In the Transient Sky – February 2013

February 2013 Highlights
* Not one but two comets should be naked eye brightness for SH observers (C/2011 L4 and C/2012 F6)
* Up north only comets 273P/Pons-Gambart and C/2012 T5 are bright enough for small scopes at 9th magnitude
* Comet C/2011 F1 (LINEAR) is also in range of small telescopes from the SH
* Small near-Earth asteroid 2012 DA14 passes 34,000 km from Earth on the 16th
* Mercury and Mars pass within 1/2° of each other low in the WSW evening sky on the 7th
* The Moon joins Mercury and Mars on the evenings of the 10th and 11th
* Moon occults Jupiter for observers in southern Australia
* Saturn rises before midnight
* Jupiter continues to dominate the evening sky
Note: If anyone has pictures or observations of these objects/events and want to share them with my readers, send them to the Transient Sky at <transientsky1@yahoo.com>.

Planets

Evening Planets

Mercury -Mercury will have three good evening apparitions for Northern Hemisphere observers this year. The first takes place this month. The innermost planet is a relatively bright -1 magnitude at the start of the month. Though it slowly fades every night it rapidly ascends higher nightly in the western sky during dusk. On the 7th it passes ~0.4° from much fainter Mars. A very thin crescent Moon is located to the lower right of the duo on the evening of the 10th and to the upper right on the 11th. By the second half of the month Mercury is fading to 1st-2nd magnitude and falling back into the twilight glow.

Mars - Use Mercury and the Moon (see above) to spot Mars this month. The red planet will be all but unobservable for most observers for the next few months as it passes behind the Sun.

Jupiter – The King of the Planets dominates the evening sky being visible nearly overhead at the end of evening twilight. Jupiter is now two months past opposition. It spends the month just north of the stars of the Hyades cluster in Taurus as it fades from magnitude -2.5 to -2.3.  The Moon pays Jupiter a visit on the evenings of the 17th and 18th.

Morning Planets

Saturn – Saturn is an early morning object rising around 1:00 am at the start of the month and 11pm by the end of the month.  All month Saturn glows at magnitude +0.5 between Virgo and Libra. The Moon passes close to Saturn on the morning of the 3rd.

Venus – Venus is too close to the Sun for easy observation this month. It will be back, this time in the evening sky, this summer.

Meteors

The year is usually split in 2 with January through June having low rates with few major showers while July through December have high rates with many major showers. Meteor activity is still near an annual maximum this month.

Sporadic Meteors

Sporadic meteors are not part of any known meteor shower. They represent the background flux of meteors. Except for the few days per year when a major shower is active, most meteors that are observed are Sporadics. This is especially true for meteors observed during the evening. During February mornings, 5 or so Sporadic meteors can be observed per hour from a dark moonless sky. The rate is near an annual minimum this month.

Major Meteor Showers

None this month.

Minor Meteor Showers

Minor showers produce so few meteors that they are hard to notice above the background of regular meteors. Info on many minor showers are provided on a weekly basis by Robert Lunsford’s Meteor Activity Outlook.

Additional information on these showers and other minor showers not included here can be found at the International Meteor Organization’s 2012 Meteor Shower Calendar.

Comets

Naked Eye Comets (V < 6.0)

C/2011 L4 (PANSTARRS)

Last month Comet PANSTARRS looked on pace to peak around magnitude -1 near its March 10th perihelion. But over the past few weeks the comet has not been brightening as quickly as hoped. As a result it is likely that the comet will be much fainter than -1 at its peak brightness and more along the lines of 2nd to 4th magnitude. The comet will still be a nice sight especially in binoculars and telescopes.

The comet was first seen by the Hawaiian based PanSTARRS asteroid survey on June 6, 2011 at a large distance of 7.9 AU from the Sun. At perihelion it will approach within 0.30 AU of the Sun. The comet is a new Oort cloud comet meaning it is making its first passage through the inner Solar System. The fact that it is a new Oort cloud comet explains its failure to brighten as quickly as first predicted. These sort of comet often appear relatively bright when far from the Sun because they still contain a large amount of very volatile ices. As the comet approaches the Sun, these ices sublimate and the comet brightens at a slower rate.

This month, the comet starts at a distance of 1.0 AU from the Sun with that distance dropping to 0.43 AU at the end of the month. A few recent observations place it at magnitude ~6.5-7.0. If it continues to brighten at its current rate it should become a naked eye object by mid-month. The comet will only be observable from the Southern Hemisphere this month as moves from the constellation of Sagittarius to Piscis Austrinus. Northern observers will have to wait till late March when the comet should be a naked eye object.

Finder charts can be found at Chasing Comets.

Ephemeris for C/2011 L4 (PANSTARRS)
Date            RA        DEC    Delta   r   Elong    V
2013 Feb 01   19h 21m  -45d 22'  1.649 1.009   34    6.8
2013 Feb 10   20h 26m  -45d 15'  1.427 0.822   34    6.0
2013 Feb 19   21h 49m  -41d 06'  1.238 0.626   30    4.5
2013 Feb 28   23h 16m  -29d 13'  1.118 0.431   22    3.0

RA = Right Ascension, DEC = Declination, Delta = distance from Earth in AU
r = distance from the Sun in AU, Elong = elongation from Sun in degrees
V = Visual magnitude

C/2012 F6 (Lemmon)

Everyone was expecting C/2011 L4 (PANSTARRS) and C/2012 S1 (ISON) to be the two naked eye comets of 2013. No one was expecting C/2012 F6 (Lemmon) to be vying for the status of naked eye comet when it was discovered by Alex Gibbs of the Mount Lemmon survey back on March 23, 2012. At that time the comet was a faint 20th-21st magnitude and 5.0 AU from the Sun. It also appeared to be an intrinsically faint comet. So faint in fact that I though it had a good chance of disintegrating near perihelion. Instead the comet has brightened at a rapid rate. If this brightening trend continues the comet may be a fine naked eye object this February through May. Perihelion will occur on March 24, 2013 at a distance of 0.73 AU from the Sun.

Over the past few days visual observers have estimated the comet at magnitude 6.2 to 6.5.

The comet is already too far south for most northern observers and the comet will continue to travel deeper into the southern sky this month. As a result, this comet will only be visible to southern observers till May.

The comet starts the month around magnitude 6.3 and will continue to rapidly brighten all month. By the end of the month the comet may be as bright as magnitude 6.0. It will be traveling through the far southern constellations of Musca, Octans, Tucana and Phoenix.

Finder charts can be found at Chasing Comets.

Ephemeris for C/2012 F6 (Lemmon)
Date            RA        DEC    Delta   r   Elong    V
2013 Feb 01   13h 32m  -81d 08'  0.993 1.221   76    6.3
2013 Feb 10   23h 00m  -81d 07'  0.993 1.098   67    5.5
2013 Feb 19   23h 52m  -65d 58'  1.053 0.981   57    4.5
2013 Feb 28   00h 03m  -52d 43'  1.154 0.877   47    4.0

RA = Right Ascension, DEC = Declination, Delta = distance from Earth in AU
r = distance from the Sun in AU, Elong = elongation from Sun in degrees
V = Visual magnitude

Binocular Comets (V = 6.0 – 8.0)

None

Small Telescope Comets (V = 8.0 – 10.0)

Comet C/2012 T5 (Bressi)

Comet Bressi was first spotted by Spacewatch observer Terry Bressi from Kitt Peak on October 14, 2012. If any of the comets in this blog post are likely to not survive perihelion, this is the one.

The comet is currently just within 1 AU of the Sun and little over 1 AU from Earth. Even after a recent outburst a week or two ago the comet is still rather faint. My observations place it at V magnitude 13.0 but this is most likely an underestimate as the observations were hampered by a very right Moon nearby and the comet’s low elevation. Visual observers place it closer to magnitude 11-12.

Comet Bressi will reach perihelion on February 24 at a distance of 0.32 AU from the Sun. It will be interesting to see if it survives. If it does it may brighten enough to be seen in small telescopes though observations will be limited to southern observers until March.

Recent observations place the comet at magnitude 10.5. If it can hold together till perihelion it should can brighten up to 8th-9th magnitude. Northern observers will only be able to follow the comet till around mid-month. After that it will solely be a southern object till next month.

Finder charts can be found at Chasing Comets.

Ephemeris for C/2012 T5 (Bressi)
Date            RA        DEC    Delta   r   Elong    V
2013 Feb 01   23h 51m  -30d 29'  1.016 0.709   41   10.5
2013 Feb 10   23h 20m  -33d 04'  0.984 0.517   30    9.8
2013 Feb 19   22h 28m  -32d 03'  0.933 0.357   21    8.9
2013 Feb 28   21h 34m  -19d 22'  0.917 0.344   20    8.0 or Puff!

RA = Right Ascension, DEC = Declination, Delta = distance from Earth in AU
r = distance from the Sun in AU, Elong = elongation from Sun in degrees
V = Visual magnitude

273P (Pons-Gambart)

On June 21, 1827, French astronomers Jean Louis Pons and Jean-Félix Adolphe Gambart discovered a comet among the stars of Cassiopeia. Both men were prolific comet finders. Pons was the most prolific discoverer of comets up until the modern era and still holds the record for most visual discoveries. A record that is unlikely to ever be broken. Between 1801 and 1827, Pons found 26 comets. Comet Pons-Gambart was his second to last comet find. Though not as prolific as Pons, Gambart is credited with 5 comet discoveries between 1822 and 1834. Comet Pons-Gambart was his 3rd find.

As the comet was already a few weeks past perihelion at discovery, it was only observed for ~1 month before it faded. Over the years, orbit computers have noticed that Pons-Gambart was on an obvious elliptical orbit and determined periods between ~45 and 65 years. The only problem was with periods that short the comet should have returned at least 2 to 4 times since 1827. Perhaps the comet was fainter now or even broke up in the intervening years to explain why it was constantly being missed.

Fast forward to this year… Robert Matson of Newport Coast, CA found evidence of an unknown comet on images taken with the SOHO spacecraft. SOHO’s SWAN imager is used to map the Lyman-α emission of the solar wind. SWAN is also very good at detecting hydrogen was dissociated water molecules released by comets. As a result, SWAN has been used to discover comets. Matson noted the presence of a comet on SWAN images from Nov. 7, 10, 11, 13 and 19. He then informed a number of observers about the new find and on Nov. 29 Terry Lovejoy of Australia found the comet.

Before the comet was even formally announed, Maik Meyer of Limburg, Germany noticed the similarities between the new SWAN/Matson comet and long-lost Comet Pons-Gambart. There is little doubt that the two are related and are probably the same object. Only problem is the 2012 observations don’t exactly match the 1827 observations assuming orbital periods of 45-65 years. A recent MPEC released by Gareth Williams of the Minor Planet Center found that the 2012 observations are consistent with a much longer period than previously assumed. It is likely that Pons-Gambart wasn’t really missed before because with a 188 year orbit this is actually its first return since 1827.

At first there was still come question as to whether the newly seen comet was Pons-Gambart and for awhile the comet was only known by its designation C/2012 V4. The Minor Planet Center has now officially announced it as 273P/Pons-Gambart.

After spending over a month too close to the Sun for observation, 273P is once again observable. This month it is a morning object traveling north from Serpens Cauda into Hercules.

Finder charts can be found at Chasing Comets.

Ephemeris for 273P/Pons-Gambart
Date            RA        DEC    Delta   r   Elong    V
2013 Feb 01   18h 30m  +05d 10'  1.636 1.132   42    9.0
2013 Feb 10   18h 22m  +10d 30'  1.538 1.243   53    9.2
2013 Feb 19   18h 10m  +16d 46'  1.432 1.359   65    9.4
2013 Feb 28   17h 54m  +24d 10'  1.331 1.477   77    9.7

RA = Right Ascension, DEC = Declination, Delta = distance from Earth in AU
r = distance from the Sun in AU, Elong = elongation from Sun in degrees
V = Visual magnitude

C/2011 F1 (LINEAR)

No one has seen this comet for a few months because it has been too close to the Sun. It should be around magnitude 9-9.5 as it slowly moves away from the Sun.

The LINEAR near-Earth asteroid survey picked up this comet back on March 17, 2011 at 18th magnitude. It passed perihelion on January 8 of this year at 1.82 AU from the Sun.

It is yet another comet that can only be seen from the Southern Hemisphere this month as it moves from Sagittarius to Microscopium.

Finder charts can be found at Chasing Comets.

Ephemeris for C/2011 F1 (LINEAR)
Date            RA        DEC    Delta   r   Elong    V
2013 Feb 01   19h 45m  -36d 01'  2.691 1.845   24    9.2
2013 Feb 10   20h 13m  -37d 51'  2.662 1.867   29    9.3
2013 Feb 19   20h 44m  -39d 26'  2.634 1.896   33    9.4
2013 Feb 28   21h 15m  -40d 44'  2.610 1.931   38    9.5

RA = Right Ascension, DEC = Declination, Delta = distance from Earth in AU
r = distance from the Sun in AU, Elong = elongation from Sun in degrees
V = Visual magnitude

Asteroids

2012 DA14

On February 15th a ~50-meter asteroid will pass 34,000 km or 21,000 miles from Earth. The asteroid will appear as a fast moving star of 8th magnitude at its closest. For observers in the United States, the asteroid will already have made its closest approach when it becomes visible. As a result it will have faded to 11th magnitude by then.

I’ll post more on this object over the next week or so.

Comets from the VATT

Last week I spent three nights observing asteroids and comet with the Vatican Observatory’s 1.8-m VATT telescope on Mount Graham in southeastern Arizona. The observing run was part of my program to characterize asteroids that could be good spacecraft targets as well as objects that are analogous to the OSIRIS-REx target asteroid. When possible I never pass up the opportunity to observe a few comets.

Though clouds affected two of the nights, the conditions were rather good. In fact, the seeing was exceptional and was as good as 0.7″ at times.

As luck would have it, the brightest comets in the sky were not visible from the VATT either because they were too far south or too close to the Sun for observation (or in the case of C/2012 K5, I just couldn’t fit it into my observing schedule).

The following is an update on a few long-period comets with some images I took from the VATT.

C/2011 L4 (PANSTARRS)

C2011L4_orbitThe big comet of the spring is supposed to be comet C/2011 L4 (Panstarrs). When discovered back in June of 2011 the brightness of the comet at a distance of ~8 AU (halfway between the distances of Jupiter and Saturn) suggested this comet could be a brilliant negative magnitude at perihelion in March of this year.

There was some questions whether this comet was on its first passage through the inner Solar System or if it had been through the neighborhood before. This is an important distinction because comets fresh from the Oort cloud have a tendency of being very active while far from the Sun. Then as the most volatile ices are sublimed off, the comet settles down into a less active state and never gets quite as bright as predicted. We have seen this many times in the past with comets being lauded as “great” or “future” comets, only to disappoint when they finally reach perihelion. Comet Cunningham in 1941, Kohoutek in 1973/74 and Austin in 1990 are prime examples

Comet PANSTARRS has an orbit that is almost indistinguishable from parabolic meaning the comet is likely to be a fresh comet from the Oort cloud. This fact had many people doubting whether it would really reach magnitude -1 as predicted by its early behavior. Now that the comet is once again observable (though only from the Southern Hemisphere) it does appear the comet’s brightening has slowed down and the comet will only reach a magnitude of +2 to +3 if that.

Recent visual observations place the comet between magnitude 7.0 and 7.5. It will continue to be a southern-only comet till mid-March when it will become visible in the early evening sky for northern observers. Sky and Telescope has some nice finder charts for the comet here. Even with a peak brightness of “only” 2nd or 3rd magnitude, the comet will be quite a sight in binoculars and small telescopes.

C/2012 F6 (Lemmon)

C2012F6_orbitIf Comet PANSTARRS is an example of the “over-hyped” comet that is “under-performing”, Comet Lemmon is the exact opposite. When discovered by the Mount Lemmon Survey last March, the comet was nothing special. Even with a perihelion distance of only 0.73 AU, the comet looked too faint to amount to much. I even placed it on my watch list for small comets that were likely to disintegrate and not survive perihelion. Instead this comet has been brightening at a much faster rate than predicted and is now the brightest comet in the sky.

Back on January 9 I spotted it in my 30×125 binoculars at magnitude 7.9. It was an easy object even though it only got ~10° above the horizon as it was speeding to the south. Its southward motion now means the comet is only visible for Southern Hemisphere observers.

The most recent visual observations place is around magnitude 6.5. If it continues like this it could rival or even surpass Comet PANSTARRS in brightness at magnitude +2 to +3 when it reaches perihelion at the end of March. For those of us up north the comet will again become visible in late April/ early May. At the time the comet will be fading but should still be around 5th magnitude.

273P/Pons-Gambart

273P_orbitThe surprise return of Pons-Gambart has been discussed in earlier posts (here, here, and here). After spending a month too close to the Sun for Earth-based observations, the comet is once again visible between magnitude 8.5 and 9.0. The comet may remain brighter than magnitude 10 and within range of small telescope users for another month or so.

Pons-Gambart has a period of ~188 years. It was seen once before in 1827 during its last perihelion passage. Its period will actually shorten by a few years results in the next return in 2191.

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C/2012 K1 (LINEAR)

C2012K1_orbitDiscovered on May 19, 2012 by the LINEAR survey at a faint 19-20th magnitude, the comet was then located at a distant 8.8 AU from the Sun. It is now ~6.8 AU out and has brightened to magnitude ~17.2. Though the comet does not look like much, it will get much brighter as it approaches its August 27, 2014 perihelion at a distance of 1.05 AU from the Sun.

Right now the comet looks on track to reach 6th magnitude at perihelion, but… similar to Comet PANSTARRS, C/2012 K1 is also an Oort cloud comet making its first visit to the inner Solar System. It is likely that it will also experience a slow down in brightening and will not get as bright as predicted. Time will tell …

In the here and now, the VATT showed K1 to be a nice small condensed comet at 17th magnitude.

C2012K1_TranSky

C/2012 S1 (ISON)

Comet ISON is the big one. Many media outlets are already calling this one the “Comet of the Century” which will shine brighter than the Full Moon. Possibly…

C2012S1_orbitAs the lesson of Comet PANSTARRS has taught us, the past behavior of a comet does not guarantee its future performance.The aforementioned Comets Cunningham and Kohoutek were also called “Comets of the Century” in their time. Neither lived up to the moniker.

ISON does have a few things going for it. The best news is its orbit which is very similar to the Great Comet of 1680. It is doubtful that ISON and the 1680 comet are one and the same. It is possible that the two comets are pieces of an older comet that split in the past. Simply being related to the 1680 comet does not mean ISON will be as spectacular as that comet but it does mean ISON has been around before and is not a new Oort cloud comet. This bodes well for ISON to brighten at a good rate and also survive perihelion.

A year ago, Comet C/2011 W3 (Lovejoy) passed even closer to the Sun than ISON will. Though Lovejoy disintegrated a few days past perihelion that was still enough time for it to produce a long bright tail that was observable for weeks (only for southern observers though, Lovejoy was invisible for Northern Hemisphere observers after perihelion). If ISON can survive it close brush with the Sun by even a few days it will produce a long bright tail that should be easily visible by northern observers (sorry southerners, ISON is our turn to enjoy a brilliant sun-grazing/skirting comet) throughout the month of December 2013.

When it reaches perihelion this November 28 (Thanksgiving Day!) it will be located only 0.012 AU from the center of the Sun or ~1.1 million km (660,000 miles) from the Sun’s surface which just under 3 times the distance from the Earth to the Moon. (Editors Note: Thanks to Joe Stieber for pointing out the error in my perihelion Sun distance!) Right now ISON is currently located at ~5 AU (the distance of Jupiter) from the Sun and still has almost 10 months to go before perihelion.

The VATT found ISON to be a nice compact 15th magnitude comet wandering among the stars of Gemini.

C2012S1_TranSky

C/2012 T5 (Bressi)

C2012T5_orbitFrom a potential great comet to an absolute runt of a comet. Comet Bressi was first spotted by Spacewatch observer Terry Bressi from Kitt Peak on October 14, 2012. If any of the comets in this blog post are likely to not survive perihelion, this is the one.

The comet is currently just within 1 AU of the Sun and little over 1 AU from Earth. Even after a recent outburst a week or two ago the comet is still rather faint. My observations place it at V magnitude 13.0 but this is most likely an underestimate as the observations were hampered by a very right Moon nearby and the comet’s low elevation. Visual observers place it closer to magnitude 11-12.

Note that unlike most comets in this blog post, Bressi is much brighter in the V versus the R. Most of the more distant comets are actually brighter in the R. The reason is that Bressi is a much more gaseous comet due to its closer distance to the Sun and perhaps even internal composition.

Comet Bressi will reach perihelion on February 24 at a distance of 0.32 AU from the Sun. It will be interesting to see if it survives. If it does it may brighten enough to be seen in small telescopes though observations will be limited to southern observers until March.

C2012T5_TranSky

C/2012 V2 (LINEAR)

C2012V2_orbitThis LINEAR comet was discovered on November 5. At perihelion on August 16, 2013 at a distance of 1.45 AU from the Sun the comet should be no brighter than 12-13th magnitude. It should remain out of reach of most visual observers.

Last week the VATT caught 2012 V2 out at a distance of ~3.1 AU from the Sun. The comet was magnitude 16 and sported a short tail extending to the northeast.

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C2012V2_TranSky

C/2012 X1 (LINEAR)

C2012X1_orbitYet another inbound Comet Linear, C/2012 X1 was first spotted last month on December 8th. It is currently at a distance of ~4.8 AU from the Sun which is just inside the distance of Jupiter’s orbit. When it reaches perihelion next year on February 21st, it will be 1.60 AU from the Sun. That’s not too close so it should only brighten to about 11th magnitude by then.

Last week the comet was seen at 18th magnitude with a broad fan tail.

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C2012X1_TranSky

C/2013 A1 (Siding Spring)

C2013A1_orbitThe first comet to be discovered in 2013 is the most recent comet to be discovered that may become bright enough for backyard observers. Rob McNaught found C/2013 A1 on January 3rd from Siding Spring, Australia. Right now the comet is further from the Sun than Jupiter is at a distance of ~7 AU. The VATT found the comet to be around V magnitude 18.7 with a nice tail to the northeast

The comet is almost 2 years from perihelion which won’t occur until October 23, 2014 at a distance of 1.39 AU from the Sun. It could become as bright as 7th magnitude at that time though a lot can happen over the next 2 years and the comet may end up significantly fainter.

C2013A1_TranSky

C/2009 P1 (Garradd)

C2009P1_orbitThe next two comets are examples of objects that were bright enough for small telescope users in the past but are now fading as they leave the inner Solar System.

Comet Garradd was a splendid sight for many months between the 2nd half of 2011 and the 1st half of 2012. During that stretch the comet was an easy binocular object of 6th-7th magnitude. Now over a year past its December 2011 perihelion (at a distance of 1.55 AU from the Sun) and 3.5 years since its discovey, the comet has retreated to a distance of 4.8 AU from the Sun which is nearly the distance of Jupiter.

My VATT images from January 20 find the comet at V magnitude 13.5. The comet displays a small condensed coma of ~1′ within a much larger diffuse coma of 3′. The bright inner coma is dust recently released by the comet while the diffuse faint outer coma is dust released when the comet was more active in the past. The fact that we are observing dust released over many months or years does make it difficult to properly measure the current activity level of the comet.

A faint broad tail can also be seen extending towards the north. Too bad the Moon was bright that night and affected the images or the tail and outer coma would have been better defined. This will be a fun comet to watch as it continues its journey back into the depths of the outer Solar System. Based on the latest orbit by Syuichi Nakano, Comet Garradd won’t be back for ~500,000 years.

C2009P1_TranSky

C/2011 UF305 (LINEAR)

C2011UF305_orbitAnother comet on the way out, C/2011 UF305 reached perihelion last July at a rather distant  2.13 AU from the Sun. Though it had a large perihelion distance it did brighten to 10th magnitude for a few months during the summer and fall of 2012.

The comet is now ~230 days past perihelion at a distance of 3 AU from the Sun. My VATT observations yield a V magnitude of ~13.8 which is still bright enough for visual observers with very large backyard telescopes to observe it. For small telescope users, the comet is well out of reach.

Drifting against the stars of Cancer, the comet was near opposition. Similar to C/2009 P1, a large diffuse dust tail can be seen extending towards the north. Most likely this is dust that was released many months ago when the comet was more active. This will also be a fun comet to see how long it can be followed as it recedes into the depth of the outer Solar System. Based on the latest orbit by Syuichi Nakano, Comet Garradd won’t be back for ~90,000 years.

C2011UF305_TranSky

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