The use of color in this manner is in most ways an illusion, at least from the point of view of human visual perception. Cones, the anatomical structures in the retina that respond to color, are not sensitive to light at low levels, so looking through even a very large telescope at the nebula one will not discern the color brought out in the photograph. The color in the image may be useful in terms of scientific visualization, for instance illustrating different emission spectra, but it’s not what the eye can see.
Astrophotography is perhaps an extreme example, but I’m philosophically confounded by the question of representation of color in the digital age. Consider what might be the modal life of a digital photo shared with others. A snapshot taken with one’s smartphone, then posted to the web via Facebook or Instagram. The issue is of calibration. How does one ensure that the color intended by the photographer is what is seen by the recipient? Without both the creator’s and recipient’s monitors calibrated to a common standard, one cannot. These standards exist, but 99.99% of the time both parties are not so calibrated. Even enthusiastic photographers tend to spring for new lenses in lieu of color calibration equipment. One can adjust color curves in image software to one’s heart’s content, but without calibration both sides, one’s artistic intent in terms of color cannot be reliably shared.
And what if the intent is simply to record the colors one sees? The problem persists and is refracted twicefold. First, how faithfully do the levels of color recorded by the digital sensor represent the spectra of light being reflected by the object? Second, what are the colors being displayed by one’s monitor?
A solution I often adopt is to directly record the color in watercolor paint. With sufficient practice in color mixing, this can work reasonably well. Soil scientists have a more scientific answer to this problem — they go to the field armed with Munsell color swatch books to match and note the color of a soil unit. And the astrophotographer in me wishes there was a market for black-and-white consumer digital cameras: these problems go away, and cameras without RGB filters are more sensitive to light.
It’s also not clear where octarine fits in any color calibration system I know of.
[Image below is one of my attempts at astrophotography, being of the Orion Nebula.]
]]>Defining one’s calendar with reference to the equinoxes still isn’t exactly the same thing as the earth being in the same position in its orbit. The year with reference to the equinoxes is called the tropical year, and is 365.242190 days long. The year with reference to the fixed stars is the sidereal year, and is 365.256363 days in length. The latter seems to be what I’m interested in identifying in my milestone, so how do we determine this?
What it seems we want to do is calculate things in heliocentric coordinates, that is, with reference to an observer standing at the middle of the sun. To figure this out, I reached for a venerable piece of astronomy software, XEphem, and did some calculations. The heliocentric longitude of the earth from the sun at the time of my birth was 201:23:09 (degrees-minutes-seconds). Changing the date in the program to April 2013, I then stepped its clock forward and back until the heliocentric longitude was 201:23:09 again. This I find occurred at 7:50 PM on April 10th. Not today at all. Hmm.
All of which is a good reminder that time is a lot more subtle of a concept than many people realize.
]]>Here’s the bit that most intrigued me from the Science News story: “Planck also found several features that surprised scientists. Most notably, it reaffirms a quirky WMAP finding that one half of the sky seems to have more fluctuations than the other. Theory predicts the universe should look the same in all directions. “ (WMAP was an earlier space mission, the second one, to produce a map of the CMB.) So this portrait of the universe at an early age is not random in all directions. Anyway, I am bothered by a statistical puzzle. We have a sample size of one — just one universe to look at here. There’s no population against which we can make a statistical test. So how can we possibly distinguish between this anisotropy being the remnant of some oddball random fluctuation during the early inflation of the universe, or the case where there’s undiscovered physics going on here?
Not that I know much at all about cosmology! At any rate I’m in one of my phases where I’m extremely interested in astronomy. I think this all started a couple months ago when Pica was knitting herself a Celestarium shawl.
]]>I first heard about the supernova last Friday or Saturday, planned to look for it on Saturday, but was foiled by the presence of haze and smoke from a brush fire 20 miles distant. I have only seen one supernova in a telescope before, back in 1998 — I think was SN 1998bu in the galaxy M96, which got to about magnitude 11.8 in brightness. We were living halfway up the mountain behind Santa Barbara, a place with much darker skies than where we are now — I have great trouble seeing 12th magnitude stars in my 7” telescope here. So I looked on Sunday, and had no luck, cursing the bright skies here.
So I looked again last night, it being important to look before the moon gets too bright in the evening sky in the next several days. First looking through the eyepiece I thought it would go well. It did. When I had hopped to the correct star field there was a suspicious object. Was it the supernova? Or perhaps it was the 11.7 magnitude comparison star on my star chart? Comparing the geometry of the stars with those on the star chart it looked more like the former, but it wasn’t until I found a pair of stars at the upper part of the field pointing at the supernova on the chart did I confirm it. The supernova was now not at all difficult to see with direct, rather than averted, vision. A look at this light curve shows what has happened: between Sunday and Thursday the supernova brightened from about magnitude 12 to around magnitude 10.7. Wow. No wonder it was now pretty easy to see. I’ll be following it over the next several weeks, though the moon will make this difficult for a couple weeks
And now to look for a comet! I just heard about Comet Garradd today: it sounds like it is pretty easy to find.
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