Sunlight ripples through a dark sky on this Swedish summer midnight as noctilucent or night shining clouds seem to imitate the river below. In fact, the seasonal clouds often appear at high latitudes in corresponding summer months. Also known as polar mesospheric clouds, they form as water vapor is driven into the cold upper atmosphere. Fine dust supplied by disintegrating meteors or volcanic ash provides sites where water vapor can condense, turning to ice at the cold temperatures in the mesosphere. Poised at the edge of space some 80 kilometers above, these icy clouds really do reflect sunlight toward the ground. They are visible here even though the Sun itself was below the horizon, as seen on July 16 from Sweden’s Färnebofjärdens National Park.
The Sun’s annual waltz through planet Earth’s sky forms a graceful curve known as an analemma. The analemma’s figure 8 shape is tipped vertically at far right in this well-composed fisheye view from Budapest, Hungary. Captured at a chosen spot on the western bank of the Danube river, the Sun’s position was recorded at 11:44 Central European Time on individual exposures over days spanning 2015 July 23 to 2016 July 4. Of course, on the northern summer solstice the Sun is at the top of the curve, but at the midpoints for the autumn and spring equinoxes. With snow on the ground, the photographer’s shadow and equipment bag also appear in the base picture used for the composite panorama, taken on 2016 January 7. On that date, just after the winter solstice, the Sun was leaving the bottom of the beautiful curve over the blue Danube.
A now famous picture from the Hubble Space Telescope featured Pillars of Creation, star forming columns of cold gas and dust light-years long inside M16, the Eagle Nebula. This false-color composite image views the nearby stellar nursery using data from the Herschel Space Observatory’s panoramic exploration of interstellar clouds along the plane of our Milky Way galaxy. Herschel’s far infrared detectors record the emission from the region’s cold dust directly. The famous pillars are included near the center of the scene. While the central group of hot young stars is not apparent at these infrared wavelengths, the stars’ radiation and winds carve the shapes within the interstellar clouds. Scattered white spots are denser knots of gas and dust, clumps of material collapsing to form new stars. The Eagle Nebula is some 6,500 light-years distant, an easy target for binoculars or small telescopes in a nebula rich part of the sky toward the split constellation Serpens Cauda (the tail of the snake).
M13 is one of the most prominent and best known globular clusters. Visible with binoculars in the constellation of Hercules, M13 is frequently one of the first objects found by curious sky gazers seeking celestials wonders beyond normal human vision. M13 is a colossal home to over 100,000 stars, spans over 150 light years across, lies over 20,000 light years distant, and is over 12 billion years old. At the 1974 dedication of Arecibo Observatory, a radio message about Earth was sent in the direction of M13. The featured image in HDR, taken through a small telescope, spans an angular size just larger than a full Moon, whereas the inset image, taken by Hubble Space Telescope, zooms in on the central 0.04 degrees.
Can you find the comet? True, a careful eye can find thousands of stars, tens of constellations, four planets, three galaxies, and the central band of our Milky Way Galaxy — all visible in the sky of this spectacular 180-degree panorama. Also, if you know what to look for, you can identify pervasive green airglow, an earthly cloud, the south celestial pole, and even a distant cluster of stars. But these are all easier to find than Comet 252P/LINEAR. The featured image, taken in el Leoncito National Park, Argentina in early April, also features the dome of the Jorge Sahade telescope on the hill on the far right. Have you found the comet yet? If so, good for you (it was the green spot on the left), but really the harder thing to find is Small Cloud of Magellan.
Did the two most famous satellite galaxies of our Milky Way Galaxy once collide? No one knows for sure, but a detailed inspection of deep images like that featured here give an indication that they have. Pictured, the Large Magellanic Cloud (LMC) is on the top left and the Small Magellanic Cloud (SMC) is on the bottom right. The surrounding field is monochrome color-inverted to highlight faint filaments, shown in gray. Perhaps surprisingly, the featured research-grade image was compiled with small telescopes to cover the large angular field — nearly 40 degrees across. Much of the faint nebulosity is Galactic Cirrus clouds of thin dust in our own Galaxy, but a faint stream of stars does appear to be extending from the SMC toward the LMC. Also, stars surrounding the LMC appear asymmetrically distributed, indicating in simulations that they could well have been pulled off gravitationally in one or more collisions. Both the LMC and the SMC are visible to the unaided eye in southern skies. Future telescopic observations and computer simulations are sure to continue in a continuing effort to better understand the history of our Milky Way and its surroundings.
Are stars better appreciated for their art after they die? Actually, stars usually create their most artistic displays as they die. In the case of low-mass stars like our Sun and M2-9 pictured above, the stars transform themselves from normal stars to white dwarfs by casting off their outer gaseous envelopes. The expended gas frequently forms an impressive display called a planetary nebula that fades gradually over thousands of years. M2-9, a butterfly planetary nebula 2100 light-years away shown in representative colors, has wings that tell a strange but incomplete tale. In the center, two stars orbit inside a gaseous disk 10 times the orbit of Pluto. The expelled envelope of the dying star breaks out from the disk creating the bipolar appearance. Much remains unknown about the physical processes that cause planetary nebulae.