Starship Asterisk*

So an occultation of Regulus by the asteroid Erigone will happen this Thursday. I'm a little upset now that I will not be able to record video because my DSLR does not have that feature and can only shoot about 5 frames per second. Well, I guess I will have to just be one of the people who reports yes or no.
http://occultations.org/regulus2014/

geckzilla wrote:So an occultation of Regulus by the asteroid Erigone will happen this Thursday. I'm a little upset now that I will not be able to record video because my DSLR does not have that feature and can only shoot about 5 frames per second. Well, I guess I will have to just be one of the people who reports yes or no.
http://occultations.org/regulus2014/

mpergo2s_with_text.png

You should check in advance how much exposure time you need to convincingly record Regulus. The lack of video mode may be a moot point. You should still be able to record the occultation start/end with your still-frame DSLR to the nearest half second at least. It is expected to last 14 seconds in total.

Some information on what is scientifically useful here:
http://occultations.org/regulus2014/r14dslr/

My lens also fails by only going to 40mm. I don't know if Regulus would even appear. I'd have to try. Then again, clouds are in the forecast so it could be an entirely moot point.

The video mode on my Nikon D5100 is so-so. It can record 25 frames per second, but I have limited control of the exposure (which must obviously be faster than 1/25s) and I'm not sure that the ISO setting is relevant. Hmmm, I might try to determine the limiting magnitude of my camera in video mode, just for fun. Not counting my telescope, I have 2 zoom lenses to test with a range from 18 to 300 mm. Pity I won't see the occultation from here.

Equinoctial Sunrise

Seen just clearing a dip in the Pikes Peak massif (1° altitude from my location), 8 minutes after the calculated sunrise time, and just a half a degree south of due east (because of the delay to get above the mountains).

I checked for any breaks in cloud cover near Regulus but no luck. I thought maybe somewhere else someone got lucky, but this update was posted at the little Facebook page which was set up:

Sadly, as of 4pm today, March 20th, there are no confirmed observations from this morning's occultation of Regulus from anywhere, including Bermuda where several IOTA members travelled in an attempt to beat the clouds and rain that blanketed the entire occultation path. From most places even the full Moon was invisible behind thick clouds that rolled overhead in a continuous layer that never seemed to end.

geckzilla wrote:I checked for any breaks in cloud cover near Regulus but no luck. I thought maybe somewhere else someone got lucky, but this update was posted at the little Facebook page which was set up:

Sadly, as of 4pm today, March 20th, there are no confirmed observations from this morning's occultation of Regulus from anywhere, including Bermuda where several IOTA members travelled in an attempt to beat the clouds and rain that blanketed the entire occultation path. From most places even the full Moon was invisible behind thick clouds that rolled overhead in a continuous layer that never seemed to end.

Oh, how disappointing!
M

geckzilla wrote:I checked for any breaks in cloud cover near Regulus but no luck. I thought maybe somewhere else someone got lucky, but this update was posted at the little Facebook page which was set up:

Sadly, as of 4pm today, March 20th, there are no confirmed observations from this morning's occultation of Regulus from anywhere, including Bermuda where several IOTA members travelled in an attempt to beat the clouds and rain that blanketed the entire occultation path. From most places even the full Moon was invisible behind thick clouds that rolled overhead in a continuous layer that never seemed to end.

Clearly, we need to find a new planet to live on. One without clouds, where fresh water just bubbles out of the ground. Or maybe even better -- The Big Rock Candy Mountains:

There is no way I am clicking that link pressing that play button and getting that song stuck in my head again!

Inspired by the beautiful APOD of two days ago:
http://apod.nasa.gov/apod/ap140402.html
... I attempted an Aussie variant from my backyard: I also pulled out my scope for the first time in a few weeks, to get my first ever telescopic view of Mars. It impressed me enough to record some video, which after stacking and sharpening, offered a lot more detail than the eyepiece. Mars is oriented here with celestial north up, showing the small polar ice cap in the northern summer, and the much larger impact basin Hellas, frosted/clouded over with dry ice in the southern hemisphere's winter. The South Pole is not illuminated and the dark equatorial region is Syrtis Major. The not quite circular appearance is due to me being a little heavy handed on the camera controls, I think, but I'm pretty impressed with my little 6" SCT: I also captured this cute one of a jet plane crossing the galactic plane and forming a mast for the good ship Argo (aka Vela, Carina & Puppis):

Very nice. A quick adjustment can lessen the impact of the orange light flooding your scene. This was just a curve adjustment in Photoshop in under a minute. A significant boost to the blue, a small decrease in the red, and a minute increase to the green.

geckzilla wrote:Very nice. A quick adjustment can lessen the impact of the orange light flooding your scene. This was just a curve adjustment in Photoshop in under a minute. A significant boost to the blue, a small decrease in the red, and a minute increase to the green.

Thanks. This is the aspect of image processing (and viewing) about which I am least perceptive. Whilst I can spot the difference between my version and yours, I would not have been able to say that my one was flooded with orange. All I do know is that this is the most light-polluted part of my sky, looking in the direction of downtown Brisbane, and it tends to make the sky in my photos look more grey/silver and less dark. In this instance, I also switched on a bright light in my backyard to illuminate the trees, which I rarely do.

Grumble, grumble ... I spent over an hour last night, attempting to stack and curve-stretch about 10 similar subs together in Deep Sky Stacker, to make the Milky Way more prominent. But I failed dismally, gave up in disgust, and reverted back to the 8s single sub with the jet it in.

Well, even if you can't perceive it, you know that anytime there are terrestrial light sources they are going to be anywhere from warm yellow incandescent bulbs to the painful orange of a high pressure sodium lamp. I sometimes wonder if I am biased too much into thinking the sky must be blue at night in the absence of clouds or auroras. Rather than trying to judge things based on how they appear I imagine the light sources present and then attempt to compensate. I imagine a lot of HPSLs in the distance emanating from your city and interacting with the atmosphere while something else, perhaps some typical residential flood light, is illuminating the foreground.

Lately I have been taking horrible photos of my room in near complete darkness to pretend like I am taking some dark sky photos. I am not impressed by my camera's sensor.

I've obviously not spent enough time under dark skies. I've never really considered a natural night sky to be bluish from Earth, but I suppose it is. Without giving it too much thought, I've always just figured the greyish or silvery skies in my images to be a better approximation to what the sky would look like without any atmosphere. I perceive the sky's background brightness as noise, and giving it as blue a tone as you have here, has brought the sky back to Earth in my mind, and I'm still struggling with that on an aesthetic level.

Nitpicker wrote:I've obviously not spent enough time under dark skies. I've never really considered a natural night sky to be bluish from Earth, but I suppose it is. Without giving it too much thought, I've always just figured the greyish or silvery skies in my images to be a better approximation to what the sky would look like without any atmosphere. I perceive the sky's background brightness as noise, and giving it as blue a tone as you have here, has brought the sky back to Earth in my mind, and I'm still struggling with that on an aesthetic level.

The sky is never visually blue from a dark site. It is grey. But photographically it has a blue cast. This is usually normalized to black in astronomical images, however. But in astro-terrestrial shots, you often see the blue. Any orange at all indicates artificial lighting.

Chris Peterson wrote:

Nitpicker wrote:I've obviously not spent enough time under dark skies. I've never really considered a natural night sky to be bluish from Earth, but I suppose it is. Without giving it too much thought, I've always just figured the greyish or silvery skies in my images to be a better approximation to what the sky would look like without any atmosphere. I perceive the sky's background brightness as noise, and giving it as blue a tone as you have here, has brought the sky back to Earth in my mind, and I'm still struggling with that on an aesthetic level.

The sky is never visually blue from a dark site. It is grey. But photographically it has a blue cast. This is usually normalized to black in astronomical images, however. But in astro-terrestrial shots, you often see the blue. Any orange at all indicates artificial lighting.

Any clouds or significant haze in my astro-terrestrial images (especially when shooting towards downtown) shows up clearly as orange to me. But in a clearer sky, I simply don't perceive orange, but silvery grey. I know the orange is there, as geckzilla has demonstrated it, but I don't think I'm as perceptive to colour at low intensities as most people. I've always known that my sky is polluted with significant amounts of artificial light, but I think I may have convinced myself that the resulting colour is preferable (though I'd much prefer no colour at all). I might try adjusting the colour balance on my camera at some stage, to see what I can see.

It's been so long since I've been in a dark place on a clear night with a bright moon in the sky but I swear I remember seeing blue shadows. If my memory is correct, it is similar to daytime conditions when the light bouncing around in the atmosphere forms the ambient color seen in some shadows. This memory could easily be fabricated, though.

I've always perceived shadowed objects to have the same RGB ratios as the fully illuminated objects, just with darker RGB values. (That's probably a clumsy way to describe it, but my first attempt was worse.)

It is not an obvious effect. If you take art lessons someone might try to teach you to notice these things. I have been taught to paint things in sunlight as if there is a slightly yellow tinge to the light and then blue in the shadows. I think this is wrong, though. The blue shadows, yes, that happens. The yellow light thing doesn't except during sunset when the colors can be quite accentuated and dramatic. If you get the chance, look at a snow covered mountain on a cloudless day. It is most easy to observe the atmospheric light within shadows on white surfaces. In absence of said glorious mountain, any white surface will do. A white house, say. The trick is to pick a place where the shadow is sharp and starkly contrasts against the sunlight. Trees and other nearby objects can potentially ruin the effect or even turn shadows green.

geckzilla wrote:It is not an obvious effect. If you take art lessons someone might try to teach you to notice these things. I have been taught to paint things in sunlight as if there is a slightly yellow tinge to the light and then blue in the shadows. I think this is wrong, though. The blue shadows, yes, that happens. The yellow light thing doesn't except during sunset when the colors can be quite accentuated and dramatic. If you get the chance, look at a snow covered mountain on a cloudless day. It is most easy to observe the atmospheric light within shadows on white surfaces. In absence of said glorious mountain, any white surface will do. A white house, say. The trick is to pick a place where the shadow is sharp and starkly contrasts against the sunlight. Trees and other nearby objects can potentially ruin the effect or even turn shadows green.

I am perfectly happy to take your word for it. At some point, I'm convinced that illusion and reality become too difficult to separate. I probably reach this point sooner than you do.

Well, you could analyze everything with photometry and dispel the illusions. Yeah, you just need a portable sensor to put in your pocket and take out anytime you wonder what color something really is.

geckzilla wrote:It's been so long since I've been in a dark place on a clear night with a bright moon in the sky but I swear I remember seeing blue shadows. If my memory is correct, it is similar to daytime conditions when the light bouncing around in the atmosphere forms the ambient color seen in some shadows. This memory could easily be fabricated, though.

Sure, that's possible with a bright Moon. But that's why I said a dark site. If you have a bright Moon, you don't have a dark site. If it's actually dark, everything is grey. There's no color to the sky (although the Milky Way may be a warm grey). And there aren't really any shadows at all.

Nitpicker wrote:I've always perceived shadowed objects to have the same RGB ratios as the fully illuminated objects, just with darker RGB values. (That's probably a clumsy way to describe it, but my first attempt was worse.)

That's largely an illusion. Your eye sees the same RGB as different RGB ratios at different intensity levels. And of course, intensity is a component of color. But it's a good illusion, related to the way we always see white as white, even though it very seldom is.

Chris Peterson wrote:

Nitpicker wrote:I've always perceived shadowed objects to have the same RGB ratios as the fully illuminated objects, just with darker RGB values. (That's probably a clumsy way to describe it, but my first attempt was worse.)

That's largely an illusion. Your eye sees the same RGB as different RGB ratios at different intensity levels. And of course, intensity is a component of color. But it's a good illusion, related to the way we always see white as white, even though it very seldom is.

I find I can very easily get confused if I try to discuss colours too much. This has now become one of those times. I only (think I) understand the technical side of colour theory in terms of the simple RGB colour model. In other words, red, green and blue are the only components of colour in my simple world, and intensity is derived from that. For example, in normalised coordinates (1,0,0) is the most intense red and (0.5,0,0) is a less intense red. As such, I don't quite understand your meaning.

Nitpicker wrote:I find I can very easily get confused if I try to discuss colours too much. This has now become one of those times. I only (think I) understand the technical side of colour theory in terms of the simple RGB colour model. In other words, red, green and blue are the only components of colour in my simple world, and intensity is derived from that. For example, in normalised coordinates (1,0,0) is the most intense red and (0.5,0,0) is a less intense red. As such, I don't quite understand your meaning.

Yes, it does get confusing. What I meant is that if you take a light source with some particular combination of wavelengths defining it, your retinal L, M, and S cones (roughly, RGB) will respond in some ratio. If you simply change the intensity of the source, not only will the absolute response of the cones change, but so will the ratios. At a physiological level, the two generate very different signals. The color you perceive, however, may be the same or different, depending on many factors. This is the basis of many color and intensity optical illusions, where we are fooled into believing that different colors are the same, or that the same colors are different.