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Jaws may have terrified you at the cinema, but the iconic great white would have been dwarfed by Carcharocles megalodon, the largest shark in the history of the planet. The giant creatures lived between 23 million and 2.6 million years ago and scientists are divided over how and why the species perished. Now, details of fossils from the huge shark that lived alongside the dinosaurs have been studied for the first time in an attempt to solve this mystery.

Explanation: Fantastic shapes lurk in clouds of glowing gas in the giant star forming region NGC 6188. The emission nebula is found about 4,000 light years away near the edge of a large molecular cloud unseen at visible wavelengths, in the southern constellation Ara. Massive, young stars of the embedded Ara OB1 association were formed in that region only a few million years ago, sculpting the dark shapes and powering the nebular glow with stellar winds and intense ultraviolet radiation. The recent star formation itself was likely triggered by winds and supernova explosions, from previous generations of massive stars, that...

Explanation: Point or tilt to see a spectacular view of Mars visible to the Curiosity rover last December. In the foreground, part of Curiosity itself is visible, including its dusty sundial. Starting about seven meters back, the robotic rover is seen posing in front of a 5-meter tall dark sand dune named Namib, one of many dunes that span Bagnold field. Further in the distance is the summit of Mt. Sharp, the 5.5-kilometer peak at the center of 150-km wide Gale crater, the crater where Curiosity landed a few years ago. The featured composite spans a full 360-degrees around by...

Explanation: The southern part of Orion, the famous constellation and mythical hunter, appears quite picturesque posing here over a famous volcano. Located in the Canary Islands off the northwest coast of Africa, the snow-peaked Teide is one of the largest volcanoes on Earth. Lights from a group planning to summit Teide before dawn are visible below the volcano's peak. In this composite of exposures taken from the same location one night last month, the three iconic belt stars of Orion are seen just above the peak, while the famous Orion Nebula and the rest of Orion's sword are visible beyond...

Explanation: How massive can a normal star be? Estimates made from distance, brightness and standard solar models had given one star in the open cluster Pismis 24 over 200 times the mass of our Sun, making it one of the most massive stars known. This star is the brightest object located just above the gas front in the featured image. Close inspection of images taken with the Hubble Space Telescope, however, have shown that Pismis 24-1 derives its brilliant luminosity not from a single star but from three at least. Component stars would still remain near 100 solar masses, making...

Explanation: This 3 month long exposure packed the days from December 22, 2015 through March 20 into a box. Dubbed a solargraph, the unconventional, unfolded picture was recorded with a pinhole camera made from a cube-shaped container, its sides lined with photographic paper. Fixed to a single spot for the entire exposure, the simple camera recorded the Sun's path through Hungarian skies. Each day a glowing trail was burned into the photosensitive paper. From short and low, to long and high, the trails follow the progression from winter solstice to spring equinox. Of course, dark gaps in the daily sun...

If modern activist groups held sway in the mid-nineteenth century, countless multitudes would have died from typhoid fever and cholera. The “miasma” paradigm held that the diseases were caused by foul air arising from putrid matter – and only dogged scientific work by William Budd, John Snow and others finally convinced medical and health authorities that the agent was lethal organisms in drinking water. Ultimately, the investigators’ persistence led to discoveries of Vibrio and Salmonella bacteria, the use of chlorine-based disinfectants for drains, water purification and hand washing, programs that kept sewage away from drinking water supplies, and steady advances...

Osprey alights on a snag above his nest to check me out and voice his displeasure with my presence.

Explanation: Comet 252P/Linear's lovely greenish coma is easy to spot in this expansive southern skyscape. Visible to the naked eye from the dark site near Flinders, Victoria, Australia, the comet appears tailless. Still, its surprisingly bright coma spans about 1 degree, posed here below the nebulae, stars, and dark rifts of the Milky Way. The five panels used in the wide-field mosaic were captured after moonset and before morning twilight on March 21. That was less than 24 hours from the comet's closest approach, a mere 5.3 million kilometers from our fair planet. Sweeping quickly across the sky because it...

The travel time from Earth to Mars using current space flight technologies is estimated to be 9 months. Last week, an innovative concept was proposed which claims to reduce the time that will be spent for Mars travel to merely three days through so-called photonic propulsion technology. But a new proposal threatens to radically shorten this period to an astounding 30 minutes. The idea was revealed by Phillip Lubin, who is a physics professor at the University of California Santa Barbara. Lubin was also responsible for the photonic propulsion technology proposal. This time, however, he identified the use of high-powered...

Explanation: Scanning the skies for galaxies, Canadian astronomer Paul Hickson and colleagues identified some 100 compact groups of galaxies, now appropriately called Hickson Compact Groups (HCGs). This sharp telescopic image captures one such galaxy group, HCG 91, in beautiful detail. The group's three colorful spiral galaxies at the center of the field of view are locked in a gravitational tug of war, their interactions producing faint but visible tidal tails over 100,000 light-years long. Their close encounters trigger furious star formation. On a cosmic timescale the result will be a merger into a large single galaxy, a process now understood...

Explanation: In one of the brightest parts of Milky Way lies a nebula where some of the oddest things occur. NGC 3372, known as the Great Nebula in Carina, is home to massive stars and changing nebulas. The Keyhole Nebula (NGC 3324), the bright structure just above the image center, houses several of these massive stars and has itself changed its appearance. The entire Carina Nebula spans over 300 light years and lies about 7,500 light-years away in the constellation of Carina. Eta Carinae, the most energetic star in the nebula, was one of the brightest stars in the sky...

Explanation: Why would the sky glow like a giant repeating rainbow? Airglow. Now air glows all of the time, but it is usually hard to see. A disturbance however -- like an approaching storm -- may cause noticeable rippling in the Earth's atmosphere. These gravity waves are oscillations in air analogous to those created when a rock is thrown in calm water. The long-duration exposure nearly along the vertical walls of airglow likely made the undulating structure particularly visible. OK, but where do the colors originate? The deep red glow likely originates from OH molecules about 87-kilometers high, excited by...

A doctoral candidate at the University of North Dakota published a paper suggesting that we should make Science, Technology, Engineering and Mathematics (STEM) courses more “inclusive” of women by making then “less competitive,” which is about the most sexist thing I’ve ever heard. “There is an opportunity for STEM courses to reduce the perception of courses as difficult and unfriendly through language use in the syllabi, and also as a guide for how to use less competitive teaching methods and grading profiles that could improve the experience of female students,” Laura Parson wrote in the paper.

This past June, American academia went into an uproar over Gov. Scott Walker’s new budget in Wisconsin,....Specifically,any professor in the system—tenured or not—could be dismissed or laid off by the 18-member Board of Regents using maddeningly vague criteria:“when such an action is deemed necessary due to a budget or program decision requiring program discontinuance,curtailment,modification or redirection.”This,when combined with the faculty’s diminished role in governing the university—and thus determining such things as which programs should continue, be curtailed, or get modified—basically meant that these regents—16 of whom were appointed by Walker—could fire anyone,at any time, for any reason.[SNIP]Professors do not want...

Ron Cowen 3-22-2016 In tunnels deep inside a granite mountain at Daya Bay, a nuclear reactor facility some 55 kilometers from Hong Kong, sensitive detectors are hinting at the existence of a new form of neutrino, one of nature’s most ghostly and abundant elementary particles.Neutrinos, electrically neutral particles that sense only gravity and the weak nuclear force, interact so feebly with matter that 100 trillion zip unimpeded through your body every second. They come in three known types: electron, muon and tau. The Daya Bay results suggest the possibility that a fourth, even more ghostly type of neutrino exists —...

Explanation: What's happened to the sky? Moonlight illuminates a snowy scene in this night land and skyscape made on 2013 January from Lower Miller Creek, Alaska, USA. Overexposed near the mountainous western horizon is the first quarter Moon itself, surrounded by an icy halo and flanked left and right by moondogs. Sometimes called mock moons, a more scientific name for the luminous apparitions is paraselenae (plural). Analogous to a sundog or parhelion, a paraselene is produced by moonlight refracted through thin, hexagonal, plate-shaped ice crystals. As determined by the crystal geometry, paraselenae are seen at an angle of 22 degrees...

Explanation: What's that at the end of the road? The Sun. Many towns have roads that run east - west, and on two days each year, the Sun rises and sets right down the middle. Today is one of those days: an equinox. Not only is today a day of equal night (("aequus"-"nox") and day time, but also a day when the sun rises precisely to the east and sets due west. Featured here is a picturesque road in northwest Illinois, USA that runs approximately east -west. The image was taken one year ago today, during the March Equinox of...

Explanation: Get out your red/blue glasses and gaze across Ceres at mysterious mountain Ahuna Mons. Shown in a 3D anaglyph perspective view, the mosaicked image data was captured in December of 2015, taken from the Dawn spacecraft's low-altitude mapping orbit about 385 kilometers above the surface of the dwarf planet. A remarkable dome-shaped feature on Ceres, with steep, smooth sides Ahuna Mons is about 20 kilometers (12 miles) in diameter at its base, rising on average 4 kilometers to a flattened summit. Similar in size to mountains found on planet Earth, no other Cerean surface feature is so tall and...

Explanation: A familiar, zigzag, W pattern in northern constellation Cassiopeia is traced by five bright stars in this colorful and broad mosaic. Stretching about 15 degrees across rich starfields, the celestial scene includes dark clouds, bright nebulae, and star clusters along the Milky Way. In yellow-orange hues Cassiopeia's alpha star Shedar is a standout though. The yellowish giant star is cooler than the Sun, over 40 times the solar diameter, and so luminous it shines brightly in Earth's night from 230 light-years away. A massive, rapidly rotating star at the center of the W, bright Gamma Cas is about 550...