39 replies to this topic

[jayhall0315]

This is a question for anyone who has observed in a Bortle Scale level one area; On a pitch black night with no moon but clear skies, can the Milky Way appear so bright that you can see your shadow on the ground?

 

I was looking at these Bortle levels and thinking about Spring when I take my small son and our scope to Yosemite NP or Pinnacles NP and was wondering if the Milky Way in real time can cast a shadow that rods in human retinas can detect  (I do not mean a shadow that some sensitive CCD sensor can detect or by some other astrophotography method).  I have traveled to truly dark areas in the past with no human civilization nearby (in the Yukon, an uninhabited island in the South Pacific, during a reseach trip to a dry valley in Antarctica, etc....) and I remember the stars being bright there but not so bright that my shadow was cast on the ground. Is this really possible?

Edited by jayhall0315, 31 December 2014 - 03:50 AM.

[T1R2]

one of the astronomy publications had a article and I remember it saying that in one of the national parks in New Mexico (Chaco Canyon, I think) it even casts shadows from three angles, yes, you read that right, 3 

I don't see why they would say that if it wasn't true, but I do not know that first hand.

[seawolfe]

I have seen my shadow cast by the Milky Way...last June near the John Day Fossil Beds Nat'l Monument.  Very dark skies, no moon, only clear night I had for the whole week's vacation.  So many stars out that I didn't need a light to see by and turned down my hand controller's backlit settings to the dimmest and it was still too bright.  Walking around the parking lot of the Picture Gorge overlook, I definitely could see my shadow and this was a week of the New Moon, so that was out and the only light around was a farmhouse barn light a mile and a half away.  The nearest town, Dayville, was 6 miles away and is a very small but nice town.  It takes two minutes to drive through it. 

[Kevdog]

one of the astronomy publications had a article and I remember it saying that in one of the national parks in New Mexico (Chaco Canyon, I think) it even casts shadows from three angles, yes, you read that right, 3 

I don't see why they would say that if it wasn't true, but I do not know that first hand.

 

When I was standing on the land I'm in the process of buying near Silver City, New Mexico I indeed saw at least 2 different shadows from the different bright areas of the milky way.  There wasn't any moon or other light sources and I could follow the angle back up to bright portions of the Milky Way.  It's quite astonishing!

[StarStuff1]

During Comet Halley days I was taking photos before the beginning of astronomical twilight. This was in a rural area in south Florida and very dark. As the bulge of the MW rose a faint shadow was observable.

 

Although I have never attended the Texas Star Party I have heard from several folks who have  and they often reported seeing the Milky Way's shadow. 

 

FWIW, a few years ago several of us club members traveled to a very dark site in the mountains of SW Virginia to observe the Perseids. As Jupiter (near opposition) rose near the meridian it cast a faint shadow. Rather startling.

[Tony Flanders]

This is a question for anyone who has observed in a Bortle Scale level one area; On a pitch black night with no moon but clear skies, can the Milky Way appear so bright that you can see your shadow on the ground?

I think that's more a question of perception than reality. One tends to think of shadows as things with fairly sharp edges, and the Milky Way, being very large indeed, casts shadows with very fuzzy edges.

The nature of the shadow is also going to depend greatly on the position of the Milky Way.

[kfiscus]

I saw my dim, fuzzy MW shadow at the Nebraska Star Party.

[ylem]

So we now can classify the MW as L.P. 

[BrooksObs]

As the guy that very carefully selected criteria for the steps to be used in the Bortle Dark Sky Scale I can tell you positively that the Milky Way - particularly the SCO/SGR region - is fully capable to casting diffuse but quite noticeable shadows at dark locations. This was actually regarded as a common sight for observers during my youth all around the country, but today it is far more difficult to find sites, particularly in the East, where such is still distinctly recognizable. 

 

As has been related here, one has no difficulty in recognizing such cast shadows from places like the observing field at the Texas Star Party's location near Mt. Locke on moonless nights and is also likely to be seen from various of the country's more remote National Parks. Obviously such shadows are best seen when cast onto a light hued surface and less so on long green grass, but the latter is certainly possible.

 

In addition the planets Venus and Jupiter and bright passages of Iridium satellites can generate cast distinct shadows as well.

 

BrooksObs

Edited by BrooksObs, 31 December 2014 - 11:32 AM.

[star drop]

One transparent night in a Bortle 4 zone Sagittarius, Scorpius and Jupiter created a faint shadow on the north side of my barn. Their combined light was bright enough for me to take notice when exiting our house. When I became fully dark adapted I could catch a hint of my shadow as well.

[Dave Mitsky]

I've seen the Milky Way cast a shadow a number of times over the years.  It's still dark enough at Cherry Springs State Park for this to happen on a good night.

 

http://www.dcnr.stat.../cherrysprings/

 

During its 2003 opposition, Mars also cast a shadow.

 

Dave Mitsky

[LDW47]

This is a question for anyone who has observed in a Bortle Scale level one area; On a pitch black night with no moon but clear skies, can the Milky Way appear so bright that you can see your shadow on the ground?

 

I was looking at these Bortle levels and thinking about Spring when I take my small son and our scope to Yosemite NP or Pinnacles NP and was wondering if the Milky Way in real time can cast a shadow that rods in human retinas can detect  (I do not mean a shadow that some sensitive CCD sensor can detect or by some other astrophotography method).  I have traveled to truly dark areas in the past with no human civilization nearby (in the Yukon, an uninhabited island in the South Pacific, during a reseach trip to a dry valley in Antarctica, etc....) and I remember the stars being bright there but not so bright that my shadow was cast on the ground. Is this really possible?

I am in a Bortle 1 sky at my remote camp and to be honest I have not experienced it !  Maybe it's my 67 year old eyes ? After reading the above comments maybe I don't know what to look for or looking at ?  LW 

Edited by LDW47, 31 December 2014 - 03:29 PM.

[kfiscus]

You'll be more likely to notice it if you are moving.

[gunfighter48]

We lived in NE Washington State for 7 years.  We were 10 miles from the Canadian border and the nearest town was 7 miles away and had a population of 300 people in a 10 radius. So we have VERY dark skies and yes the light from the Milky Way will cast a shadow.  On a full moon nights you could drive the 7 miles from the town to our house by moon light itself, no head lights needed!!! Some of the local hunters would hunt coyotes in the winter with a little snow on the ground and a full Moon. With snow on the ground and a full moon it was almost like early morning light!

[LDW47]

We lived in NE Washington State for 7 years.  We were 10 miles from the Canadian border and the nearest town was 7 miles away and had a population of 300 people in a 10 radius. So we have VERY dark skies and yes the light from the Milky Way will cast a shadow.  On a full moon nights you could drive the 7 miles from the town to our house by moon light itself, no head lights needed!!! Some of the local hunters would hunt coyotes in the winter with a little snow on the ground and a full Moon. With snow on the ground and a full moon it was almost like early morning light!

You are talkng the light of the full moon now thats a different story than the light from the MW !   LW

[StarmanDan]

I've seen my shadow from the MW many times at TSP.  Most noticeable when the central part of the MW is overhead. A light colored ground material like a concrete path helps. 

[GlennLeDrew]

I think only the central bulge region in Sgr/Sco has sufficient brightness to make an impression against the glow from even a very dark site's -8m sky. I'm very sceptical of the Sct or Cyg clouds doing this. The central bulge is estimated by me as being roughly -5 to -5.5m. The base glow from the sky is at least -8m. (Discrete stars are less than 1/10 as bright as sky glow.) And so even the brightest region of the milky way is at least 2.5m, or 10 times fainter than the sky. A source that is only 10% brighter than the illumination it's competing against dies not make a prominent shadow. At these light levels a source some 5% as bright as the sky makes a shadow which is getting down to near the detection threshold. This is about 1/2 as bright as the bulge region.

No other reasonably compact region of the Milky Way comes close to meeting this criterion.

A way o check on this is to lay down a white sheet, and shove a stick through the middle, on the upper end of which is a ball whose height above the sheet is some 3X its diameter. One could check for any darkenings under and around the ball. A camera would provide confirmation, after suitable stretching of the image(s).

A white sheet of high albedo facing the sky has a surface brightness not much less than the mean sky surface brightness. If the latter is, say, 21.3 MPSAS, the sheet's SB would probably be about 21.2 or so. A sufficient exposure of the sheet would equal that which shows rather strong sky glow if the camera were to be aimed upward.

[gunfighter48]

 

We lived in NE Washington State for 7 years.  We were 10 miles from the Canadian border and the nearest town was 7 miles away and had a population of 300 people in a 10 radius. So we have VERY dark skies and yes the light from the Milky Way will cast a shadow.  On a full moon nights you could drive the 7 miles from the town to our house by moon light itself, no head lights needed!!! Some of the local hunters would hunt coyotes in the winter with a little snow on the ground and a full Moon. With snow on the ground and a full moon it was almost like early morning light!

You are talkng the light of the full moon now thats a different story than the light from the MW !   LW

 

Sorry I wasn't clear. The light of the Milky Way would definitely cast a shadow.  Also the area we lived in was so dark that you could drive by the light of the full moon. With snow on the ground the full moon light was as bright as early morning/dawn sunlight. I haven't lived in any other areas that had as dark a sky as our place in NE Washington. There were a few places in Montana that came very close though. I'm hoping to get back to NE Washington this summer and spend 4 or 5 days with a couple of my scopes. The sky is just as dark today as it was in the 60's when we lived there.

[BigC]

I have noticed my shadow(s)  while observing on a Moonless night in my rural yard. Not sharp but definitely there.And it is really amazing how much brighter the stars become after an hour or more in the dark .The  adaption that occurs after 30 minutes  may be all one can get in (sub)urban setting but if not hampered by streetlights adaption continues for at least a couple hours.

Edited by BigC, 01 January 2015 - 11:01 PM.

[jzeiders]

Back in the 1970s I and some friends went to Death Valley between Christmas and New Years to do some astrophotography. We set up camp outside the park on some abandoned mining property. We were on a large mound of quartz tailings. This mound was several football fields across and about 40 feet high with a level top and a road cut into the side that allowed access to the top. So the ground was dazzling white during the day and at night we could easily see our shadows cast by the winter Milky Way. There were no other light sources anywhere around save the stars It was amazing how bright it was after we were thoroughly dark adapted for several hours out there.

 

Even though it was very clear and dark, seeing was somewhat turbulent most of the nights.

 

Jack

[Dave Mitsky]

On a number of occasions at very dark sites, I've held a sheet of white paper towards the Milky Way. When I moved my hand in front of the paper, a shadow was readily visible.

Dave Mitsky

[jayhall0315]

Wow, gentlemen. Thanks for so many first hand reports. I will definitely try exactly what you describe this spring Dave at Yosemite NP, when I take my family over there.  I have also heard many  good reports about the seeing at Big Bend NP in southwest Texas and as you describe Johnny, in NE Washington state. (isn't that where that odd 80's show Twin Peaks was set?)  Amazing to think that perhaps ~ 95 billion suns more than 27,000 LY distance, even when obscured by the dust from the 2 KPC ring, the 5 KPC arm, the Norma Arm, etc.....can reach magnitude -5.5.

 

Glen, what do the abbreviations mean?  I assume sgr means sagittarius, cyg means cygnus, sco means scorpius and sct means scutum?

[MEE]

When in the spring are you going? The brighter sections of the MW (Scorpius through Cygnus) will be visible in the predawn hours. Still, worth staying up late to see!

In the evenings, the zodiacal light should be quite prominent. I've read that it can cast shadows if the sky is dark enough. Other things to look for: can you see a difference in color between the zodiacal light and Milky Way?

How far can you extend the zodiacal light? Can you extend it 1/3 of the way across the sky? Halfway? 2/3? All the way to the opposite horizon?

This MAY be the best way to determine how dark the sky really is from there (other than using an SQM- do you have one? Or at least the phone app?)

Others: are there faint extensions of the MW (both the winter and summer sections) the OP should look for to determine sky darkness? I'm talking about width (Taurus, Lyra, etc)?
Good luck!

[MEE]

I think there is the issue of whether or not the sky background itself is casting a shadow. How can one tell that it is truly the MW casting the shadow?

[MEE]

You may be interested in this discussion:

http://www.cloudynig...s/?fromsearch=1

If the photo isn't in the thread (I can't see it) then here it is:

https://m.flickr.com...N04/7460132952/

Photo taken by Jia Hao