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This Week’s Sky at a Glance, April 24 – May 2

Fri, 04/24/2015 - 12:22
Some daily sky sights among the ever-changing Moon, planets, and stars.

More than a month after it erupted, the nova in the Sagittarius Teapot continues to fluctuate between about magnitude 4.5 and 6. As of April 24th it had taken another uptick to about 4.8. If it's a "slow nova," as certainly seems to be the case, it could become even brighter this summer. It's now well placed in the south just before the beginning of dawn. See article with charts and up-to-date light curve.

Friday, April 24

The Moon tonight rests on (or near) one side of a big, almost equilateral triangle: bright Jupiter to the Moon's upper left, Pollux upper right of the Moon, and Procyon to the Moon's lower left.

As the Moon waxes past first quarter, it glides under Jupiter and the Sickle of Leo.

As the Moon waxes past first quarter, it glides under Jupiter and the Sickle of Leo.

Saturday, April 25

First-quarter Moon (exact at 7:55 p.m. EDT). Jupiter shines closer to the upper left of the Moon this evening. As the night grows late, the sky turns to put Jupiter directly above the Moon. Although they may look close together, Jupiter is nearly 2,000 times farther away — and 40 times larger in diameter.

Sunday, April 26

After dark now the Big Dipper has turned to lie almost upside down; face east-northeast and look very high. Its handle arcs around toward Arcturus a little more than a Dipper-length to the Dipper's lower right.

Monday, April 27

The waxing gibbous Moon shines under Regulus this evening, as shown here.

Among Jupiter's moons, telescope users in the western half of North America can watch the shadow of Io eclipse Europa from 10:59 to 11:02 p.m. PDT. At mid-eclipse, Europa will be dimmed by 1.4 magnitudes.

(Now that Jupiter is far from opposition, we see shadows in the Jovian system falling far enough sideways that an eclipsed satellite and its eclipser appear widely separated in a telescope's view. So we can see the eclipsed satellite dimming by itself, uncontaminated by the light of the eclipser. The tables in Sky & Telescope for these events presume that the two satellites appear blended and give their combined magnitude. See Bob King's article Catch the Last Best Antics of Jupiter’s Moons.)

Tuesday, April 28

Look very low in the northeast in twilight to catch the rising of Vega, the "Summer Star." By nightfall it's up in better view. Once Vega wins clear of the thick low air, it shines as the equal of Arcturus, the "Spring Star" high in the east very far to the upper right.

Wednesday, April 29

Far below the Moon at nightfall, and less far to the right of Spica, spot the springtime constellation Corvus: the four-star, sail-shaped Crow.

Thursday, April 30

Happy May Eve. As dusk fades, look for the Pleiades about 2° upper right of Mercury low in the west-northwest. Bring binoculars.

Friday, May 1

For May Day, Venus shines directly between the horn-tips of Taurus, Zeta and Beta Tauri (Elnath). It's closest to brighter Beta.

The Moon, two days from full, shines a few degrees above Spica this evening. Far off to their left or upper left is brighter Arcturus, pale yellow-orange.

Venus has just passed between the Zeta and Beta Tauri on May 2nd, and Aldebaran far below is lining up with Mercury. (These scenes are drawn for 40° north latitude. Far north or south of there, the scene will be tilted compared to this view.)

Venus has just passed between the Zeta and Beta Tauri on May 2nd, and Aldebaran far below is lining up with Mercury. (These scenes are drawn for 40° north latitude. Far north or south of there, the scene will be tilted compared to this view.)

Saturday, May 2

May is here, but wintry Sirius still twinkles low in the southwest as twilight fades — off the left edge of the scene above. How much later into the spring can you keep Sirius in view?


Want to become a better astronomer? Learn your way around the constellations. They're the key to locating everything fainter and deeper to hunt with binoculars or a telescope.

This is an outdoor nature hobby; for an easy-to-use constellation guide covering the whole evening sky, use the big monthly map in the center of each issue of Sky & Telescope, the essential guide to astronomy. Or download our free Getting Started in Astronomy booklet (which only has bimonthly maps).

Once you get a telescope, to put it to good use you'll need a detailed, large-scale sky atlas (set of charts). The standards are the little Pocket Sky Atlas, which shows stars to magnitude 7.6; the larger and deeper Sky Atlas 2000.0 (stars to magnitude 8.5); and once you know your way around, the even larger Uranometria 2000.0 (stars to magnitude 9.75). And read how to use sky charts with a telescope.

You'll also want a good deep-sky guidebook, such as Sue French's Deep-Sky Wonders collection (which includes its own charts), Sky Atlas 2000.0 Companion by Strong and Sinnott, the bigger Night Sky Observer's Guide by Kepple and Sanner, or the beloved if dated Burnham's Celestial Handbook.

This Week's Planet Roundup Jupiter on April 13th.

Jupiter on April 13th. South is up. The South Equatorial Belt remains slightly wider than the North Equatorial Belt. The Red Spot Hollow has an unusual plume extending from its north (bottom) edge, and new white material has broken out in the Red Spot's turbulent wake. Image by Christopher Go.

Saturn on March 2, 2015

Saturn on March 2nd, imaged with superb resolution by Damian Peach during very good seeing. South is up. The dark North Polar Hexagon is distinctly hexagonal here — though its shape wasn't discovered until the Cassini spacecraft orbited Saturn!


Mercury (about magnitude –0.6) is having a fine apparition in evening twilight. Look for it very far to the lower right of Venus. Mercury gets a little higher every day, but it's also fading.

Venus (magnitude –4.1, in Taurus) blazes in the west during and after twilight — the brilliant "Evening Star." It doesn't set in the west-northwest until nearly two hours after dark. In a telescope Venus is still small and gibbous, but each week it grows and thins as it approaches us along its orbit.

Mars (magnitude +1.4) is disappearing deep in the sunset, to the lower right of much brighter Mercury. Use binoculars or a wide-field scope to say goodbye to it at last.

Jupiter (magnitude –2.1, in Cancer) shines high a little west of south as the stars come out, and less high in the southwest after dark. It's the second-brightest point of light in the sky after Venus. In a telescope, Jupiter has shrunk to 38 arcseconds wide.

Saturn (magnitude +0.1, just above the head of Scorpius) rises around the end of twilight and is highest in the south around 1 or 2 a.m. daylight-saving time. Below or lower left of Saturn by 9° is orange Antares, less bright. The next brightest star in the area is Delta Scorpii, about half as far from Saturn. Delta Sco is now in its 15th year of outburst!

Uranus is deep in the glow of dawn.

Neptune (magnitude +7.9, in Aquarius) is low in the east-southeast at the beginning of dawn. The farther south you are, the higher it will be.


All descriptions that relate to your horizon — including the words up, down, right, and left — are written for the world's mid-northern latitudes. Descriptions that also depend on longitude (mainly Moon positions) are for North America.

Eastern Daylight Time (EDT) is Universal Time (UT, UTC, or GMT) minus 4 hours.


“This adventure is made possible by generations of searchers strictly adhering to a simple set of rules. Test ideas by experiments and observations. Build on those ideas that pass the test. Reject the ones that fail. Follow the evidence wherever it leads, and question everything. Accept these terms, and the cosmos is yours.”

— Neil deGrasse Tyson, 2014.


The post This Week’s Sky at a Glance, April 24 – May 2 appeared first on Sky & Telescope.

Categories: Astronomy Headlines

Hubble Telescope’s Silver Anniversary

Fri, 04/24/2015 - 06:44

It's been 25 years since the Space Shuttle Atlantis lofted the Hubble Space Telescope into orbit. Yet astronomers were not unanimous in their enthusiasm for the project, as this debate from 1990 recalls.

Hubble Space Telescope in orbit

With a mass of 11 tons and 43 feet (13.2 m) long, the Hubble Space Telescope has been peering into the depths of the universe since 1990. Here's its seen in February 1997, during the second of five Space Shuttle servicing missions.

We sometimes forget how many astronomical discoveries were made before the advent of the Hubble Space Telescope, which left Earth on this date 25 years ago. Likewise, few now recall that the mission ended up costing some $2 billion just to get it to the launch pad, seven years behind schedule and roughly 100% over budget. And then there was the "epic fail" resulting from its misshapen primary mirror, now a distant memory thanks to the installation of corrective optics by visiting astronauts in late 1993.

As the Space Shuttle Atlantis and its crew of five rocketed skyward from Florida on April 24, 1990, we all had high hopes that this go-for-broke spacecraft would become "astronomy's discovery machine." Today, few would argue that the Hubble's observations, which continue unabated thanks to five servicing missions by astronaut crews and sustained funding that's nearing $10 billion all told, have revolutionized astronomy.

Understandably, NASA and the European Space Agency (which shared in HST's development) have much to celebrate.

Westerlund 2 as viewed by Hubble's WFC3

The colorful nebula Gum 29, 20,000 light-years away in the constellation Carina, is the host for a giant cluster of 3,000 young stars named Westerlund 2. Here's an animation of an imaginary flight through Westerlund 2.
NASA / ESA / Hubble Heritage Team / A. Nota / Westerlund 2 Science Team

Yesterday a dazzling cosmic portrait by HST's Wide Field Camera 3 was unveiled by John Grunsfeld, who now serves as associate administrator of NASA's Science Mission Directorate but is better known as the astronomer-astronaut who lovingly repaired and upgraded HST on the servicing missions in 1999, 2002, and 2009. Lots of Hubble highlights appear on the websites of NASA and ESA. In fact, there's even a website devoted to Hubble's silver anniversary.

With all that HST has accomplished, it's worth noting that astronomers were not unanimous in their approval of the project during its long, tortured development. Reproduced below are a pair of Focal Points, written by renowned astronomers of that era, that ran opposite each other in Sky & Telescope's April 1990 issue. These essays offer a window into the soaring hopes and some of the concerns they had — that we all had — at the dawn of the Hubble era. Enjoy!

Is the Space Telescope a Mistake? No! Launch of Hubble Space Telescope

Liftoff! The Space Shuttle Discovery soars skyward on April 24, 1990. Squeezed in its cargo bay is a precious payload: the Hubble Space Telescope.

Some people have suggested that the Hubble Space Telescope (HST) is a mistake. They say that a different approach would have served the astronomical community much better. We disagree. HST will be a powerful, though admittedly costly, new tool for astronomers. Of course, this presupposes that HST works as designed — as we'll learn during the year ahead. If it does, we anticipate that it will make major discoveries and spur important advances in astronomy.

In 1959 one of us (A.B.M.) initiated the Space Division at Kitt Peak National Observatory. At the time NASA planned to launch four small Orbiting Astronomical Observatories. Ultimately, two of these OAO spacecraft failed during or soon after launch. However, OAO 2 (launched in 1968) and Copernicus (in 1972) flew very successful missions.

The division's goal was to look beyond these pioneering craft to the day when astronomers would regularly use large telescopes in space. Since then we have watched NASA's Space Telescope project from a distance, sometimes happy with its progress, sometimes not.

By the end of the 1960s it had become clear that an orbiting telescope with an aperture of 2 to 3 meters was technically feasible and scientifically desirable as a follow-on to the OAOs. Little did we dream that so many years would elapse between the start of the Large Space Telescope project (as it was then called) and the launch of HST. On our bookshelf we have two thick technical reports that show the telescope with essentially the same appearance HST has today - they are dated 1970 and 1972!

At the time, the project had an estimated cost of about $400 million, approximately what the four OAOs together had cost. If anyone had realized that the true price tag would be closer to $2 billion, HST might never have been born.

In retrospect this cost escalation was inevitable, for four reasons. First, NASA added many advanced capabilities to the observatory. Second, the optical system had to be better than any developed for use on the ground yet lightweight enough to be launched into space. Third, there was considerable over-optimism regarding the technical challenges involved in making such a complex spacecraft highly reliable. And finally, HST was tied to the Space Shuttle, leading to a costly three-year delay in the wake of the Challenger disaster.

Despite all that, there are signs that our high expectations for HST are justified. For example, the Space Telescope Science Institute (STScI) is in place with an excellent staff designed both to support the operation of HST and to see that it yields the maximum benefit to the entire astronomical community. Indeed, the institute's efforts have already borne fruit — STScI recently published a star catalogue listing nearly 19 million objects, the most comprehensive such collection ever produced (S&T: December 1989, page 583).

Even marrying HST to the shuttle has its silver lining. Astronauts can revitalize HST every five years or so, amortizing the nation's large investment over perhaps two decades. Already new instruments to be carried aloft for installation into HST are being built. They will provide new capabilities for the mission's second five years. HST's long lifetime may prove to be very important, allowing time for new discoveries to influence the observatory's ultimate capabilities.

Astronauts with Hubble

Astronauts John Grunsfeld (left) and Richard Linnehan work to replace the Hubble Space Telescope's power control unit during a March 6th space walk. One of the orbiting observatory's new solar-cell arrays, installed earlier in the week, looms at right.

A good indicator of the scientific importance of HST is the intense competition by astronomers to place objects of their special interest in the observing schedule (S&T: February, 1989, page 153). During the first year of general, or "guest," observations, HST will far from satisfy the demand for observing time. Yet, many more astronomers will be able to use the data after one year of proprietary ownership by the original observers.

Some astronomers say that the $2 billion cost to put one HST in orbit could have been better spent building several 8-meter telescopes on high mountains. In the mid-1950s, when an advisory committee presented its decision to build Kitt Peak National Observatory, a parallel argument was heard: it would drain off money from university astronomy. Instead Kitt Peak, along with the National Radio Astronomy Observatory, led the way to increasing the National Science Foundation's budget for astronomy, thereby benefiting many university observatories. We have faith that HST will similarly pave the way for a new generation of ground-based telescopes to follow up its discoveries.

Already astronomers are dreaming of the next generation of space telescopes and the quantum leap in capabilities they will bring. Whether or not these come about within the next two decades, HST itself will keep astronomers pushing back the frontiers of astronomy.


Aden Meinel was the first director of Kitt Peak National Observatory. The Meinels later retired from the University of Arizona and the Jet Propulsion Laboratory. Marjorie died in 2008, Aden in 2011.

Is the Space Telescope a Mistake? Yes, but . . .

In my answer to this question, "but" means that the Hubble Space Telescope (HST) will be a magnificent instrument. It also means that Lyman Spitzer, Jr., who began promoting the idea of orbiting telescopes in 1946 and who has been the guiding spirit of space-based astronomy for 44 years, deserves the gratitude and admiration all astronomers feel for him. In 1946 Spitzer wrote of a 3-meter Large Space Telescope (LST): "The chief contribution of such a radically new and more powerful instrument would be, not to supplement our present ideas of the universe we live in, but rather to uncover new phenomena not yet imagined, and perhaps to modify profoundly our basic concepts of space and time." We all share Spitzer's hope that HST will fulfill this promise.

"Yes" means that I remember other words of Lyman Spitzer, words that HST's promoters have forgotten or disregarded: "To provide for a leisurely orbit and thus for relatively constant conditions, such an observatory should preferably be at some distance away from the Earth, probably as far as telemetering techniques and celestial mechanics might allow." In 1968 he added, "Quite apart from the engineering desirability of launching smaller space telescopes before building the large instrument, the astronomical requirement for a continuing series of smaller space telescopes should be an overriding consideration in setting the pace of the LST effort."·

eagle nebula in visible and infrared

The Hubble Space Telescope produced these visible-light (left) and near-infrared composite images of these fingers of gas in the Eagle Nebula, also known as the Pillars of Creation. The visible image is color-coded for chemical composition: blue is doubly ionized oxygen, green is ionized hydrogen, and reddish orange is ionized sulfur. The infrared image cuts through much of the gas and reveals stars inside.
NASA / ESA / Hubble Heritage Team (STScI / AURA)

The advantages of a high orbit have been abundantly confirmed by the International Ultraviolet Explorer (lUE), a small space telescope that has been used by more than a thousand observers since it was launched in 1978. IUE sits in a geosynchronous orbit, in constant line-of-sight communication with observers at control centers in Maryland and Spain. As seen from IUE, the Earth obscures only 2 percent of the sky. These advantages were denied HST by the decision to place it in a low-altitude orbit, where Earth blocks roughly half the sky at any time. The difficulties of programming observations from low orbit will limit HST's efficiency to a maximum of about 35 percent, comparable to that of a ground-based telescope, even though it won't have to contend with daylight and clouds.

The scientific output of IUE has also demonstrated the wisdom of Spitzer's call for a continuing series of smaller telescopes as pacesetters for HST. IUE can observe objects typically only down to magnitude 16 and with an angular resolution of 3 arc seconds. In spite of these severe limitations, the satellite has poured out an immense quantity of information about all kinds of celestial objects, from planets to supernovae.

HST will be able to observe objects some 10 magnitudes fainter than IUE with an angular resolution at least 30 times sharper — a great leap forward indeed! Unfortunately, its mirror's collecting area is only 30 times that of IUE, so that the photons from a 26th-magnitude object are collected by HST 300 times slower than those from a 16th-magnitude object are by IUE. Thus, to utilize HST at the limit of its capabilities will be very time-consuming. There are many exciting objects in the sky, and most of them are faint. HST will never have enough time. No single telescope, whether in orbit or on the ground, can provide the world's astronomers with the observing time they need to explore the richness of the universe.

Comet S-L 9's impact with Jupiter

Hubble's view of a large dark feature on Jupiter, bigger than Earth, was created by the impact of fragment "G" from Comet Shoemaker-Levy 9 on July 18, 1994.
H. Hammel / MIT / /NASA

So "yes" does not mean it was a mistake to build the Hubble Space Telescope at all. "Yes" means it was a mistake to sell HST to Congress and to the public as the space telescope for the rest of the 20th century. It was a mistake to push HST ahead of more modest space telescopes that could have been flying earlier. If we had even one imaging telescope in the I-meter class, looking at the sky with 0.l-arc-second resolution, many of the discoveries that HST will make might have been made 10 years sooner. If we had flown a series of I-meter instruments, operating like IUE and paving the way for HST, we would be able to use the precious observing time of HST much more effectively.

But we should not waste time now grieving over our past mistakes. Let us be grateful for what we have, and make the best of it.


Dyson, now 91, was a scientist at Princeton's Institute for Advanced Study until his retirement in 1994. He authored several popular books, including Disturbing the Universe (1979), Infinite in All Directions (1988), and A Many-Colored Glass: Reflections on the Place of Life in the Universe (2007).

To learn how Hubble has fundamentally altered our perceptions of the universe, read Govert Schilling's detailed analysis in Sky & Telescope's June issue.

The post Hubble Telescope’s Silver Anniversary appeared first on Sky & Telescope.

Categories: Astronomy Headlines

Markarian’s Chain

Fri, 04/24/2015 - 04:35

The post Markarian’s Chain appeared first on Sky & Telescope.

Categories: Astronomy Headlines

Runaway Compact Galaxies?

Thu, 04/23/2015 - 13:39

Astronomers have discovered 195 compact elliptical galaxies, upping the known number of these weird galaxies sixfold.

Andromeda Galaxy

Reader Francesco di Biase created this composite image of M31, the Andromeda Galaxy. The bright, whitish orb above the disk is M32, a classic example of a compact elliptical.
Francesco di Biase / S&T Gallery

In the galactic zoo of today’s universe, there’s a breed called the compact elliptical. These are not to be confused with compact cores, which I wrote about last week — compact cores exist in the early universe and can be hundreds of times more massive; they’re probably the progenitors of today’s most massive ellipticals. Compact ellipticals, conversely, are puny balls of old stars, weighing maybe a few billion solar masses. That gives them a mere tenth the mass of the Milky Way’s central bulge.

(And yes, astronomy has confusing nomenclature. Don’t blame the messenger.)

Astronomers have found about 30 of these little pot-bellied galaxies, include M32, one of the Andromeda Galaxy’s galactic entourage. Most lie in clusters, and observers have found debris around some, suggesting that compact ellipticals were once larger but had their outer edges ripped from them by other galaxies. But a couple sulk off by themselves, making the tidal disruption theory problematic: if there’s nothing around to strip material off these galaxies, did they really shrink?

In the April 24th Science, Igor Chilingarian (Smithsonian Astrophysical Observatory and Moscow State University, Russia) and Ivan Zolotukhin (Moscow State University, Russia, and IRAP, France) significantly boost the number of compact ellipticals we know about, reporting their discovery of 195 of these objects. These galaxies exist in clusters (56), groups (128), and in isolation (11).

Given the galaxies’ motions and sizes, the authors suggest that interactions with two or more other galaxies (instead of just one) could sling these diminutive ellipticals into the cosmic outback. That would explain how galaxies created via tidal disruption are out in the sticks, where there aren’t many galaxies to interact with. The isolated compact ellipticals astronomers have found would therefore be runaway galaxies.

But astronomers need to check this theory with rigorous computer simulations — it’s by no means conclusive. Other researchers have suggested that isolated compact ellipticals might arise when dwarf galaxies merge. With no additional stuff nearby to feed on, the compact ellipticals would simply stop growing and never reach full size. This new, larger population of compact ellipticals will thus help astronomers explore their origin.


Reference: I. Chilingarian and I. Zolotukhin. “Isolated compact elliptical galaxies: Stellar systems that ran away.” Science. April 24, 2015.

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Categories: Astronomy Headlines

Celebrate Astronomy Day!

Thu, 04/23/2015 - 05:13

April 25th is Spring Astronomy Day, when hundreds of organizations worldwide host special family-oriented events to showcase the wonder and excitement of the night sky.

Grand Canyon Star Party 2013. National Park Service / Kristen M. Caldon

Grand Canyon Star Party 2013.
National Park Service / Kristen M Caldon

One day each spring and fall, astronomy clubs, planetariums, and other groups of sky lovers band together to share the wonders and excitement of astronomy with their communities. The theme of Astronomy Day is “Bringing Astronomy to the People,” and amateur astronomers and science fans the world over can hardly wait to share their excitement about the sky with the general public.

Doug Berger, then president of the Astronomical Association of Northern California, founded this annual event in 1973 as a way of drawing local attention to the science and the hobby through exhibits and activities at urban centers. Since then, the celebration has mushroomed in size and scope. Hundreds of astronomy clubs, observatories, museums, colleges, and planetariums worldwide now host special family-oriented Astronomy Day events and festivities, often with the assistance of the Astronomical League. Some organizations extend their activities over an entire week.


Astronomy Day has traditionally been celebrated between mid-April and mid-May, on the Saturday closest to the first-quarter Moon. In 2007, the Astronomical League began promoting an additional day in the autumn. In 2015, Spring Astronomy Day falls on April 25th. Fall Astronomy Day will be on September 19th, two days before the first-quarter Moon. However, local organizers often host events on other dates that better suit their needs, or to accommodate a special event like an eclipse, planetary alignment, or bright comet, so be sure and check their calendars.

Solar viewing at NEAF

Solar observing has become a regular fare at many Astronomy Day activities worldwide. Here attendees at Northeast Astronomy Forum & Telescope Show enjoy views of the Sun in hydrogen-alpha light.

Why Participate?

This event is a great way for your club to gain visibility in your community. Having the public look through telescopes and at your displays spreads interest in astronomy throughout the general public and might even attract new members to your club. It provides a platform for discussing light pollution — an issue that should concern everyone. Perhaps most important, Astronomy Day is great morale-booster for you and your fellow club members. It brings people together for a day of sharing their love of the sky with others.

If you don't belong to an astronomy club and want to find a local club or planetarium that might be hosting an Astronomy Day celebration, check out our directory of clubs, observatories, planetariums, and science museums from around the world.

More Information

To assist organizations and individuals in planning Astronomy Day programs, the Astronomical League and Sky & Telescope have prepared a free, fact-filled Astronomy Day Handbook. Written by David H. Levy and updated by Gary Tomlinson, the 76-page guide offers time-tested suggestions for conducting large and small endeavors. It also includes the rules and entry forms for the Astronomy Day Award, a prize co-sponsored by Sky & Telescope, the American Astronomical Society, and the Astronomical League, and given annually to the groups whose programs do the best job of "Bringing Astronomy to the People."

Grand Canyon National Park Star Party 2013. National Park Service / Michael Quinn

Grand Canyon National Park Star Party 2013.
National Park Service / Michael Quinn

The Astronomical League maintains the official Astronomy Day web page, which describes the event's background and where to find an Astronomy Day activity in your area. Additional listings can be found through the Night Sky Network.

Also available for printing and handing out is the Astronomical League's The ABCs of Stargazing sheet, which can help you explain the basics of our hobby to newcomers. And don't forget our ever-popular Good Outdoor Neighbor Lighting flyer, a clear, simple info sheet on light pollution and how anyone can minimize it.

Astronomy Day is deliberately planned for dark-sky viewing, but the easiest target for new converts to find is the Moon, so you might want to pick up a few Sky & Telescope Moon maps to help answer the questions you're sure to get about our nearest neighbor.

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Categories: Astronomy Headlines

Hubble Investigates Ghosts of Quasars Past

Wed, 04/22/2015 - 13:47

A galaxy-size blob of gas discovered eight years ago by a Dutch schoolteacher has galvanized the study of the spectral remains of once-bright quasars.

Hanny's Voorwerp

Hanny's Voorwerp, seen here in green south of spiral galaxy IC 2497, was a deep blue in the Galaxy Zoo image that van Arkel saw. The exact hue depends on image processing, but the color is unique. Nearly 200 Galaxy Zoo volunteers found 19 more of these so-called Voorwerpjes.
NASA / ESA / W. Keel

In 2007, a fuzzy blue blob earned a Dutch schoolteacher worldwide fame. As she sifted through image after image in the citizen-science project Galaxy Zoo, Hanny van Arkel spotted a smudge just south of the galaxy IC 2497. She had already clicked on to the next image, having classified the galaxy as a anti-clockwise spiral, when she thought to herself, “Wait, what was that?”

The smudge she discovered turned out to a galaxy-size reservoir of gas 16,000 light-years across. Intense radiation had stripped its oxygen atoms of their outer electrons, imbuing the gas with its distinctive hue (deep blue in some images, bright green in others, depending on the image processing).

The neighboring galaxy isn’t bright enough to have stripped the electrons — at least not in the present day. What van Arkel had spotted was the echo of a recent past, when the supermassive black hole at IC 2497’s center had powered a potent beacon of light, called a quasar.

Roughly 30,000 years ago, the quasar’s intense radiation had traveled from the galaxy’s core to the nearby cloud to blast the electrons off the cloud’s atoms. Sometime between then and now, the quasar faded away, leaving a normal-looking spiral galaxy with a dormant black hole at its center. The echo of light in the glowing cloud remains because the stripped electrons take a long time to find a new home in the sparse intergalactic environment.

Soon known as Hanny’s Voorwerp (Dutch for “Hanny’s Object”), the find galvanized a follow-up search for more so-called Voorwerpjes. Bill Keel (University of Alabama) led the charge of nearly 200 Galaxy Zoo volunteers as they hunted through Hubble Space Telescope images, searching for blobs with that distinctive color and offset by more than 33,000 light-years from the nearest galaxy.

Out of almost a million galaxy images, only 19 made the cut. Of these, eight clouds were echoing light from quasars that had faded from their former glory. These ghosts may share the untold story of how and why quasars turn off.

Light echoes

These eight light echoes jumped out of Galaxy Zoo data thanks to the distinctive green hue of the ionized gas, offset from the nearest galaxy by a minimum of 33,000 light-years.
NASA / ESA / W. Keel

Light Echoes of a Messy Past

To learn that story, Keel’s team first needed to understand where these glowing clouds come from. The authors found that the host galaxies of all eight faded quasars, most of which are in elliptical galaxies, show signs of recent or ongoing mergers. Some exhibit tidal tails left over from a cannibalized galaxy; others contain dusty disks warped by galactic encounters.

NGC 5972 and the ghost of quasars past

Hubble found green wisps of ionized gas extending out to 160,000 light-years around galaxy NGC 5972.
NASA / ESA / W. Keel

The lit-up reservoirs outside the galaxies are probably the gaseous remains of these mergers. For one, the glowing gas clouds are roughly in the same spot as the tidal debris from the collisions. For another, spectra show that the gas clouds are rotating, motion that’s likely leftover from the now-cannibalized galaxy.

Surprisingly, none of these gas-rich mergers appears to have triggered much, if any, star formation. In the original Hanny’s Voorwerp, a galaxy-scale wind from IC 2497 generated new stars in the nearest part of the glowing gas cloud, a scenario in keeping with general ideas of galaxy evolution. So Keel and his colleagues expected to find similar star formation triggered in these galaxy/cloud pairs.

But instead they found that galaxy-scale outflows, such as supernova-driven winds or winds/jets from the central black hole, don’t seem to play a large role in any of the objects. And there aren’t many stars forming near the tidal debris or in the host galaxies themselves.

Did the once-bright quasar quench any existing star formation? Keel is working on assembling another sample of faded quasars, this time in non-interacting galaxies, to help understand the mechanics of quasar radiation without the complicating influence of mergers. In the meantime, Keel and his colleagues plan to turn their focus from the host galaxies to the history of the faded quasars themselves, studying how and why the quasars faded.

Alluring beasts in and of themselves, quasars play a fascinating role in the evolution of the universe too. Find out more in our FREE Black Holes eBook.

The post Hubble Investigates Ghosts of Quasars Past appeared first on Sky & Telescope.

Categories: Astronomy Headlines

How to See All Six Apollo Moon Landing Sites

Wed, 04/22/2015 - 08:04

Walk in the astronauts' footsteps as you explore the places they visited in the heyday of Apollo program. Use these helpful maps to start you on your way.

Far away home

Apollo 17 astronaut Harrison Schmitt with the American flag. Earth glows blue 240,000 miles in the distance.
Credit: NASA

We all love dark moonless skies, but let's face it, the Moon's out two weeks a month. How can you ignore it? You've doubtless observed craters and mountain ranges and probed for volcanic features like rills and domes. But here and there among the nooks and crannies, you'll find six of the most remarkable locales on the Moon — the Apollo landing sites. They're the only places where humanity has achieved one of its oldest dreams and "touched the stars".

As you're well aware, no telescope on Earth can see the leftover descent stages of the Apollo Lunar Modules or anything else Apollo-related. Not even the Hubble Space Telescope can discern evidence of the Apollo landings. The laws of optics define its limits.

Hubble's 94.5-inch mirror has a resolution of 0.024″ in ultraviolet light, which translates to 141 feet (43 meters) at the Moon's distance. In visible light, it's 0.05″, or closer to 300 feet. Given that the largest piece of equipment left on the Moon after each mission was the 17.9-foot-high by 14-foot-wide Lunar Module, you can see the problem.

Did I say problem? No problem for NASA's Lunar Reconnaissance Orbiter (LRO), which can dip as low as 31 miles (50 km) from the lunar surface, close enough to image each landing site in remarkable detail.

Apollo locator and scenes

Six Apollo missions successfully landed on and departed from the Moon between July 1969 and December 1972. Top, clockwise: James Irwin salutes the flag at Hadley Rill; Harrison Schmitt collects rock samples in the Taurus-Littrow Valley; Buzz Aldrin's footprint in the lunar regolith; Charlie Duke placed a photo of his family on the Moon and took a picture of it; Edgar Mitchell photographs the desolate landscape of the Fra Mauro highlands; and Pete Conrad jiggles the Surveyor 3 probe to see how firmly it's situated.
NASA, collage by Bob King

LRO's orbital imagery and photos taken in situ by the Apollo astronauts will serve to illuminate our ramblings from one Apollo site to the next. All the landing sites lie on the near side of the Moon and were chosen to explore different geologic terrains. Astronauts bagged 842 pounds (382 kg) of Moon rocks, which represented everything from mare basalts to ancient highland rocks to impact-shattered rocks called breccias. Apollo 12 astronauts even found the first meteorite ever discovered on another world, the Bench Crater carbonaceous chondrite.

They're all still there

Photos of each of the six Apollo landing sites photographed from low orbit by NASA's Lunar Reconnaissance Orbiter. ALSEP stands for Apollo Lunar Surface Experiments Package. The astronauts' tracks as well as the rover and other items are plainly visible. Click for a large version.

With the Moon waxing this week and next, the advancing line of lunar sunrise will expose one site after another beginning with Apollo 17 in the Moon's eastern hemisphere and finishing with Apollos 12 and 14 in the western. To see each locale, a 4-inch or larger telescope magnifying 75× or higher will get the job done. But the larger the scope and higher the power, the closer you'll be able to pinpoint each landing site and better able to visualize the scene.

Below are the approximate times and current dates after New Moon when each landing locale first becomes fully illuminated by the Sun:

* Apollos 17 and 11: Six days past New (April 24)
* Apollo 16: Seven days, or First Quarter (April 25)
* Apollo 15: Eight days (April 26)
* Apollos 12 and 14: Ten days (April 28)

Five guideposts to six landing sites

All the landing sites can be found using these five prominent lunar craters. North is up in this view.
Credit: NASA/LRO

The base images for all the sites are photographs taken by the LRO. I encourage you to drop by the ACT-REACT QuickMap site, which features a zoomable lunar map of LRO photos that will practically take you down to the lunar surface. Click the "paper stack" icon and uncheck Sunlit Region to see a fully-illuminated Moon, no matter the current phase. Checking the Nomenclature box will bring up the names of craters, rills and many other features. More details about each of the LRO Apollo photos can be found here.

Following are maps for pinpointing each Apollo location. South is up, and clicking on the images will link you to higher resolution versions. Time to strap on your boots and follow in the footsteps of the first people to walk on the Moon.

First Apollo

Apollo 11 landed on July 20, 1969, on the relatively smooth and safe terrain of the Sea of Tranquility. For an extra challenge, see if you can spot the three craters named for the Apollo 11 astronauts just north of the landing site. They range from 2.9 miles (Armstrong) to 1.5 miles (Collins) across.

Apollo 12 meets Surveyor 3

Pete Conrad and Alan Bean achieved a pinpoint landing on Nov. 19, 1969, in the Ocean of Storms south of the grand rayed crater Copernicus, landing within walking distance of the Surveyor 3 probe.

Can you spot the golf balls?

Apollo 14 touched down on Feb. 5, 1971, in the Fra Mauro formation. Somewhere in the scene are two golf balls hit by Alan Shepard with a makeshift club he brought from Earth.

A Stroll along the rill

James Irwin and David Scott spent three days alongside Hadley Rille in the rugged Apennine Mountains after landing Apollo 15 on July 30, 1971. This was the first mission to use the Lunar Rover, greatly expanding the amount of ground the astronauts could cover.

In search of ancient rocks

Apollo 16 touched down in the lunar highlands on April 21, 1972, in the Cayley Formation, where astronauts John Young and Charles Duke hoped to find older Moon rocks than those previously found near the younger maria.

Final mission

Harrison Schmitt and Eugene Cernan landed the final Apollo mission in the Taurus-Littrow Valley on Dec. 11, 1972. The astronauts once again searched for ancient highland material. In the process, they broke a rear fender on the lunar rover and re-attached it using maps and duct tape.
Credit: NASA/LRO

Matching a "backwards" telescopic view to a standard view Moon map can be tricky. That's why we created the Sky & Telescope Mirror Image Field Map of the Moon.

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Observing Report: Revisiting the Herschel Sprint

Wed, 04/22/2015 - 05:59

Amateur astronomer Mark McCarthy makes another run at the Herschel Sprint

The night of April 16, 2015, I made my second attempt at a drift method Herschel Sprint. I made a few changes from my March 2015 attempt. I used a 20-inch f/5.25 telescope, so I should have every chance to see all the objects on the list. I used a zoom eyepiece which when set at 18mm yielded 148× and 0.3° true field of view (TFOV). I used HIP48413 (RA 9h 52m 59s, Dec 0° 00′ 13.6″) as my calibration star, as before. The time of its meridian transit, according to Stellarium, was 9:20:30 p.m. PDT. But, rather than using a clock and a list to follow each object’s right ascension, I pressed the “record” button on my digital recorder the moment the calibration star was at meridian and centered in the eyepiece. I hoped this would allow me to simply record my observations without removing my eye from the eyepiece; so long as I said “centered” when the object being described was centered in the eyepiece, the recording would give me a fairly accurate elapsed time which I could later compare to the object list and charts to confirm what I saw. Using my inclinometer to find the upper and lower limits of the sweep’s declination band, I used C-clamps to attach wood blocks to the altitude bearing on my telescope to restrict altitude movement within the band. I was thus freed from worrying about navigation and could concentrate on observing and describing, as Herschel could. All I had to do was gently, so as not to disturb the telescope’s collimation, bob the telescope up and down in an even tempo to cover all of the sky within the band.


Herschel discovered the barred spiral galaxy NGC 4448 in Coma Berenices on April 11, 1785.

I once again observed from the Fremont Peak Observatory Association’s site at Fremont Peak State Park (elevation 2700’), California. The temperature dropped into the 40s after dark and it was windy. Seeing was 5/7 and transparency 4/5; SQML was 20.60.

It’s very difficult for me to untangle my observations and report my results. I spent a good part of this weekend transcribing my recording and noting the elapsed time of each of my comments. When I review these times versus what the elapsed time of the Sprint objects would be from my calibration star, I have very few matches. NGC 3274 is a certain match: according to the Sprint list it would appear at 00:39:18 elapsed time. My comment at 00:39:14 on the recording is “close to center, there's a triangle of stars, between two at the base there’s cloudiness, a galaxy, E-W elongation” which closely matches what I find on the NGC/IC Project photograph and description. But few of the others have an obvious corresponding match.

One reason was the unevenness of my altitude movement tempo. Before starting I timed my calibration star’s transit across the eyepiece from east to west; it took 74 seconds. To cover the band completely I tried to move the telescope up in the band in 20 seconds, then down in 20 seconds, and so on. This should cover the band in altitude in thirds of eyepiece FOV. But the sky moves quickly through the eyepiece at that pace, leaving very little time to perceive and describe what one sees. Very often I could not keep that pace, or I might linger on an object just to make an observation of it, spoiling my timing and making me miss small swaths of sky, which incrementally added up to a lot of missed sky. Often I would see a galaxy just at the western edge of the FOV, having nearly missed it, and have just a few seconds to describe it. The swiftness of an object’s passage through the FOV is evidenced in the poor quality of my descriptions, which for the most part are brief and just describe the overall impression, and are not helpful to confirm the object from a photograph or another’s description later. As a result, most of my observations are unidentified.

Since my first attempt in March, I read Discoverers of the Universe by Michael A. Hoskin. In it I learned that William’s brother Alexander had fitted the telescope with a mechanism which would ring a bell when the telescope was at the top and bottom limits of a sweep’s declination band, to give William’s assistant, pulling on the ropes, cues when to raise or lower the telescope. I wondered whether William had the assistant use a metronome to help maintain an even tempo — William was a musician, after all. However, metronomes did not come into use until the early 19th century. In any case, a musician’s timing helps. In order to keep a smooth, even movement, I needed to grasp my UTA in both arms, in a hug, and move the telescope with my body, adjusting my head to keep my eye positioned — this became physically tiring as the night progressed.

From the book I also learned Herschel could move his telescope a small amount in azimuth and could track an object for about 15 minutes. This gave him more time to perceive and describe interesting objects. Also, Caroline did not rely on just a sidereal clock but primarily on Flamsteed’s catalogue (volume 3 of the Historia Coelestis Britannica). Caroline would list out the stars which would be in the path of that night’s sweep, and forewarn William of their coming; William would then describe the nebulae’s distance and position from these reference stars. I lacked this second set of eyes to help with navigation. As the night progressed I realized that my elapsed time would not be enough to help locate an object later; since many of the objects appeared on the edges of the FOV, my elapsed time would be many seconds off. So I tried to remark whether I was near the top or bottom of the band, and to remark on any double star, red star (which might be a carbon star), or pattern of stars which might give me more reference points when reviewing the charts later. This has been of some help so far, but my progress is slow.

In all I recorded 175 observations. The majority of these were not bright, easily seen galaxies, but faint objects which I decided to describe in case later I could confirm them as galaxies. There were a large number of NGC, IC, and MGC objects in the band of the sweep, so it’s possible I observed objects not on the Herschel Sprint list. I wanted to cover my bases by describing everything I had the slightest suspicion of being a galaxy. I separate the objects I observed into three categories:

High confidence: 56 objects were palpable hits, clearly visible as galaxies. Whether bright or faint, I was able to verbalize a complete description of the nucleus, core, halo, size, and position angle. I am in the process of identifying these on my charts.

Medium confidence: 62 objects I suspect are galaxies but I am not sure. My descriptions are typically “low surface brightness,” “dim patch,” “some glow with AV,” “small, faint.” My uncertainty comes from my lack of experience observing anything dimmer than a typical 11-12th apparent magnitude galaxy. These might be the usual fare for those used to observing faint objects; I am unfamiliar how they would appear in the eyepiece.

Low confidence: 57 objects are very uncertain. My descriptions are along the lines of “dim hazy star” or “mistiness.”  Too uncertain to have more than a slight suspicion they are galaxies. I’d need to find them on a chart to prove it to myself — and to gain more experience observing very faint objects to recognize them correctly.

It’s frustrating not to have more certainty in what I saw, and I will spend the next few weeks settling a final tally. On the one hand, I had the desire to bear witness and “prove” I saw the objects by identifying them. But on the other hand, through the night I permitted myself to have that feeling of discovery. I can hear the excitement in my voice during playback when an obvious galaxy comes into view, such as at elapsed time 1:09:30: “real pretty one, right near the top of the band, glowing core, stellar nucleus with AV, elongated NE-SW, pretty one. Large. Spanning 1/3 FOV, fat, 3:2  a nice fat one,” or at 2:45:39: “big, beautiful long one, bright core, you can see a dark lane, it's so long, oh my god and it's nearly out of FOV, I just barely got it. That's a nice one. 30 seconds too late.”

And that sums up the experience of visual astronomy for me. I feel the melancholy thrill of beauty fleetingly held; the intellectual astonishment trying to understand our true relation to the universe; the challenge of describing it to others so they may share. That Herschel was able to do these things so successfully speaks to his greatness. As I remarked to another observer, when doing the Herschel Sprint, you know you are in the presence of the Master.

— Mark McCarthy, Fremont, California, April 16, 2015

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Penjelajah Langit

Wed, 04/22/2015 - 05:55

Penjelajah Langit


Perum Teratai Asri F 11, RT 03, Pandeyan, Sewon Bantul
Yogyakarta 55283


Eko Hadi G








Penjelajah Langit is an astronomy club that was born from KafeAstronomi. On its way, Penjelajah Langit under the auspices and full responsibility from KafeAstronomi. Penjelajah Langit was created to be a facilitator, astronomy educator and a education division KafeAstronomi which have the main task is to realize the vision of Bringing Astronomy to the people.

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Categories: Astronomy Headlines


Wed, 04/22/2015 - 04:49

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One Galaxy Among Billions

Wed, 04/22/2015 - 04:48

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NGC6888 in Narrowband

Wed, 04/22/2015 - 04:47

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Lyrid Meteor Shower in 2015

Tue, 04/21/2015 - 13:45

Although typically weak, the annual Lyrid display will benefit from moonless skies. This year's peak, late on April 22nd, favors Europe over North America.

This month’s Lyrid meteor shower isn't one of the year's strongest displays, but the Moon is only a thin, waxing crescent and so won't offer much competition. As with January’s Quadrantids, the Lyrids put on a fairly brief performance, and this year the predicted peak (23:00 UT on April 22nd) favors those in Europe but comes too early for North Americans. (Those of you on the East Coast might fare a little better than skywatchers in the Far West.)

Radiant of the Lyrid meteor shower

The Lyrid shower's radiant rises as early as 10 p.m., but you'll likely see more meteors once it climbs much higher in the sky before dawn. Even then, don't expect to see more than a few per hour radiating from a point near the Lyra-Hercules border.
Sky & Telescope diagram

The Lyrid meteors appear to radiate from a location near the Hercules-Lyra border, which is high in the sky from about 11 p.m. until dawn.

To be honest, you’re likely to see no more than a few meteors per hour. At its best, this shower’s typical zenithal hourly rate (the number you could count under a very dark sky with Lyra near the zenith) is about 15 or 20. That’s enough to be clearly a shower if you’re watching and counting for an hour or more. But it’s a far cry from the 90 to 120 per hour expected on the moonless late nights coming up for this August’s Perseids and December’s Geminids.

The Lyrid meteor shower has been observed for more than 2,000 years; Chinese records say "stars fell like rain" during the shower of 687 BC. But in recent times the Lyrids have generally been weak, though at intervals of about 12 years the shower occasionally delivers up to 10 times more meteors than normal. The Lyrids did show a brief surge to a ZHR of 90 in 1982, but a spike like that hasn’t been reported in any of the appearances since.

Such predictions are uncertain, because the orbital periods of the Lyrid dust particles and Comet Thatcher (C/1861 G1), which shed them, are about 400 years. It’s likely that the gravitational attraction of Jupiter perturbs these particles into separate, narrow concentrations within the overall Lyrid stream. Whenever Earth plows through one of them, we get quite a show. Dynamicists predict that major outburst might occur in 2040.

My S&T colleague Alan MacRobert points out that the half year from January 7th to July 7th has remarkably few meteor showers compared to the other half of the year, for no known reason but chance. Only the April Lyrids and the May Eta Aquariids make it onto lists of major showers, while nine or ten rich meteoroid streams intersect the other side of Earth’s orbit.

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Categories: Astronomy Headlines

Inside the June 2015 Issue

Tue, 04/21/2015 - 09:18

June 2015 Sky & Telescope Experiencing the Ethereal

The universe is a vast place largely beyond human comprehension. Yet even if we can't really understand the concept of 1 billion light-years, we can still experience the universe with our limited capabilities — whether that be through the spellbinding images from the Hubble Space Telescope, featured in our cover story celebrating Hubble's 25th anniversary, or through the low-tech but just as captivating solargraphs that capture the motions of the Sun. We experience the universe in an even more visceral way when we observe through our eyes and telescopes, for example, by charting a galaxy cluster more than 1 billion light-years a way. Or, as Sky & Telescope readers have done for decades, by precisely measuring crater timings during a lunar eclipse. As we enter into summer, Saturn, the Moon, and the stars of the Serpens Caput beckon, and the universe awaits.

Feature Articles eagle nebula in visible and infrared

Hubble images the iconic Pillars of Creation in visible-light and near-infrared in celebration of the telescope's 25th anniversary.
NASA / ESA / Hubble Heritage Team (STScI / AURA)

How Hubble Changed the Face of Astronomy
The first of the "Great Observatory" space telescopes transformed what astronomers knew — and didn't know — about the universe.
By Govert Schilling

Measuring Earth's Shadow: 170 Years of Crater Timings
A very long-running lunar eclipse project reaches fruition.
By Roger Sinnott

The Science of Jules Verne's Fiction
Nineteenth-century science and technology shaped two classic tales of imaginary spaceflight.
By Dean Regas

Catch the Sun in a Can
Here's a fun astrophotography project that anyone can do.
By Maciej Zapiór

Abell Galaxy Cluster 2065
Follow this observer's guide to the Corona Borealis galaxy cluster.
By Howard Banich

Beyond the Printed Page ring system around J1407b

Artist's conception of super-ring system surrounding the exoplanet J1407b.
Ron Miller

Super-Saturn Rings by John Bochanski
Watch a video showing the complicated light pattern that revealed rings around an extrasolar planet.

See Saturn and Its Moons
Saturn is closest in May and June, so take the opportunity for a closer look with our mobile app.

Celebrate Hubble
Find images, activities, and events near you to mark Hubble's 25th anniversary.

Lunar Librations by Sean Walker
Librations and other lunar data for June 2015.

ALSO IN THIS ISSUE Sharp view of Saturn, June 1, 2014

Christopher Go took this extraordinarily sharp image of Saturn during excellent seeing on June 1, 2014.

They Meet At Last
Jupiter and Venus come together in an epic conjunction.
By Fred Schaaf

Saturn At Its Best
Saturn is closest in May and June, with its rings tipped wide open.
By Alan MacRobert

A Heaven Full of Stars
Split the Serpent's star systems into their colorful components.
By Sue French

Table of Contents
See what else June's issue has to offer.

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