Astronomy: Cassini’s Final Breathtaking Views of Saturn’s Moon Dione

Credit: NASA/JPL-Caltech/Space Science Institute

Above: NASA’s Cassini spacecraft captured this parting view showing the rough and icy crescent of Saturn’s moon Dione following the spacecraft’s last close flyby of the moon on Aug. 17, 2015. Cassini obtained a similar crescent view in 2005. The earlier view has an image scale about four times higher, but does not show the moon’s full crescent as this view does.

Five visible light (clear spectral filter), narrow-angle camera images were combined to create this mosaic view. The scene is an orthographic projection centered on terrain at 0.4 degrees north latitude, 30.6 degrees west longitude on Dione. An orthographic view is most like the view seen by a distant observer looking through a telescope.

The view was acquired at distances ranging from approximately 37,000 miles (59,000 kilometers) to 47,000 miles (75,000 kilometers) from Dione and at a sun-Dione-spacecraft, or phase, angle of 145 degrees. Image scale is about 1,300 feet (400 meters) per pixel.

North on Dione is up and rotated 34 degrees to the right.

Credit: NASA/JPL-Caltech/Space Science Institute

Above: Dione hangs in front of Saturn and its icy rings in this view, captured during Cassini’s final close flyby of the icy moon. North on Dione is up. The image was obtained in visible light with the Cassini spacecraft wide-angle camera on Aug. 17, 2015.

The view was acquired at a distance of approximately 45,000 miles (73,000 kilometers) from Dione and at a sun-Dione-spacecraft, or phase, angle of 35 degrees. Image scale is 3 miles (4 kilometers) per pixel.

Credit: NASA/JPL-Caltech/Space Science Institute

Above: This view from NASA’s Cassini spacecraft looks toward Saturn’s icy moon Dione, with giant Saturn and its rings in the background, just prior to the mission’s final close approach to the moon on August 17, 2015. At lower right is the large, multi-ringed impact basin named Evander, which is about 220 miles (350 kilometers) wide. The canyons of Padua Chasma, features that form part of Dione’s bright, wispy terrain, reach into the darkness at left.

Imaging scientists combined nine visible light (clear spectral filter) images to create this mosaic view: eight from the narrow-angle camera and one from the wide-angle camera, which fills in an area at lower left. The scene is an orthographic projection centered on terrain at 0.2 degrees north latitude, 179 degrees west longitude on Dione. North on Dione is up.

The view was acquired at distances ranging from approximately 106,000 miles (170,000 kilometers) to 39,000 miles (63,000 kilometers) from Dione and at a sun-Dione-spacecraft, or phase, angle of 35 degrees. Image scale is about 1,500 feet (450 meters) per pixel.

The Cassini mission is a cooperative project of NASA, ESA (the European Space Agency) and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA’s Science Mission Directorate, Washington. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colorado.

On the Web:

Cassini-Huygens mission visit http://saturn.jpl.nasa.gov and www.nasa.gov/cassini.

The Cassini imaging team homepage

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Astronomy: The Week Ahead – Sun 2 Aug to Sat 8 Aug 2015

 

Sunday August 2

The Moon attains perigee at 03:11 today, its closest point to Earth during this lunar month. In a waning gibbous phase it is nearly 18 days old with 89% illumination. You can watch it rise just before 10 p.m. in Aquarius over the eastern horizon.

Monday August 3

The eastern morning sky an hour before sunrise features many familiar winter constellations. And today the planet Mars wanders in among them, shining red low on the horizon. Can you find it before dawn washes it out? If you do, compare its color to the giant red stars Aldebaran in Taurus, and Betelgeuse in Orion.

Mars is in Gemini, shining at a bright magnitude 1.70, around 239 million miles from us.

Tuesday August 4

Get your binoculars out and look due south above the stinger of Scorpius tonight, to find Messier 6 (M6), The Butterfly Cluster. This open cluster is visible without optical aid from even reasonably dark locations, at a bright magnitude 4.2. It is 33 arcminutes in size, comparable to the angular size of the full Moon. At 1,600 light years distance, imagine how brilliant these young stars would be were they the distance of some of our brightest neighbors in the sky! Although their discovery is officially attributed to Giovanni Battista Hodierna in 1654, it is very reasonable to believe Ptolemy saw it, and its neighbor M7 (The Ptolemy Cluster) in the First century.

Wednesday August 5

After Pisces has risen, look for the waning gibbous Moon, then, with binoculars, less than two degrees away you’ll find the green-toned planet Uranus at magnitude 5.8 very nearby the magnitude 5.1 star Zeta Piscium. The Moon is 384,399 km distant, Uranus 1.8 billion miles from us, and Zeta 148 light years away. Zeta is an optical double star (not a binary), with its components 23 arcseconds apart.

Thursday August 6

Tonight is last quarter Moon, rising after midnight at 00:26. It is a good weekday night for deep-sky observing, and if not for the Moon we’d be looking for the Southern Iota Aquariid Meteor Shower. If you still want to try for some meteors, here is the radiant, where this shower will appear to emanate from. Expect 7-8 meteors an hour, averaging magnitude 3.

Friday August 7

The constellation name Lacerta is Latin for Lizard. This is a small and faint constellation created by Polish astronomer Johannes Hevelius in 1687. You’ll find it along the Milky Way between the W of Cassiopeia and Cygnus (the northern cross). Its brightest star, Alpha Lacertae, is a dim magnitude 3.76, so this constellation is a challenge to discern. See if you make out its zigzag shape.

Saturday August 8

Located between Cor Caroli in Canes Venatici, and Arcturus in Bootes, M3 is a bright and easy globular cluster to see in binoculars and any telescope. Arcturus is found by taking the handle of the Big Dipper and making an “arc to Arcturus”. Similarly, you can use the dipper’s handle to make a right angle to Cor Caroli. The cluster will be visible easily in binoculars or a finderscope, slightly closer to Arcturus than the halfway point to Cor Caroli. M3 is 16 arcminutes in size, large for the northern hemisphere, and shines at magnitude 6.19 at a distance of 33,000 light years. This is an impressive cluster of over 500,000 stars!

Happy viewing!

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Astronomy: How A Comet Interacts with Solar Wind

July 30, 2015: Rosetta is making good progress in one of its key investigations, which concerns the interaction between the comet and the solar wind.
Screenshot from a simulation of plasma interactions between Comet 67P/C-G and the solar wind around perihelion. Image Credit: Modelling and simulation: Technische Universität Braunschweig and Deutsches Zentrum für Luft- und Raumfahrt; Visualisation: Zuse-Institut Berlin, European Space Agency (ESA)

The solar wind is the constant stream of electrically charged particles that flows from the Sun, carrying its magnetic field out into the Solar System. Like all comets, 67P/Churyumov–Gerasimenko must navigate this flow in its orbit around the Sun.

It is the constant battle fought between the comet and the solar wind that helps to sculpt the comet’s ion tail. Rosetta’s instruments are monitoring the fine detail of this process.

Using the Rosetta Plasma Consortium Ion Composition Analyzer, Hans Nilsson from the Swedish Institute of Space Physics and his colleagues have been studying the gradual evolution of the comet’s ion environment. They have seen that the number of water ions— molecules of water that have been stripped of one electron— accelerated away from the comet increased hugely as 67P/C-G moved between 3.6AU (about 538 million km) and 2.0AU (about 300 million km) from the Sun. Although the day-to-day acceleration is highly variable, the average 24-hour rate has increased by a factor of 10,000 during the study, which covered the period August 2014 to March 2015.

The water ions themselves originate in the coma, the atmosphere of the comet. They are placed there originally by heat from the Sun liberating the molecules from the surface ice. Once in gaseous form, the collision of extreme ultraviolet light displaces electrons from the molecules, turning them into ions. Colliding particles from the solar wind can do this as well. Once stripped of some of their electrons, the water ions can then be accelerated by the electrical properties of the solar wind.

Not all of the ions are accelerated outwards, some will happen to strike the comet’s surface. Solar wind particles will also find their way through the coma to hit home. When this happens, they cause a process called sputtering, in which they displace atoms from material on the surface—these are then ‘liberated’ into space.

Peter Wurz from the University of Bern, Switzerland, and colleagues have studied these sputtered atoms with Rosetta’s Double Focussing Mass Spectrometer (DFMS), which is part of the ROSINA experiment.

They have so far discovered sodium, potassium, silicon and calcium, which are all present in a rare form of meteorites called carbonaceous chondrites. There are differences in the amounts of these atoms at the comet and in these meteorites, however. While the abundance of sodium appears the same, 67P/C-G shows an excess of potassium and a depletion of calcium.

Most of the sputtered atoms come from the winter side of the comet. Although this is the hemisphere that is mostly facing away from the Sun at present, solar wind particles can end up striking the surface because they are deflected during interactions with ions in the comet’s coma. This can be a significant process so long as the density of the coma ions is not too large. But at some point the comet’s atmosphere becomes dense enough to be a major defence, protecting the icy surface.

As the comet gets closer to the Sun, the sputtering will eventually stop because the comet will release more gas and the coma will become impenetrable. When this happens, the solar wind ions will always collide with atoms in this atmosphere or be deflected away before striking the surface.

The first evidence that this deflection is taking place at 67P/C-G has been measured with the Rosetta Plasma Consortium Ion and Electron Sensor, by Thomas Broiles of the Southwest Research Institute (SwRI) in San Antonio, Texas, and colleagues.

Their observations began on August 6, 2014 when Rosetta arrived at the comet, and have been almost continuous since. The instrument has been measuring the flow of the solar wind as Rosetta orbits 67P/C-G, showing that the solar wind can be deflected by up to 45° away from the anti-solar direction.

The deflection is largest for the lighter ions, such as protons, and not so much for the heavier ions derived from helium atoms. For all ions the deflection is set to increase as the comet gets closer to the Sun and the coma becomes ever denser.

As all this happens, Rosetta will be there to continue monitoring and measuring the changes. This was the raison d’être for the rendezvous with this comet. Previous missions have taken snapshots during all too brief fly-bys but Rosetta is showing us truly how a comet behaves as it approaches the Sun.

This blog post is based on the papers “Evolution of the ion environment of comet 67P/Churyumov-Gerasimenko: Observations between 3.6 and 2.0 AU ” by H. Nilsson et al.; “Rosetta observations of solar wind interaction with the comet 67P/Churyumov-Gerasimenko” by T.W. Broiles et al.; and “Solar Wind Sputtering of Dust on the Surface of 67P/Churyumov-Gerasimenko ” by Peter Wurz et al., which have all been accepted for publication in Astronomy and Astrophysics, and “Dynamical features and spatial structures of the plasma interaction region of 67P/Churyumov–Gerasimenko and the solar wind” by C. Koenders et al, which is published in Planetary and Space Science.

On the Web: SIMULATION OF PLASMA INTERACTIONS BETWEEN COMET 67P/C-G AND THE SOLAR WIND AROUND PERIHELION

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Astronomy: Saturn’s Moon Titan Not So Titanic

Credit: NASA/JPL-Caltech/Space Science Institute

Although Titan (3200 miles or 5150 kilometers across) is the second-largest moon in the solar system, Saturn is still much bigger, with a diameter almost 23 times larger than Titan’s. This disparity between planet and moon is the norm in the solar system.

Earth’s diameter is “only” 3.7 times our moon’s diameter, making our natural satellite something of an oddity. (Another exception to the rule: dwarf planet Pluto’s diameter is just under two times that of its moon.) So the question isn’t why is Titan so small (relatively speaking), but why is Earth’s moon so big?

This view looks toward the anti-Saturn hemisphere of Titan. North on Titan is up. The image was taken with the Cassini spacecraft wide-angle camera on April 18, 2015 using a near-infrared spectral filter with a passband centered at 752 nanometers.

The view was acquired at a distance of approximately 930,000 miles (1.5 million kilometers) from Titan. Image scale is 56 miles (90 kilometers) per pixel.

The Cassini mission is a cooperative project of NASA, ESA (the European Space Agency) and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA’s Science Mission Directorate, Washington. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colorado.

On the Web:

For more information about the Cassini-Huygens mission 

The Cassini imaging team homepage

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Astronomy: Venus-Mass Planet Orbiting Brown Dwarf

An international team of Polish, Korean, American, Israeli, and Italian astronomers have announced the unusual discovery of a Venus mass planet OGLE-2013-BLG-0723LB/Bb, orbiting a cool brown dwarf star.

Both the planet and it’s brown dwarf host, are in a wide orbit around a larger stellar companion OGLE-2013-BLG-0723LA, with perhaps another, (as yet unconfirmed) much larger third stellar companion at a much larger separation distance than the two confirmed binary stellar objects.

The discovery was made using the technique of microlensing which gives astronomers reliable information about the mass of the planet : 0.69 ± 0.06 M⊕ (Earth) and it’s orbital distance : 0.34 ± 0.03 AU or 439993738 km. This distance places the planet in an orbit very similar to that of Mercury (0.38 AU) but our Sun is far hotter than this cool brown dwarf.

The microlensing event OGLE-2013-BLG-0723 was first discovered by the Optical Gravitational Lensing Experiment (OGLE-IV) in one of the starfields towards the Galactic bulge that OGLE astronomers Udalski et al. observed on May 12th 2013, using the 1.3 meter Warsaw Telescope at the Las Campanas Observatory in Chile.

The planetary system is estimated to lie some 0.49 ± 0.04 kilo parsecs towards the Galactic Center, having been identified by it’s lensing effect on a background star that is a further 6.51 kilo parsecs from Earth.

This new planetary find may prove to be very important. OGLE-2013-BLG-0723LBb is a missing link between planets and moons. This is because its brown dwarf host OGLE-2013-BLG-723LB  is intermediate between stars and planets, in both size and hierarchical position.

The scaled mass and host-companion separation of this Venus-mass planet and brown dwarf host are in many ways similar to planets and moons in the solar system. That is, a Venus-mass planet orbiting a brown dwarf, may be viewed either as a scaled down version of a planet and star, or as a scaled up version of a moon and planet, orbiting a star.

So this system is an intermediate between Neptune-Triton or Jupiter-Callisto planet-moon systems, and the Sun-Mercury or the Sun-Venus star-planet systems.

It suggests that in all cases, planets and moons are formed in an accretion disk. Planets form around all types and size of star, and moons are formed in an accretion disk around planets. The process is the same, regardless of the size or scale of the individual objects.

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Astronomy: NASA’s Chandra Finds Evidence for Serial Black Hole Eruptions

NGC5813 courtesy of NASA’s Chandra X-ray Observatory, NASA’s Marshall Center
Credit: X-ray: NASA/CXC/SAO/S, Radall.
Optical: SDSS

Astronomers have used NASA’s Chandra X-ray Observatory to show that, multiple eruptions from a supermassive black hole over 50 million years have rearranged the cosmic landscape at the center of a group of galaxies.

Scientists discovered this history of black hole eruptions by studying NGC 5813, a group of galaxies about 105 million light years from Earth. These Chandra observations are the longest ever obtained of a galaxy group, lasting for just over a week. The Chandra data are shown in this new composite image where the X-rays from Chandra (purple) have been combined with visible light data (red, green and blue).

Galaxy groups are like their larger cousins, galaxy clusters, but instead of containing hundreds or even thousands of galaxies like clusters do, galaxy groups are typically comprised of 50 or fewer galaxies. Like galaxy clusters, groups of galaxies are enveloped by giant amounts of hot gas that emit X-rays.

The erupting supermassive black hole is located in the central galaxy of NGC 5813. The black hole’s spin, coupled with gas spiraling toward the black hole, can produce a rotating, tightly wound vertical tower of magnetic field that flings a large fraction of the inflowing gas away from the vicinity of the black hole in an energetic, high-speed jet.

The researchers were able to determine the length of the black hole’s eruptions by studying cavities, or giant bubbles, in the multi-million degree gas in NGC 5813. These cavities are carved out when jets from the supermassive black hole generate shock waves that push the gas outward and create huge holes.

The latest Chandra observations reveal a third pair of cavities in addition to two that were previously found in NGC 5813, representing three distinct eruptions from the central black hole. (Mouse over the image for annotations of the cavities.) This is the highest number of pairs of cavities ever discovered in either a group or a cluster of galaxies. Similar to how a low-density bubble of air will rise to the surface in water, the giant cavities in NGC 5813 become buoyant and move away from the black hole.

To understand more about the black hole’s history of eruptions, the researchers studied the details of the three pairs of cavities. They found that the amount of energy required to create the pair of cavities closest to the black hole is lower than the energy that produced the older two pairs. However, the rate of energy production, or power, is about the same for all three pairs. This indicates that the eruption associated with the inner pair of cavities is still occurring.

Each of the three pairs of cavities is associated with a shock front, visible as sharp edges in the X-ray image. These shock fronts, akin to sonic booms for a supersonic plane, heat the gas, preventing most of it from cooling and forming large numbers of new stars.

Close study of the shock fronts reveals that they are actually slightly broadened, or blurred, rather than being very sharp. This may be caused by turbulence in the hot gas. Assuming this is the case, the authors found a turbulent velocity—that is, the average speed of random motions of the gas—of about 160,000 miles per hour (258,000 kilometers per hour). This is consistent with the predictions of theoretical models and estimates based on X-ray observations of the hot gas in other groups and clusters.

A paper describing these results was published in the June 1st, 2015 issue of The Astrophysical Journal and is available online. The first author is Scott Randall from the Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, MA and the co-authors are Paul Nulsen, Christine Jones, William Forman and Esra Bulbul from CfA; Tracey Clarke from the Naval Research Laboratory in Washington DC; Ralph Kraft from CfA; Elizabeth Blanton from Boston University in Boston, MA; Lawrence David from CfA; Norbert Werner from Stanford University in Stanford, CA; Ming Sun from University of Alabama in Huntsville, AL; Megan Donahue from Michigan State University in East Lansing, MI; Simona Giacintucci from University of Maryland in College Park, MD and Aurora Simionescu from the Japan Aerospace Exploration Agency in Kanagawa, Japan.

NASA’s Marshall Space Flight Center in Huntsville, Alabama, manages the Chandra program for the agency’s Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, controls Chandra’s science and flight operations.

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Astronomy: The Week Ahead – Sun 03 May to Sat 09 May

Sunday May 03

Tonight is a planetary show! The moon is full at 20:42 PDT. This full moon’s names are Full Flower Moon, Full Corn Planting Moon or Milk Moon. It is the season of abundance. Watch it rising in the east as the sky darkens, followed by Saturn in an hour eighteen degrees east. Look west in the darkening twilight to find Jupiter high above brilliant Venus low to the west, and Mercury skimming the horizon below Venus to the right. Spring has just one more full moon, then summer observing season begin!

Monday May 04

Jupiter was at Eastern Quadrature at 1:44 a.m. today, at a right angle to the sun from the earth. Jupiter observing season is quickly coming to a close for 2015. Tonight you can enjoy the last part of a shadow transit of Io, and a view of the Great Red Spot (GRS) as the giant planet slides toward the western horizon and sunset. Don’t wait till it’s dark, or the shadow transit will be over.

Tuesday May 05

Rising in the east on early May mornings is the constellation Pegasus, the Winged Horse. Its famous asterism, The Great Square, is marked on its corners by the bright stars Alpheratz, Algenib, Markab and Scheat. Trailing off the northern corner star Alpheratz is a pair of star chains, defining another famous constellation, which shares Pegasus’ star Alpheratz.

Wednesday May 06

Mercury is at its greatest elongation tonight during sunset at 20:30 PDT. Occasionally the universe puts on a beautiful celestial show, and tonight is such an evening, with Orion bidding us adieu sinking into the sunset for another season, Mercury, Venus and Jupiter forming an ascending display rising toward nightfall. Go out and enjoy this excellent view!

Thursday May 07

Galaxy season is well upon us, with Downtown Virgo being where the action is. Located between the stars Vindemiatrix in Virgo, and Denebola in Leo, M84 and M86 are central in the Virgo Galaxy Cluster, approximately 45 million light years distant. Get yourself to a darker sky, set up your telescope and enjoy the show. You’ll find yourself galaxy hopping, instead of star hopping, in this busy part of the sky!

Friday May 08

Tonight Venus is in conjunction with the great open cluster M35 in Gemini. At less than two degrees separation, they will fit easily in a binocular field of view. If you have a wide field eyepiece, they should form a spectacular pair together at low magnification. Don’t forget to peek for Mercury too, skimming the western horizon as twilight darkens.

Saturday May 09

Look for Hercules and Ophiuchus in the predawn skies today. Their Alpha (brightest) stars sit very close together in our sky, and they share similar Arabic names. Rasalhague shines at magnitude 2.1, and is only 47 light years distant, truly a neighbor of ours. Rasalgethi is dimmer, at 2.75, and much more remote at distance of 384 light years. Rasalgethi is also an excellent double star in a telescope. The primary is a variable star, ranging from magnitude 3.0 to 4.0. Its companion is separated by 4.6 arcseconds – resolvable in most telescopes, shining at magnitude 5.4. They orbit each other over a 3600 years period.

Happy viewing!

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Astronomy: The Hubble Space Telescope Turns 25

The brilliant tapestry of young stars flaring to life resemble a glittering fireworks display in this 25th anniversary NASA Hubble Space Telescope image to commemorate a quarter century of exploring the solar system and beyond since its launch on April 24, 1990.

The sparkling centerpiece of Hubble’s silver anniversary fireworks is a giant cluster of about 3,000 stars called Westerlund 2, named for Swedish astronomer Bengt Westerlund, who discovered the grouping in the 1960s. The cluster resides in a raucous stellar breeding ground known as Gum 29, located 20,000 light-years away from Earth in the constellation Carina.

To capture this image, Hubble’s Wide Field Camera 3 pierced through the dusty veil shrouding the stellar nursery in near-infrared light, giving astronomers a clear view of the nebula and the dense concentration of stars in the central cluster. The cluster measures between 6 to 13 light-years across.

The giant star cluster is only about 2 million years old and contains some of our galaxy’s hottest, brightest, and most massive stars. Some of its heftiest stars unleash torrents of ultraviolet light and hurricane-force winds of charged particles that etch at the enveloping hydrogen gas cloud.

The nebula reveals a fantasy landscape of pillars, ridges, and valleys. The pillars, composed of dense gas and thought to be incubators for new stars, are a few light-years tall and point to the central star cluster. Other dense regions surround the pillars, including reddish-brown filaments of gas and dust.

This is a big week for the Hubble Space Telescope.

Twenty-five years ago, on April 25, 1990, the Hubble Space Telescope was released into orbit from the Space Shuttle Discovery. Astronomers from around the world are taking stock of the amazing achievements of Hubble over the past 25 years: observations that continually challenge our view of our own Solar System, discoveries of extrasolar planetary systems, a more complete view of star and planet formation, understanding how galaxies evolve from just after the Big Bang to the present day, putting constraints on the nature of the enigmatic dark matter, and even helping to discover that the majority of the mass-energy in the universe is in the form of a mysterious repulsive force known as dark energy. To top it all off, thanks in large part to five servicing missions, Hubble is a more powerful telescope today than at any point in its history.

Astronomers are not only celebrating Hubble’s iconic achievements of the past, they are looking forward to what Hubble can accomplish over the next five years. This anniversary week at the Space Telescope Science Institute (STScI) in Baltimore, Md, a symposium is being held called Hubble 2020: Building on 25 Years of Discovery. STScI is the science operations center of the Hubble Space Telescope, so it is a fitting location for astronomers to gather to discuss the past and the future of Hubble science. For the adventurous out there who would like to test and strengthen their astronomy acumen, watch the astronomy symposium online, where astronomers discuss science results with other astronomers.

Hubble Update.

Part of the conversation happening around the past, present, and future science of Hubble focuses on Hubble’s exploration of the deep universe. As it so happens, April 2015 is also the month where the imaging and processing of the Hubble Frontier Fields data are half-way complete. Of course, astronomers will be pouring over the images for years to come — the science results from the Frontier Fields are just beginning.

Shown in the images below are the first three completely imaged Frontier Fields galaxy clusters (Abell 2744, MACS J0416, MACS J0717) and their respective neighboring parallel fields.

Shown here are the first three completed Frontier Fields galaxy clusters and their associated parallel fields. Labeled, from the top, are galaxy cluster Abell 2744, the neighboring Abell 2744 parallel field, galaxy cluster MACS J0416, the neighboring MACS J0416 parallel field, galaxy cluster MACS J0717, and the neighboring MACS J0717 parallel field. The MACS J0717 galaxy cluster image and its associated parallel field are still being processed, so we expect new versions of these images shortly.
Credit: NASA, ESA, and J. Lotz, M. Mountain, A. Koekemoer, and the HFF Team (STScI)

Astronomers are already looking forward to the future of deep-field science. While much of the discussion this week is about Hubble, astronomers generally acknowledge that to truly build off of Hubble’s discoveries, we need the next-generation Great Observatory, the James Webb Space Telescope (JWST). JWST is scheduled to launch in the fall of 2018.

It goes without saying that the participants of the Hubble 2020 symposium are incredibly excited at the prospect of these two behemoths of science — these machines of discovery —  exploring the universe at the same time.

On the Web: Events celebrating Hubble’s 25th anniversary

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Astronomy: April 2015 Lyrid Meteor Shower – Where to Watch

The Lyrids Meteor Shower will peak on 22 April.
Photo: NASA

The night sky will light up with a brilliant display of shooting stars over the next few days, as the annual Lyrid meteor shower makes its appearance for 2015.

Considered the oldest-known meteor shower, the Lyrids will peak on 22 and 23 April, with stargazers able to spot between 10 to 20 meteors per hour.

Typically the first good meteor shower of the year, the Lyrids are visible from most parts of the world, although the timing this year may favor Europe. According to the Slooh Community Observatory, which will host a live stream of the event on Wednesday, 22 April 2015, it is set to be a good year for the Lyrids because the moon will be a slender waxing crescent and will not obscure the view of the meteor shower.

The Lyrids

The April Lyrids have been observed for the past 2,600 years. They are the strongest annual shower of meteors from debris of a long-period comet, mainly because as far as other intermediate long-period comets go (between 200 and 10,000 years), this one has a relatively short orbital period of about 415 years.

The source of the shower is particles of dust shed by the long-period comet Comet C/1861 G1 Thatcher. As the comet sheds debris, the fragments of rock and dust strike the Earth’s upper atmosphere at around 110,000 miles per hour, vaporizing the debris and creating streaks of light. Sometimes, Earth may pass through a thick clump of comet debris, meaning more meteors will be visible.

Lyrid “fireballs” are created when brighter meteors cast shadows for a split second, leaving behind smoky debris. The radiant of the shower is located in the constellation Lyra, near the brightest star of the constellation, Alpha Lyrae, or Vega. The Lyrids can appear anywhere in the sky.

Meteors occur when comet debris enters the earth’s atmosphere.
Photo: NASA

Shooting stars and their glowing trail

Shooting stars are not actually stars but fast-moving fragments of rock and debris left behind by a comet, and as the Earth moves around the sun, some of these pieces are pulled toward Earth by gravity. Around a quarter of the meteors produced during the shower will leave behind an ionised gas trail that glows for just a few seconds.

When a meteor enters Earth’s atmosphere it is moving so fast that its atoms collide with air molecules and electrons are ‘knocked’ loose – creating free electrons and positively charged ions. As the shooting star passes, the negatively charged free electrons are attracted to the positively charged ions and combine with them. When this happens energy is released in the form of light, creating the glowing trail behind shooting stars.

It is important to find somewhere will as little light pollution as possible and remember to wrap up warmly. You can also watch the event in the comfort of your own home, via the Slooh Community Observatory.

Below are various dark sky reserves and viewing areas popular with UK & US astronomers. You can find others using the Dark Sky Discovery website.

Watch the meteor in the UK:

London: The WaterWorks Nature Reserve, between Clapton and Leyton Midland Road rail station.

Manchester: Heaton Park is the largest municipal park in the city and contains an astronomy club.

Birmingham: Warley Woods is accessible by bus or car from the city. Those driving should take the A456 Hagley Road westbound from the centre.

Newcastle: Northumberland National Park is an internationally designated Dark Sky Park.

Cardiff: Brecon Beacons is a fantastic area for stargazing as it offers some of the darkest skies in the UK.

Belfast: Oxford Island National Nature Reserve is around 25 miles from the city, located on the shores of Lough Neagh.

Edinburgh: The Royal Observatory, in the Hermitage of Braid, is a good place to try and spot a shooting star.

Watch the meteor shower in the US

Pennsylvania: Cherry Springs State Park is a gold-certified International Dark Sky Park, one of only a handful in the US. There is a night sky viewing area, located north of Route 44, which is always open.

New York: The Carl Schurz Park on the Upper East Side is the home of the Amateur Astronomers Association on Friday evenings.

California: Death Valley National Park is also a gold-certified International Dark Sky Park, with very little artificial light within its 3.4 million acres. Another good location, the Templin Highway in Angeles National Forest, is a 45 minute drive from downtown LA.

Philadelphia: The Tuckahoe State Park is two hours out of the city and is a good place to stargaze.

Arizona: The Kitt Peak National Observatory, near Tucson, is home to the world’s largest collection of optical telescopes. The clear, dark skies of the Sonoran desert are a famous favourite for astronomers.

Utah: Bryce canyon has very little light pollution. Its skies are best seen during new moons, when the Milky Way and over 7,000 stars can be seen with the naked eye.

Illinois: The Hickory Knolls Discovery Center in St Charles is a nature conservatory and a Dark Sky Park.

New Mexico: Chaco Culture National Historical Park has more than 4,000 prehistoric archaeological sites and is a great location to try and spot the Lyrids.

Texas: The Big Bend National Park in west Texas has gone to some lengths to keep its International Dark Sky status, including by changing the lighting to shielded LEDs.

Alaska: The Denali National Park and Preserve has minimal light pollution and high altitudes, and also offers incredible views of the Aurora Borealis.

Happy viewing!

Crash

Astronomy: The Week Ahead – Mon 20 Apr to Sat 25 Apr

This Wide Field Camera 3 image, dubbed “Mystic Mountain”, was released in 2010 to commemorate Hubble’s 20th anniversary in space.

Monday April 20

M22 is a huge globular cluster visible without optical aid in dark skies. It is a bright fuzzy patch in binoculars, and a grand sight in any telescope, although with an 8″ or larger, you will resolve hundreds of its stars. At 10,600 light years it is one of the nearest globulars. It is one of four globulars known to contain a planetary nebula.

Tuesday April 21

The realm of the galaxies is now rising in the east after sunset. You’ll find the area between Virgo’s bright star Spica, Denebola in Leo, and Arcturus in Bootes.

The heart of the Virgo Galaxy Cluster lies predominantly in and above the arc of stars higher in Virgo, above Porrima. If you learn to recognize Virgo’s shape, you’ll have many enjoyable observing sessions viewing dozens of galaxies in this area. In fact, they are so plentiful that you will find yourself not star hopping, but “galaxy hopping.”

Wednesday April 22

Return tonight to Virgo in the east. Use your telescope to look for the classic edge-on spiral galaxy M104. A good star-hop is to use nearby Corvus to cut diagonally across the sail shape, then beyond about half the same distance. Move the telescope up slightly at a right angle and look for a slash-type shape in the eyepiece. Add magnification to observe the dark lane and its small bright core.

M104 is part of the Virgo Cluster of galaxies, about 28 million light years away. M104 is about one third the size of our Milky Way.

Thursday April 23

The Lyrid Meteor Shower reaches its climax tonight. The best time to watch is from midnight on.

The Lyrids are a remnant of Comet Thatcher (C/1861 G1) in its 415-year orbit of our Sun. Without a Moon to brighten tonight’s sky during the meteor shower, prospects are good to see 10 to 20 meteors per hour.

Dress warm, have a thermos of hot chocolate, sit in a comfortable chair, and watch toward the radiant, shown here in the northeast, near Lyra’s bright star Vega.

Friday April 24

Mizar is a famous multiple-star system in the equally famous Big Dipper of Ursa Major, which is currently directly over our north star Polaris an hour after sunset.

Mizar and its brightest companion, Alcor, can be seen as a naked-eye pair. Native American tribes used the pair as an eye test, to distinguish who could be a hunter, with keen eyes, and who could not.

The system is actually a quadruple star. Mizar shines at magnitude 2.23, Alcor at 3.99, lying 83 light years away from Earth. They are a lovely sight in any telescope!

Saturday April 25

Tonight is the First Quarter Moon is in the constellation Cancer, and will be bright enough to overwhelm any of the constellations stars. It will form a very pretty pair with Jupiter, a bit higher up, also in Cancer. Lower toward the western horizon, Venus will be very bright. Mercury is just hidden behind the hills of the western horizon and will start popping up tomorrow. Watch for Mercury to pair with the Pleiades skimming the horizon on the evening of May 1.

Happy viewing!

Crash