An 11,000 square kilometer observatory
On March 26, 2011, the Royal Astronomical Society of Canada designated Jasper National Park a Dark-Sky Preserve. At 11,228 square kilometers, it is the world's second-largest such preserve and the largest that is readily accessible, as it contains a town within its borders. The designation required a formal focus on protecting the night sky by eliminating unnecessary artificial light and educating the public about the effects of light pollution.
The darkness of a location is measured by astronomers in magnitudes per square arcsecond. In the core areas of the Jasper preserve, the sky quality reaches levels darker than 21.7 mag/arcsec², with an overall average of 21.4 mag/arcsec². This level of darkness, close to that of a sky with no light pollution at all, allows for exceptional viewing of celestial objects. It means the sky itself has a natural, faint glow from atmospheric and cosmic sources, but human-generated light is almost entirely absent. To maintain this standard, all new exterior lighting within the park must comply with strict dark-sky regulations, which specify shielding and direction.
What a dark sky reveals
The absence of light pollution makes faint and distant celestial objects visible to the naked eye. The Andromeda Galaxy (M31), a spiral galaxy 2.5 million light-years away, can be seen as a faint smudge in the constellation Andromeda. The Milky Way appears not as a hazy band but as a structured feature with visible dust lanes and nebulae.
The extreme darkness also allows for the observation of two elusive phenomena: the zodiacal light and the gegenschein. The zodiacal light is a faint, triangular glow seen after sunset or before sunrise, caused by sunlight scattering off interplanetary dust in the plane of the solar system. The gegenschein, or "counter-glow," is an even fainter, oval-shaped light patch directly opposite the Sun in the night sky. It is also sunlight reflecting off cosmic dust. Both are so faint that even minimal skyglow from a distant city can obscure them. During winter, clear, cold nights often provide views of the aurora borealis. Each October, the preserve hosts the Jasper Dark Sky Festival, which includes science talks, workshops, and stargazing events.