What if you could see, separately, all the colors of the Ring? And of the surrounding stars? There’s technology for that. The featured image shows the Ring Nebula (M57) and nearby stars through such technology: in this case, a prism-like diffraction grating. The Ring Nebula is seen only a few times because it emits light, primarily, in only a few colors. The two brightest emitted colors are hydrogen (red) and oxygen (blue), appearing as nearly overlapping images to the left of the image center. The image just to the right of center is the color-combined icon normally seen. Stars, on the other hand, emit most of their light in colors all across the visible spectrum. These colors, combined, make a nearly continuous streak — which is why stars appear accompanied by multicolored bars. Breaking object light up into colors is scientifically useful because it can reveal the elements that compose that object, how fast that object is moving, and how distant that object is.
Thor not only has his own day (Thursday), but a helmet in the heavens.�� Popularly called Thor’s Helmet, NGC 2359 is a hat-shaped cosmic cloud with wing-like appendages. Heroically sized even for a Norse god, Thor’s Helmet is about 30 light-years across. In fact, the cosmic head-covering is more like an interstellar bubble, blown with a fast wind from the bright, massive star near the bubble’s center. Known as a Wolf-Rayet star, the central star is an extremely hot giant thought to be in a brief, pre-supernova stage of evolution. NGC 2359 is located about 15,000 light-years away toward the constellation of the Great Overdog. This remarkably sharp image is a mixed cocktail of data from broadband and narrowband filters, capturing not only natural looking stars but details of the nebula’s filamentary structures. The star in the center of Thor’s Helmet is expected to explode in a spectacular supernova sometime within the next few thousand years.
The photographer had this shot in mind for some time. He knew that objects overhead are the brightest — since their light is scattered the least by atmospheric air. He also that knew the core of our Milky Way Galaxy was just about straight up near midnight around this time of year in South Australia. Chasing his mental picture, he ventured deep inside the Kuipto Forest where tall radiata pines blocked out much of the sky — but not in this clearing. There, through a window framed by trees, he captured his envisioned combination of local and distant nature. Sixteen exposures of both trees and the Milky Way Galaxy were recorded. Antares is the bright orange star to left of our Galaxy’s central plane, while Alpha Centauri is the bright star just to the right of the image center. The direction toward our Galaxy’s center is below Antares. Although in a few hours the Earth’s rotation moved the Galactic plane up and to the left — soon invisible behind the timber, his mental image was secured forever — and is featured here.
What does the Andromeda galaxy look like in ultraviolet light? Young blue stars circling the galactic center dominate. A mere 2.5 million light-years away, the Andromeda Galaxy, also known as M31, really is just next door as large galaxies go. Spanning about 230,000 light-years, it took 11 different image fields from NASA’s Galaxy Evolution Explorer (GALEX) satellite telescope to produce this gorgeous portrait of the spiral galaxy in ultraviolet light in 2003. While its spiral arms stand out in visible light images, Andromeda’s arms look more like rings in ultraviolet. The rings are sites of intense star formation and have been interpreted as evidence that Andromeda collided with its smaller neighboring elliptical galaxy M32 more than 200 million years ago. The Andromeda galaxy and our own comparable Milky Way galaxy are the most massive members of the Local Group of galaxies and are projected to collide in several billion years — perhaps around the time that our Sun’s atmosphere will expand to engulf the Earth.
Point your telescope at tonight’s first quarter Moon. Along the terminator, the shadow line between night and day, you might find these two large craters staring back at you with an owlish gaze. Alphonsus (left) and Arzachel are ancient impact craters on the north eastern shores of Mare Nubium, the lunar Sea of Clouds. The larger Alphonsus is over 100 kilometers in diameter. A low sun angle highlights the crater’s sharp 1.5 kilometer high central peak in bright sunlight and dark shadow. Scouting for potential Apollo moon landing sites, the Ranger 9 spacecraft returned closeup photographs of Alphonsus before it crashed in the crater just northeast (left) of its central mountain in 1965. Alpetragius, between Alphonsus and Arzachel, is the small crater with the deeply shadowed floor and overly large central peak.
Venus, named for the Roman goddess of love, and Mars, the war god’s namesake, come together by moonlight in this serene skyview, recorded on July 11 from Lualaba province, Democratic Republic of Congo, planet Earth. Taken in the western twilight sky shortly after sunset the exposure also records earthshine illuminating the otherwise dark surface of the young crescent Moon. Of course the Moon has moved on. Venus still shines in the west though as the evening star, third brightest object in Earth’s sky, after the Sun and the Moon itself. Seen here above a brilliant Venus, Mars moved even closer to the brighter planet and by July 13 could be seen only about a Moon’s width away. Mars has since slowly wandered away from much brighter Venus in the twilight, but both are sliding toward bright star Regulus. Alpha star of the constellation Leo, Regulus lies off the top of this frame and anticipates a visit from Venus and then Mars in twilight skies of the coming days.
In silhouette against a crowded star field along the tail of the arachnalogical constellation Scorpius, this dusty cosmic cloud evokes for some the image of an ominous dark tower. In fact, clumps of dust and molecular gas collapsing to form stars may well lurk within the dark nebula, a structure that spans almost 40 light-years across this gorgeous telescopic portrait. Known as a cometary globule, the swept-back cloud, is shaped by intense ultraviolet radiation from the OB association of very hot stars in NGC 6231, off the upper edge of the scene. That energetic ultraviolet light also powers the globule’s bordering reddish glow of hydrogen gas. Hot stars embedded in the dust can be seen as bluish reflection nebulae. This dark tower, NGC 6231, and associated nebulae are about 5,000 light-years away.
What happens when a black hole destroys a neutron star? Analyses indicate that just such an event created gravitational wave event GW200115, detected in 2020 January by LIGO and Virgo observatories. To better understand the unusual event, the featured visualization was created from a computer simulation. The visualization video starts with the black hole (about 6 times the Sun’s mass) and neutron star (about 1.5 times the Sun’s mass) circling each other, together emitting an increasing amount of gravitational radiation. The picturesque pattern of gravitational wave emission is shown in blue. The duo spiral together increasingly fast until the neutron star becomes completely absorbed by the black hole. Since the neutron star did not break apart during the collision, little light escaped — which matches the lack of an observed optical counterpart. The remaining black hole rings briefly, and as that dies down so do the emitted gravitational waves. The 30-second time-lapse video may seem short, but it actually lasts about 1000 times longer than the real merger event.
What will become of our Sun? The first hint of our Sun‘s future was discovered inadvertently in 1764. At that time, Charles Messier was compiling a list of diffuse objects not to be confused with comets. The 27th object on Messier’s list, now known as M27 or the Dumbbell Nebula, is a planetary nebula, one of the brightest planetary nebulae on the sky — and visible toward the constellation of the Fox (Vulpecula) with binoculars. It takes light about 1000 years to reach us from M27, featured here in colors emitted by hydrogen and oxygen. We now know that in about 6 billion years, our Sun will shed its outer gases into a planetary nebula like M27, while its remaining center will become an X-ray hot white dwarf star. Understanding the physics and significance of M27 was well beyond 18th century science, though. Even today, many things remain mysterious about planetary nebulas, including how their intricate shapes are created.
Where’s the Moon? Somewhere in this image, the Earth’s Moon is hiding. The entire Moon is visible, in its completely full phase, in plain sight. Even the photographer’s keen eye couldn’t find it even though he knew exactly where to look — only the long exposure of his camera picked it up — barely. Although by now you might be congratulating yourself on finding it, why was it so difficult to see? For one reason, this photograph was taken during a total lunar eclipse, when the Earth’s shadow made the Moon much dimmer than a normal full Moon. For another, the image, taken in Colorado, USA, was captured just before sunrise. With the Moon on the exact opposite side of the sky from the Sun, this meant that the Sun was just below the horizon, but still slightly illuminating the sky. Last, as the Moon was only about two degrees above the horizon, the large volume of air between the camera and the horizon scattered a lot of light away from the background Moon. Twelve minutes after this image was acquired in 2012, the Sun peeked over the horizon and the Moon set.