This group is popular in the northern spring. Famous as the Leo Triplet, the three magnificent galaxies gather in one field of view. Crowd pleasers when imaged with even modest telescopes, they can be introduced individually as NGC 3628 (left), M66 (bottom right), and M65 (top). All three are large spiral galaxies but they tend to look dissimilar because their galactic disks are tilted at different angles to our line of sight. NGC 3628, also known as the Hamburger Galaxy, is temptingly seen edge-on, with obscuring dust lanes cutting across its puffy galactic plane. The disks of M66 and M65 are both inclined enough to show off their spiral structure. Gravitational interactions between galaxies in the group have left telltale signs, including the tidal tails and warped, inflated disk of NGC 3628 and the drawn out spiral arms of M66. This gorgeous view of the region spans almost two degrees (four full moons) on the sky. The field covers about a million light-years at the trio’s estimated distance of 30 million light-years. Of course the spiky foreground stars lie within our own Milky Way.
Strange shapes and textures can be found in neighborhood of the Cone Nebula. The unusual shapes originate from fine interstellar dust reacting in complex ways with the energetic light and hot gas being expelled by the young stars. The brightest star on the right of the featured picture is S Mon, while the region just below it has been nicknamed the Fox Fur Nebula for its color and structure. The blue glow directly surrounding S Mon results from reflection, where neighboring dust reflects light from the bright star. The red glow that encompasses the whole region results not only from dust reflection but also emission from hydrogen gas ionized by starlight. S Mon is part of a young open cluster of stars named NGC 2264, located about 2500 light years away toward the constellation of the Unicorn (Monoceros). Even though it points right at S Mon, details of the origin of the mysterious geometric Cone Nebula, visible on the far left, remain a mystery.
Sit back and watch two black holes merge. Inspired by the first direct detection of gravitational waves in 2015, this simulation video plays in slow motion but would take about one third of a second if run in real time. Set on a cosmic stage the black holes are posed in front of stars, gas, and dust. Their extreme gravity lenses the light from behind them into Einstein rings as they spiral closer and finally merge into one. The otherwise invisible gravitational waves generated as the massive objects rapidly coalesce cause the visible image to ripple and slosh both inside and outside the Einstein rings even after the black holes have merged. Dubbed GW150914, the gravitational waves detected by LIGO are consistent with the merger of 36 and 31 solar mass black holes at a distance of 1.3 billion light-years. The final, single black hole has 63 times the mass of the Sun, with the remaining 3 solar masses converted into energy in gravitational waves. Since then the LIGO and VIRGO gravitational wave observatories have reported several more detections of merging massive systems, while last week the Event Horizon Telescope reported the first horizon-scale image of a black hole.
Rigil Kentaurus is the bright star near the top of this broad southern skyscape. Of course it’s probably better known as Alpha Centauri, nearest star system to the Sun. Below it sprawls a dark nebula complex. The obscuring interstellar dust clouds include Sandqvist catalog clouds 169 and 172 in silhouette against the rich starfields along the southern Milky Way. Rigil Kent is a mere 4.37 light-years away, but the dusty dark nebulae lie at the edge of the starforming Circinus-West molecular cloud about 2,500 light-years distant. The wide-field of view spans over 12 degrees (24 full moons) across southern skies.
What’s that passing in front of the Sun? It looks like a moon, but it can’t be Earth’s Moon, because it isn’t round. It’s the Martian moon Phobos. The featured video was taken from the surface of Mars late last month by the Curiosity rover. Phobos, at 11.5 kilometers across, is 150 times smaller than Luna (our moon) in diameter, but also 50 times closer to its parent planet. In fact, Phobos is so close to Mars that it is expected to break up and crash into Mars within the next 50 million years. In the near term, the low orbit of Phobos results in more rapid solar eclipses than seen from Earth. The featured video has been sped up — the actual transit took about 35 seconds. A similar video was taken of Mars’ smaller and most distant moon Diemos transiting the Sun. The videographer — the robotic rover Curiosity — continues to explore Gale crater, most recently an area with stunning vistas and unusual rocks dubbed Glen Torridon.
Sometimes Saturn disappears. It doesn’t really go away, though, it just disappears from view when our Moon moves in front. Such a Saturnian eclipse was visible along a small swath of Earth — from Brazil to Sri Lanka — near the end of last month. The featured color image is a digital fusion of the clearest images captured by successive videos of the event taken in red, green, and blue, and taken separately for Saturn and the comparative bright Moon. The exposures were taken from South Africa just before occultation — and also just before sunrise. When Saturn re-appeared on the other side of the Moon almost two hours later, the Sun had risen. This year, eclipses of Saturn by the Moon occur almost monthly, but, unfortunately, are visible only to those with the right location and with clear and dark skies.
What’s happening in the sky? The atmosphere over northern Norway appeared quite strange for about 30 minutes last Friday when colorful clouds, dots, and plumes suddenly appeared. The colors were actually created by the NASA-funded Auroral Zone Upwelling Rocket Experiment (AZURE) which dispersed gas tracers to probe winds in Earth’s upper atmosphere. AZURE’s tracers originated from two short-lived sounding rockets launched from the Andøya Space Center in Norway. The harmless gases, trimethylaluminum and a barium/strontium mixture, were released into the ionosphere at altitudes of 115 and 250 km. The vapor trails were observed dispersing from several ground stations. Mapping how AZURE’s vapors dispersed should increase humanity’s understanding of how the solar wind transfers energy to the Earth and powers aurora.