An Observer's Guide for Watching Comet ISON's Light Show in the Sky

8/13/2019 An Observer's Guide for Watching Comet ISON's Light Show in the Sky

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n observer's guide for watching Comet ISON's light show in the sky

The incoming Comet ISON is now in the home stretch of its long-awaitedhairin loo around the sun on Thanksgiving !ay" making it a great target for amateur astronomers and starga#ers$ %ut there are some tis and info you'll want to kee in mind before you go comet hunting$

Comet ISON is on track for an e&tremely close shave of the sun when it flies by arth's closest star on Thursday$ The comet will aroach within amere ()*"*** miles +,$ million kilometers. of the sun during the encounter" leading many scientists and amateur astronomers to wonder if the comet will survive its Thanksgiving !ay rende#vous with the sun$

In !ecember" Comet ISON is e&ected to reach its greatest brilliance$ It is during that month that it will be most interesting to both amateurs andthe ublic$ /See more ama#ing hotos of Comet ISON in the night sky0

lthough forecasting the brightness of a comet months before its arrivalat erihelion has always been ha#ardous" in the case of ISON until recently its brightening trend has been very difficult to deciher$ 1 until Nov$,)" the comet's increase in brightness was rogressing at a rather sluggish ace" but then suddenly a noticeable outburst began taking lace$

Comet ISON's brilliant flare-u2rom Nov$ ,) to ," Comet ISON brightened by )$3 magnitudes on the scale used to determine the brightness of ob4ects in sace$ That's a 3-foldincrease in brightness to the observer5 %etween Nov$ ,6 and , alone" ISON more than doubled in brightness$ long with this surge in activity" soaring rates of dust and gas were being released from its nucleus$


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mateur and rofessional astronomers around the world have been tracking Comet ISON in telescoes" with N S sacecraft and other observatories tracking the ob4ect from sace$

In the wake of this recent activity" e&erienced comet watchers are growing more confident that the comet has a chance to be ranked among oneof the brightest in the last half century$ 7 ll this I regard as very romising for something 8uite significant to be seen from ISON come the early days of !ecember"7 comet e&ert 9ohn %ortle said$ /:ow to ;hotograh Comet ISON +Ste-by-Ste ? ssential 2acts0

It is very difficult to say recisely 4ust how bright Comet ISON will ultimately become when it asses nearly ()*"*** miles of the ,,"***-degrees 2ahrenheit surface of the sun" while being sub4ected to enormous tidal andgravitation forces that could cause the comet to fracture into ieces$ If th


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is haens" it could release a tremendous amount of dust causing the comet to become many times brighter and unfurl a tremendously bright tail$

s the comet loos around the sun" and begins its return 4ourney out of the inner solar system" it 7may7 be dimly visible in daylight by merely blocking out the sun with your hand$ Soon after sunrise" ISON will be ositioned within about degrees to the right of the sun$ !uring the rest of the day" the comet will aear to get closer to the sun" while raidly moving ina clockwise fashion below and then to the sun's left$ The comet will aear closest to the sun 4ust before $m$ ST when it will aear less thanhalf the aarent width of the sun from the sun's limb" or edge$ The comet's velocity as it whis in a hairin turn around the sun will reach a ma&imum of )@$A miles er second or ?@@"A) mh +,$) million kmBh.5

:eed this warning5e strongly warn all readers that only e&erienced observers should attemt observation of Comet ISON as it whis around the sun$ Diewing the comet itself oses no danger" but otential danger lies in staring directly at the sun whose infrared rays can burn the retina of the eye without causing any ain$ 9ohn %ortle agrees> 7hen it's within 4ust a few hours of itserihelion ISON will be so close to the solar limb it will be an imossibletask to sot for virtually all observers$7 /:ow to See Comet ISON in November Sky E Dideo0

Fou can safely watch the comet whi around the sun on your comuter here from the Garge ngle and Sectrometric Coronagrah &eriment +GSCO. on the SO:O sacecraft$ ISON should be within G SCOHs field of view from ( a$m$ ST on ednesday to ( $m$ ST on 2riday$

Soon after erihelion" erhas on the mornings of 2riday andBor Saturday" the ghostly dust tail might be visible low in the eastern sky" but the comet's brilliant head will still be embedded dee in the morning twilight$Image> ISON sky ma


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Stardate$orgComet ISON's osition in !ecember *,) is shown on this sky ma$

%elow is a look at Comet ISON's e&ected behavior in the coming weeks"given in ,*-day intervals$

!ec$ ,-,*> The changes in the comet wrought by erihelion assage become evident$ ;ossibly the comet is brighter than e&ected during the firstfew days of this eriod$ On !ec$ ," the tail could be as much as , degrees long +your clenched fist held at armHs length measures roughly ,* degrees.$

%ecause of ISON's close assage to the sun" the tail could aear very bright" while the comet's head might aear #ero magnitude +as bright as the stars Dega or Caella." and erhas brighter$ ach morning the tail shoots out from the head like a narrow searchlight beam and will increase consicuously in length as ISON backs into darker morning skies$ The comet's head begins to rise before the onset of morning twilight = about ,**minutes before sunrise = on !ec$ A and the tail length reaches to erhas * degrees by !ec$ ,*$ The comet's brightness by !ec$ ,* should subside to between magnitude ) +a star of medium brightness. and 3 +a faintstar.J the comet will have receded to 3,$@ million miles +?$( million kilometers. from the sun$

!ec$ ,,-*> Comet ISON's altitude at the break of dawn increases from ,) degrees on !ec$ ,, to degrees on !ec$ ,3$ The latter date will be thelast morning in !ecember that ISON can be viewed in a comletely dark skyJ the bright moon that morning sets at 3>3 a$m$ local time and twilightbegins at 3>)) a$m$ local time$ So you will have 4ust an eight-minute window of comlete darkness$ The full moon of !ecember will occur on the following day$

%ut within a few days" attention will shift to evening visibility as the moo


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n will be setting about an hour later each night while the comet begins tobecome increasingly evident low in the northwest sky after sunset$ On !ec$ *" Comet ISON sets at A>@ $m$ local time" ,@ minutes after the end of evening twilight$

Keanwhile" the distance between the arth and comet is raidly decreasing to @$3 million miles +A?$) million km. by !ec$ *$ The comet will be inthe constellation of Corona %orealis" the brightness of the head should hover somewhere between magnitude @ +the brightness of a moderately faint star. and A +a very faint star at the threshold of naked-eye visibility.$%y this time" the ghostly tail may aear to reach * degrees to )* degrees$

!ec$ ,-),> ith the moon comletely absent from the evening sky and Comet ISON climbing noticeably higher in the north-northwest sky with each assing evening" the full slendor of the comet is revealed$ %ut againwe stress = observers must get away from the bright lights of cities to view the comet in all its glory = seen against a dark backdro it could be asight not to be forgotten$

On Christmas !ay" Comet SON has moved far enough northward in declination to become a circumolar ob4ectJ that is" it does not rise nor set but remains above the hori#on all night long$ The comet's closest aroachto the arth comes the following day> t 3>@ $m$ ST" it will be )6"?6("3A miles +A@"*?"6* km. away$ The total light of the coma should continue to hold somewhere between magnitude @ and A$ s seen against a very dark sky with the unaided eye" the cometHs coma may aear half thediameter of the full moon$ The gas tail should san many degrees" while the much brighter dust tail will continue to stretch toward the north for atleast * degrees = even @* degrees is ossible$

9an$ ,-,*> The rest of Comet ISON's night sky dislay will seem anticlimactic" for the comet shrinks and fades raidly now as it ulls away from both the sun and the arth" with the magnitude droing from erhas A to ? = below the threshold of naked-eye visibility even under a dark sky$


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The coma is e&ected to be 8uite large and diffuse" growing more so daily$ Dery straight and narrow" the tail initially should be traceable some ,*degrees to ,3 degrees shortening to ossibly down to 3 degrees by !ec$,*$ The

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An Observer's Guide for Watching Comet ISON's Light Show in the Sky