5 April 15

The Perils Of Color In The Digital Age

Last fall we bought a digital DSLR, and this has led me to dabble in a bit of astrophotography, even buying a good equatorial mount to facilitate this. Astrophotography is an interesting hobby. Practiced at its upper echelons (which I have no aspirations towards), it calls for extremes of technique, patience, and expensive gear. The aesthetic which many astrophotographers aim for is a quite colorful image showing many subtleties in the details of a nebula or other deep-sky object.

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.]

Orion Nebula

Posted by at 06:15 PM in Design Arts | Link | Comment

11 April 13

Sidereal Birthdays

I had a milestone birthday today — the earth has orbited around the sun 50 times since I was born. Unpacking that statement a bit, I puzzle over what point exactly marks that milestone? The usual notion I suppose would be to say that since I was born way back when at 4:04 PM on 11 April, therefore that time this year would be the milestone point. But that however is with reference to the Gregorian calendar, which keeps the date of the equinoxes more-or-less in the same point in the calendar by inserting leap days every four years except on centuries not divisible by four. Obviously, leap days are discrete insertions into the calendar, which is why the actual date of the vernal equinox varies between the 19th and the 21st of March depending upon the year.

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.

Posted by at 08:43 PM in Astronomy | Link | Comment

22 March 13

A Universe of One

Yesterday I noticed on Twitter that #Planck was trending. I knew by that time what this was about, but was still surprised to see the name of the great early-twentieth century physicist having moments of social media fame. What had happened yesterday was that there was a press conference announcing the release of data from the Planck satellite mission to map the cosmic microwave background (CMB) radiation with ultrahigh precision. Universe is a teeny bit older than thought reads this story on Science News. Cosmologists have much to tackle ahead of them with this new data, so a few folks will be kept busy for years here.

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.

Posted by at 08:47 PM in Astronomy | Link | Comment

2 September 11

Catching A Supernova

I saw the second supernova in my life last night. This would be SN 2011fe, which was discovered on August 24 by an automated sky survey at the Palomar Observatory. It is in the galaxy M101 (the Pinwheel Galaxy), which about 21 million light years distant, Two things are unusual about it. First, I believe it is the nearest supernova to occur since SN 1987A (a mere 168,000 light years away, back in 1987). Second, thanks to the automated observing network, it is the youngest type IA supernova ever observed, caught within 12 hours of the explosion. The supernova is destined to be one of the most studied such events for this generation of astronomers

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.

Posted by at 08:56 PM in Astronomy | Link | Comment [1]

10 February 11


When I was cycling to work through campus this morning past the grassy landscaped hillocks just east of one of the engineering buildings, I saw a small refractor telescope pointing southeast set up on a tripod on the grass with a person hovering nearby. I realized that it was being aimed at the sun, which means only one thing: there are sunspots to look at! Any radio geek knows the significance of that: lots of sunspots means higher levels of ionization in the upper atmosphere which means better conditions for shortwave communications. Indeed, when I got into the office and looked at the little Firefox add-on in the lower right corner of the browser, it said that the solar flux index was up to 91, not very high in historical terms, but definitely a sign that the laggardly Solar Cycle 24 now is getting off the ground. Look for good radio DXing possibilities in the days and months ahead.

Posted by at 07:58 PM in Astronomy | Link | Comment [1]

12 June 08

I Jinxed The Sun

The sun is being awfully slow to come out of solar minimum, as reported here and here. This may be good for those who are keeping satellites alive in orbit but it is terrible for those trying to make radio contacts on shortwave. In fact, we have been at solar minimum ever since I got my license to transmit on HF, back in January 2007. This is surely not a coincidence. Maybe we’re entering another period like that of the Maunder Minimum.

The poor state of the ionosphere not withstanding, I managed two contacts this evening on HF, one into Washington state, another to Santa Fe, New Mexico.

Posted by at 10:15 PM in Radio | Link | Comment

26 May 08

Phoenix Arriving

Yesterday the Phoenix spacecraft successfully landed on Mars to the jubilation of space enthusiasts everywhere. Despite this being on another planet, there was a witness to the event: the Mars Reconnaissance Orbiter took an amazing photograph from a distance of 760 kilometers showing Phoenix parachuting down for the landing which went flawlessly.

Posted by at 04:18 PM in Astronomy | Link | Comment [1]

7 May 08

Cosmological Graffiti

Cosmological graffiti I’ve been puzzling over this graffiti which is by the bike path underneath the freeway near the UCD Arboretum for some time now. Browsing through my copy of the Oxford Dictionary of Astronomy this evening an answer came to me. The upside-down V must be a capital lambda and the statement would be a reference to the cosmological constant.

This parameter was introduced by Einstein as a modification of the theory of general relativity because of his belief at that time that the universe was static. Later, after Hubble discovered that the universe was expanding, Einstein withdrew this modification and considered it to be his “biggest blunder”. Stepping forward into the late 1990s with the discovery that the expansion of the universe is accelerating, this parameter has now made its way back into contemporary cosmology, as something needs to counteract gravitation. What could be more theologically profound?

Hey, the physics building is only a half-kilometer away from from the graffiti.

Posted by at 11:15 PM in Astronomy | Link | Comment [1]

4 May 08

Cosmic Latte

Next time you are in Starbucks sipping your latte, marvel at the coincidence that it is the color of the universe, all averaged out.

It’s not getting really dark now here until 9:30 PM. This doesn’t leave too much time for stargazing!

Posted by at 08:25 PM in Astronomy | Link | Comment [1]

30 April 08

Into The Virgo Cluster

Look to the east these spring evenings and you will see a triangle of three bright stars: Arcturus, in the constellation Bootes, Denebola, marking the tail of the lion Leo, and Spica, in the constellation Virgo. In that triangle lies one of the biggest challenges in my Messier big year: navigating the Virgo cluster of galaxies.

This is the nearest big cluster of galaxies, about 60 million light years distant, containing maybe 2000 galaxies total. In dark skies many of these can be seen in a moderately-sized telescope, and it is quite a region for the amateur astronomer to get lost in. In bright skies it is a challenge to see any galaxies at all, and finding the 16 or so galaxies on the Messier list takes effort.

There is about one week left until the moon goes into the evening sky again, so I need to make progress now. Last night I viewed M98, M99, and M100, starhopping east from Denebola. M98 was quite tough, M99 and M100 were faint but evident.

Posted by at 07:57 PM in Astronomy | Link | Comment [1]