Starship Asterisk*

MarkBour wrote:

Ron-Astro Pharmacist wrote: . . . Which brings up another phenomenon - that the bright crescent appears larger, out of proportion, to the rest of the moon? My wife commented on it the other night. It's more apparent "live" but some photos also seem to appear that way. Wonder why?

I'm not at all sure it's the only thing going on, though. It could well be that some cameras are also "spreading the light" in some circumstances.

Ron-Astro Pharmacist wrote: . . . Which brings up another phenomenon - that the bright crescent appears larger, out of proportion, to the rest of the moon? My wife commented on it the other night. It's more apparent "live" but some photos also seem to appear that way. Wonder why?

Chris Peterson wrote:

Nitpicker wrote:

Chris Peterson wrote:(Very few electronic sensors have individually addressable pixels... but perhaps you meant something different by that terminology.)

All I really meant was that the value recorded by each pixel on a digital image sensor, can be converted from an analog signal, to a digital value, and stored in the digital computer memory on board the camera.

I suspected something like that. Of course, this is analogous in many ways to digitally scanned film.

Nitpicker wrote:

Chris Peterson wrote:(Very few electronic sensors have individually addressable pixels... but perhaps you meant something different by that terminology.)

All I really meant was that the value recorded by each pixel on a digital image sensor, can be converted from an analog signal, to a digital value, and stored in the digital computer memory on board the camera.

Chris Peterson wrote:

Nitpicker wrote:Whilst the pixels are normally arranged in a regular fashion (which is all but implied in the word "array"), the more important difference is that the pixels are all individually addressable.

Even more important is that there actually are pixels. Film grains are not even close to being the equivalent of pixels. They are binary, and respond to light in clusters. The result is that film has fairly poor resolution, and worse, has a MTF that is highly dependent on contrast. CCDs and other electronic sensors have pixels that are independent of each other, so their frequency response is independent of contrast.

(Very few electronic sensors have individually addressable pixels... but perhaps you meant something different by that terminology.)

Nitpicker wrote:Whilst the pixels are normally arranged in a regular fashion (which is all but implied in the word "array"), the more important difference is that the pixels are all individually addressable.

rstevenson wrote:

Nitpicker wrote:Electronics can be analog or digital. (I used to own an electronic film camera.) The kind of image produced by a "digital" camera is a "digital image". Other names with more or less the same meaning are "raster image" or "bitmap image". They are all images formed by a 2-D array of pixels, rather than a light sensitive photographic emulsion.

I think you'd have to add to your definition, nit, that the array of pixels be regular. After all, those tiny crumbs of silver in film emulsions are discrete bits themselves, just not very regularly arrayed. (I seem to recall that one innovation, perhaps in the 70s, was to get the silver grains to spread more evenly and to lie flatter, resulting in a faster, more fine-grained appearing film.)

Rob

floyd51 wrote:I'm familiar with diffraction spikes, but why does Venus have eighteen of them?

The wide field, about eleven full moons, suggests the photograph was "camera only", no telescope.

Nitpicker wrote:Electronics can be analog or digital. (I used to own an electronic film camera.) The kind of image produced by a "digital" camera is a "digital image". Other names with more or less the same meaning are "raster image" or "bitmap image". They are all images formed by a 2-D array of pixels, rather than a light sensitive photographic emulsion.

Chris Peterson wrote:

marson wrote:To pick a nit, why say "digital camera" instead of "camera"? Digital is default today.

Habit by those who grew up with film? I prefer "electronic camera" since the sensors which have replaced film are fundamentally analog devices, not digital ones.

FloridaMike wrote:

Chris Peterson wrote:
The dark side? What's that?

It can only be seen from the dark continent....

Chris Peterson wrote:
The dark side? What's that?

Indigo_Sunrise wrote:

Ron-Astro Pharmacist wrote:Is it difficult to predict when Venus may occult Mars as seen from Earth? They were obviously very close February 22nd but I can't find a future prediction for another occultation of that type.

A Wiki search of "History of Mars observation" lists the below.
"On October 13, 1590, the German astronomer Michael Maestlin observed an occultation of Mars by Venus…"
From: Breyer, Stephen (March 1979). "Mutual occultation of planets". Sky and Telescope 57 (3): 220.

http://www.seasky.org/astronomy/astrono ... rrent.html

I just read an article about this very thing, (Venus occulting Mars, as seen from Earth). IIRC, it seems as though it is so infrequent, as in 'lining up' only every thousand years or so. I'll see if I can find where I was reading it.......


ETA: From here:

An occultation involving two planets is extremely rare, however. For instance, the last time Venus occulted Mars was on October 13, 1590, and the next time will be June 4, 2327.

This image is an awesome-almost-occultation!

Ron-Astro Pharmacist wrote:Is it difficult to predict when Venus may occult Mars as seen from Earth? They were obviously very close February 22nd but I can't find a future prediction for another occultation of that type.

A Wiki search of "History of Mars observation" lists the below.
"On October 13, 1590, the German astronomer Michael Maestlin observed an occultation of Mars by Venus…"
From: Breyer, Stephen (March 1979). "Mutual occultation of planets". Sky and Telescope 57 (3): 220.

http://www.seasky.org/astronomy/astrono ... rrent.html

An occultation involving two planets is extremely rare, however. For instance, the last time Venus occulted Mars was on October 13, 1590, and the next time will be June 4, 2327.

bactame wrote:Yes this image is great but doesn't show enough of the dark side. Anybody seen the Netflix film "Aliens on the Moon"? It shows quite a bit and raises the question of an extended family of man on the dark side. Most of it is provocative at best but raises the question that we might have friends out there.

marson wrote:To pick a nit, why say "digital camera" instead of "camera"? Digital is default today.