“New” Comet Blues – Comet McNaught Falls Short

We should have known better. Early predictions called for Comet 2009 R1 (McNaught) to get as bright as 2nd magnitude. As recently as 2 weeks ago, I posted that it was on pace to reach magnitude 3.5 to 4.0. Now even that fainter magnitude was too bright. For the past 2+ weeks the comet has failed to brighten as seen from Earth. The plot below shows a fit (red line) to visual observations from early April to June 10. If the comet had continued to brighten at that rate it would be brighter than magnitude 4 by now. The blue curve is a fit to observations since June 10 and shows a comet that is at its peak and may even fade a little before reaching perihelion.

Apparent visual lightcurve for Comet C/2009 R1 (McNaught). Visual observations from the ICQ/CSC, COBS, CometObs. Created with Seiichi Yoshida's COMET program. Credit: Carl Hergenrother.

.

How can the comet fade before reaching perihelion? The next plot shows how we can more accurately measure the brightness behavior of a comet. First the comets magnitude is normalized to a distance of 1 AU from Earth and to a phase angle of 0 degrees. Normalization to a geocentric distance of 1 AU is done by subtracting 5 log (Δ) from the magnitude, where Δ is the distance from Earth in AU at the time of the observations. Normalization to 0 degrees phase angle is done with Joseph Marcus’ function for dust scattering. I’m not going to go into any more detail on the Marcus function but interested readers will find it in the journal International Comet Quarterly, Vol. 29, No. 4.

The lightcurve shows a comet brightening at a normal and healthy rate until the comet reached a distance of 0.7-0.8 AU from the Sun. A brightening rate of 9.0 log r is in the ballpark for a long-period comet like McNaught. (Note, I discarded a few April observations from the fit because they seem to be a few magnitudes to faint. At this preliminary stage, their exclusion produces a more realistic fit to the April/May/early June data.) Sunward of ~0.7-0.8 AU the comet’s brightening slows considerable.

Heliocentric lightcurve for Comet C/2009 R1 (McNaught) normalized to 1 AU from Earth and o deg phase angle. Visual observations from the ICQ/CSC, COBS, CometObs. Credit: Carl Hergenrother.

.

Another way to plot the data for McNaught suggests that the comet is producing less gas and dust and in an absolute sense has been fading for 2 weeks now. The below plot is not only normalized to 1 AU from the Earth and to o degrees phase angle but also to 1 AU from the Sun. In this case a 5 log (r) term is subtracted from the visual magnitude in addition to the 2 normalization terms mentioned above. An object that was releasing a constant amount of gas and dust would have a horizontal line with no slope on the plot, an object releasing more gas/dust as it approached the Sun would show a positive slope (line going up and to the right) while an object releasing less gas/dust would have a negative slope (line going down and to the right). For some reason Comet McNaught saw its gas/dust production start to decrease after reaching a distance of 0.7-0.8 AU from the Sun, or roughly around the date of June 10.

Heliocentric lightcurve for Comet C/2009 R1 (McNaught) normalized to 1 AU from Sun and Earth and o deg phase angle. Visual observations from the ICQ/CSC, COBS, CometObs. Credit: Carl Hergenrother.

.

Extrapolating the latest brightness trends gives us a better idea of where the comet stands when compared to other comets that had perihelia of ~0.4 AU.

Peak absolute magnitude (near perihelion) of long-period and Halley-type comets. Credit: Carl Hergenrother.

.

So what’s happening to Comet McNaught? The comet is a dynamically “new” comet. In layman’s terms the comet is on its first pass through the inner Solar System after spending the past 4.5 billion years in deep freeze in the outer reaches of the Solar System. We can tell this by its orbit which is nearly parabolic. The early brightness was due to very volatile ices which sublimate at low temperatures. These very volatile ices have now been depleted and the comet is relying on the usual assortment of cometary ices (water ice, carbon monoxide, etc.) to drive the creation of a coma and tail. So in a way, the comet faked us out by acting bigger and brighter than it really was.

“New” comets have been seen before and they have disappointed before. The most famous was Comet Kouhotek in 1973/74. Back in my early years of comet observing, C/1989 X1 (Austin) was predicted to be a bright comet. I even remember an issue of Sky and Telescope magazine with a cover tagline of “Monster Comet Coming”. As the lightcurve below shows, the comet brightened normally until it was about 1.2 AU from the Sun. After that the comet’s dust/gas production decreased even though perihelion was at a small distance of 0.35 AU. Rather than a brilliant naked eye comet, Austin was a 5th magnitude fuzzball even though it passed much closer to Earth than Comet McNaught ever will.

As for the future of Comet McNaught, it will poorly visible very close to the horizon for the next week or so. After that the comet will be forever invisible to northern observers. Perhaps observers in the southern hemisphere will get a shot at a rapidly fading McNaught in a few months. After that the comet will probably never be seen again. Its current orbit is hyperbolic which means the comet will be ejected from the Solar System never to return.

Heliocentric lightcurve for Comet C/1989 X1 (Austin). Visual observations from the ICQ. Credit: Carl Hergenrother.

Partial Lunar Eclipse Tonight

Sheesh… I almost forgot. Tonight a partial lunar eclipse will occur over much of North and South America, the entire Pacific Basin, and eastern Asia.

The Moon will enter the umbra (darkest part of the Earth’s shadow) at 10:16 UT (6:16 EDT, 3:16 PDT) on June 26. Mid-eclipse occur at 11:38 UT (4:38 PDT). The Moon leaves the umbra at 12:59 UT (5:59 PDT).

The eclipse is partial because only about 50% of the Moon will be in the dark umbral shadow of the Earth.

For more info see NASA’s page on the eclipse here.

Looking ahead, mark December 21/22 on your calendar. On that night a total Lunar eclipse will be visible high in the sky over all of North America.

Tonight’s Comet McNaught Finder Charts

The comet is still an easier (easier being a relative term) object to see in the morning sky. It also helps to live further north. In fact, it is impossible to see the comet south of the equator.

The comet is still in northern Auriga a few degrees to the east of the 0th magnitude star Capella. For observers requiring a better, fainter star chart, try this one.

Finder chart for finding Comet C/2009 R1 on the evening of June 26 and morning of June 24. Created with Stellarium.

Finding Comet McNaught Tonight (June 23/24)

Comet C/2009 R1 (McNaught) is still 2 weeks from perihelion (its closest approach to the Sun). Unfortunately it has become a difficult object to see as it is located very close to the northwest horizon in evening twilight and close to the northeast horizon in morning twilight. Also not helping is the fact that the comet’s brightening trend has stalled for the past 2 weeks at magnitude 5.0 to 5.5. More on that later today when I present another analysis of its lightcurve.

Last night I woke up early in the morning and attempted to observe the comet. Luckily for me the comet rose above the mountains right between 2 trees to the northeast of my house. Though visible in 10×50 binoculars, the comet was only slightly fuzzy and I probably would not have recognized it as a comet if I wasn’t already looking for it. At magnitude ~5.5 it might have been visible as a faint star to observers under very dark skies.

Below are rough finder charts for finding the comet this evening and morning. Though visible in the evening, the comet is easier (relatively) to see in the morning sky. Regardless of morning or evening, you will need an unobstructed view of the horizon. Also binoculars or a telescope will help. If you are lucky enough to live where it is very dark, then you might see if with just your eye. In that case the comet will appear as a faint star. In small binoculars, the comet will appear as a slightly fuzzy star (though under dark skies a tail may be visible). With larger binoculars or in a telescope the comet should be an obvious blue-green “fuzz ball” with a faint tail extending away from the horizon. Try using the bright 0th magnitude star Capella as a guide to where to find the comet. For observers requiring a better, fainter star chart, try this one.

Finder chart for finding Comet C/2009 R1 on the evening of June 23 and morning of June 24. Created with Stellarium.

Meteor Activity Outlook for June 19-25, 2010

The Meteor Activity Outlook is a weekly summary of expected meteor activity written by Robert Lunsford, Operations Manager of the American Meteor Society and contributor to this blog. The original unedited version of this week’s Meteor Activity Outlook can be found at the American Meteor Society’s site.

June is another slow month for meteor activity. There are no major showers active in June and only the Antihelion source can be counted on for continuous activity. Even the Antihelion is located so far south this time of year that rates rarely exceed two per hour as seen from the northern hemisphere. Sporadic rates reach their nadir in June as seen from the mid-northern hemisphere (45 N). Sporadic rates seen from the mid-southern hemisphere (45 S) continue to rise this month toward a maximum in July.

During this period the moon reaches its first quarter phase on Saturday June 19th. At this time the moon will be located ninety degrees east of the sun and will set near 0100 for observers located in mid-northern latitudes. Next week the waxing gibbous moon will set later and later, shrinking the window of opportunity to view in optimum, dark conditions. The estimated total hourly rates for evening observers this week is ~2 for those in the northern hemisphere and ~3 for those south of the equator. For morning observers the estimated total hourly rates should be ~8 from the northern hemisphere and ~18 as seen from the southern hemisphere. The actual rates will also depend on factors such as personal light and motion perception, local weather conditions, alertness and experience in watching meteor activity.

The radiant positions and rates listed below are exact for Saturday night/Sunday morning June 19/20. These positions do not change greatly day to day so the listed coordinates may be used during this entire period.

The following showers are expected to be active this week:

June Bootids (JBO)

Perhaps a few June Bootids (JBO) may be seen this week during the evening hours, radiating from a position near 14h:44m (221) +49. This area of the sky lies in northern Bootes, ten degrees northwest of the fourth magnitude star Beta Bootis. This radiant is best placed as soon as it becomes dark. Rates at this time should be less than one for those located in the northern hemisphere and near zero for observers south of the equator. Maximum activity is expected on June 27th. With an entry velocity of 18 km/sec., the average June Bootid meteor would be of very slow speed.

Antihelions (ANT)

The wide Antihelion (ANT) radiant is now centered at 18h:44m (281) -23. This area of the sky lies in western Sagittarius some four degrees northeast of the third magnitude star Kaus Borealis (Lambda Sagittarii). This radiant is best placed near 0200 local daylight time (LDT) when it lies on the meridian and is located highest in the sky. Due to the large size of this radiant, any meteor radiating from southern Ophiuchus, southern Serpens Cauda, Sagittarius, Scutum, or southwestern Aquila could be a candidate for this shower. Rates at this time should be near one per hour as seen from the northern hemisphere and two per hour as seen from south of the equator. With an entry velocity of 30 km/sec., the average Antihelion meteor would be of medium-slow speed.

Delta Piscids (DPI)

Recent studies of the IMO video database by Sirko Molau and Juergen Rendtel have revealed an active radiant in Pisces this time of year. The Delta Piscids (DPI) are only active for five nights (June 20-24) with maximum activity occurring on June 23rd. On that morning the radiant is located at 00h:44m (011) +06. This area of the sky is located in central Pisces near the fourth magnitude star Delta Piscium. This radiant is best placed during the last hour before dawn when it lies highest in a dark sky. Even at maximum activity hourly rates are expected to be less than one. This shower would be better seen from locations south of the equator where the nights are longer and the radiant would located higher in the eastern sky at the start of morning twilight. With an entry velocity of 71 km/sec., the average Delta Piscid meteor would be swift.

As seen from the mid-northern hemisphere (45N) one would expect to see approximately five sporadic meteors per hour during the last hour before dawn as seen from rural observing sites. Evening rates would be near two per hour. As seen from the mid-southern hemisphere (45S), morning rates would be near fourteen per hour as seen from rural observing sites and three per hour during the evening hours. Locations between these two extremes would see activity between the listed figures. Morning rates are slightly reduced due to moonlight.

The list below presents a condensed version of the expected activity this week. Rates and positions are exact for Saturday night/Sunday morning.

Shower Name                RA     DEC   Vel     Rates
                                        km/s   NH    SH
JBO June Bootids         14h 44m  +49    18    <1     0
ANT Antihelions          18h 44m  -23    30     1     2
DPI Delta Piscids        00h 44m  +06    71    <1    <1

RA - Right Ascension
DEC - Declination
Vel - Velocity relative to Earth (in km per sec)
Rates - Rate of visible meteors per hour from a
        dark site
NH - Northern Hemisphere
SH - Southern Hemisphere

June 9/10 to 17/18 Meteors

It was more of the same over the past week. Meteor rates are still low. With no showers, major or minor, being active, most of the meteors are background sporadics.

It is too bad that rates are so low in June because the weather in Tucson is great for observing. Every night is crystal clear with barely a cloud to be seen. The big question is which will come first, the uptick in meteors that occur every July or the summer rains that herald Tucson’s annual monsoon.

Obs  Date(UT)      Time    TOT SPO ANT
TUS  2010-06-18   05h49m    8   8   0
TUS  2010-06-17   07h49m    10  10  0
TUS  2010-06-16   07h49m    7   6   1
TUS  2010-06-15   07h50m    7   6   1
TUS  2010-06-14   07h50m    8   7   1
TUS  2010-06-13   07h49m    8   7   1
TUS  2010-06-12   07h42m    16  15  1
TUS  2010-06-11   06h25m    7   7   0
TUS  2010-06-10   07h05m    13  11  2

TUS - Camera in Tucson operated by Carl Hergenrother
SDG - Camera in San Diego operated by Bob Lunsford
TotTime - Total amount of time each camera looked for meteors
TOT - Total number of meteors detected
SPO - Sporadics (meteors not affiliated with any particular meteor shower)
ANT - Antihelion

The Latest on Comet McNaught

Comet 2009 R1 (McNaught) is the center of attention in the early dawn sky. The 5th magnitude comet is brightening as it plunges toward the Sun. Though not an impressive sight to the naked eye or in small binoculars, observers with large binoculars and telescopes (or dark skies) will be well rewarded.

I’ve been able to observe the comet a few times over the past few nights. On Monday morning I drove to the outskirts of Tucson to get a glimpse of the comet under dark skies. Though the sky is dark enough so the Milky Way is bright and distinct, the comet was just barely visible to the naked eye. Even then it appeared as nothing more than a faint star where one shouldn’t be. Based on that observation I put its brightness at magnitude +5.3.

In small 10×50 binoculars, the comet was a small fuzz not much bigger than the stars around it. The coma is only ~6 arc minutes across in the 10x50s so this is not a large comet. The gas tail was about a degree in length but was very faint and barely noticeable.

It took my giant 30×125 binoculars to really show the comet in all its glory. The coma (or head) of the comet was a brilliant blue-green. The color being due to the fluorescence of cyanogen (CN) and diatomic carbon (C2) in the comet’s atmosphere. The faint gas tail extended for over 2 degrees. Even a short 0.3 degree dust tail was visible. Interestingly this comet doesn’t show much yellow coloring which is the color of dust (really the color of the Sun reflecting off the dust). The lack of dust makes it a dust-poor or, conversely, a gas-rich comet.

The comet is currently 0.61 AU from the Sun and 1.14 AU from Earth. In 2 weeks it will be at perihelion and only 0.41 AU from the Sun though at a more distance 1.30 AU from Earth. There have been some published reports that the comet will become a brilliant object at 2nd magnitude. Unless there is an unexpected outburst the comet will not get that bright. Based on brightness measurements over the past few months, the comet is on track to peak at a magnitude of 3.5 to 4.0 (see figure below).

Unfortunately the comet will also be dropping closer and closer to the Sun. Even though 3rd magnitude is rather bright for a comet, its close location relative to the Sun will make it very difficult to observe. Most observers will be unable to observe the comet in another week or so, if not already. Even from my dark sky location, the mountains to the north of Tucson are already making it difficult to see the comet before the start of dawn.

Apparent magnitude estimates for Comet 2009 R1 (McNaught) up till June 15. Created with Seiichi Yoshida's COMET program. Credit: Carl Hergenrother.

.

With a little more analysis we can determine if Comet 2009 R1 (McNaught) is a typically bright comet. The plot below shows the peak brightness near perihelion for comets with perihelion distances less than 1.5 AU. The brightness is not the apparent magnitude (how bright the comet looked to observers on Earth) but the heliocentric brightness (brightness of the comet normalized to 1 AU from the observer, 1 AU from the Sun and at a phase angle of zero degrees). This is done to “place” the comets at the same distance and orientation from the Sun and observer and allow a direct comparison between each comet. For example a candle a few feet from you looks much brighter than a distant star but it is the distance that makes it appear brighter. If both candle and star were located at the same distance the star would be many times brighter.

Since Comet McNaught is not yet at perihelion and we don’t know how bright it will be at that time, we plotted its brightness and orbital circumstances for June 14th. It is obvious that it’s a comet of just above average brightness for a comet at that distance from the Sun (the average heliocentric brightness is the blue line). Note that it is about 2 magnitude (6 times fainter) than Comet Halley. I also labeled Comet Hale-Bopp which is an obvious outlier on the plot and truly a once-in-a-lifetime comet.

Peak absolute magnitude (near perihelion) of long-period and Halley-type comets. Position of Comet 2009 R1 (McNaught) is valid for June 14. Credit: Carl Hergenrother.

.

CCD observers have been producing some great images of the comet and its 2 tails. Check out Michael Jager’s website “Comet Pieces” for some of the best images out there.

Thanks to Gianluca Masi of Rome, Italy for sharing some images he took with a Celestron C14 at the Bellatrix Observatory in Ceccano, Italy. I was able to apply a radial gradient filter to bring out the fine detail. The image below shows a multitude of rays in the gas (ion) tail. These rays are very dynamic and can change on hourly time scales. Though there is some evidence of structure in the head of the comet, it is very subtle. This is too bad because well defined dust jets can be used to measure the rotation period of the nucleus and made out dust-producing active areas.

Image of Comet 2009 R1 (McNaught) taken on 2010 June 6.10 UT by Gianluca Masi with the Bellatrix Observatory Celestron C14. Radial gradient processing by C. Hergenrother. Credit: Gianluca Masi/Bellatrix Obseratory.

Follow

Get every new post delivered to your Inbox.

Join 106 other followers