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The Secrets Behind All Those Gorgeous Photos of Space

In an era when NASA’s vast photographic archive is a click away and even the Curiosity Rover is on Instagram, it’s easy to lose sight of the fact that photographing the cosmos is an amazing achievement and a complex process.

Travis Rector reminds us of this in his excellent book, Coloring the Universe. Rector is an astronomer and an expert on the topic; he’s used everything from the Hubble Space Telescope to the Very Large Array to make more than 250 photos during the past two decades. He and his co-authors, Kim Arcand and Megan Watzke of the Chandra X-Ray Observatory, bring a photographer’s sensibility to the book, explaining just how NASA made some of the stunning photos we too often take for granted.

“People have a lot of questions about [space] images, such as ‘Are the colors real’ or ‘Is this what it really looks like?'” says Rector. “We wanted to write a book to answer these questions, so that people can better understand and appreciate what they’re seeing when they look at pictures of space.”

Astronomers have focused their cameras on the cosmos since the mid-19th century. They started with the moon, of course, and then looked ever further into space to the sun and other stars. Refracting telescopes and highly sophisticated reflecting telescopes designed specifically became more widespread in the early 20th century and grew ever larger through the mid-1900s.

Electronic imaging came to the fore in the 1970s, and by the end of the century NASA and others were using multi-mirror telescopes and space-based telescopes like the Hubble—which brought astrophotography into the Internet era when it launched in 1990. Four years later, Hubble captured fragments of the Shoemaker-Levy 9 comet pummeling Jupiter and people worldwide overloaded NASA’s servers trying to download photographs. “[It] demonstrated how effectively the internet could share new images and science results—something we take for granted today,” Rector says.

Astrophotography is far more difficult than simply pointing a lens at the sky. The best photos come from powerful telescopes like the Hubble or Gemini North hooked up to highly specialized cameras. Using the Hubble as an example, scientists aim the telescope toward the expanse of sky they want to explore, with a pointing accuracy of 0.007 arc seconds—which NASA says is like being able to shine a laser on a dime 200 miles away. Incoming light is reflected off a primary mirror almost 8 feet in diameter onto the secondary mirror, which reflects it into the telescopes optical equipment, which includes half a dozen cameras.

NASA likes to say the Hubble can see objects with an angular size as small as 0.05 arc seconds, which is like being in Washington, DC, and spotting two fireflies in Tokyo. The telescope captures images in monochromatic grayscale. Filters sensitive to specific wavelengths of light recreate color; the final images that amaze us are composites.

The Hubble—which will be succeeded by the James Webb Space Telescope when it launches in 2018—is much more than a telescope; it is in may way a time machine, peering into the distant past at the very origin of the cosmos. The telescope has seen locations 13.8 billion light years away, and has collected more than 100 terabytes of data, according to NASA. “When the data arrive from the telescope it’s like Christmas,” Rector says. “I pretty much can’t get anything else done until I’ve had a chance to take a peek.”

Rector created many of the striking photographs in Coloring the Universe. To make his image of the IC 1396 portion of the Elephant Trunk nebula, Rector used the Mayall 4-meter telescope at the Kitt Peak National Observatory in 2009. He covered the detectors of a Mosaic I camera with two narrowband filters allow only hydrogen alpha and sulphur light to pass and a broadband infrared filter.

The amazing image reveals a dark, gaseous form stirring within a red sky splattered with stars. “Cameras that can see kinds of light other than what our eyes see have vastly improved our ability to study the universe,” Rector says. “Having data in a digital format has also enabled us to analyze astronomical objects in ways never imagined before. As a result we really are in a golden age of astronomy.”

Rectors fell in love with astronomy as a child when he watched the Perseid meteor shower while camping in Colorado. Photography is his way of getting others excited about it too. “I love making these images because it is a way to share with people what our telescopes can see,” Rector says. “It’s a visceral way to connect with the scientific discoveries these amazing machines enable astronomers to make.”

Image 1: hydrogen alpha filter. Image 2: sulphur (assigned blue). Image 3: I-band filter shows near-infrared light (assigned orange). Image 4: Final composite. T. A. Rector (University of Alaska Anchorage) and H. Schweiker (WIYN and NOAO/AURA/NSF)

Link to the book
https://www.coloringtheuniverse.com/book
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IRAS 10082-5647
Reflection Nebula

The pearly wisps surrounding the central star IRAS 10082-5647 in this Hubble image certainly draw the eye towards the heavens. The divine-looking cloud is a reflection nebula, made up of gas and dust glowing softly by the reflected light of nearby stars, in this case a young Herbig Ae/Be star.

The star, like others of this type, is still a relative youngster, only a few million years old. It has not yet reached the so-called main sequence phase, where it will spend around 80% of its life creating energy by burning hydrogen in its core.

Until then the star heats itself by gravitational collapse, as the material in the star falls in on itself, becoming ever denser and creating immense pressure which in turn gives off copious amounts of heat.

Stars only spend around 1% of their lives in this pre-main sequence phase. Eventually, gravitational collapse will heat the star’s core enough for hydrogen fusion to begin, propelling the star into the main sequence phase, and adulthood.

The Advanced Camera for Surveys aboard the Hubble Space Telescope captured the whorls and arcs of this nebula, lit up with the light from IRAS 10082-5647. Visible (555 nm) and near-infrared (814 nm) filters were used, coloured blue and red respectively. The field of view is around 1.3 by 1.3 arcminutes.

Credit:ESA/Hubble & NASA
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NGC 4183
Spiral Galaxy

Hubble portrays a dusty spiral galaxy

The NASA/ESA Hubble Space Telescope has provided us with another outstanding image of a nearby galaxy.

The galaxy NGC 4183, seen here with a beautiful backdrop of distant galaxies and nearby stars. Located about 55 million light-years from the Sun and spanning about eighty thousand light-years, NGC 4183 is a little smaller than the Milky Way.

This galaxy, which belongs to the Ursa Major Group, lies in the northern constellation of Canes Venatici (The Hunting Dogs).

NGC 4183 is a spiral galaxy with a faint core and an open spiral structure. Unfortunately, this galaxy is viewed edge-on from the Earth, and we cannot fully appreciate its spiral arms. But we can admire its galactic disc.

The discs of galaxies are mainly composed of gas, dust and stars. There is evidence of dust over the galactic plane, visible as dark intricate filaments that block the visible light from the core of the galaxy.

In addition, recent studies suggest that this galaxy may have a bar structure. Galactic bars are thought to act as a mechanism that channels gas from the spiral arms to the centre, enhancing star formation, which is typically more pronounced in the spiral arms than in the bulge of the galaxy.

British astronomer William Herschel first observed NGC 4183 on 14 January 1778.

This picture was created from visible and infrared images taken with the Wide Field Channel of the Advanced Camera for Surveys. The field of view is approximately 3.4 arcminutes wide.

This image uses data identified by Luca Limatola in the Hubble's Hidden Treasures image processing competition.

Credit:ESA/Hubble & NASA. Acknowledgement: Luca Limatola
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NGC 3923.
Elliptical Galaxy

Description
The glowing object in this image is an elliptical galaxy called NGC 3923. It is located over 90 million light-years away in the constellation of Hydra.

NGC 3923 is an example of a shell galaxy where the stars in its halo are arranged in layers.

Finding concentric shells of stars enclosing a galaxy is quite common and is observed in many elliptical galaxies. In fact, every tenth elliptical galaxy exhibits this onion-like structure, which has never been observed in spiral galaxies. '

The shell-like structures are thought to develop as a consequence of galactic cannibalism, when a larger galaxy ingests a smaller companion.

As the two centres approach, they initially oscillate about a common centre, and this oscillation ripples outwards forming the shells of stars just as ripples on a pond spread when the surface is disturbed.

NGC 3923 has over twenty shells, with only a few of the outer ones visible in this image and its shells are much more subtle than those of other shell galaxies. The shells of this galaxy are also interestingly symmetrical, while other shell galaxies are more skewed.

Copyright ESA/Hubble & NASA
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ESO 77-14
Interacting galaxies

Description
This Hubble image of ESO 77-14 is a stunning snapshot of a celestial dance performed by a pair of similar sized galaxies. Two clear signatures of the gravitational tug of war between the galaxies are the bridge of material that connects them and the disruption of their main bodies.

The galaxy on the right has a long, bluish arm while its companion has a shorter, redder arm.

This interacting pair is in the constellation of Indus, the Indian, some 550 million light-years away from Earth. The dust lanes between the two galaxy centres show the extent of the distortion to the originally flat discs that have been pulled into three-dimensional shapes.

Copyright NASA/ ESA/ STScI/AURA (The Hubble Heritage Team) - ESA/Hubble Collaboration/ University of Virginia, Charlottesville, NRAO, Stony Brook University (A. Evans)
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NGC 4298, NGC 4302
A close galactic pair

This image displays the galaxies NGC 4302 – seen edge-on – and NGC 4298, both located 55 million light-years away. They were observed by Hubble to celebrate its 27th year in orbit.

The galaxy NGC 4298 is seen almost face-on, allowing us to see its spiral arms and the blue patches of ongoing star formation and young stars. In the edge-on disc of NGC 4302 huge swathes of dust are responsible for the mottled brown patterns, but a burst of blue to the left side of the galaxy indicates a region of extremely vigorous star formation.

The image is a mosaic of four separate captures from Hubble, taken between 2 and 22 January 2017, that have been stitched together to give this amazing field of view.

Two different types of light emitted by the galaxies – visible and near-infrared – have been combined to give a rich and colourful image. This light was captured by Hubble's Wide Field Camera 3, one of the telescope's most advanced imaging instruments.

Copyright: NASA, ESA, and M. Mutchler (STScI)
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Orion Nebula
Asteroid Zips By Orion Nebula

This image shows the potentially hazardous near-Earth object 1998 KN3 as it zips past a cloud of dense gas and dust near the Orion nebula.

NEOWISE, the asteroid-hunting portion of the Wide-field Infrared Survey Explorer, or WISE, mission, snapped infrared pictures of the asteroid, seen as the yellow-green dot at upper left. Because asteroids are warmed by the sun to roughly room temperature, they glow brightly at the infrared wavelengths used by WISE.

Astronomers use infrared light from asteroids to measure their sizes, and when combined with visible-light observations, they can also measure the reflectivity of their surfaces.

The WISE infrared data reveal that this asteroid is about .7 mile (1.1 kilometers) in diameter and reflects only about 7 percent of the visible light that falls on its surface, which means it is relatively dark.

In this image, blue denotes shorter infrared wavelengths, and red, longer. Hotter objects emit shorter-wavelength light, so they appear blue. The blue stars, for example, have temperatures of thousands of degrees. The coolest gas and dust appears red.

The asteroid appears yellow in the image because it is about room temperature: cooler than the distant stars, but warmer than the dust.

JPL manages the Wide-field Infrared Survey Explorer for NASA's Science Mission Directorate, Washington. The principal investigator, Edward Wright, is at UCLA.

Credit: NASA/JPL-Caltech
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NGC 1398
Spiral Galaxy

Ribbons and Pearls

Explanation: Why do some spiral galaxies have a ring around the center? Spiral galaxy NGC 1398 not only has a ring of pearly stars, gas and dust around its center, but a bar of stars and gas across its center, and spiral arms that appear like ribbons farther out.

The featured image was taken with ESO's Very Large Telescope at the Paranal Observatory in Chile and resolves this grand spiral in impressive detail. NGC 1398 lies about 65 million light years distant, meaning the light we see today left this galaxy when dinosaurs were disappearing from the Earth.

The photogenic galaxy is visible with a small telescope toward the constellation of the Furnace (Fornax). The ring near the center is likely an expanding density wave of star formation, caused either by a gravitational encounter with another galaxy, or by the galaxy's own gravitational asymmetries.

Credit: European Southern Observatory
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Venus
Venus at Night in Infrared from Akatsuki

Explanation: Why is Venus so different from Earth? To help find out, Japan launched the robotic Akatsuki spacecraft which entered orbit around Venus late in 2015 after an unplanned five-year adventure around the inner

Solar System. Even though Akatsuki was past its original planned lifetime, the spacecraft and instruments were operating so well that much of its original mission was reinstated.

Also known as the Venus Climate Orbiter, Akatsuki's instruments investigated unknowns about Earth's sister planet, including whether volcanoes are still active, whether lightning occurs in the dense atmosphere, and why wind speeds greatly exceed the planet's rotation speed.

In the featured image taken by Akatsuki's IR2 camera, Venus's night side shows a jagged-edged equatorial band of high dark clouds absorbing infrared light from hotter layers deeper in Venus' atmosphere.

The bright orange and black stripe on the upper right is a false digital artifact that covers part of the much brighter day side of Venus.

Analyses of Akatsuki images and data has shown that Venus has equatorial jet similar to Earth's jet stream.

Credit: JAXA, ISAS, DARTS; Processing & Copyright: Damia Bouic
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NGC 474
Elliptical Galaxy

Shells and Star Streams

Explanation: What's happening to galaxy NGC 474? The multiple layers of emission appear strangely complex and unexpected given the relatively featureless appearance of the elliptical galaxy in less deep images.

The cause of the shells is currently unknown, but possibly tidal tails related to debris left over from absorbing numerous small galaxies in the past billion years.

Alternatively the shells may be like ripples in a pond, where the ongoing collision with the spiral galaxy just above NGC 474 is causing density waves to ripple through the galactic giant.

Regardless of the actual cause, the featured image dramatically highlights the increasing consensus that at least some elliptical galaxies have formed in the recent past, and that the outer halos of most large galaxies are not really smooth but have complexities induced by frequent interactions with -- and accretions of -- smaller nearby galaxies.

The halo of our own Milky Way Galaxy is one example of such unexpected complexity. NGC 474 spans about 250,000 light years and lies about 100 million light years distant toward the constellation of the Fish (Pisces).

Credit: CFHT, Coelum, MegaCam, J.-C. Cuillandre (CFHT) & G. A. Anselmi (Coelum)
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