The Darkest skies in Southern Canada

It is a mosaic of 9 images taken with a 50 mm f/1.4 lens and 20 minutes exposure at f/4 (12.5mm aperture!) with a Canon 350D and IR filter removed. The lower image is a full resolution cutout (1.3%) showing the amount of detail available. The visual appearance is similar (except for the colors and number of stars) and shows much detail in the hub. This view of the Milky Way is perhaps one of the best wide-angle images ever taken, it shows the remarkably dark skies in this area. Image courtesy of N. Chamaillard ( 2007).

As you can see the southern horizon is BLACK! This is vital is order to get an exceptional view of the Milky Way. The 401 corridor of Kingston and Belleville are so far way (>120km) that they simply don't register. It's an awesome sight to behold.

The importance of having a dark sky cannot be underestimated. CCD cameras can achieve good images in less than perfect skies but the same cameras can go much deeper with the same exposure in a darker sky. Here you can see the effect that skies of different brightness have on the imaging performance.

The table is calculated for the using the photometric tool. 21.82 mag/arcsec² is the sky brightness at the site. (MMO= Mont-Megantic Observatory, RAO=Rothney Astrophysical Observatory, DAO= Dominion Astrophysical Observatory, DDO=David Dunlop Observatory, EO=Elginfield Observatory, sky conditions are approximate only).

Exposure times (derived with the photometric tool) with signal-to-noise ratios (s/n) 20 under different sky conditions using the r' (visual) filter. The darker the sky the shorter the exposure for the same s/n, the site is situated at the far right at 21.8 mag/arcsec2.

Much effort was expended to locate the best possible site for the Madawaska Highlands Observatory. Several criteria were established to determine the location.

1. Low sky brightness (i.e. a very dark site).
2. Good seeing
3. High elevation
4. Access
5. Long term viability
6. Lowest possible latitude.

By using the Sky Brightness Map (Cinzano, Thiene, Italy 1998) superimposed on Google Earth, it becomes obvious that an exceedingly dark peninsula exist between Ottawa and Toronto in an area known as the Madawaska Highlands. The area, centered on the town of Denbigh Ontario, has an elevation of ~400 metres, amongst the highest in Ontario. This is the most southerly area in Canada with exceptionally black skies, with a sky brightness of ~21.9 magnitudes/arcsec².

Upon examining the topographic maps to determine a precise location with the highest possible elevation with a relatively easy access it was determined the area bordering Lennox & Addington, Frontenac and Renfrew counties met our criteria.

Nighttime visits in the area on December 12/13, 2007 and again on February 28/29 confirmed the incredible darkness. With a limiting magnitude of 7.1, the sky was filled with stars to the point were some constellations were hard to make out. The Milky Way was some 60 degrees wide at its broadest in the Cassiopeia area. Numerous dark patches in the northern Milky Way were quite obvious. Something we had never seen before. M33 was easily seen straight on, and you could tell that it was a broad round object. The area around Orion was pitch black and filled with stars an incredible sight to behold. The zodiacal light obvious on both occasions, visible as a diffuse light pyramid in the west. A Sky Quality Metre (SQM) reading on May 28/29 2008 gave a reading of 21.82 magnitudes/arcsec². A perfect sky is considered 22.10 mag/arcsec².

The night sky in the area is considered a truly dark sky. For example the zodiacal light, a very faint light created by solar light reflecting off dust particles in the plane of the solar system, is considered a most difficult phenomena to see. It appears in the west as a very faint diffuse pyramid shape glow aligned with ecliptic and fades within 1 hour or so after the end of twilight. The zodiacal light has been seen on every visit the site. People around you are barely distinguishable and disappear all together when more than a few metres away. Clouds are not visible until the stars start disappearing or above a light bubble. The Milky Way is seen all the way to the horizon and some almost 60 degrees broad in some areas. These are all common sights at the site.

The most significant light bubble is from Ottawa. With a maximum height of around 10 degrees and a width of some 20 degrees. Smaller bubbles of less than 5 degrees could be seen from Kingston, Belleville and Toronto. Just barely visible 2 degree bubbles were visible from Smith-Falls+Perth and Renfrew.

The site is located about 100 minutes [drive] from Ottawa and about 3.5 hours from Toronto. The largest nearby town is Denbigh with a population of about 200. Bancroft with a population of 4000, is to the west, Renfrew in the northeast has a population of 7,500 with Belleville and Kingston are about 120 km to the SSW and SSE. Ottawa is about 120 km away in the ENE and Toronto is 250 km away to the southwest. According to the Sky Brightness map the site it is located in the gray area which has a Bortle rating of 2, which limiting magnitude of 7.1-7.5. There is a very broad buffer zone of anywhere from 50 to 100 km of blue (Bortle 3) that will give the site a least 100 years of exceptionally dark skies.

Next: Sky Brightness Map