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Mars casting shadows

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#1 Redbetter

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Posted 15 November 2020 - 09:51 AM

In recent years I have posted about noticing that Jupiter and Sirius cast shadows at dark sites.  Folks generally recognize that Venus can cast shadows.  Last night was brighter than normal for dark sky, only 21.1 MPSAS, but I had some open ground and sky to work with.  It occurred to me that this was the first good opportunity I have had this opposition to see if Mars was casting a shadow.   Indeed it was. 

 

The shadow is most noticeable from something like one's legs, where less of the shadow near the feet can be illuminated by other parts of the sky.  Longer shadows are more difficult to discern this way.  And, of course, the brighter the sky is, the weaker a point source shadow will be--the shadow will have reduced contrast.  


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#2 Special Ed

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Posted 15 November 2020 - 12:44 PM

I'll have to try this.



#3 mikemarotta

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Posted 17 November 2020 - 09:53 AM

I am not surprised. I have gotten better views of Mars with a blue filter that cuts the glare. (The Moon filter is too much.). Mars is bright.


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#4 Sheol

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Posted 23 November 2020 - 07:31 PM

      Mars was pretty darn bright back in October, still is even. I bet if I was down in Ft. Davis the 4th planet would cast a shadow.

 

    Clear Skies,

      Matt.



#5 Rich (RLTYS)

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Posted 01 December 2020 - 04:12 PM

Never knew that Mars could cast a shadow. shocked.gif



#6 ButterFly

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Posted 04 December 2020 - 12:52 PM

I notice shadows easier with an arm or fingers over my chart.  The bright white of the chart is lit only by the sky.  It has several distinct shadows on it at different angles from various sources.  A shadow against a dark ground is much harder to see.  Sagittarius during the summer was insane.



#7 Dave Mitsky

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Posted 04 December 2020 - 01:22 PM

Mars definitely cast a shadow around opposition in 2003.



#8 Sheol

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Posted 04 December 2020 - 07:33 PM

             I find that quite believable, Dave. Planet 4 was a blazing red star rivaling Jupiter it seemed to me that year. Sadly, I only had my dubious vintage era eyeballs to observe with. Even so, quite the show!

 

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#9 Voyager 3

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Posted 05 December 2020 - 05:14 AM

From a bortle 8 or worse in my location , the moon and sun can cast shadows shocked.gif .



#10 Sheol

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Posted 05 December 2020 - 06:45 PM

             Ok, we are assuming a slightly darker sky condition than bortle 8!

 

           Matt.


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#11 Rocklobster

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Posted 07 December 2020 - 12:10 AM

I'll take everyone's word for it, bit I have to say, honestly, I'm finding it very hard to believe that even Venus would cast a shadow and I've seen it at its brightest.

I've was at a B2 location this past September (end of) and Mars was high and bright and the moon was below the horizon. I can't even picture Mars casting any sort of shadow there.

But hey..what do I know? If so many of you say it's possible, then so be it. I just can't imagine how.

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#12 Sheol

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Posted 08 December 2020 - 07:16 PM

             Well, I saw Mars last night. No shadows will be cast now. It has faded considerably since October. But I've seen areas where the Milky Way ( Summer) could cast a shadow, so Venus, Jupiter, & Mars have no problem. It just depends on how dark your viewing area is. That is the main key. If there are a lot of porchlights/streetlights competing with natural light sources, forget about it.

 

                  Clear Skies,

                        Matt.



#13 Redbetter

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Posted 13 December 2020 - 01:44 AM

I'll take everyone's word for it, bit I have to say, honestly, I'm finding it very hard to believe that even Venus would cast a shadow and I've seen it at its brightest.

I've was at a B2 location this past September (end of) and Mars was high and bright and the moon was below the horizon. I can't even picture Mars casting any sort of shadow there.

But hey..what do I know? If so many of you say it's possible, then so be it. I just can't imagine how.

Venus' shadows are obvious to me in dark sky.  This is a well known phenomenon.  Venus is so bright that it is somewhat of a nuisance.  I suppose today that people are less familiar with Venus casting shadows because they rarely are away from light pollution and not well dark adapted.  

 

Jupiter was one I noticed by happenstance in Bortle 2 conditions in an unlit room with two wide high windows.  I noticed the shadow of my arm against a beige wall as I reached for the door handle and looked back to determine the particular illumination source. 

 

Shadows like this are more readily seen against a white backdrop because the illumination levels are low and that provides the eye more surface brightness to work with.  There are some articles out there that confirm Jupiter, etc. and seem to have come to the same conclusions as far as methods I have employed.    

 

The difficulty is in determining the shadow cast by a point source vs. the sky in general.  Back when visual observing was still of some importance, there was an article about observing shadows cast by stars all the way down to 2.9 magnitude.  To go that deep the method was more specific in excluding wider sources of extraneous light from the sky itself.   1902 article.


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#14 ButterFly

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Posted 13 December 2020 - 03:13 AM

That's a fantastic article!

 

I'll be constructing a "window box" for the next trip out to my dark site.  I'm planning on a carboard box with a sheet of white paper on one of its longer sides.  A window on the other side with a bar running down its middle to make two side by side holes.  And a peeping hole on one of the other sides.

 

The "light and dark mottlings which move with the ripples on the surface" is definitely something I want to see!



#15 starblue

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Posted 14 December 2020 - 04:11 AM

I'll take everyone's word for it, bit I have to say, honestly, I'm finding it very hard to believe that even Venus would cast a shadow and I've seen it at its brightest.

I've was at a B2 location this past September (end of) and Mars was high and bright and the moon was below the horizon. I can't even picture Mars casting any sort of shadow there.

But hey..what do I know? If so many of you say it's possible, then so be it. I just can't imagine how.

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General astronomical knowledge was more widespread in the past--you didn't have to be an astronomer to know that Venus cast shadows:

 

She and Leslie and Gilbert were on their way to the Four Winds Point,
having plotted with Captain Jim to watch the New Year in at the light.
The sun had set and in the southwestern sky hung Venus, glorious and
golden, having drawn as near to her earth-sister as is possible for
her.  For the first time Anne and Gilbert saw the shadow cast by that
brilliant star of evening, that faint, mysterious shadow, never seen
save when there is white snow to reveal it, and then only with averted
vision, vanishing when you gaze at it directly.

 

"It's like the spirit of a shadow, isn't it?" whispered Anne.  "You can
see it so plainly haunting your side when you look ahead; but when you
turn and look at it--it's gone."

 

That's a quote from the novel "Anne's House of Dreams", from the "Anne of Green Gables" series of novels by Lucy Maud Montgomery. The author was a Presbyterian minister's wife on Prince Edward Island (among other places in Canada), hardly any kind of astronomer, and the characters Anne and Gilbert are a teacher and doctor, respectively. This particular book was first published in 1922 but the era in the series takes place around the turn of the century. The excerpt is also an accurate, if inadvertent, description of averted vision: look away, you see it; look at it, it's gone.

 

If you prefer pictures, here's a photo of the phenomenon at spaceweather.com taken 100 miles west of Austin, Texas, in dark skies.



#16 Rocklobster

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Posted 14 December 2020 - 04:30 AM

General astronomical knowledge was more widespread in the past--you didn't have to be an astronomer to know that Venus cast shadows:

That's a quote from the novel "Anne's House of Dreams", from the "Anne of Green Gables" series of novels by Lucy Maud Montgomery. The author was a Presbyterian minister's wife on Prince Edward Island (among other places in Canada), hardly any kind of astronomer, and the characters Anne and Gilbert are a teacher and doctor, respectively. This particular book was first published in 1922 but the era in the series takes place around the turn of the century. The excerpt is also an accurate, if inadvertent, description of averted vision: look away, you see it; look at it, it's gone.

If you prefer pictures, here's a photo of the phenomenon at spaceweather.com taken 100 miles west of Austin, Texas, in dark skies.

That's a 20sec exposure at 12000ISO. I thought we were discussing shadows cast that are visible to the naked eye.

I have no doubt Venus casts a shadow. Photons will be stopped. I just can't ever imagine it would be visible to humans.

As for your quote.good find, I'm just not sure I believe it. Sorry.

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#17 Rocklobster

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Posted 14 December 2020 - 04:32 AM

Well, a few other people in this thread confirm it. I'll believe you, but it's VERY reluctantly.



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#18 Rocklobster

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Posted 14 December 2020 - 04:35 AM

Venus' shadows are obvious to me in dark sky. This is a well known phenomenon. Venus is so bright that it is somewhat of a nuisance. I suppose today that people are less familiar with Venus casting shadows because they rarely are away from light pollution and not well dark adapted.

Jupiter was one I noticed by happenstance in Bortle 2 conditions in an unlit room with two wide high windows. I noticed the shadow of my arm against a beige wall as I reached for the door handle and looked back to determine the particular illumination source.

Shadows like this are more readily seen against a white backdrop because the illumination levels are low and that provides the eye more surface brightness to work with. There are some articles out there that confirm Jupiter, etc. and seem to have come to the same conclusions as far as methods I have employed.

The difficulty is in determining the shadow cast by a point source vs. the sky in general. Back when visual observing was still of some importance, there was an article about observing shadows cast by stars all the way down to 2.9 magnitude. To go that deep the method was more specific in excluding wider sources of extraneous light from the sky itself. 1902 article.

Again, I'll take your word for it, but I remain skeptical.

I was in a B2 site this end of September when Mars was high and bright and Jupiter was also visible earlier . No moon. There was no way either of those were casting anything.

You saw it. Great. I'll have to see it myself to believe it.



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#19 starblue

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Posted 14 December 2020 - 05:06 AM

That's a 20sec exposure at 12000ISO. I thought we were discussing shadows cast that are visible to the naked eye.

...

Reread Montgomery's description. It's not poetic license--it's an accurate description of the phenomenon. Subtle but real--it's easily seen on a white background. You can also see the Gegenschein naked-eye but I've never heard of anyone photographing it in a few seconds.



#20 Redbetter

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Posted 14 December 2020 - 05:52 AM

That's a 20sec exposure at 12000ISO. I thought we were discussing shadows cast that are visible to the naked eye.

I have no doubt Venus casts a shadow. Photons will be stopped. I just can't ever imagine it would be visible to humans.

As for your quote.good find, I'm just not sure I believe it. Sorry.

I regularly see things that photographers spend tens of minutes or hours of exposure time on (mostly nebulae.)  Others do the same, so that isn't anything unusual.  The eye's effective integration time when fully dark adapted is a few tenths of a second at most.  The difference is that visually the fine resolution is missing (and so is color except on the highest surface brightness objects).  

 

There are many reports of Venus casting shadows if you search around.  There are online article mentions of it as well.  The surprising thing to me is that you had never heard of this.  

 

Again, I'll take your word for it, but I remain skeptical.

I was in a B2 site this end of September when Mars was high and bright and Jupiter was also visible earlier . No moon. There was no way either of those were casting anything.

You saw it. Great. I'll have to see it myself to believe it.

There are various things I have not seen that are known to be visible, but because I have not seen them doesn't mean they aren't visible.  It just means that I haven't gotten around to trying them yet, or have not had the right combination of conditions, or perhaps my eyes are not up to it.  The green flash was like that for me until I finally caught the right conditions one sunset in Hawaii--and the one my wife and I caught was a weak one.  The objects that folks have the most trouble with are low contrast/low surface brightness or just visually dim.  In many cases, the difference is experience and whether or not people have actually tried.

 

A better question to ask yourself is: what is your experience level for noticing such phenomena in dark sky?  If you didn't notice this sort of thing in September (before this thread was posted) then perhaps it was because you were simply unaware of it.   

 

There are quite a few things that I see naked eye that few amateurs even try to locate that way or don't realize are visible.  Some are relatively easy in rural sky, like Uranus which I find visually comparing my charts to the ecliptic in the general area, looking for an un-plotted ~6 mag star.  I confirm by pointing my scope at the "star" to reveal it is actually a planet.  I have seen Ceres and Vesta naked eye multiple times at favorable oppositions. 

 

Those are point sources.  Then there are targets more applicable to this subject: lower brightness, lower contrast objects like the gegenschein, zodiacal band, zodiacal light, Barnard's Loop, the Angelfish Nebula, various comets, etc.  I see the first three in the list even at low altitude Bortle 3 sites if the conditions are good and each are well placed.  I track the gegenschein throughout the year at various sites, except when it is lost lower in the sky or enmeshed in the Milky Way glow.  I use it and the zodiacal band as ways to measure transparency since the band disappears first or is seen less completely in all but the best condtions. 

 

Are you familiar with these features naked eye?  There is no shame in not being familiar with them if you haven't.  Most astronomers are not familiar with them.  I finally learned to recognize them when I began observing regularly in Bortle 2 conditions.  The better you become at recognizing such features, the more likely you are to be able to detect shadows from the brightest planets and stars. 

 

As an example of something I have not seen that is associated with the above, there are Kordylewski's clouds.  While they have been reported visually by a couple of astronomers who have studied and imaged them with special apparatus in published work, these are exceedingly faint and variable by nature, and only likely to be reasonably possible at my darker sites a few nights a year.  



#21 Redbetter

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Posted 20 December 2020 - 05:54 AM

I had some dark sky observing time in the snow on Friday night.  The provided an opportunity to look for shadows from several sources.  It was interesting seeing shadows cast simultaneously from Sirius and Mars as well as some more dispersed shadow such as from the northern Milky Way/Cassiopeia region.  The latter was a glow between some tall trees at the time creating some directional contrast of my movement rather than point source.




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