The Universe Reveals Its True Colors in This Stunning Milky Way Photo
Miguel Claro is a professional photographer, author and science communicator based in Lisbon, Portugal, who creates spectacular images of the night sky. As a European Southern Observatory Photo Ambassador and member of The World At Night and the official astrophotographer of the Dark Sky Alqueva Reserve, he specializes in astronomical “Skyscapes” that connect both Earth and night sky. Join Miguel here as he takes us through his photograph “Under the Darkness the Sky is Anything but Black.”
Our eyes are not so good at distinguishing colors in darkness, but a simple DSLR camera can show us that the universe is anything but black.
The scene above, captured from Noudar Park in Portugal’s Dark Sky Alqueva Reserve, shows a colorful star field around the bright arm of the Milky Way, which is visible behind a thin layer of clouds.
Each star’s color is related to its type and temperature, and the colors can range from blue and white, to yellow or even orange. The hottest stars show a blue color, while the coolest can reveal an orange-reddish color.
What may look like “Christmas balls” adorning the old olive tree in the foreground are not only stars, but also the planets Mars and Saturn shining brightly in the center of the tree in yellow-orange and white.
Editor’s note: If you have an amazing night sky photo you’d like to share with us and our news partners for a possible story or image gallery, please contact managing editor Tariq Malik at [email protected].
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Miguel Claro is a professional photographer, author and science communicator based in Lisbon, Portugal, who creates spectacular images of the night sky. As a European Southern Observatory photo ambassador, a member of The World At Night and the official astrophotographer of the Dark Sky Alqueva Reserve, he specializes in astronomical skyscapes that connect Earth and the night sky.
Secrets of the night sky: The colors of stars explained
P-M Heden of The World at Night took this photo from Uppsala, Sweden in September 2012. This deep landscape shot required only a wide aperture and filter to boost contrast. P-M Heden / Clearskies.se / The World at Night
July 22, 2013, 5:12 PM UTC
By Joe Rao
One of the pleasures people can get out of stargazing is noticing and enjoying the various colors that stars display in dark skies.
These hues offer direct visual evidence of how stellar temperatures vary. A good many of the summer luminaries — such as brilliant Vega which this week stands nearly overhead at around midnight — are bluish-white, but we can easily find other, contrasting colors there as well.
Look at reddish Antares, which is due south at around 10 p.m. EDT, and the yellowish-white Altair, which stands high in the south at 1 a.m. EDT. Considerably removed from this summer retinue, brilliant yellow-orange Arcturus holds forth in solitary splendor about halfway up in the west-southwest as darkness falls on these balmy July evenings. [Images: Best Stargazing Events of July 2013 (Sky Maps)]
Double color
Probably the most colorful double star in the night sky can now be found about two-thirds of the way up from the eastern horizon to the point directly overhead at 10 p.m. local daylight time: Albireo in the constellation of Cygnus, the swan, also known as the Northern Cross. Albireo supposedly marks the swan’s beak, or the base of the cross.
A small telescope or even a pair of steadily held binoculars will readily split Albireo into two tiny points of light of beautiful contrasting colors: the brighter one a rich yellowish-orange, the other a deep azure blue, both placed very close together.
Astronomer Garrett P. Serviss referred to Albireo as “… unrivaled for beauty, the larger star being pale topaz and the smaller a deep sapphire.”
You can get an absolutely stunning view of the double star with a telescope magnifying between 18 and 30 power.
Astronomers think Albireo is a physical pair, although they have never found evidence of any orbital motion between these two colorful stars.
The projected separation between the two is just over 400 billion miles. At least 55 solar systems could be lined-up edge-to-edge, across the space that separates the components of this famous double star.
Rods and cones
Star colors are not easy to see chiefly because our eyes’ color sensors — the cones of the retina — are quite insensitive to dim light. At night, the rods take over, but they are effectively color-blind. Only the brightest stars can excite the cones, unless binoculars or a telescope is used to intensify a star’s light.
Color perception is aided further by the close juxtaposition of a contrasting pair of stars as in Albireo.
There is an interesting rule about the colors of telescopic double stars. If the stars of the pair are equally bright, they have the same color. If they are unequal in brightness, they have different colors. If the brighter star is the redder of the two, as in the case of Albireo, it is a giant star; if it is the bluer, then it belongs in the main sequence of stars along with the sun.
Editor’s note: If you have an amazing night sky photo of any celestial sight that you’d like to share for a possible story or image gallery, please contact SPACE.com Managing Editor Tariq Malik at [email protected].
Joe Rao serves as an instructor and guest lecturer at New York’s Hayden Planetarium. He writes about astronomy for Natural History magazine, the Farmer’s Almanac and other publications, and he is also an on-camera meteorologist for News 12 Westchester, N.Y. Follow us @Spacedotcom, Facebook and Google+. Original article on SPACE.com.
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The Color Balance of the Night Sky
Night sky over the Altiplano. Composite image of two exposures: One with and one without the star tracker. Nikon D850, 28 f/1.4 G at f/2, 30 seconds.
On a recent trip to the Altiplano of Bolivia and Chile I took along a star tracker. This was appropriate for a place, world famous for deep-sky astronomy, star gazing, and night-sky photography. The air is dry (at around 10% relative humidity), there is very little light pollution and the cold temperatures at altitudes above 4000 m prevent air stratification. In addition, the night-sky on the Southern hemisphere contains interesting objects, such as the Magellanic Clouds, and the Omega Centauri Cluster.
At this time of the year (May) the Milky Way is up at a low position in the southern sky so that it can be captured with a moderate wide-angle lens, allowing to include some elements of the landscape. These conditions present themselves at about three hours after sunset (around 21:30 local time), which doesn’t pose a threat on dinner or bedtime. And finally, Jupiter and Saturn are at nice positions with respect to the Sagittarius cloud (the Galactic Center) of the Milky Way.
Aligning the sky tracker with the Southern celestial pole causes some problem though, because Sigma Octantis is a very faint star (magnitude 5.4), barely visible to the naked eye and impossible to track through the polar scope. Therefore, I set up the tracker with a compass and an inclinometer at 23 deg., which yielded satisfactory results within exposure times of 60 sec at 20-28 mm focal length.
A common rule of thumb to figure out your maximum shutter speed for sharp stars when no tracker is used, is to divide 500 by the focal length; the 500 Rule. This number depends somewhat on the sensor size, but we have no more than 20 sec for the 28 mm lens.
Having captured the scene, the question arises how to post-process the image. The digital camera sensors are more sensitive to colors at low luminance values than the human eye. Many photographers set the color balance to fluorescent and render the sky dark blue to black, which reflects the perceptional human vision, which is also reflected by the color palette of the aboriginal art of the Milky Way.
Night-sky photograph with incandescent (3000 K) white-balance setting. Perhaps art, but definitely not science.
But what do we want to show? Notice that I am not talking about the false-color images that render the narrow lines in the infrared spectrum. Do we want to show the perception or a more objectively correct rendering according to the emitted light? It is indeed possible to verify the hues based on the colors of bright stars that we can detect with the naked eye after a sufficiently long adaptation of the night vision.
In a moonless sky (where there is no Rayleigh scattering), the clouds of the Milky Way are reddish brown and the stars have colors ranging from magenta, red and orange to bluish white. The true colors of stars are known from their spectra and the spectral response of the human eye. Let us take, for example, Antares, a relatively bright star of spectral type M1.5. It doesn’t appear blue to our eyes. The spectral class M (containing lines from oxide molecules in the visible part of the spectrum) corresponds to some light-orange/red according to the daylight illuminance D65 and corresponds to a color temperature* of 2400 – 3700 kelvin (K). The Sun (and consequently the planets such as Jupiter**) is at around 5800 K.
A more objective rendering of the night sky. White-balance 5300 K, tint -2 (almost “sunny”) so that Antares (circled, 2400 – 3700 K) is rendered in faint yellow/red.
Color temperatures over 6000 K are bluish (cool) colors, while color temperatures below 3000 K are yellowish (warm in an analogy to radiated heat flux of traditional incandescent lighting). The fact that warm lighting in this sense has a lower (cooler) color temperature, and that a low temperature of the white-balance setting renders the output bluish, may lead to confusion. Since most light sources do not resemble blackbody radiators, white balance uses a second variable in addition to color temperature: the green-magenta shift (hue). The hue in the night-sky images can be checked with the clearly visible stars of the Sagittarius cloud of the Milky Way that are of some faint magenta color.
There are a few other light sources in the night sky that we must consider.
- Airglow due to oxygen and hydroxy emission-line light in the upper Earth atmosphere. This causes the night sky to never be completely dark; it’s the same colors as the polar aurora. At high levels red, below 100 km green. Photographs taken from the ISS show this clearly.
- Light pollution reflecting on aerosols in the atmosphere (generally orange, around 3000 K).
- Zodiacal light, that is, sunlight scattered by interplanetary dust. Blue-gray.
- Light from so-called emission nebulae, i.e., magenta, and intense pink seen in the Large Magellanic Cloud.
Putting it all-together, a “sunny” light-balance is a good starting point for the RAW processing of night-sky images. It requires some tweaking of the hue to bring out the airglow and render the light pollution faithfully. Everything else is perhaps art, but not science.
I feel more at home at the later discipline. SR
Gear used: Nikon D850, Nikon 28 f/1.4 G, Nikon 14-24 f/2.8 G, Sky-Watcher Star Adventurer
*According to Wien’s displacement law, which states that the wavelength of the peak of the blackbody radiation spectrum yields a measure of the color temperature (724 nm, a medium red, corresponding to 4000 K).
**This is only true on average, because Jupiter’s gaseous atmosphere with its clouds of ammonia are quite varied in color.
