Nov 19, 2013 12:08 pm

I know that I've seen an image very similar to this (top one) here at one time and it explained it perfectly, but it is not the one neufer posted. I did a search for shadow, mirage, mountain shadow and several others but I can't find it. I remember that when I saw that post that I immediately said to myself "Eureka, this explains that shot from Mt. Chokai (the very first one)". I wish I could find that post again. It was in one of the "Picture of the Day" posts and it was between August 2011 and now seeing as I took the photo in August 2011 and when I saw it I was excited to think that it explained my shot! Sorry that you all have not yet been able to find it, same as me! That said, however, I do appreciate all of your posts and help here.

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Re: Help with the name of an astronomical phenomena please?

Postby Nitpicker » Wed Nov 20, 2013 12:23 am

From the filename set on your 4:50 AM photo (the first one), I just checked the time of sunrise at Mount Chokai on 9-Aug-2011. (The time of sunrise is based on the horizon being at the same elevation as the observer. You probably would have been higher than your ENE horizon, so sunrise would have been slightly earlier from your point of view.)

The definition of sunrise/sunset is as shown here:


On 9-Aug-2011, sunrise was at 4:47 AM and the full disc of the Sun was just apparent above the horizon at 4:50 AM (clouds notwithstanding). These times were about a minute earlier on the previous day.

The presence of anti-crepuscular rays in the photo, implies the presence of crepuscular rays radiating from the Sun, which implies clouds partially obscuring the sunrise, which could explain why you had difficulty in seeing the Sun when you chanced to look behind you. Other explanations could be that you were slightly below and to the west of the peak of Mount Chokai, or that your memory from two and a half years ago is not quite perfect, or that your clock was slightly off, or that you were a bit sleepy for having scaled a mountain before dawn. The time of this photo is said to be 4:50 AM, which if precise, coincided with the full disc of the Sun appearing just above the horizon. But (at least part of) the Sun would likely still have been "below" the peak of Mount Chokai, meaning that (at least some of) the crepuscular rays hitting the peak were inclined upwards, such that the shadow of the peak was cast onto the anti-twilight arch of the sky, rather than the Sea of Japan.

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Re: Help with the name of an astronomical phenomena please?

Postby danwiz » Wed Nov 20, 2013 11:51 pm

WOW nitpicker - you did a heck of a lot of research for me! I appreciate it and I believe that you are correct. Thank you so very much. I think that we can let this matter sleep now. Thanks to everybody else who replied too. I'll never forget you all.

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Re: Help with the name of an astronomical phenomena please?

Postby Nitpicker » Wed Nov 20, 2013 11:56 pm

Well, Stellarium, Google Maps and Wikipedia did most of the hard labour. Happy to help.


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