The Eclipse of 2017: One Week To Go!

Will the total solar eclipse of 21 August 2017, which will transit across the continental USA, live up to the hype? The eclipse will also be visible as a partial eclipse from pretty much all of Canada and Mexico.

I've already seen that some writers are expecting the eclipse to be the most-photographed event in history (at least far). I'm planning on seeing the eclipse first hand, as are many other astronomy fans and photographers. My contacts near our planned main observing site are worrying about the traffic. Stores specializing in astronomy gear are selling out of excise viewers.

Whether or not the event – compounded by human interest – lives up to it all depends on the weather too. Right now I'm hopeful it will cooperate. Long-range forecasts (always to be taken with a grain of salt) show a sunny day expected on the 21st at my planned observing site. Just in case, though, I do have a backup site thanks to the suggestions of friends in the area.

In the mean time, many people planning on attending the eclipse in its totality are practicing their photographic methods. I've been preparing by running a series of tests of interval exposures with wide-angle lenses. Shot through solar filters, these photos are then stacked together to create a single image showing the track of the sun through the sky.

Above, a Nikon D800 dSLR on a sturdy tripod with a wide angle lens and a solar filter, set up to take photos every 30 seconds. The sun moves through the sky at a rate of about 15 degrees per hour. At a diameter of about 30 arc-minutes this means that the sun shifts by its own diameter every two minutes.

I've also been running through other equipment options, such as whether I should try to set up a telescope and motorized mount to follow the sun. Given the travel distance and the practicalities of carting around heavy gear, I'm now planning to minimize the kit and maximize the experience, but also be equipped to take some interesting snaps.

On to more mundane things today though, like having a plumber over this morning to replace some old plastic water lines that are now prone to leak.

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“Night-Time Photography” at RBG: An Unabashed Plug

This post is a plug for a new public program at Royal Botanical Gardens that I will be presenting in February and March. The goal of the program is to introduce participants to photographing the night sky with camera and tripod, although we will talk a little about telescopes, too.

There are many wonderful things to photograph at night. You can take a look at some of my examples here at the Pine River Observatory blog, on my page entitled “Astrophotography Gallery.” We’ll consider both celestial objects – like the moon and stars – and also landscapes at night.

The stars make arcs in the sky in long exposures. This image was composed from about 120 individual wide angle photos taken with a Nikon D7000 on a tripod.

The stars make arcs in the sky in long exposures. This image was take along the shores of Lake Huron in August, 2012. It was composed from about 120 individual wide angle photos taken with a Nikon D7000 on a tripod, using free software called StarStaX.

On the first night, in the classroom at RBG Centre in Burlington, we’ll take a look at examples of night-time photography, and go through the basics of photography at night, including the kinds of scenes likely to be encountered and the equipment that might be used. There will be a light (pardon the pun) orientation to objects in the night sky, discussions about where and when photos may be most effective, and what limits photography at night. We’ll also talk about handling photographic equipment in cold weather.

The second night will be a practical  night out shooting the sky. The date for the second night is variable and will be shifted as needed, primarily to accommodate the weather. Keep your fingers crossed for some clear nights at the beginning of March!

The third night will be “show and tell” for the participants, and examples of working with software to prepare final images. It will likely be in later March, but might also be shifted, with the permission of everyone, to accommodate fitting in appropriate outside time.

There are still a few places. You can reach the RBG’s on-line ticketing program at: http://tickets.rbg.ca/PEO/all_events.asp

To find “Night-Time Photography,” select the link entitled “For The Nature Lover” at the lower left side of the page.

This program is being offered for a fee that goes to support Royal Botanical Gardens’ important charitable objectives. I’m not getting paid for this program. Just so you know.

Royal Botanical Gardens presents "Nighttime Photography" in 2013

Royal Botanical Gardens presents “Night-Time Photography” in February and March 2013

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 is "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 how the moon would look if it was sitting in front of us on a sunny day.

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. This view is particularly good for tracing the history of astronomy in the names of the craters visible.

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