Filling the Long Cloudy Winter Nights

The past few weeks in southern Ontario have been particularly cloudy, and it’s most frustrating. Like a lot of people, I’ve been itching to get outside at night. Three nights ago there was a break in the clouds for a few moments and I was able to spot Jupiter. Sigh.

Well, not to dwell on the negative, here at Pine River Observatory we’re putting the time to good use.

1. Reading

Apart from re-reading a couple of classics for inspiration – notably Carl Sagan’s Pale Blue Dot and Cosmos, I’ve been working my way along through The Ever-Changing Sky: A Guide to the Celestial Sphere by James B. Kaler and dipping into the delightful Observing and Photographing the Solar System by Dobbins, Parker and Capen, a product of the Association of Lunar and Planetary Observers, or A.L.P.O. I’m also leafing through Sky & Telescope’s Pocket Sky Atlas, dreaming of observing and photographing nights to come.

2. Planning for 2013

There’s a chance I’ll be doing some travel in 2o13, and I’m already thinking of seeking clearer – or new – skies. Am checking out observatories near my destinations, astronomy clubs, and in general, what might be possible if I tack a few days of holidays onto work-related trips.

I’ve also started to prepare a list of “must see” objects for 2013 for stargazing at Pine River. I’m using Carte de Ciel, the free sky carting software, to take a look ahead and see what might be accessible at appropriate times from my various locations. They’re “starter” objects, but I’m hoping to see and photograph the North America Nebula, Flame and Horsehead Nebulas, and the Orion Nebula, to start.

3. Preparing Equipment

My “fixer upper” project this winter has been to clean up and repair an old 80mm achromatic reflector that I picked up for a song (and a few dollars) at a local ‘scope shop. I had been looking at the thing for months; it was sitting on the floor of the shop in a big wooden case. I guess I’m a sucker for old optical equipment (“Well, D’uh” says everyone who knows me) and after a little poking and prodding at the old beast, I did indeed buy it.

An old 80 mm refractor – my fixer-upper project for Winter 2013.

It’s branded as a “Polaroscope” – a brand about which I have found little on-line. In the case was:

• the 80mm f/15 optical tube with finder
• the mount, in pieces and looking like it had been used as a car jack, and relatively crudely finished wooden tripod legs and metal triangular spreader/tray
• a 1.25″ diagonal with a large mirror

The 80 mm Polaroscope refractor certainly has a certain presence in the livingroom. Will it live up to its potential in the field?

I’ve been having fun cleaning up this instrument and making some repairs. The eyepiece collar looked like it had been run over by a truck, and was jammed into the focuser with nothing more secure than a winding of aluminum duct tape. I’ve cleaned it up, replaced the eyepiece thumbscrews, bent it a little better back into place, and epoxyed it into the focuser tube. The lens cell looks pretty good, but the mount is still pretty dirty. The finder scope will need more work – its mounting rings were pretty screwed up too. For now, I’ve put the tube on a much heavier mount to get things started. The original mount will likely be the last thing I work on; it’s functional but grimy.

The details are that it’s branded “Polaroscope,” is an 80mm refractor (I assume it’s an achromatic), 1,200 mm focal length, f/15. Once cleaned up I’m hoping to put it to use at star parties for planetary and lunar observations. I’ve already used it for a little lunar photography, with a Nikon D5100 at prime focus.

The trademark on the objective lens cell of the 80mm refractor. Look familiar to anyone?

4. Blogging

In December 2012 I set out to create the Pine River Observatory blog, and so far, so good! Preparing material, formatting images, and actually writing blog posts have kept me busy through a fair bit of the Holiday break this year. I have been able to maintain the somewhat hectic pace of a posting per day since starting the blog on the 20th of December. I anticipate bringing that down to perhaps one or two posts per week once I’m back at work, but am also hoping to have a lot more to post once I can see some clear sky at night and not just freakin’ clouds!

Looking Forward to 2013

There are always lots of things happening in astronomy. Here are some anticipated highlights for 2013.

In the Sky

On 28 April 2013 the planet Saturn will be at opposition – the closest approach that the ringed planet makes to us during the mutual orbits of earth and Saturn. Will be the best time during the year to look at Saturn with a telescope. There’s also a partial (“penumbral”) lunar eclipse on the 18th of October, which might be visible in Ontario.

Nice meteor showers show up every year, assuming that the weather cooperates. Here are some of the more prominent ones:

• Just after New Year, on January 3-4, the Quadrantids Meteor Shower is at its peak. A dark location after midnight is recommended; find the constellation Bootes to find the expected radiant point.
• In August, the Perseids Meteor Shower presents its peak on the 12th and the 13th. This is always a favourite meteor shower, with as many as 60 meteors per hour showing up.
• November has the Leonids Meteor Shower, peaking on the 17th and 18th. This shower looks like it’s originating in the constellation Leo, and will be best viewed after midnight.
• In December, weather permitting, the Geminids Meteor Shower has its peak December 13-14. Best viewing will be after midnight, in the east.

Perhaps the most anticipated sights in 2013 are two comets expected to make interesting – and possibly spectacular – shows. Comet 2014 L4 (PanSTARRS) is currently being watched by astronomers in the southern hemisphere, but by March it should reach its greatest brightness and be visible up here in the north (http://cometography.com/lcomets/2011l4.html). 2014 L4 (PanSTARRS) is predicted to peak at a magnitude near -0.5 between 8-12 March 2013 (like a very bright star). Like the vast majority of comets, it will come no where near to the earth, never getting any closer than 0.3 AU – a third of the distance from the earth to the sun. By late May it should be very high in the night sky in the north – perhaps 5 degrees from Polaris – but will be much fainter too.

A German engraving of the Great Comet of 1680. Some sources are prediction that Comet C/102 S1 (ISON) will be as spectacular… but only time will tell.

Also eagerly anticipated is Comet C/2012 S1 (ISON), (http://cometography.com/lcomets/2012s1.html). It was discovered this past September and might (emphasis might) be one of the greatest comets of recent memory. It will dip very close to the sun – about 0.1 AU or one tenth of the way from the earth to the sun – and may reach its maximum brightness on 28 November 2013. While very hard to predict, the size and orbit of the comet has some astronomers predicting a magnitude (brightness) of -13 for this beast. That’s brighter than the full moon! It may also have a very long tail. As comets are best described as irregular, big dirty snowballs, just how they behave when the sun starts to heat them up and generate their tails and other features is impossible to predict with precision. I’ll post updates (as will everyone interested in the sky, I’m sure!) as they become available.

(source of 17th C. illustration: http://ksj.mit.edu/tracker/2012/10/kehouflop-redux-out-near-saturn-monster).

On the Ground

This year the Hamilton Amateur Astronomers is hosting ASTROCATS 2013: The Canadian Astronomy Telescope Show, May 25th & 26th at the Sheridan College Athletics Centre, Oakville, Ontario. Unfortunately yours truly can’t attend, but it should be a great show, with a lot of vendors representing the best in astronomy gear (come to think of it, it’s likely a GOOD THING I can’t go. The national debt couldn’t take the strain): http://astrocats.ca/.

SkyFest is the annual three-day event put on by the North York Astronomical Association. August 8-11, 2013, held at River Place Park, RR 3, Ayton, Ontario (northwest of Mount Forest). It’s Canada’s biggest star party: http://www.nyaa.ca/index.php?page=/sf13/sf.home13.

My Favourite Amateur Astronomy News from 2012: September’s Impact on Jupiter

There were some great astronomy news stories in 2012, but one really stands out for me as a demonstration of why amateur astronomy can still be “more” than a hobby. Dedicated amateur astronomers can make real contributions to science.

Early on the morning of September 10, Mr. Dan Peterson was observing the planet Jupiter with a 12″ telescope in Texas, and saw a bright flash on one side of the planet. The flash lasted perhaps 1.5 to 2 seconds, and was reported to be very bright. Mr. Peterson posted his observation on an astronomy web forum (http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/5413921/Main/5413225). A few hours later another amateur, Mr. George Hall, posted a photograph of the flash, confirming the earlier report (http://georgeastro.weebly.com/uploads/1/3/3/4/13344093/jupiterimpact.jpg).

This event – likely the impact of a small, previously unknown comet – into the Solar System’s largest planet – would not have been observed at all unless amateurs had seen it, as was the case. With the large number of planets and other interesting objects in our Solar System (especially comets and asteroids), the professional scientific community and the incredible instrumentation provided by earth-based and space-based telescopes can’t monitor everything all the time. There are no spacecraft in the vicinity of Jupiter, and even if there had been, observing an unpredictable event that lasted 2 seconds would be down to sheer luck even if there was a spacecraft near-by.

Even the world-wide network of amateur astronomers can’t catch everything that happens, of course, but the chances are that transient events will be picked up by an amateur first. This isn’t a new situation. The Association of Planetary and Lunar Observers (yes, they use the acronym A.L.P.O. – http://www.alpo-astronomy.org/) has been organizing, recording, and helping people to share observations on the planets, comets, asteroids, and just about everything else in the solar system, for decades. With 14 different “observing sections” covering everything from meteors to remote planets, A.L.P.O. is a great example of people contributing to new knowledge – true citizen scientists. A.L.P.O. even publishes its own journal, in production since the 1940s. Membership is open to anyone interested, whether or not you are making regular observations. They are international and welcome all interests.

There are several ways in which amateurs are contributing to astronomy around the world right now. In addition to observations of Solar System events and the discovery of comets, some are making detailed measurements of the brightness of individual stars over time, called stellar photometry. Many stars are variable, changing their brightness over time for several different reasons. For example, the American Association of Variable Star Observers (http://www.aavso.org/) links up and supports people making observations of stars that are changing brightness because of their intrinsic physics, or even because of orbiting companion stars (occulting binaries).

What’s more, even in today’s light-polluted urban environments, like Southern Ontario, amateur observing programs like these can continue. The moon and the planets out to Saturn, at least, are so bright that useful observations can be made even with the ubiquitous background glow in the sky reducing the contrast of what we can see. Getting involved in a meaningful way in these programs is also not dependent on having large, expensive telescopes. There are observing sections in A.L.P.O. for people observing the sky with nothing more sophisticated than a pair of binoculars, or just their eyes. Knowledge of the sky, patience, and making careful, organized notes are the most important tools any astronomer – amateur or not – brings to the science.

© 2012, David Allan Galbraith

Four Hundred Years Ago Today Galileo Discovered Neptune – Almost

The discovery of the planet Neptune – the eighth and most distant major planet from our sun – nearly took place on December 27th and 28th, 1612 – four hundred years ago today. Most text books record that it was formally discovered over 230 years later.

On that day, Galileo Galilei turned his telescope toward Jupiter, and made detailed notes on the four moons now called the Galilean moons. He also recorded a “fixed star in his notes.” He was actually looking at the planet Neptune. He saw it again a month later, recording its position accurately in meticulous diagrams in his notebooks.

Of course, Galileo doesn’t need any additional discoveries to add to his fame, but historians are always looking over the notes of notable scientists to see what they actually recorded. Standish and Nobili (1997, below) believe that Galileo actually recorded the position of Neptune a total of four times while making notes about Jupiter and the four moons that, as a group, are named after him

What happened two hundred years later was a more complex story than just a recording of an observation. By 1821 astronomers had compiled tables of the motions of all of the planets out as far as Uranus, the seventh planet in the solar system, Between 1844 and 1846 both British and French astronomers made calculations based on the orbital information of Uranus and started a hunt for an unknown, but predicted, 8th planet. Credit for actually spotting Neptune and realizing what he was seeing goes to Johann Gottfried Galle in Berlin in 1846. He was working with predictions from Urbain Le Verrier in France (who was right about where a new planet should be to within about 1° in the sky) and John Couch Adams in Britain (who was a little further off, at 12°, but both predictions were amazing considering the times).

Sources

• A detailed account of Galileo’s observations of Neptune is provided in Standish, E. M., and Nobili, A. M. 1997. Galileo’s Observations of Neptune. Baltic Astronomy 6: 97-104. Available on-line at: http://articles.adsabs.harvard.edu//full/1997BaltA…6…97S/0000097.000.html
• A summary of the history of the discovery of Neptune is available on-line: Caine, F. 2012. Who Discovered Neptune? Universe Today March 12, 2012.  http://www.universetoday.com/21621/who-discovered-neptune/

© 2012, David Allan Galbraith

Blogging as a Learning Experience

I’ve jumped into presenting the Pine River Observatory blog as a personal project this month. Now that I’ve a few posts under my belt perhaps a little commentary is appropriate.

I want to be upfront with everyone who’s taking a few minutes to read these posts (thank you, by the way). I am not a professional astronomer or physicist, and I don’t consider myself to be very experienced as an amateur astronomer, either.  Those of you who may know me personally will understand this point, but the question may still be in you minds: why, then, am I putting a blog out there for the world to see? What to I bring to the P.R.O. blog that might be worth-while for others to consider?

Hopefully you’ll be interested in the learning trajectory I have set for myself and may feel like following along.  The blog is a challenge to myself, to set up something that demands my attention and concentration, and that provides me with a chance to develop tools and ideas for my own application in astronomy and astrophotography. Critically, it gives me a ready platform to share some of the products of my creativity, in written and visual forms.

Looking north along the shore of Lake Huron toward Kincardine and the Bruce Nuclear Power Plant. A 30 second exposure taken 14 August 2012 at 11:30 PM, ISO 5000, f/3.5, Nikon D800 and 24mm wide-angle lens, with white balance set in the camera to a manual cool setting. Captured were a meteor (top left) and the Pleiades (M45; middle right).

I hope you will also enjoy the images I have been posting, and will continue to prepare and post. I am enchanted with viewing the night sky, and in capturing images of such a sweeping and inspiring nature.

What I do bring to the blog is a life-long passion for science, and a special interest in physics and astronomy that are nearly on a par with my professional fascination with biology and evolution. The two go hand in hand in many ways, and a certain synergy between these great branches of natural science will undoubtably creep into future postings. I envision that this blog will have a somewhat broader basis over time than “just” astronomy; it will not be an on-line log book of my own observations (although it might include such a feature at some point). I will be looking to add context to what I see in the sky, and to events as they unfold in science more generally, and I hope this will make the blog a richer experience for it. I also hope that you will feel free to provide me with feedback on the journey. Your thoughts are always appreciated.

© 2012, David Allan Galbraith

Some Lunar Landmarks in Science Fiction

The moon has often been the setting for great stories in science fiction, but only rarely have actual locations been depicted in some way. Usually a generic cratered, dusty surface suffices for “the moon” for any a film-maker. When I was growing up, two of my favourite visual science fiction depictions were Stanley Kubrick’s 1968 film 2001: A Space Odyssey, and Gerry and Sylvia Anderson’s TV series Space: 1999, in production from 1975 to 1977. Not only did both make explicit reference to the year in which (some of the) events they portrayed took place, but they also at least made a nod to real lunar locations.

Three craters identified as locations in 2001: A Space Odyssey and Space: 1999. Photograph taken 25 October 2012, Hamilton, ON, with Sigma 150-500 mm telephoto lens and Nikon D7000.

Two locations on the moon were settings for important events in 2001: A Space Odyssey, both in the rugged southern portion of the visible side of the moon. The story revolved around humans finding artifacts deliberately left behind millions of years ago, as tests for the evolution of a space-fairing culture. One of these monoliths was buried under the Crater Tycho (43° S, 11° W) and was given the name TMA-1, or Tycho Magnetic Anomaly 1. In the story, a strong magnetic field was detected in the area of the crater, prompting American astronauts to undertake some lunar archaeology. Near by, in the Crater Clavius (58° S, 14° W), the Americans had already established a large underground moon base – very handy! Both of these craters are real, prominent, and can be observed easily from earth.

It should also be noted that Russian’s future space efforts were not ignored in 2001: A Space Odyssey. During a short meeting with Russian scientists on board an earth-orbiting space station, Dr. Haywood Floyd finds out that the Russians are coming back to earth from their own base, Tchalinko,  in Crater Tsiolkovsky, on the far side of the moon.

The action in the British TV series Space: 1999 revolved around a group of people trapped on the moon when it was blasted out of orbit and into deep space by an enormous explosion, the result of a nuclear waste storage accident on the far side. Leaving aside that this the scenario poses monumental physics problems, it’s fun to note that the moon base in this program, “Alpha,” was apparently located in a real crater, Plato, at a lunar latitude of about 52° N, longitude 9° W. The location was not divulged during the episodes of the series, but the location was revealed during the second season by publicity produced by the studio, according to the web site “Space: 1999 Net” (http://www.space1999.net/catacombs/main/cguide/umext.html; The same article points out that there were somewhat conflicting references to lunar geography throughout the program. Clearly, some film-makers need to hire better technical advisors).

Tycho, Clavius and Plato are all worthy objectives for a backyard telescope. All three are also likely among the first craters that a novice lunar observer will get to know, and all are quite different. Tycho (86 km across) is a recent crater; the impact that produced the crater also produced the moon’s most prominent set of rays. Clavius (225 km across) is much larger and older – at around four billion years, the oldest of the three – and has been disrupted by more recent craters. Plato (109 km across) is a very flat crater, its bowl filled with dark lava in the same way that the lunar maria are. Only a few small craters break up its otherwise flat surface, which looks much like Mare Imbrium to the south.

There have been many more references to the moon in fiction, of course – but these are a couple of my favourites.

© 2012, David Allan Galbraith

Merry Christmas – a gift for the future

I cannot think of a more powerful message than that offered up by “Symphony of Science” (http://www.symphonyofscience.com/ – AKA John Boswell, AKA melodysheep) in their original music video, composed from the words of Carl Sagan and Stephen Hawking, in A Glorious Dawn. All of the work of this program, and this piece in particular, have captivated me since this past November, when I was introduced to them in a presentation on finding hope in a climate change universe, by Grant Linney.

My very low-cost present to you: enjoy, contemplate, be moved – and take action to help secure a positive, bright, and rational future for our children’s children’s children:

Light Pollution and Dark Skies

The world is full of the unintentional consequences of human activities. Light pollution is one of them. Where can you go to escape it?

We’re contending serious problems because of climate change, the release of chemical compounds into our environment that mimic hormones, the extinction of many, many species of animals and plants, and the list goes on. The overwhelming majority of these problems are unintentional. No one sat around thinking what a great idea it would be to lose a large portion of the earth’s biodiversity by accident. Light pollution is not on the same scale of problems as the present mass extinction crisis, but some species are badly affected by it (especially birds and insects). It has also been recognized as an issue of loss of cultural and scientific heritage.

On 5 December 2012, NASA released a series of images and videos of the earth’s surface as it looks at night, derived from photos taken by a NASA-NOAA satellite. The images have been dubbed “The Black Marble” and received a fair bit of press coverage (http://www.nasa.gov/mission_pages/NPP/news/earth-at-night.html). The images are beautiful, certainly, and you get a real sense of the mass – the spread – of the human population from them. We are truly a global species (David Suzuki has dubbed us a “SuperSpecies” – influencing the lives and fates of most, if not all, other species on earth).

They are also in a sense a map of “Dark Sky” areas – places where you can still hope to get a view of the night sky without the overwhelming warm glow of stray photons from street lamps, cars, highrises – well, you get the picture. Here’s Southern Ontario, a cropped view of one of NASA’s images, a stunning high-resolution composite covering much of North America (the source file is at: http://www.nasa.gov/images/content/712129main_8247975848_88635d38a1_o.jpg).

Southern Ontario at night from space, cropped from a much larger image published by NASA in December 2012, part of the “Black Marble” project. Photo credit: NASA

So, where can you go in Southern Ontario to see dark skies? A great start are areas already designated as dark sky parks or preserves. Here are some main ones, plotted on an inverted version of the NASA photo:

 

Prominent Dark Sky locations in Southern Ontario, plotted on an inverted image of the area from space at night. Dark areas represent highest concentrations of light pollution. Original photo credit: NASA

1. Gordon’s Park, Manitoulin Island (the island follows practices to encourage a “dark sky” environment) –  Designated a Dark-Sky Preserve by the Royal Astronomical Society of Canada
2. Bruce Peninsula Fathom Five National Marine Park, near Tobermory –  Designated a Dark-Sky Preserve by the Royal Astronomical Society of Canada
3. Bluewater Outdoor Education Centre – Wiarton, ON
4. Point Pelee National Park –  Designated a Dark-Sky Preserve by the Royal Astronomical Society of Canada
5. Torrance Barrens – NE of Orillia. Designated a Dark-Sky Preserve by the Royal Astronomical Society of Canada in November 2012
6. Lennox-Addington Dark Sky Viewing Area – about 60 km NNW of Napanee, ON

Other areas recommended by some sources include:

• Binbook Conservation Area – about 16 KM south of Hamilton, a favourite site of the Hamilton Amateur Astronomers
• Fingal Wildlife Management Area, 30 km from London, Ontario.
• Bon Echo Provincial Park, 100 km north of Prince Edward County
• Charleston Lake Provincial Park, west of Brockville

UNESCO has a dark skies designation program underway, noting that dark skies are of scientific and also of cultural value. Royal Astronomical Society of Canada is also promoting the idea of Urban Star Parks – but there seems to only be one designation so far, in New Brunswick.

Links:

• http://www.lennox-addington.on.ca/must-see/dark-sky-viewing-area.html
• http://www.rasc.ca/dark-sky-site-designations
• http://www.skynews.ca/pages/dark.html

Text © 2012, David Allan Galbraith

Star Stuff? Try “Big Bang Stuff!”

One of the (deservedly) frequently quoted observations by my hero Carl Sagan is that we are all star-stuff. The chemical elements in our bodies – and everything we see around us on Planet Earth – were forged in exploding stars billions of years ago. This is a profound realization. It seems to me that doesn’t go far enough, however.

I started thinking about the origins of the elements in our bodies, and made a connection I haven’t seen elaborated before. To explain myself, I have to explain the origin of the universe first.

The 98 elements that occur in nature are divided up by astronomers into two groups: hydrogen and helium, and “metals:” all the other stuff. Hydrogen and helium were the products of the evolution of matter following the big bang. The “metals” were subsequently produced in a process dubbed nucleosynthesis: nuclear fusion taking place within stars (the process was worked out over half a century ago; the landmark paper is E. M. Burbidge, G. R. Burbidge, W. A. Fowler, F. Hoyle. 1957. Synthesis of the Elements in Stars, Rev. Mod. Phys. 29: 547). The proportions of these things are considered very important. The ration of hydrogen to helium in the observable universe is one of the hallmark tests for cosmology and models of the origins of the universe. Different models predict different ratios, and only the natural ration of about 76% hydrogen to 24% helium gets to decide which models fly.

The other stuff is used to characterize stars, with a measure called metallicity – the proportion of the stuff of the star that is not hydrogen or helium. For example, the metallicity of the sun is approximately 1.8% by weight. Put the other way, the sun is 98.2% hydrogen+helium by weight. This quantity is very helpful to astronomers as it’s a measure of the age of stars, among other things. The older the star, the higher the expected metallicity, as the metals are added by the very process of fusion. Looked at one way, it’s stellar pollution.

This started me thinking about human metallicity. There’s a nice summary on Wikipedia on the elemental composition of the human body (http://en.wikipedia.org/wiki/Composition_of_the_human_body). Here are the top ten elements and the percentage of the body, by weight and atomic proportion, that they represent:

• Oxygen – 65% by weight but 24% by atomic proportion
• Carbon – 18% by weight but 12% by atomic proportion
• Hydrogen – 10% by weight but 63% by atomic proportion (!!)
• Nitrogen – 3% by weight but 0.58% by atomic proportion
• Calcium – 1.4% by weight but 0.24% by atomic proportion
• Phosphorus – 0.78% by weight but 0.14% by atomic proportion
• Potassium – 0.25% by weight but 0.033% by atomic proportion
• Sulfur – 0.25% by weight but 0.038% by atomic proportion
• Sodium – 0.15% by weight but 0.037% by atomic proportion
• Chlorine – 0.15% by weight but 0.024% by atomic proportion

Ok, so what, I hear you say. Well, look at #3 in this list – hydrogen. Ten percent of our body mass is hydrogen, in chemical compounds like water, sugars, and all sorts of other things. However, two facts about hydrogen are important. First, it’s the lightest element there is, so 10% by weight is a big number by atoms. Second, hydrogen was not made by nucleosynthesis. It was made by the Big Bang itself – and sixty-three percent of the atoms in our bodies are hydrogen.

If we shift our attention away from overall proportions by mass and re-list things by number of atoms, we see a different picture of our own composition. Yes, we are star-stuff – but 63% of the atoms in our bodies have their origins in the Big Bang itself. These humble hydrogen atoms that are the majority population in our bodies – and are the most abundant stuff in the visible universe –  went through stars that exploded, but they came from the Big Bang. In a real sense, so did we.

© 2012, David Allan Galbraith

How does the Moon “Really Look?”

A few weeks ago a friend and colleague at Royal Botanical Gardens, Bill Kilburn, asked me a deceptively simple question. After looking at some of my photographs of the moon, he asked me what it really looked like. I had mentioned that the surface of the moon was actually very dark. Our natural satellite looks very bright to us at night, and it’s easy to over-expose a photo of the moon, especially if you set your camera to an automatic exposure setting.

Bill’s question challenged me to try to take a photograph of the moon that has an appearance more in keeping with our understanding of the moon’s natural reflectivity, or albedo. Before starting to take photos, I needed to think about the matter of light and exposure.

Normally, cameras are calibrated with one of several roughly equivalent systems of standardization regarding their sensitivity to light. The actual standards are established by the International Standards Organization, or ISO, and there are several ways that cameras are calibrated according to the standard. The standards were first established for photographic film, but today the standard (technically, it’s called ISO 12232:2006) applies to the camera itself: its complex systems of light-recording sensors and tiny computers that process the images they record.

The system is designed to allow photographers to match up the sensitivity (the “ISO number”), the shutter speed of the camera, and the aperture or “f-stop” to achieve a properly exposed image. For any given ISO number (higher numbers mean more sensitive to light), proper exposure will be a function of both the shutter speed (faster speeds mean less light gets in) and f-stop (higher numbers mean less light gets in). While that sounds complicated, there is a simple old photographer’s rule of thumb that applies very well: the “Sunny-16 rule.”

Sunny-16 states that on a sunny day, for any ISO number, the image of an object in sunlight will be correctly exposed if the f-stop is set to f/16 and the shutter speed is set to the reciprocal of the ISO number. Still sounds complicated? Here are a couple of examples:

• If ISO=400 and the lens is set to f/16, then the correct shutter speed is 1/400.
• If ISO=100 and the lens is set to f/16, then the correct shutter speed is 1/100.

Makes more sense now? Working from this idea, that a sunny scene should be properly exposed under the Sunny-16 rule, I reasoned that if I set my camera to ISO=400, shutter speed = 1/400 seconds, and aperture to f/16, then the image of the moon (which is fully exposed to the sun) should be recorded by the camera as though it was sitting in front of me on a sunny day. There is a big assumption in this, but really only one: that the full thickness of the earth’s atmosphere is actually as transparent to visible light as is a few dozen or hundreds of feet of air would be for a terrestrial scene on a sunny day.

So, armed with these three settings (IS0 400, 1/400 of a second and f/16) I set up my camera and telephoto lens and took some photos of the moon. Here is a frame recorded at that setting without any changes “post camera” to brightness or contrast:

The moon at it “really looks.” Photographed on the morning of 6 December 2012 along Fallsview Road in Dundas, Ontario. The camera was set to ISO 400, shutter speed 1/400th of a second, and aperture of f/16. By the “Sunny-16” rule in photography, this should record roughly how the moon would look if it was sitting in front of us on a sunny day… minus the blue sky of course.

The technical details of the moon’s brightness are available from NASA (http://nssdc.gsfc.nasa.gov/planetary/factsheet/moonfact.html). There are a couple of ways of measuring the albedo, or reflectivity, of a surface, but either way, the moon reflects to us between 11% and 12% of the light that strikes it. This is similar to the albedo of slightly weathered asphalt. There are some areas on the moon that are darker, and some lighter, than this. The relatively new crater Aristarchus, for example, is considered to be the brightest feature on the moon’s surface.

It must also be noted that your own computer monitor or tablet may not display the image “exactly right.” Unless it’s been calibrated for brightness, the gray scales represented in the image may look a little different to you.

The same image, adjusted to bring out detail and make the moon look a little brighter, looks like this:

The western half of the moon, photographed before dawn on 6 December 2012, from Dundas, Ontario. Adjusted for brightness and contrast to appear more like the moon does to the naked eye than the image above. Note that there are details visible in the western part of the image (to the left) in the original copy that are washed out by this brighter view.

This is a bit more like we’re used to seeing it. Part of the difference lies in contrast at night. Once our eyes are dark-adjusted, we’re much more sensitive to light than we are in the day, and the moon – coal-dark as it is – appears much brighter than we think it does in the daytime.

© 2012, David Allan Galbraith