Half the park is after dark! With a combination of dry air, little light pollution, and high elevation, Great Sand Dunes National Park and Preserve is an excellent and easily accessible dark sky viewing location! In 2019, Great Sand Dunes became certified as an International Dark Sky Park by the International Dark Sky Association, meeting strict standards for sky darkness, limiting outdoor lighting, and working with neighboring communities to reduce light pollution.
Olbers's paradox, also known as the dark night paradox, is an argument in astrophysics and physical cosmology that says that the darkness of the night sky conflicts with the assumption of an infinite and eternal static universe. In the hypothetical case that the universe is static, homogeneous at a large scale, and populated by an infinite number of stars, any line of sight from Earth must end at the surface of a star and hence the night sky should be completely illuminated and very bright. This contradicts the observed darkness and non-uniformity of the night.[1]
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The darkness of the night sky is one piece of evidence for a dynamic universe, such as the Big Bang model. That model explains the observed non-uniformity of brightness by invoking expansion of the universe, which increases the wavelength of visible light originating from the Big Bang to microwave scale via a process known as redshift. The resulting microwave radiation background has wavelengths much longer (millimeters instead of nanometers), which appears dark to the naked eye and bright for a radio receiver.
Edward Robert Harrison's Darkness at Night: A Riddle of the Universe (1987) gives an account of the dark night sky paradox, seen as a problem in the history of science. According to Harrison, the first to conceive of anything like the paradox was Thomas Digges, who was also the first to expound the Copernican system in English and also postulated an infinite universe with infinitely many stars.[3] Kepler also posed the problem in 1610, and the paradox took its mature form in the 18th-century work of Halley and Cheseaux.[4] The paradox is commonly attributed to the German amateur astronomer Heinrich Wilhelm Olbers, who described it in 1823, but Harrison shows convincingly that Olbers was far from the first to pose the problem, nor was his thinking about it particularly valuable. Harrison argues that the first to set out a satisfactory resolution of the paradox was Lord Kelvin, in a little known 1901 paper,[5] and that Edgar Allan Poe's essay Eureka (1848) curiously anticipated some qualitative aspects of Kelvin's argument:[1]
To show this, we divide the universe into a series of concentric shells, 1 light year thick. A certain number of stars will be in the shell 1,000,000,000 to 1,000,000,001 light years away. If the universe is homogeneous at a large scale, then there would be four times as many stars in a second shell, which is between 2,000,000,000 and 2,000,000,001 light years away. However, the second shell is twice as far away, so each star in it would appear one quarter as bright as the stars in the first shell. Thus the total light received from the second shell is the same as the total light received from the first shell.
Thus each shell of a given thickness will produce the same net amount of light regardless of how far away it is. That is, the light of each shell adds to the total amount. Thus the more shells, the more light; and with infinitely many shells, there would be a bright night sky.
The poet Edgar Allan Poe suggested that the finite size of the observable universe resolves the apparent paradox.[8] More specifically, because the universe is finitely old and the speed of light is finite, only finitely many stars can be observed from Earth (although the whole universe can be infinite in space).[9] The density of stars within this finite volume is sufficiently low that any line of sight from Earth is unlikely to reach a star.
This problem is addressed by the fact that the Big Bang theory also involves the expansion of space, which can cause the energy of emitted light to be reduced via redshift. More specifically, the extremely energetic radiation from the Big Bang has been redshifted to microwave wavelengths (1100 times the length of its original wavelength) as a result of the cosmic expansion, and thus forms the cosmic microwave background radiation. This explains the relatively low light densities and energy levels present in most of our sky today despite the assumed bright nature of the Big Bang. The redshift also affects light from distant stars and quasars, but this diminution is minor, since the most distant galaxies and quasars have redshifts of only around 5 to 8.6.
The redshift hypothesised in the Big Bang model would by itself explain the darkness of the night sky even if the universe were infinitely old. In the Steady state theory the universe is infinitely old and uniform in time as well as space. There is no Big Bang in this model, but there are stars and quasars at arbitrarily great distances. The expansion of the universe causes the light from these distant stars and quasars to redshift, so that the total light flux from the sky remains finite. Thus the observed radiation density (the sky brightness of extragalactic background light) can be independent of finiteness of the universe. Mathematically, the total electromagnetic energy density (radiation energy density) in thermodynamic equilibrium from Planck's law is
Stars have a finite age and a finite power, thereby implying that each star has a finite impact on a sky's light field density. Edgar Allan Poe suggested that this idea could provide a resolution to Olbers's paradox; a related theory was also proposed by Jean-Philippe de Cheseaux. However, stars are continually being born as well as dying. As long as the density of stars throughout the universe remains constant, regardless of whether the universe itself has a finite or infinite age, there would be infinitely many other stars in the same angular direction, with an infinite total impact. So the finite age of the stars does not explain the paradox.[13]
We have been using SketchUp Pro + Enscape for, I believe, just over a year now, and we have become very accustomed to manipulating the plugin and it's many versatile options. We are a design firm specializing in high-end residential outdoor environments, so it's typical for us to show several day time scenes, followed by afternoon scenes, and then several night time scenes with lots of lighting elements. I'm well versed in the atmosphere settings such sun brightness, ambient brightness, night time brightness, synthetic light brightness, etc. We have often changed these settings from model to model, and even from scene to scene in order to get the lighting just right for each shot. But as of today, something seems very wrong and I cannot figure out what happened or what changed.
Traditionally, I have adhered closely to most of the standard brightness settings, and when I include lighting features in the model, I typically don't have to set their individual illumination values above 30 - 50 points. When altering the time using the short cut keys (U + I), there is always a smooth transition between day, afternoon, and night. The natural light dims, and the synthetic lights come on and slowly get stronger until the sun is completely gone. And once night time arrives, you can always see the stars, the clouds, and especially the moon.
Right now, when I get to a night time hour, the sky is completely dark. All surfaces are dark. It's as if there is zero ambient brightness or sky brightness during night time, even if I slide all of the brightness settings to their maximum value. I cannot see stars, or moon or clouds. And in order to see any of the synthetic lights, I have to change their individual illumination properties up into the 10,000 - 100,000 value region on the slider scale.
***EDITED: I have added some screen grabs to show what I'm referring to. The daytime light settings seem to be behaving like normal. It's just the night time lighting that is not performing as it usually does. Also, in case anyone is curious, The purple lights in the foreground are individually set at about 1,000cd. The purple lights off in the distance are raised up higher and are set at about 500cd. And the fire material off to the left is a self-illuminated material set at 100,000cd. None of this is displaying correctly.
Stargazers have the chance to see stars, planets and other celestial bodies in incomprehensible numbers and unforgettable brilliance. Jupiter and Saturn are both clearly visible in the night sky. You may be able to witness the International Space Station making its orbit around Earth.
The City of Flagstaff and the northern Arizona region have achieved worldwide recognition for innovative leadership in the protection of dark skies. Beginning with Ordinance 400 in 1958 that addressed searchlights, over a half-century of policy decisions and implementations have fostered an astronomy industry that now includes Lowell Observatory, the U.S. Naval Observatory, the Navy Prototype Optical Interferometer, the National Undergraduate Research Observatory, the U.S. Geological Survey Astrogeology Center, and the new Discovery Channel Telescope. Public support for protection of the night sky for both general enjoyment and professional deep space research has become an established element of community and regional identity.
To remain one of the premiere astronomic sites in the world, to properly recognize preservation of naturally dark night skies as a persistent expression of community values, and to better-utilize a critical economic and tourism attractant, the region must implement evolving standards that proactively address problems associated with increased artificial light, air pollution, illuminated signage, and development - both adjacent to major scientific instruments and within the region. ff782bc1db
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