Melissa Cheng

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APOD: Arp 188 and the Tadpole's Tail (2012 Nov 08) Image Credit: Hubble Legacy Archive, ESA, NASA; Processing: Bill Snyder (Heavens Mirror Observatory) Explanation: In this stunning vista, based on image data from the Hubble Legacy Archive, distant galaxies form a dramatic backdrop for disrupted spiral galaxy Arp 188, the Tadpole Galaxy. The cosmic tadpole is a mere 420 million light-years distant toward the northern constellation Draco. Its eye-catching tail is about 280 thousand light-years long and features massive, bright blue star clusters. One story goes that a more compact intruder galaxy crossed in front of Arp 188 - from right to left in this view - and was slung around behind the Tadpole by their gravitational attraction. During the close encounter, tidal forces drew out the spiral galaxy's stars, gas, and dust forming the spectacular tail. The intruder galaxy itself, estimated to lie about 300 thousand light-years behind the Tadpole, can be seen through foreground spiral arms at the upper right. Following its terrestrial namesake, the Tadpole Galaxy will likely lose its tail as it grows older, the tail's star clusters forming smaller satellites of the large spiral galaxy. Starship Asterisk* • APOD Discussion Page Starship Asterisk* • On This Day in APOD

APOD: NGC 6357's Cathedral to Massive Stars (2012 Nov 18) Image Credit: NASA, ESA and J. M. Apellániz (IAA, Spain) 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, nearly making it the record holder. This star is the brightest object located just above the gas front in the above 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 them among the more massive stars currently on record. Toward the bottom of the image, stars are still forming in the associated emission nebula NGC 6357. Appearing perhaps like a Gothic cathedral, energetic stars near the center appear to be breaking out and illuminating a spectacular cocoon. Starship Asterisk* • APOD Discussion Page Starship Asterisk* • On This Day in APOD

APOD: Umbra World (2012 Dec 14) Image Credit & Copyright: Dennis L. Mammana (TWAN) Explanation: On the morning of November 14, sky gazers from around the world gathered on this little planet to stand in the dark umbral shadow of the Moon. Of course, the Moon cast the shadow during last month's total solar eclipse, and the little planet is actually a beach on Green Island off the coast of Queensland, Australia. The picture itself, the first little planet projection of a total solar eclipse, is a digitally warped and stitched wrap-around of 8 images covering 360x180 degrees. To make it, the intrepid photographer had to remember to shoot both toward and away(!) from the eclipse during the excitement of totality. Near this little planet's horizon, the eclipsed Sun is just above center, surrounded by the glowing solar corona. Venus can be spotted toward the top of the frame. At bottom right, bright star Sirius shines at the tip of an alarmingly tall tree. Starship Asterisk* • APOD Discussion Page Starship Asterisk* • On This Day in APOD

APOD: Orion over El Castillo (2012 Dec 21) Image Credit & Copyright: Stéphane Guisard (Los Cielos de America, TWAN) Credits: D. Flores and B. Pichardo (IA-UNAM), P. Sánchez and R. Nafate (INAH) Explanation: Welcome to the December solstice, a day the world does not end ... even according to the Mayan Calendar. To celebrate, consider this dramatic picture of Orion rising over El Castillo, the central pyramid at Chichén Itzá, one of the great Mayan centers on the Yucatán peninsula. Also known as the Temple of Kukulkan it 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. In fact, the Mayans were accomplished astronomers and mathematicians, accurately using the cyclic motions of the stars, Sun, Moon, and planets to measure time and construct calendars. Peering through clouds in this night skyscape, stars in the modern constellation Orion the Hunter represented a turtle in the Mayan sky. Tak sáamal. Starship Asterisk* • APOD Discussion Page Starship Asterisk* • On This Day in APOD

APOD: A Solar Ballet (2013 Jan 15) Video Credit: NASA/Goddard/SDO AIA Team Explanation: Sometimes, the Sun itself seems to dance. On just this past New Year's Eve, for example, NASA's Sun-orbiting Solar Dynamic Observatory spacecraft imaged an impressive prominence erupting from the Sun's surface. The dramatic explosion was captured in ultraviolet light in the above time lapse video covering four hours. Of particular interest is the tangled magnetic field that directs a type of solar ballet for the hot plasma as it falls back to the Sun. The scale of the disintegrating prominence is huge -- the entire Earth would easily fit under the flowing curtain of hot gas. A quiescent prominence typically lasts about a month, and may erupt in a Coronal Mass Ejection (CME) expelling hot gas into the Solar System. The energy mechanism that creates a solar prominence is still a topic of research. As the Sun nears Solar Maximum this year, solar activity like eruptive prominences should be common. Starship Asterisk* • APOD Discussion Page Starship Asterisk* • On This Day in APOD

APOD: In the Center of the Trifid Nebula (2013 Jan 28) Image Credit: Subaru Telescope (NAOJ), Hubble Space Telescope, Martin Pugh; Processing: Robert Gendler Explanation: Clouds of glowing gas mingle with dust lanes in the Trifid Nebula, a star forming region toward the constellation of the Archer (Sagittarius). In the center, the three prominent dust lanes that give the Trifid its name all come together. Mountains of opaque dust appear on the right, while other dark filaments of dust are visible threaded throughout the nebula. A single massive star visible near the center causes much of the Trifid's glow. The Trifid, also known as M20, is only about 300,000 years old, making it among the youngest emission nebulae known. The nebula lies about 9,000 light years away and the part pictured here spans about 10 light years. The above image is a composite with luminance taken from an image by the 8.2-m ground-based Subaru Telescope, detail provided by the 2.4-m orbiting Hubble Space Telescope, color data provided by Martin Pugh and image assembly and processing provided by Robert Gendler. Starship Asterisk* • APOD Discussion Page Starship Asterisk* • On This Day in APOD

APOD: Sakurajima Volcano with Lightning (2013 Mar 11) Image Credit & Copyright: Martin Rietze (Alien Landscapes on Planet Earth) Explanation: Why does a volcanic eruption sometimes create lightning? Pictured above, the Sakurajima volcano in southern Japan was caught erupting in early January. Magma bubbles so hot they glow shoot away as liquid rock bursts through the Earth's surface from below. The above image is particularly notable, however, for the lightning bolts caught near the volcano's summit. Why lightning occurs even in common thunderstorms remains a topic of research, and the cause of volcanic lightning is even less clear. Surely, lightning bolts help quench areas of opposite but separated electric charges. One hypothesis holds that catapulting magma bubbles or volcanic ash are themselves electrically charged, and by their motion create these separated areas. Other volcanic lightning episodes may be facilitated by charge-inducing collisions in volcanic dust. Lightning is usually occurring somewhere on Earth, typically over 40 times each second. Starship Asterisk* • APOD Discussion Page Starship Asterisk* • On This Day in APOD

Today is the last day of the International Dark Sky Week! Unfortunately I've been swamped with my upcoming projects I haven't had time to post here in a few days. From the comments I've read on earlier posts, some people don't understand why losing the dark matters. Light pollution interferes with living systems in many ways, causing, for example, sea turtles to lose their way to the sea, migrating birds to become confused and strike buildings, and plant seasonal cycles to be disturbed. It also affects human hormone cycles and our day-and-night cycles of sleep and wakefulness. Using light carelessly wastes energy, resources used to make the energy, and interferes with everyone’s visibility not only of stars but also of things on the ground that we need to see. The last image, or images I would like to share in honor of IDSWeek is a body of work by the artist Thierry Cohen ( He photographs major cities, noting the precise time, angle, and latitude and longitude of his exposures. He then shoots the sky at the same angles from remote places at the same latitude, and digitally combines the images to show what the night sky would look like if we could turn off the lights. I want to thank the International Dark-Sky Association for all of their support and hard work promoting dark sky awareness! Celebrate the Night! Light Right! Goldpaint Photography For more information, please read below. Light pollution and human health In the USA today, 56% of children between the ages of 8 and 12 own their own cell phone and many are able to download and use astronomy apps. However, only 1% of those children will be able to see the majority of the objects shown by those apps because of light pollution. This makes for many disappointed, and disillusioned children; uninspired to pursue science. Not only is that frightening from a social and cultural standpoint, it is also terrifying as a health concern. Being exposed to light at night continues to be shown as a factor leading to health problems including obesity, depression, and even cancer, among others. Glare on the Eyes Bright points of light from poorly designed roadway lighting produce a condition known as “disability glare.” Disability glare is so intense that it causes us to avert our eyes from the veil of light being scattered across our retinas. This condition can temporarily cast everything except the light source into virtual invisibility. Older drivers are especially vulnerable to disability glare, because as we age the eye loses its ability to quickly adjust to changing levels of illumination. Fully shielded roadway lighting reduces this hazard and creates a safe and more pleasant driving experience by distributing the light evenly. Circadian Rhythm The 24-hour day/night cycle, known as the circadian clock, affects physiologic processes in almost all organisms, including humans. These processes include brain wave patterns, hormone production (melatonin), cell regulation and other biologic activities. Disruption of these rhythms can result in insomnia, depression, cancer, and cardiovascular disease. In 2012 the American Medical Association has recognized light at night as a carcinogen and a health risk. More information may be found at: Melatonin Melatonin is a naturally occurring hormone which is released by darkness and inhibited by light. It serves many functions in the human body, primarily regulating the daily cycles of our systemic activities. Reduction or elimination of light at night can help maintain a robust melatonin rhythm. While any kind of light can interfere with melatonin production, the short wavelength, blue portion of the spectrum is the most potent for melatonin suppression in humans. Sleep disorders Exposure to the artificially extended daytime of our lighted modern world can lead to desynchornization of our internal rhythms. According to the National Institution of Health (NIH), a shift in our clocks impairs our ability to sleep and wake at the appropriate times and leads to a decrease in cognitive and motor skills. A good night’s sleep helps reduce weight gain, stress, depression, and the onset of diabetes. The NIH believes humans function best when they sleep at night and act in the daytime. If outdoor light is shining into your window and disrupting your sleep, it is recommend you block out the light or request that the light be shielded for everyone’s benefit. Emerging Research

APOD: Horsehead: A Wider View (2013 May 03) Composition and Processing: Robert Gendler Image Data: ESO, VISTA, HLA, Hubble Heritage Team (STScI/AURA) Explanation: Combined image data from the massive, ground-based VISTA telescope and the Hubble Space Telescope was used to create this wide perspective of the interstellar landscape surrounding the famous Horsehead Nebula. Captured at near-infrared wavelengths, the region's dusty molecular cloud sprawls across the scene that covers an angle about two-thirds the size of the Full Moon on the sky. Left to right the frame spans just over 10 light-years at the Horsehead's estimated distance of 1,600 light-years. Also known as Barnard 33, the still recognizable Horsehead Nebula stands at the upper right, the near-infrared glow of a dusty pillar topped with newborn stars. Below and left, the bright reflection nebula NGC 2023 is itself the illuminated environs of a hot young star. Dense clouds below the base of the Horsehead and on the outskirts of NGC 2023 show the tell-tale far red emission of energetic jets, known as Herbig-Haro objects, also associated with newborn stars. Starship Asterisk* • APOD Discussion Page Starship Asterisk* • On This Day in APOD

APOD: A Supercell Thunderstorm Cloud Over Montana (2013 May 05) Image Credit & Copyright: Sean R. Heavey Explanation: Is that a spaceship or a cloud? Although it may seem like an alien mothership, it's actually a impressive thunderstorm cloud called a supercell. Such colossal storm systems center on mesocyclones -- rotating updrafts that can span several kilometers and deliver torrential rain and high winds including tornadoes. Jagged sculptured clouds adorn the supercell's edge, while wind swept dust and rain dominate the center. A tree waits patiently in the foreground. The above supercell cloud was photographed in July west of Glasgow, Montana, USA, caused minor damage, and lasted several hours before moving on. Starship Asterisk* • APOD Discussion Page Starship Asterisk* • On This Day in APOD