Sh2-308: A Dolphin Shaped Star Bubble
Which star created this bubble? It wasn't the bright star on the bubble's right. And it also wasn't a giant space dolphin. It was the star in the blue nebula's center, a famously energetic Wolf-Rayet star. Wolf-Rayet stars in general have over 20 times the mass of our Sun and expel fast particle winds that can create iconic looking nebulas. In this case, the resulting star bubble spans over 60 light years, is about 70,000 years old, and happens to look like the head of a dolphin. Named Sh2-308 and dubbed the Dolphin-Head Nebula, the gas ball lies about 5,000 light years away and covers as much sky as the full moon -- although it is much dimmer. The nearby red-tinged clouds on the left of the featured image may owe their glow and shape to energetic light emitted from the same Wolf-Rayet star.
A Multiple Green Flash Sunset
Yes, but can your green flash do this? A green flash at sunset is a rare event that many Sun watchers pride themselves on having seen. Once thought to be a myth, a green flash is now understood to occur when the Earth's atmosphere acts like both a prism and a lens. Different atmospheric layers create altitude-variable refraction that takes light from the top of the Sun and disperses its colors, creates two images, and magnifies it in just the right way to make a thin sliver appear green just before it disappears. Pictured, though, is an even more unusual sunset. From the high-altitude Cerro Tololo Inter-American Observatory in Chile one day last April, the Sun was captured setting beyond an atmosphere with multiple distinct thermal layers, creating several mock images of the Sun. This time and from this location, many of those layers produced a green flash simultaneously. Just seconds after this multiple-green-flash event was caught by two well-surprised astrophotographers, the Sun set below the clouds.
Aurora Over Arctic Henge
Reports of powerful solar flares started a seven-hour quest north to capture modern monuments against an aurora-filled sky. The peaks of iconic Arctic Henge in Raufarhöfn in northern Iceland were already aligned with the stars: some are lined up toward the exact north from one side and toward exact south from the other. The featured image, taken after sunset late last month, looks directly south, but since the composite image covers so much of the sky, the north star Polaris is actually visible at the very top of the frame. Also visible are familiar constellations including the Great Bear (Ursa Major) on the left, and the Hunter (Orion) on the lower right. The quest was successful. The sky lit up dramatically with bright and memorable auroras that shimmered with amazing colors including red, pink, yellow, and green -- sometimes several at once.
Venus and the Da Vinci Glow
On March 23 early evening skygazers could watch Venus and a young crescent moon, both near the western horizon. On that date Earth's brilliant evening star, faint lunar night side and slender sunlit crescent were captured in this telephoto skyscape posing alongside a church tower from Danta di Cadore, Dolomiti, Italy. Of course the subtle lunar illumination is earthshine, earthlight reflected from the Moon's night side. A description of earthshine, in terms of sunlight reflected by Earth's oceans illuminating the Moon's dark surface, was written over 500 years ago by Leonardo da Vinci. On March 24, from some locations the Moon could be seen to occult or pass in front of Venus. Around the planet tonight, a waxing lunar crescent will appear near the Pleiades star cluster.
Outbound Comet ZTF
Former darling of the northern sky Comet C/2022E3 (ZTF) has faded. During its closest approach to our fair planet in early February Comet ZTF was a mere 2.3 light-minutes distant. Then known as the green comet, this visitor from the remote Oort Cloud is now nearly 13.3 light-minutes away. In this deep image, composed of exposures captured on March 21, the comet still sports a broad, whitish dust tail and greenish tinted coma though. Not far on the sky from Orion's bright star Rigel, Comet ZTF shares the field of view with faint, dusty nebulae and distant background galaxies. The telephoto frame is crowded with Milky Way stars toward the constellation Eridanus. The influence of Jupiter's gravity on the comet's orbit as ZTF headed for the inner solar system, may have set the comet on an outbound journey, never to return.
Spiral Galaxy NGC 2841
A mere 46 million light-years distant, spiral galaxy NGC 2841 can be found in planet Earth's night sky toward the northern constellation of Ursa Major. This sharp image centered on the gorgeous island universe also captures spiky foreground Milky Way stars and more distant background galaxies within the same telescopic field of view. It shows off the bright nucleus of NGC 2841, along with its inclined galactic disk, and faint outer regions. Dust lanes, small star-forming regions, and young star clusters are embedded in the galaxy's patchy, tightly wound spiral arms. In contrast, many other spirals exhibit broader, sweeping arms with large star-forming regions. NGC 2841 has a diameter of over 150,000 light-years, making it even larger than our own Milky Way. X-ray images suggest that extreme outflows from giant stars and stellar explosions create plumes of hot gas extending into a halo around NGC 2841.
M31: The Andromeda Galaxy
How far can you see? The most distant object easily visible to the unaided eye is M31, the great Andromeda Galaxy, over two million light-years away. Without a telescope, even this immense spiral galaxy appears as an unremarkable, faint, nebulous cloud in the constellation Andromeda. But a bright white nucleus, dark winding dust lanes, luminous blue spiral arms, and bright red emission nebulas are recorded in this stunning fifteen-hour telescopic digital mosaic of our closest major galactic neighbor. But how do we know this spiral nebula is really so far away? This question was central to the famous Shapley-Curtis debate of 1920. M31's great distance was determined in the 1920s by observations that resolved individual stars that changed their brightness in a way that gave up their true distance. The result proved that Andromeda is just like our Milky Way Galaxy -- a conclusion making the rest of the universe much more vast than had ever been previously imagined.
Dark Nebulae and Star Formation in Taurus
Can dust be beautiful? Yes, and it can also be useful. The Taurus molecular cloud has several bright stars, but it is the dark dust that really draws attention. The pervasive dust has waves and ripples and makes picturesque dust bunnies, but perhaps more importantly, it marks regions where interstellar gas is dense enough to gravitationally contract to form stars. In the image center is a light cloud lit by neighboring stars that is home not only to a famous nebula, but to a very young and massive famous star. Both the star, T Tauri, and the nebula, Hind's Variable Nebula, are seen to vary dramatically in brightness -- but not necessarily at the same time, adding to the mystery of this intriguing region. T Tauri and similar stars are now generally recognized to be Sun-like stars that are less than a few million years old and so still in the early stages of formation. The featured image spans about four degrees not far from the Pleiades star cluster, while the featured dust field lies about 400 light-years away.
Equinox at the Pyramid of the Feathered Serpent
To see the feathered serpent descend the Mayan pyramid requires exquisite timing. You must visit El Castillo -- in Mexico's Yucatán Peninsula -- near an equinox. Then, during the late afternoon if the sky is clear, the pyramid's own shadows create triangles that merge into the famous illusion of a slithering viper. Also known as the Temple of Kukulkan, the impressive step-pyramid stands 30 meters tall and 55 meters wide at the base. Built up as a series of square terraces by the pre-Columbian civilization between the 9th and 12th century, the structure can be used as a calendar and is noted for astronomical alignments. The featured composite image was captured in 2019 with Jupiter and Saturn straddling the diagonal central band of our Milky Way galaxy. Tomorrow marks another equinox -- not only at Temple of Kukulcán, but all over planet Earth.
Wolf-Rayet 124
Driven by powerful stellar winds, expanding shrouds of gas and dust frame hot, luminous star Wolf-Rayet 124 in this sharp infrared view. The eye-catching 6-spike star pattern is characteristic of stellar images made with the 18 hexagonal mirrors of the James Webb Space Telescope. About 15,000 light-years distant toward the pointed northern constellation Sagitta, WR 124 has over 30 times the mass of the Sun. Produced in a brief and rarely spotted phase of massive star evolution in the Milky Way, this star's turbulent nebula is nearly 6 light-years across. It heralds WR 124's impending stellar death in a supernova explosion. Formed in the expanding nebula, dusty interstellar debris that survives the supernova will influence the formation of future generations of stars.
The Medusa Nebula
Braided and serpentine filaments of glowing gas suggest this nebula's popular name, The Medusa Nebula. Also known as Abell 21, this Medusa is an old planetary nebula some 1,500 light-years away in the constellation Gemini. Like its mythological namesake, the nebula is associated with a dramatic transformation. The planetary nebula phase represents a final stage in the evolution of low mass stars like the sun as they transform themselves from red giants to hot white dwarf stars and in the process shrug off their outer layers. Ultraviolet radiation from the hot star powers the nebular glow. The Medusa's transforming star is the faint one near the center of the overall bright crescent shape. In this deep telescopic view, fainter filaments clearly extend below and right of the bright crescent region. The Medusa Nebula is estimated to be over 4 light-years across.
Millions of Stars in Omega Centauri
Globular star cluster Omega Centauri, also known as NGC 5139, is 15,000 light-years away. The cluster is packed with about 10 million stars much older than the Sun within a volume about 150 light-years in diameter. It's the largest and brightest of 200 or so known globular clusters that roam the halo of our Milky Way galaxy. Though most star clusters consist of stars with the same age and composition, the enigmatic Omega Cen exhibits the presence of different stellar populations with a spread of ages and chemical abundances. In fact, Omega Cen may be the remnant core of a small galaxy merging with the Milky Way. Omega Centauri's red giant stars (with a yellowish hue) are easy to pick out in this sharp, color telescopic view.
Jupiter and Venus Converge over Germany
This was a sky to show the kids. Early this month the two brightest planets in the night sky, Jupiter and Venus, appeared to converge. At their closest, the two planets were separated by only about the angular width of the full moon. The spectacle occurred just after sunset and was seen and photographed all across planet Earth. The displayed image was taken near to the time of closest approach from Wiltingen, Germany, and features the astrophotographer, spouse, and their two children. Of course, Venus remains much closer to both the Sun and the Earth than Jupiter -- the apparent closeness between the planets in the sky of Earth was only angular. Jupiter and Venus have passed and now appear increasingly far apart. Similar planetary convergence opportunities will eventually arise. In a few months, for example, Mars and Venus will appear to congregate just as the Sun sets. Jupiter & Venus Conjunction Gallery: Notable Submissions to APOD
W5: The Soul Nebula
Stars are forming in the Soul of the Queen of Aethopia. More specifically, a large star forming region called the Soul Nebula can be found in the direction of the constellation Cassiopeia, whom Greek mythology credits as the vain wife of a King who long ago ruled lands surrounding the upper Nile river. Also known as Westerhout 5 (W5), the Soul Nebula houses several open clusters of stars, ridges and pillars darkened by cosmic dust, and huge evacuated bubbles formed by the winds of young massive stars. Located about 6,500 light years away, the Soul Nebula spans about 100 light years and is usually imaged next to its celestial neighbor the Heart Nebula (IC 1805). The featured image is a composite of exposures made in different colors: red as emitted by hydrogen gas, yellow as emitted by sulfur, and blue as emitted by oxygen.
Rainbow Tree
What lies at the end of a rainbow? Something different for everyone. For the photographer taking this picture, for example, one end of the rainbow ended at a tree. Others nearby, though, would likely see the rainbow end somewhere else. The reason is because a rainbow's position depends on the observer. The center of a rainbow always appears in the direction opposite the Sun, but that direction lines up differently on the horizon from different locations. This rainbow's arc indicates that its center is about 40 degrees to the left and slightly below the horizon, while the Sun is well behind the camera and just above the horizon. Reflections and refractions of sunlight from raindrops in a distant storm in the direction of the rainbow are what causes the colorful bands of light. This single exposure image was captured in early January near Knight's Ferry, California, USA.
