Astronomy & Science

Celestial Harvest Showpiece Roster

Sky&Telescope -

Download a handy list of 300 of the best deep-sky objects to explore with telescopes from 2- to 14-inches in aperture.

Albireo
Houssem Ksontini

Downloadable from this post (Celestial Showpiece Roster — .xlsx file) are 300 of the finest deep-sky treasures for viewing and exploration with telescopes from 2- to 14-inches in aperture. Nearly all of them can be seen in the smallest of glasses, and many even in binoculars. Arranged in alphabetical order by constellation (which makes it more convenient to pick out objects for a given night’s observations than one ordered by coordinates), it features brief descriptions of each entry. Primary data sources were Sky Catalogue 2000.0 and the Washington Double Star Catalog.

Constellation (CON) abbreviations are the official three-letter designations adopted by the International Astronomical Union. Right Ascension (RA) in hours and minutes, and Declination (DEC) in degrees and minutes, are given for the current standard Epoch 2000.0. Other headings are the class or type of object (TYPE)*, apparent visual magnitude/s (MAG/S) and angular size or separation (SIZE/SEP) in arc-minutes or arc-seconds. (Position angles for double stars are not given due to the confusion resulting from the common use of star diagonals with refracting and compound telescopes, producing mirror-reversed images of the sky.

Observers desiring the latest values of these as well as component separations should consult the Washington Double Star Catalog on-line at http://ad.usno.navy.mil/wds/.) Approximate distance in light-years (LY) is also given in many cases. Double and multiple stars dominate this roster due to their great profusion in the sky and also their easy visibility on all but the worst of nights. This list extends down to –45 degrees Declination, covering that 3/4ths of the entire heavens visible from mid-northern latitudes. (Two “must see” showpieces actually lie slightly below this limit.) *Type key: SS = First-Magnitude/Highly-Tinted &/or Variable Single Star, DS = Double or Multiple Star, AS = Association or Asterism, OC = Open Cluster, GC = Globular Cluster, DN = Diffuse Nebula, PN = Planetary Nebula, SR = Supernova Remnant, GX = Galaxy. (Also: MW = Milky Way under remarks.)

This list was compiled based on my book Celestial Harvest: 300-Plus Showpieces of the Heavens for Telescope Viewing & Contemplation (Dover). The number shown in ( ) following each object indicates how many of 21 classic and modern deep-sky showpiece lists include it. Bolded entries = best of the finest!

Download the Celestial Showpiece Roster — .xlsx file.

The post Celestial Harvest Showpiece Roster appeared first on Sky & Telescope.

This Week’s Sky at a Glance, October 20 – 28

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Cassiopeia and Double Cluster. Akira Fujii photo.

This week, the big W of Cassiopeia stands almost on end high in the northeast. Below it, binoculars will show the Double Cluster of Perseus.

Friday, October 20

• The modest Orionid meteor shower continues in the early-morning hours for the next couple of nights. The apparent radiant point of the shower is near Orion's Club, low in the east after midnight and high in the south by the beginning of dawn. The morning sky is free of moonlight. See Orionid Meteors Max Out Sunday Morning.

• Look for Capella sparkling low in the northeast after dinnertime this week. Then find the little Pleiades cluster to its right by about three fists at arm's length. They rise higher as evening grows late, harbingers of the cold months to come.

Upper right of Capella, and upper left of the Pleiades, the stars of Perseus stand astride the Milky Way. To the upper left of Perseus, the Milky Way runs through Cassiopeia.

Saturday, October 21

• After dark, spot the W of Cassiopeia high in the northeast. It's standing almost on end. The third segment of the W, counting down from the top, points almost straight down. Extend that segment twice as far down as its own length, and you're at the Double Cluster in Perseus. This pair of star-swarms is dimly apparent to the unaided eye in a dark sky (use averted vision), and it's visible from almost anywhere with binoculars. It's a lovely sight in telescopes.

Moon and Saturn at dusk, Oct. 22-24, 2017

Newly returned to the evening sky, the waxing crescent Moon passes low Antares (use binoculars!) and then Saturn in the southwestern twilight.

Sunday, October 22

• This is the time of year when the Big Dipper lies down horizontal low in the north-northwest after dark. How low? The farther south you are, the lower. Seen from 40° north (New York, Denver) even its bottom stars twinkle nearly ten degrees high. But at Miami (26° N) the entire Dipper skims along out of sight just below the northern horizon.

Monday, October 23

• Look low in the southwest in late twilight for Saturn glowing about 7° left of the waxing crescent Moon (as seen from North America), as shown here.

Tuesday, October 24

• Now, at dusk, Saturn appears about 6° to the lower right of the thickening Moon, as shown here.

Wednesday, October 25

The Ghost of Summer Suns. Halloween is approaching, and this means that Arcturus, the star sparkling low in the west-northwest in twilight, is taking on its role as "the Ghost of Summer Suns."

What does this mean? For several days centered on October 25th every year, Arcturus occupies a special place above your local landscape. It closely marks the spot where the Sun stood at the same time, by the clock, during hot June and July — in broad daylight, of course. So, as Halloween approaches every year, you can see Arcturus as the chilly ghost of the departed summer Sun.

Thursday, October 26

• Draw a line from Altair, the brightest star very high above the Moon in the southwest after dark, to the right to brighter Vega, very high in the west. Continue the line half as far onward, and you hit the Lozenge: the pointy-nosed head of Draco, the Dragon. Its brightest star is orange Eltanin, the tip of the Dragon's nose, which points toward Vega.

Friday, October 27

• First-quarter Moon (exactly first-quarter at 6:22 p.m. Eastern Daylight Time). At nightfall, you'll find Altair shining about 30° (three fists at arm's length) to the Moon's upper right.

Much closer to the Moon's upper right, by only about 6°, are 3rd-magnitude Alpha and Beta Capricorni. Alpha is the upper one. Can you resolve Alpha into a tiny twin pair with your unaided eyes? Binoculars make it easy — and should also resolve Beta, another wide double, although its components are somewhat closer and very unequal.

Saturday, October 28

• Now Altair appears a little farther to the Moon's upper right after dark. Just upper right of Altair, by a finger-width at arm's length, is orange Tarazed. It looks like Altair's little sidekick, but it's actually a much bigger and brighter star far in the background. Altair is 17 light-years away. Tarazed is about 360 light-years away and 100 times as luminous.

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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.

Pocket Sky Atlas, jumbo edition

The Pocket Sky Atlas plots 30,796 stars to magnitude 7.6, and hundreds of telescopic galaxies, star clusters, and nebulae among them. Shown above is the Jumbo Edition for easier reading in the night. Larger view. Sample chart.

Once you get a telescope, to put it to good use you'll need a detailed, large-scale sky atlas (set of charts). The basic standard is the Pocket Sky Atlas (in either the original or Jumbo Edition), which shows stars to magnitude 7.6.

Next up is the larger and deeper Sky Atlas 2000.0, plotting stars to magnitude 8.5; nearly three times as many. The next up, once you know your way around, is 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, or the bigger Night Sky Observer's Guide by Kepple and Sanner.

Can a computerized telescope replace charts? Not for beginners, I don't think, and not on mounts and tripods that are less than top-quality mechanically (meaning heavy and expensive). And as Terence Dickinson and Alan Dyer say in their Backyard Astronomer's Guide, "A full appreciation of the universe cannot come without developing the skills to find things in the sky and understanding how the sky works. This knowledge comes only by spending time under the stars with star maps in hand."

This Week's Planet Roundup

Mercury is hidden in the glare of the Sun.

Venus (magnitude –3.9) rises around the beginning of dawn and shines very low due east as dawn brightens.

Mars (magnitude +1.8, only 1/200 as bright as Venus) is higher in the dawn, to the upper right of Venus and widening. Their separation grows from 10° on October 21st to 14° by the 28th. Venus is slowly getting lower, Mars higher.

Jupiter is out of sight, passing through conjunction behind the Sun.

Saturn (magnitude +0.5, in southern Ophiuchus) glows low in the southwest at dusk.

Uranus (magnitude 5.7, in Pisces) and Neptune (magnitude 7.8, in Aquarius) are well up after dark in the east and southeast, respectively. Use our finder charts online or in the October Sky & Telescope, page 50.

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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, GMT, or Z time) 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

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"Objective reality exists. Facts are often determinable. Vaccines save lives. Carbon dioxide warms the globe. Bacteria evolve to thwart antibiotics, because evolution. Science and reason are not fake, are not a political conspiracy. They are how we discover reality. Civilization's survival depends on our ability, and willingness, to use them."
— Alan MacRobert, your Sky at a Glance editor

______________________

"Facts are stubborn things."
— John Adams, 1770

 

The post This Week’s Sky at a Glance, October 20 – 28 appeared first on Sky & Telescope.

New High-End Search for Lunar Impacts

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A professional observatory in Greece has begun recording flashes created when bits of interplanetary debris strike the Moon.

The Moon's battered face bears witness to the countless times something has slammed into the lunar surface, and new craters (albeit very small ones) form all the time. Even these mini-collisions occur at 20 km (12 miles) per second, while the very fastest are 70 km/s. If the chunk of debris has a mass of at least a few tens of grams, it creates a momentary white-hot flash — and if that occurs somewhere on the Moon's night side, it's an observable event.

Lunar flashes seen by NELIOTA project

So far the NELIOTA project has captured 22 impacts on the Moon. Colors indicate the estimated temperature of each strike, from 1,770 K (dull red) to 3,730 K (white).
ESA / Chrysa Avdellidou

We have front-row seats for these crash landings, but they're rarely seen. Over the past 20 years only a handful of lucky telescopic observers on Earth have spotted one inadvertently.

In 2005, a team from NASA's Marshall Space Flight Center started routine monitoring of the lunar disk using a network of 14-inch telescopes, particularly during annual meteor showers such as the Perseids and Geminids, and it's captured hundreds of flashes to date. Other monitoring efforts are MIDAS, operating in Spain, and ILIAD in Morocco.

Recently a new player has upped the scientific stakes. Since February, European astronomers have been staring at the lunar night using the 1.2-meter Kryoneri telescope on Peloponnese in Greece. The 22-month effort, called NELIOTA, records strikes down to 12th magnitude — far fainter than other programs can achieve.

Lunar impact flash

The NELIOTA project records about a quarter of the lunar disk. Here an impact flash (right edge below center) punctuates the lunar night.
NELIOTA project

At this week's meeting of the AAS's Division for Planetary Sciences in Provo, Utah, researcher Chrysa Avdellidou (European Space Agency) reported that to date the system has captured 22 flashes. That's one impact per 1.8 hours of observing, compared to one per 2.8 hours for the NASA system.

The power of NELIOTA, apart from the telescope's large aperture, lies in using a beam-splitter to feed a 17-by-14-arcminute field of view to two high-frame-rate video cameras simultaneously. One camera records the lunar night in red light (R band, 641 nm) and the other in the near infrared (I band, 798 nm).

This combination captures longer events, lasting from 43 to 182 milliseconds, because the collision sites remain hot after the visible-light flash has faded from view. "You can watch the cooling of each impact plume," Avdellidou says.

Moreover, the two wavelengths provide a way to extract each impact's temperature and an estimate for the colliding object's mass.

But such calculations are tricky — partly because there's no way to know exactly how fast these interplanetary bullets are striking the Moon and partly because the amount of kinetic energy that goes into creating the flash (its luminous efficiency) is guesswork.

Composite lunar flash

A sequence of frames, taken every 33 milliseconds (left to right), shows how a lunar impact flash disappears quickly in visible light (top pair) but lingers longer when recorded in near-infrared light.
NELIOTA project

So far, the flashes have varied from 1,770 to 3,730 Kelvins, a range that fits theoretical predictions well. Avdellidou isn't convinced that these blackbody temperatures are telling the whole story, however. So she wants to conduct a series of hypervelocity laboratory experiments in simulated lunar materials to see how the target's composition affects the intensity and duration of each lunar flash.

In the meantime, she's using mapping data from NASA's Lunar Reconnaissance Orbiter to try to determine the composition of each impact site. This spacecraft is also very good at spotting fresh impacts on the Moon. So, with luck, LRO scientists can use NELIOTA's high-quality images to track down where some of the larger strikes have occurred — the "smoking gun" that would provide crucial links between an impactor's kinetic energy and the brightness of its flash.

The post New High-End Search for Lunar Impacts appeared first on Sky & Telescope.

Orionid Meteors Max Out Sunday, Zodiacal Light Returns

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See what cosmic dust can do! Head outside this weekend for the peak of the Orionid meteor shower and an eyeful of zodiacal light.

How to See Orionid Meteors

The Orionid meteor shower peaks before dawn on October 22nd. The radiant is located northeastern Orion his upraised club.

It's all about the dust. Something that most people consider a nuisance or even a danger plays a crucial role in so many universal processes. Without it, there'd be no planets and no us, since dust is required to build these things. Dust provides the nuclei upon which water vapor condenses to form rain and clouds, and by extension, rainbows. No dust, no rainbows.

Comet tails? Dust. Meteor showers? Dust again. This week, the wasteful ways of Comet Halley will literally come to light as particles shed by the comet from coma and tail tear through the upper atmosphere. Earth's orbit intersects that of the famous comet twice a year, first in early May to bring the Eta Aquariid meteor shower, then again in the third week of October to fire up the Orionids.

The shower's expected to peak on Sunday morning, October 22nd. For a couple days before and after, rates will be around 10 per hour, but at maximum, we can expect up to 25 dusty darts per hour to shoot from Orion's upraised club under dark skies. No worries about the Moon, either, which sets in the evening sky long before the radiant rises.

Orionids are swift, striking the atmosphere at 238,000 km/hour, a combination of the stream's speed and Earth's orbital velocity of 108,000 km/hour — the nightside of the planet faces directly into the shower in the early morning hours so we get bonked head on. Orionid meteors can zip across the sky so fast, I've done double-takes wondering if what I just saw was a meteor or not.

Meteors start as meteoroids, solid particles in space in orbit about the Sun. They range in size from grains of sand to small pebbles and generally weight less than a gram or two. But what they lack in mass, they make up for in speed.

A bit of Halley returns early

An Orionid meteor flashes above Bellatrix in October 2014.
Bob King

Much of the kinetic energy possessed by a moving meteoroid is converted into heat and light when it strikes the air between 80 and 120 km above our heads. Air molecules slam into and excite atoms in the particle, while the particle's extreme speed excites molecules in the surrounding air. The clash pumps the electrons in both materials into higher energy states, but only briefly. A moment later they return to their previous "relaxed" states,  launching packets of light (photons) of different colors in the process. We see that this all as a bright streak or "shooting star." A blue-green meteor betrays the dust's excited magnesium, an orange one, sodium.

Most meteor showers produce occasional meteors that leave a wake or train that can last for many seconds. They're caused by free electrons sprung loose from their comfy atomic homes to wend their way back to their parent ions for a luminous reunion. Every meteor is another example of how the finger of the cosmos touches Earth. Let there be light.

Use the scroll and left button on your mouse to explore this interactive graphic of the Orionid meteor shower.
Peter Jenniskens / Ian Webster

While the radiant, the point in the sky from which the Orionids appear to stream, is up by midnight, you'll get the best view of the shower when Orion stands tall in the southeastern sky between 2:00 and 5:30 a.m. Meridian crossing occurs at 5 a.m. local time. Plan to spend an hour or more with the shower to see a good assortment of meteors. I don a warm coat and lay out on sleeping bag on the deck or driveway in a state of relaxed awareness, ready for whatever might come.

As always, sporadic meteors are part of the mix. These "strays" pepper the sky at the rate of 4–8 meteors per hour toward dawn and are easily parsed from shower meteors by following their trails backwards — if they don't point to the radiant, they're pretenders.

Click and Forget About It

An intervalometer makes meteor photography easy and greatly improves your chances of catching one.
Bob King

If you have a camera and tripod, see if you can capture an Orionid or two with a time exposure. I use a 20-mm focal length lens set to f/2.8 (wide-open aperture), ISO 1600, and 30-second exposures. You can use your finger to press the shutter button or purchase an inexpensive intervalometer on eBay or Amazon, or at your local camera store, that will automatically take pictures at set intervals, thereby freeing you up to relax and watch meteors. Point the camera off to one side of the radiant, or for something more scenic, include the shower's namesake constellation in the photo. One bit of advice: regularly check your front lens element. In cool, damp conditions it can fog up in as little as a half hour. A quick blast from a hair dryer will take care of the problem.

If you plan to watch the shower, stay up a little longer into early twilight for yet another manifestation of the beauty of dust — the zodiacal light. The light has two seasons, dusk in spring and dawn in autumn. If you have a dark eastern sky and face that direction about two hours before sunrise, you'll notice a big cone of diffuse light, broad at the base and tapering along its length. The soft, glowing nature of the light resembles that of the Milky Way. But while the Milky Way’s appearance results from the combined light of billions of distant suns, the zodiacal light originates from sunlight scattered off quadrillions (at least!) of tiny, dust-mote sized comet grains and bits of asteroid debris.

Dust Meets Dust

An early Orionid meteor streaks across the zodiacal light Wednesday morning, October 18th, at the start of dawn. Venus reflects off Lake Superior at bottom. Under dark skies the light cone stands about 5–6 outstretched fists (50–60°) tall and about 3 fists, or 30°, wide. Yes, it's big! 
Bob King

The dust nearest the Sun is lit brightest, hence the bright and broad base of the cone. The farther up and away you look from the Sun, the less intense the scattered light and the fainter the cone becomes. Though visible well before dawn, I've found the zodiacal light most impressive at the very start of twilight or about 1 hour 45 minutes before sunup.

Like you, I'm hoping for clear skies this weekend. My wish, as always, is to see more of what dust can do before I'm forced to bite it.

The post Orionid Meteors Max Out Sunday, Zodiacal Light Returns appeared first on Sky & Telescope.

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