Astronomy & Science

Happy 30th Birthday, Supernova 1987A

Sky&Telescope -

Supernova 1987A remnant and rings, wide field

At center is the ongoing three-ring circus of the Supernova 1987A remnant, as recently imaged by Hubble. The two bright stars superposed on it are unrelated foreground or background objects.
NASA / ESA / R. Kirshner / P. Challis

The first naked-eye supernova since the invention of the telescope lit up the global astronomy world on the morning of February 23, 1987, as news spread by phone and teletype. Supernova 1987A in the Large Magellanic Cloud eventually reached magnitude 2.9, before beginning a long fade and a cascade of unexpected developments that continues to this day. We published a full recap in the February Sky & Telescope, page 36.

Here's a video that, obviously, we couldn't print! On Friday (February 24th) NASA and the European Space Agency released this animation of the evolving supernova remnant, as seen in 23 years of Hubble Space Telescope images:

Starting in 1994, we see the exploded star's central debris cloud fade and expand into an irregular shape, inside a bright red ring of stationary hydrogen gas. The ring, a light-year across, took shape thousands of years earlier from material expelled from the aging star as it neared the end of its life. We see blobs in the ring light up as the outermost shock wave first strikes them starting in the mid- and late 1990s. The blobs remain lit as they shrink back and erode under the onslaught. Eventually the ring will be blown away completely.

The visual appearance, of course, just scratches the surface of the intricate events that astronomers have deduced by spectroscopy and imaging at wavelengths from radio to X-rays — not to mention the neutrinos and the initial ultraviolet flare from the explosion's early seconds and hours. The story is far from over!

Here's the press release from the ESA, with more images and a 3-D animation. Here's NASA's version, with more explanatory material. And here's from the National Radio Astronomy Observatory.

The post Happy 30th Birthday, Supernova 1987A appeared first on Sky & Telescope.

This Week’s Sky at a Glance, February 24 – March 4

Sky&Telescope -

Canis Major, with Sirius

When Sirius shines high in the south, straight below it by 4° is the binocular star cluster M41, appearing small and compact in this wide-field view. This scene spans almost all of Canis Major.
Akira Fujii

Friday, February 24

• Sirius blazes high in the south on the meridian by about 8 or 9 p.m. now. Using binoculars, examine the spot 4° south of Sirius (directly below it when on the meridian). Four degrees is somewhat less than the width of a typical binocular's field of view. Can you see a dim little patch of speckly gray haze? It shows especially well in the photo here. That's the open star cluster M41, about 2,200 light-years away. Sirius, by comparison, is only 8.6 light-years away.

Saturday, February 25

• Have you ever seen Canopus, the second-brightest star after Sirius? In one of the many interesting coincidences that devoted skywatchers know about, Canopus lies almost due south of Sirius: by 36°. That's far enough south that it never appears above your horizon unless you're below latitude 37° N (southern Virginia, southern Missouri, central California). And there, you'll need a very flat south horizon. Canopus crosses due south just 21 minutes before Sirius does.

When to look? Canopus is precisely due south when Beta Canis Majoris — Mirzam the Announcer, the star about three finger-widths to the right of Sirius — is at its highest point due south (roughly 8:00 p.m. now, depending on how far east or west you are in your time zone). Look straight down from Mirzam then. Mirzam is the brightest star to the right of Sirius in the photo above.

Sunday, February 26

• Mars and Uranus are in conjunction this evening, 0.6° apart (as seen around the time of nightfall for the Americas). Outdoors, spot Mars to the upper left of Venus blazing in the west. Mars is magnitude 1.3; Uranus is only one-seventieth as bright at magnitude 5.9; you'll need at least binoculars. You'll find Uranus to Mars's left or upper left. They'll both fit in a telescope's low-power field of view. Nothing else that close to Mars is that bright.

• Look east after dark this week for the constellation Leo already climbing up the sky. Its brightest star is Regulus, and the Sickle of Leo extends upper left from there. As the saying goes, Leo announces spring — or at least the approach of spring.

• New Moon (exact at 9:58 a.m. EST). An annular eclipse of the Sun crosses parts of southernmost South America, the South Atlantic, and east-central Africa. Much larger areas of South America and Africa get a partial eclipse. See February 26th’s Annular Solar Eclipse.

Moon with Venus and Mars, Feb. 28 - March 2, 2017

The waxing crescent Moon passes left of Venus and Mars. (The Moon is alwats shown here three times its actual apparent size. The blue 10° scale is about the size of your fist held at arm's length).

Monday, February 27

• Can you catch the thin crescent Moon far below Venus after sunset, as shown here? The best view may be more like 30 minutes after sunset. The Moon is only about 1½ days old at the time of dusk in the Americas. Binoculars will help find it in a bright sky.

Tuesday, February 28

• Now the thickening Moon in twilight forms a roughly fist-sized triangle with bright Venus and fainter Mars, as shown here.

Wednesday, March 1

• The Moon again hangs in the west at dusk, with Venus now about 15° to its lower right. As twilight deepens, look for Mars appearing about 5° to the Moon's right. After dark, can you still identify 6th-magnitude Uranus, now 2.1° below Mars? Uranus appears distinctly nonstellar at medium power in a telescope.

• Algol is at minimum brightness, magnitude 3.4 instead of its usual 2.1, for a couple hours centered on 6:28 p.m. EST. It takes several more hours to rebrighten. Comparison-star chart, with star magnitudes given to the nearest tenth.

Thursday, March 2

• The Moon, Mars, and Venus form a diagonal line in the west at nightfall.

• This is the time of year when Orion stands straight upright due south as the stars come out. Later in the evening, and later in the month, he begins his long tilt down toward the west.

• Certain deep-sky objects contain secret surprises within or near them. Get out your telescope and sky atlas for a go at Bob King's eight Hidden Gems in Common Deep-Sky Objects now in evening view.

Friday, March 3

• The Moon hangs below Aldebaran, the Hyades, and the Pleiades in the west this evening. But get ready for tomorrow night, when. . . .

Saturday, March 4

• The dark limb of the first-quarter Moon occults (crosses over) orange Aldebaran for viewers in most of the contiguous United States, Mexico, and Central America. We're calling this the best lunar occultation of 2017. See the March Sky & Telescope, page 48. Several fainter Hyades stars will also be occulted.

Get world maps and local predictions for the occultations of Aldebaran and three Hyades stars. (The UT dates are either March 4th or 5th).

In addition, the International Occultation Timing Association has set up a special web page for the Aldebaran graze, with fine-scale Google Maps of the northern graze line from Connecticut across the Great Lakes to Vancouver.

_________________________

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 — which may sound like a lot, but it's less than one per square degree on the sky. Also plotted are many hundreds of telescopic galaxies, star clusters, and nebulae. Shown above is the new Jumbo Edition for easier reading in the night. Click image for larger view.

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 Jupiter and Spica in early dawn, late Feb. 2017

All this week as dawn begins to brighten, Jupiter and Spica shine over the four-star pattern of Corvus, the Crow.

Mercury is hidden in the glare of the Sun.

Venus (magnitude –4.7, in Pisces) dazzles in the west during twilight, then lower in the west after dark. It starts dropping rapidly now from week to week; its distance from much-fainter Mars, to its upper left, increases this week from 10° to 14°.

In a telescope Venus is a striking crescent, thinning and enlarging. It's now about 46 arcseconds from cusp to cusp and 18% sunlit. It will continue to sink, expand, and wane in phase until inferior conjunction on March 25th.

Venus in a telescope is least glary, and steadiest and highest, when viewed in bright twilight. So get your scope on it as soon as you can see it naked-eye, even before sunset.

Mars (magnitude +1.3) is the faint "star" upper left of Venus. They widen from 10° to 14° apart this week. In a telescope Mars is just a tiny fuzzblob 4.6 arcseconds across.

Jupiter on Feb. 23, 2017

Jupiter on February 23rd, with bright Io casting its shadow across the planet's face. Damian Peach in the UK took this image remotely with a 1-meter telescope in Chile. "Note the dark spot in the northern half of the Great Red Spot," he writes. The usual extra-red marking in the middle of the Great Red Spot also shows well. North is up.

Jupiter (magnitude –2.3, in Virgo) rises around 9 p.m. and is high by 11 or midnight. Spica dangles 4° lower right of it after they rise, more directly below it in the early-morning hours, and lower left of it in early dawn as shown above. Jupiter is creamy white; Spica is an icier shade of white with a trace of blue (once it's fairly high).

In a telescope Jupiter is 42 arcseconds across its equator, nearly the 44 arcseconds it will attain in the weeks around its April 7th opposition.

Saturn (magnitude +0.5, at the Ophiuchus-Sagittarius border) rises in the early morning hours and glows in the southeast before and during dawn. In early dawn, redder Antares (magnitude +1.0) twinkles 18° to Saturn's right.

Uranus (magnitude 5.9, in Pisces) passes Mars this week. The two planets appear closest, 0.6° apart, on the evening of February 26th, as told for that date above. Finder chart showing Uranus among its background stars (without Mars).

Neptune is hidden behind the glare of the Sun.

__________________________

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 Standard Time (EST) is Universal Time (UT, UTC, or GMT) minus 5 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

"Objective reality exists. Facts are often determinable. Science and reason are no political conspiracy; they are how we discover objective reality. Civilization's survival depends on our ability, and willingness, to do this."
— Alan MacRobert, your Sky at a Glance editor

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

March For Science on April 22nd, to “champion publicly funded and publicly communicated science as a pillar of human freedom and prosperity.”

 

The post This Week’s Sky at a Glance, February 24 – March 4 appeared first on Sky & Telescope.

February 26th’s Annular Solar Eclipse

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Die-hard eclipse chasers have journeyed to the Southern Hemisphere to catch a short and dramatically thin "ring" eclipse of the Sun.

Path of February 2017 annular eclipse

This month's annular solar eclipse is a far-southern event. Red lines show the moment of mid-eclipse in Universal Time; blue lines show the maximum fraction of the Sun's diameter covered by the Moon.
Sky & Telescope diagram; source: Fred Espenak

Whenever the Moon passes directly in front of the Sun, termed a central solar eclipse, we Earthlings usually conjure up visions of the awe and spectacle of totality.

But that's not always the case. The orbital geometry of the Earth-Moon system is subtle. At this time of year, Earth is relatively close to the Sun in its not-quite-circular obit, so the solar disk appears larger than average. And this coming weekend's new Moon is about midway between its perigee on February 18th and its apogee on March 3rd — so its disk won't be particularly large.

The upshot is that when the Moon and Sun meet in the sky on Sunday, February 26th, the result will be an annular or ring eclipse of the Sun. Astronomers calculate that the magnitude of this eclipse — the ratio of the Moon's apparent diameter to the Sun's — is 0.9922. So this event will be very nearly total and only barely annular. It'll be a dramatic sight along the centerline, as the ring at mid-eclipse will be no more than about 15 arcseconds wide!

This geometry also means that the path of annularity — called the antumbra — is very narrow, 31 km (19 miles) wide at the point of greatest eclipse though flaring to as much as 96 km (60 miles) at the endpoints. The culminating ring in this 3¼-hour-long event will last for at most 44 seconds.

Track of Feb. 2017's eclipse across South America

Many eclipse-chasers are traveling to southern Argentina, where the prospects for clear skies on eclipse day are most favorable.
Xavier Jubier

The eclipse will be confined almost entirely to the Southern Hemisphere. The path of annularity crosses parts of southern Chile and Argentina, the South Atlantic Ocean (where mid-eclipse occurs at 14:53 Universal Time), Angola, and (at sunset) the Zambia-Congo border.

Partial phases sweep over most of South America, Africa, and Antarctica, as the globe above shows. North Americans are left out entirely.

According to meteorologist Jay Anderson, the weather prospects in Africa are relatively poor. But they're much better in South America and especially over the flat Patagonian plains of southern Argentina, where the likelihood of a cloud-free morning is 60% or better. Not surprisingly, that's where most eclipse-chasers are headed.

So wish them all clear skies — and let's hope they take plenty of dramatic images of this celestial treat.

Check out Fred Espenak's website for more details.

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Seven Earth-Sized Planets Orbit Dim Star

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Astronomers have found seven Earth-sized planets around a cool red dwarf, all of which have the potential for liquid surface water.

illustration of TRAPPIST-1 planet sky

Artist’s concept of what the sky might look like from one of the seven known terrestrial planets in the TRAPPIST-1 system.
ESO / M. Kornmesser

The star TRAPPIST-1 is an unassuming, M8 red dwarf star. It lies 39 light-years away in the constellation Aquarius. With a diameter only one-tenth that of our star, the dwarf puts out less than a thousandth as much light as the Sun.

Last year, Michaël Gillon (University of Liège, Belgium) and colleagues announced that a trio of small exoplanets orbits this pipsqueak star (although the third world was of dubious reality). Now, after an intensive follow-up campaign, the team has discovered that there are actually seven planets, not three. All are likely rocky. Three lie in TRAPPIST-1’s putative habitable zone — the region where, given an Earth-like composition, liquid water could be stable on the surface. But all, with enough hand-waving, might have a chance at liquid water.

From Three to Seven triple transit of Trappist-1

This plot is a light curve, showing how the brightness of the faint dwarf star TRAPPIST-1 varies as three of its planets pass across its face in a triple transit on December 11, 2015. Data come from the HAWK-I instrument on ESO’s Very Large Telescope. All three planets are probably rocky, and e and f are in the star's habitable zone.
ESO / M. Gillon et al.

The astronomers detected the exoplanets using the transit technique, which catches the tiny dip in starlight when a planet passes in front of its host star from our perspective. The discovery roller-coaster began when the team found that what it had thought was a combined transit of planets #2 and #3 was in fact the crossing of three planets.

The observers next assailed TRAPPIST-1 with an impressive flurry of ground-based observations. But the big breakthrough came with the Spitzer Space Telescope, which observed the star for 20 days. These data caught 34 clear transits. The team was then able to combine their ground- and space-based observations and slice and dice them to determine that the signals likely came from seven different planets.

Only six of those are firm detections, however. Number 7, or planet h, is iffy in its specs: The team only detected a single transit for it, and astronomers prefer to see three transits before calling something a candidate planet. Expect astronomers to haggle over this one in months ahead.

Mini Solar System? orbit comparisons for solar system and TRAPPIST-1

All of the seven exoplanets discovered around TRAPPIST-1 orbit much closer to their star than Mercury does to the Sun, as shown here in this comparison of the TRAPPIST-1 orbits with the Galilean moons of Jupiter and the planets of the inner solar system. But because TRAPPIST-1 is far fainter than the Sun, the worlds are exposed to similar levels of irradiation as Venus, Earth and Mars.
ESO / O. Furtak

Let’s assume for now that all seven exoplanets are real. All their orbits would easily fit inside Mercury’s circuit around the Sun. Their years range from 1.5 to 12 Earth days long, with the period of outermost h being anywhere between 14 to 35 days. The smallest two worlds are about three-fourths as wide as Earth, the largest 10% wider. The biggest orbit is less than 20% as large as Mercury’s.

One of the wonderful things about this system is that the exoplanets’ orbits are resonant with one another. This means that their orbital periods are rough integer multiples of one another — for example, in the same span of time that the innermost planet whips around the star eight times, the second planet takes five laps, the third three, and the fourth two. This setup gravitationally links the planets together and can lead to tiny shifts in their positions. Based on these shifts, the team could calculate the planets’ gravitational influences on one another, and hence their approximate masses and densities. All are consistent with being rocky, the team concludes in the February 23rd Nature.

Such resonant orbits arise when worlds migrate from their original locations, Gillon explains. Astronomers think that when lightweight planets form far out in a star’s planet-forming gaseous disk, gas drag and such will make them advance inward. During this inbound migration, the worlds catch one another in resonant orbits, such that they can form a kind of “chain of planets,” he says. In this case, the migration landed the exoplanets in what the team calls the “temperate zone” — orbits with enough incoming starlight that, with the right conditions, the planets might at least sometimes have liquid surface water. It’s a looser definition than that for “habitable zone.”

The planets are also all likely tidally locked with their star, meaning they always point the same hemisphere at it, as the Moon does to Earth. So close to the star, the planets could experience huge tidal pulls, stretching and squeezing their interiors and spurring heating and even volcanism, similar to what we see on Jupiter’s Galilean moons.

TRAPPIST-1 is quiet for an M dwarf — notably less active that Proxima Centauri, which also has a habitable-zone planet (although it’s likely a desert world). But unfortunately, astronomers don’t know how old the star is. It’s also unclear whether the planets’ orbits are stable: the researchers haven’t determined the seventh planet’s orbit, nor do they know if there are other worlds in the system mucking things up.

This kind of star, called an ultra-cool dwarf, is very common; roughly 15% of stars in the nearby galaxy fall into this category, Guillon estimates.

Are These Worlds Habitable? trappist-1 orbits

This diagram shows the relative sizes of the orbits of the seven planets orbiting the ultra-cool dwarf star TRAPPIST-1. The shaded area is the habitable zone. Although drawn here, the orbit of the outermost planet, TRAPPIST-1h, is not currently well known. The dotted lines show alternative limits to the habitable zone based on different theoretical assumptions.
ESO / M. Gillon et al.

The next goal is to look at the exoplanets’ atmospheres. If any of the worlds host life, then it might leave chemical fingerprints in the atmospheres. There’s no single compound that’s a smoking gun — for example, oxygen can come from life or from water molecules broken up by starlight into their constituent hydrogen and oxygen atoms. But certain combinations of chemical compounds (such as methane, carbon dioxide, and molecular oxygen) would be highly suggestive.

The team is developing a program to use the Hubble Space Telescope to look at the starlight passing through the planets’ (maybe extant) atmospheres as they transit, to detect any compounds that might have absorbed light. Follow-up will come with the James Webb Space Telescope, which will be more apt for this project because it focuses on infrared wavelengths, and TRAPPIST-1 puts out most of its light in infrared.

Study coauthor Amaury Triaud (Institute of Astronomy, UK) favors planet f as the most promising for life. With a girth of 1.05 Earth radii and about 60% Earth’s density, TRAPPIST-1f might be rich in water and/or ice. It receives about as much energy from its star as Mars does from the Sun, and with a good atmosphere it could be habitable. (Mars is technically in the Sun’s habitable zone.)

During a press conference Triaud painted this picture of what we might see, were we to stand on one of these worlds:

The amount of light reaching your eye would be something like 1/200 as much as you receive from the Sun on Earth — similar to what you experience at the end of sunset. However, it’d still be quite warm, because there’s still about the same amount of energy reaching you from the star as Earth receives from the Sun — it’s just that most of that comes in infrared, which you can’t see but your skin can feel. The star would be a salmon-like color. On TRAPPIST-1f, he estimated, the star would be three times wider in the sky than the Sun is to us.

“The spectacle would be beautiful,” he said.

 

Read more about the result in the European Southern Observatory’s press release.

References:

M. Gullion et al. “Seven temperate terrestrial planets around the nearby ultracool drwarf star TRAPPIST-1.” Nature. February 23, 2017.

Ignas Snellen. “Earth’s Seven Sisters.” (editorial) Nature. February 23, 2017.

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Three Crescents and a Sinking Comet

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If you're crazy about crescents, you'll find your happy place this week between the Moon and Venus. Meanwhile, we shift our focus from 45P/H-M-P to another famous periodic comet, 2P/Encke.

Razor's Edge

In Pearce, Arizona, Matt BenDaniel recorded the Moon at dawn on October 15, 2001, only 30.8 hours before new.

What makes a crescent special? Is it the contrast of pointed horns and bowed arc or simply the Moon's fragile appearance that's so breathtaking? If I could find the bumper sticker, I'd happily slap I Brake For Crescents on the back of my car.

Late February crescendos with crescents — two brought to us by the Moon and one via Venus. On Friday morning, February 24th, face southeast about 40 minutes before sunrise to spy a sliver Moon not two days from new with its back to the Sun. Low altitude may color the crescent peach, adding to the beauty of the sight.

Three nights later on February 27th, watch for an even thinner Moon to materialize low in the western sky less than a day and a half past new, horns pointed up and ready to charge into the night like a Pamplona bull.

Crescent Exits Stage East

To begin your crescent catching, find a location with a good view toward the southeastern horizon. This map shows the sky Friday morning and an ~40-hour-old waning crescent Moon.
Stellarium

In late February, the ecliptic arcs sharply up and away from the western horizon, which gives the Moon a swift kick into the evening sky and makes sighting the young crescent easy work.

Opposing Crescents

We'll be able to see opposing crescents — and the ghostly earth-lit disk — in the span of just three days later this week and early next.
Virtual Moon Atlas / C. Legrand & P. Chevalley

Since phases of the Moon and the Earth — as seen from the Moon — are complementary, a sickle Moon implies a nearly full Earth for an astronaut staring back in our direction. Earth, being nearly four times as large as the Moon appears in our sky, reflects a great deal of sunlight back at the Moon, lighting up the remainder of the lunar disk in an ember-like luminescence called earthshine. Earthshine is most obvious when the Moon mimics that Mona Lisa smile.

Lunar Lookalike

Venus cuts a cool crescent in this photo taken on February 20th by Shahrin Ahmad of Sri Damansara, Malaysia. The planet was 28% illuminated at the time.

Venus throws its scimitar in the ring, too! Since greatest eastern elongation in mid-January, Venus has been slimming down while also growing in apparent size as it approaches inferior conjunction on March 25th. Currently a banana-thick crescent measuring 43″ from tip to toe, the planet is large enough to show a shape in any telescope, even 10× binoculars.

The crescent will become larger and strikingly thinner in the coming weeks, so be sure to keep an eye on it. Just like the Moon, the Venusian crescent will flip from one side of the planet to the opposite when it reappears west of the Sun in the morning sky in late March.

Now that I've dragged you by the horns this far, you'll be happy to know there's more than one reasonably bright evening comet vying for your attention. We've been tracking 45P/Honda-Mrkos-Pajdusakova for the past couple weeks, and while it's still just visible in binoculars and now sports a short tail, periodic comet 2P/Encke has been slowly brightening at the same time. Pity it's only now reaching magnitude +9 and soon will be departing the evening sky.

Tuning-Fork Comet

In what has to be one of the most interesting tails ever to be photographed on a comet, this view of 2P/Encke was made on February 16th and shows a bright, compact coma, a faint "tuning fork" tail to the upper right, and dust in the plane of the comet's orbit at lower left. Amazing!
Damian Peach

As I write this, the comet is cozying up to Venus in Pisces, a compact fuzzy glow of magnitude +8.8. It's brightening as it runs westward toward the Sun and will reach perihelion on March 10th. Comet 2P/Encke could become as bright as magnitude +6.5 in the next 10 days and become visible in binoculars shortly before disappearing in the solar glow around March 6th. The best time to catch it is near the end of evening twilight. On February 27th, the thin lunar crescent and Venus will neatly frame the comet. Photos anyone?

Quickly Bright, Then Out of Sight

Use this map, which shows Comet 2P/Encke's nightly position (7 p.m. CST) from February 22nd through March 7th. Stars are shown to magnitude +8 and north is up. Click for a large version to save and print out.
Created with Chris Marriott's SkyMap

Meeting of Three

On February 27th, watch for two crescents to frame Comet 2P/Encke.
Map: Bob King, Source: Stellarium

For northern hemisphere observers, that's all she wrote, but southern skywatchers will have another go at 2P/Encke when it returns to the morning sky in late March at magnitude +8 and fading.

Magnificent Portrait

Comet 45P/H-M-P with a huge coma and broad tail sails past the Whale Galaxy (NGC 4631, at right) and the Hockey Stick Galaxy (NGC 4656) on February 19th.
José J. Chambó

And of course don't forget 45P/Honda-Mrkos-Pajdusakova. Now that it's become well placed in a moonless sky, amateur astronomers have been having better luck recording new details, including a fresh, new tail. The photo above, taken by José J. Chambó, perfectly captures the comet's ethereal beauty in the context of deep space.

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Mornington Peninsula Astronomical Society

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NAME

Mornington Peninsula Astronomical Society

ADDRESS

The Briars
Mount Martha, Victoria
Australia

CONTACT

David Rolfe

PHONE

+61 4 13610626

EMAIL

welcome@mpas.asn.au

URL

http://www.mpas.asn.au

NUMBER OF MEMBERS

150

OTHER INFORMATION

MPAS is approaching 50 years and welcomes members from all over the world to our observing site, located on the outer edge of Melbourne, Victoria, Australia.

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Juno Will Stay in Current Orbit Around Jupiter

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NASA has announced that its Juno mission will remain in a wide-ranging path around Jupiter.

Jupiter's south pole

Stormy times over Jupiter's southern pole. This image was captured by JunoCam on February 2, 2017, from a range of 62,800 miles (101,000 kilometers).
NASA / JPL-Caltech / SwRI / MSSS / John Landino

NASA has decided to leave the Juno spacecraft in its current 53-day orbit around Jupiter for the remainder of the mission. The decision follows the discovery of a possible engine malfunction in October 2016. Maintaining a wide-ranging orbit will allow the spacecraft's instruments to safely complete the mission's science objectives, while avoiding the risk of another engine malfunction stranding the spacecraft in an unplanned orbit.

“Juno is healthy, its science instruments are fully operational, and the data and images we've received are nothing short of amazing,” says Thomas Zurbuchen (NASA-Science Directorate) in a recent press release. “The decision to forego the burn is the right thing to do — preserving a valuable asset so that Juno can continue its exciting journey of discovery.”

Launched on August 5, 2011, atop an Atlas 5 rocket from Cape Canaveral Air Force Station, Juno entered its initial and current orbit on July 4, 2016. The plan was to make two wide initial capture orbits around Jupiter, burning the main engine on October 19, 2016, to enter a series of 34 shorter, 14-day science orbits.

NASA/JPL

The original plan for NASA's Juno spacecraft, with two initial capture orbits versus the final phase of science orbits.
NASA / JPL

However, the unexpected occurred last October: Juno went into safe mode following what was to be the final firing of the spacecraft's main engine. Telemetry later indicated that a pair of helium check valves in the main engine took several minutes to open, longer than on previous firings.

Saving Juno

Engineers analyzed the situation and decided that the best bet was for the spacecraft to stay put, rather than risk another firing of the main engine. Juno will still be able to accomplish its main mission objectives, including probing the magnetosphere, radiation belts, and the gas giant's deep interior. It will now focus on documenting the far reaches of the planet's magnetic field as well. Also, the quality of the data gathered on each pass will remain the same, as the closest passage on the current orbit is identical to those on the hoped-for science orbits. The only difference now is the span of time between passes.

Juno's current orbit takes it from a perijove (closest approach) of just 2,600 miles (4,100 kilometers) over the Jovian cloud tops, to far out past the orbit of Callisto with an apojove of 8.1 million miles (5 million kilometers) distant.

Juno has completed four orbits of Jupiter thus far, giving us some amazing never-before-seen views of the planet's polar regions, and we're expecting to see some of the first science papers using this data in the coming months. Citizen scientists are also making good use of images provided by JunoCam, presenting us with some compelling views.

Juno approaches Jupiter

Jupiter as seen by Juno's JunoCam on first approach last August.
NASA / JPL-Caltech / SwRI / MSSS

The next perijove pass is set for March 27, 2017.

There's another silver lining to the engine anomaly, as Juno may get a brief reprieve before its grand finale. The original plan called for the mission to terminate by entry into Jupiter's atmosphere about a year from now, in February 2018. Juno receives a large amount of radiation on each successive pass, degrading the instruments and spacecraft controls. Engineers planned for a controlled entry in order to protect Jovian moons, such as Europa, from contamination. Orbital precession also carries Juno deeper into Jupiter's radiation belts on each successive pass. Now, NASA plans to operate the mission through July 2018, for a total of 12 orbits, before proposing for a mission extension.

The extended orbit might just be good news after all, as Juno gets a longer rest period between successive doses of instrument damaging radiation. In the end, Juno's loss of an operable main engine might just be science's gain.

The post Juno Will Stay in Current Orbit Around Jupiter appeared first on Sky & Telescope.

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