Comet Hergenrother in Outburst

Fourteen years ago, a 25 year old version of myself stumbled across a faint new comet in the constellation of Aquarius. Circling the Sun every ~7 years, the comet is intrinsically faint and could be rightly considered a runt. This year the comet was perfectly placed with perihelion and opposition occurring within days of each other (perihelion on October 1). As a result this comet which only comes within 1.41 AU of the Sun is also passing within 0.42 AU of Earth. Based on its previous behavior it should have only brightened to 14-15th magnitude which is nothing special. Surprisingly it has experienced a series of outbursts and is now bright enough to be seen in small telescopes or even binoculars at magnitude 9.2 to 9.8.

Discovery images of Comet 168P/Hergenrother from Nov. 22, 1998. Credit: Catalina Sky Survey.

I’m probably one of the last people to write about the outburst of comet 168P/Hergenrother which is surprising since it’s one of my finds. It was discovered on images taken with the Catalina Schmidt (then a 0.41-m) telescope during the course of the Catalina Sky Survey (CSS). It was the 2nd of my four comet discoveries and my first CCD find [my first comet, C/1996 R1 (Hergenrother-Spahr) was found with photographic film]. Though I was the first to spot the comet the actual images were taken by either me, John Brownlee and/or Tim Spahr. Discovery images can be seen to the right. It’s not much to look at and the bad column sure didn’t help.

At that time, the CSS had just finished upgrading the Schmidt from a photographic instrument to a digital CCD equipped instrument. We still had a ways to go and didn’t even have automatic detection software yet. Instead we would take 3 images spaced about 10-15 minutes apart and difference (subtract one image from another after lining them up relative to field stars) 2 of the images. Objects that didn’t move such as stars would mostly disappear leaving a positive and negative spot for moving objects. We would then blink all three of the original images to make sure our suspects were real objects. It was highly inefficient but resulted in a few new near-Earth asteroid and comet discoveries before the automated detection system was available.

The 2012 return started routinely wit the comet brightening up to its expected 15th magnitude. The first sign of outburst activity was reported by J. J. Gonzalez (Spain) who visually sighted 168P at magnitude 11.2 on September 6. A second outburst must have occurred around the start of October. By October 3rd, observers such as Michael Mattiazzo (Australia) were reporting the comet at magnitude 9.8. Over the last few weeks brightness estimates have ranged between 9.2 and 10.0.

My own estimates are given below:

Oct. 11.10, 9.2, 6′ (C. W. Hergenrother, Tucson, Arizona, 30×125 binoculars);
Oct. 09.13, 9.6, 6′ (C. W. Hergenrother, Tucson, Arizona, 30×125 binoculars);
Oct. 08.19, 9.3, 3′ (C. W. Hergenrother, Tucson, Arizona, 30×125 binoculars);
Oct. 04.10, 9.8, 1.5′ (C. W. Hergenrother, Tucson, Arizona, 30×125 binoculars);
Oct. 04.10, 9.9, 2′ (C. W. Hergenrother, Tucson, Arizona, 0.31-m reflector).

The comet was easy in 30×125 binoculars from my backyard (LM = +5.7-6.0). Though the comet was visible in 10×50 binoculars it was hard to make an accurate brightness estimate due to the dense star field. My yard is fairly dark for a suburban site. If you live under brighter skies a larger telescope will be required to see the comet.

Since the start of its outbursts, the comet has looked relatively normal in CCD images with no sign of jets or secondary nuclei. Yesterday, Gianluca Masi (Italy) emailed me with images showing a ‘cloud’ of material tailward of the nucleus. Luckily I was scheduled on the University of Arizona’s Kuiper 1.5-m telescope and was able to confirm Gianluca’s observation. The image below shows the “cloud” trailing the nucleus in the anti-solar direction.

.

So what’s happening? Luckily we saw something similar back in 2006 when comet 73P/Schwassmann-Wachmann 3 made a close approach to Earth. SW3 had undergone a splitting event back in 1995 which produced two major components (the original nucleus and a smaller secondary one). The smaller component (called 73P-B) was still experiencing outbursts and shedding material in 2006. From time to time, “clouds” of material would appear to drift back from the nucleus. High-resolution images showed this “cloud” to be composed of hundreds of small mini-comets, many probably no larger than a meter in size. As these mini-comets disintegrated they would produce short-lived mini-comae that lasted for only a day or so.

Look familiar?

Comet 73P-B (Schwasmann-Wachmann 3) as seen on 2006 Apr. 19.49 UT in Sloan i filter images taken with the Smithsonian Astrophysical Observatory SAO 1.2-meter on Mount Hopkins. Credit: Carl Hergenrother.

.

Only a few weeks later the Hubble Space Telescope and ground-based telescopes such as the Vatican 1.8-m were able to resolve 73P-B’s “clouds” into a group of hundreds of mini-comets. More images of 73P-B taken with the SAO 1.2-m, Kuiper 1.5-m and VATT 1.8-m can be found here.

Image of comet 73P-B on 2006 May 1.3 UT with the Vatican 1.8-meter on Mount Graham. Credit: Carl Hergenrother.

.

Could the same thing be happening with 168P? Possibly. Right now we aren’t sure what is exactly going on with 168P. The fact that the comet is experiencing outbursts means it is releasing a large amount of dust. It is very possible that it has also released a number of meter sized boulders. These boulders may be releasing dust causing the “cloud” visible trailing the main nucleus. Perhaps larger telescopes will provide better images over the coming weeks.

In the meantime, the comet is still visible to small telescope users as it moves northward from Pegasus to Andromeda. A finder chart can be found at Comet Chasing.

I can’t lie that I’ve had been waiting for this apparition of 168P and hoping it would become bright enough to be seen visually. As both an amateur and professional astronomer I still get a thrill seeing a comet with my own eyes. Having it be one of mine makes it even better. (Of my four discoveries, this is the 2nd I’ve been able to see visually. C/1996 R1 was 10th magnitude at discovery.) I look forward to seeing what other surprises 168P throws our way.

Good job, little 168P!

Orionids Peak This Weekend

Everyone know that the most famous comet is Comet Halley. Once every 76 years or so, Hally visits the inner Solar System. Sometimes is can be quite spectacular (such as in 1910), other times not so much (as in 1986). For those that missed Halley in ’86, it will be back again in 2061. If you don’t want to wait that long, there is a way to see pieces of Halley every year. Dust released by Halley over the past few thousand years produce meteor showers in early May (the η-Aquariids) and mid-October (the Orionids).

Computer simulations of the past movements of Halley and its dust suggest that many of this year’s Orionid meteors were released by Halley between 1265 BC and 910 BC (for some points of reference, the Trojan War took place around 1200 BC and King David ruled around 1000 BC).

This year the Orionids are forecast to peak tonight (Oct 20/21) though this shower usually produces high rates for a few days on either side of its peak time. According to the Live ZHR page on the International Meteor Organization’s page, rates last night reached a ZHR of 20-30. Tonight rates should be a little better, probably between 30-40. ZHR’s been as high as 70 per hour in the past but during the last 2 years ZHRs only reached 35-45 per hour. This year’s activity should be similar to the last few years.

The Orionids appear to come from an area in northern Orion. This area, called the radiant, rises around 10pm local time. It is best to wait till the radiant is high in the sky before looking for meteors (say 1am). The radiant is highest around 3:30am which is the best time to look. Meteors can appear anywhere in the sky so you don’t have to look at the radiant. The chart below is for around 3-4am local time and shows the radiant and directions of the Orionids.

.

Hints for watching the Orionids:

  1. Orionid meteors are not visible before ~10-11 pm. Even then the radiant is too low to see many meteors. It is best to go out sometime between 2 am and the start of dawn.
  2. Even though the Zenithal Hourly Rate (ZHR) for the Orionids may be as high as 40 per hour this year.  Most people will see fewer meteors. The ZHR is calculated for perfect conditions (radiant overhead, dark skies, and no obstructions in your view). If you observe from rural areas where the Milky Way is bright and obvious you might see 40 per hour. Suburban skies were the Milky Way is just barely visible will probably only produce 10-20 per hour. City observers will see only a few per hour.
  3. It may take some time to see some meteors. Going out for a minute or two won’t cut it. Plan to spend at least 30 minutes of more outside. Also allow your eyes some time to get adapted to the dark. It will take at least 10-20 minutes after walking out of a well-lit house to start seeing faint enough to see most Orionids.
  4. Find a spot that is safe, free of as many obstructions (trees, buildings, etc) as possible and free of annoying lights shining in your face. This is not always possible these days. You don’t need to look directly at the radiant. In fact, it is better to place the radiant just outside your field of view. As long as you do this, it won’t matter what direction you look in.
  5. Be prepared to be cold. The early October mornings can get very chilly. Dress warm and bring a blanket. Also plan to be as comfortable as possible. A nice reclining chair works great. It will keep your neck from being strained and keep you off of the cold ground.
  6. Enjoy the show! The split second meteors are tiny dust grains from Comet Halley released thousands of years ago; are hitting the Earth’s atmosphere at speeds of ~40 miles per second (~66 km per second) and are burning up 60 miles (100 km) above your head.

Meteor Activity Outlook for October 20-26, 2012

The following is a slightly edited version of Bob Lunsford’s excellent weekly summary of meteor activity. The original version can be found at the American Meteor Society’s site.

Meteor activity in general increases in October when compared to September. A major shower (the Orionids) is active all month long with many minor showers. Both branches of the Taurids become more active as the month progresses, providing slow, graceful meteors to the nighttime scene. The Orionids are the big story of the month reaching maximum activity on the 22nd. This display can be seen equally well from both hemispheres which definitely helps out observers located in the sporadic-poor southern hemisphere this time of year.

During this period the moon reaches its first quarter phase on Sunday October 21st. At this time the moon is located ninety degrees east of the sun and well set near 2300 (11pm) local daylight time (LDT). As the week progresses the waxing gibbous moon will set later and later in the morning, interfering with meteor observing. The estimated total hourly meteor rates for evening observers this week is near three for observers located at mid-northern latitudes and two for observers in mid-southern latitudes. For morning observers the estimated total hourly rates should be near thirty eight from the mid-northern hemisphere and twenty seven from the mid-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. Rates during the evening hours are reduced this week due to moonlight.

The radiant (the area of the sky where meteors appear to shoot from) positions and rates listed below are exact for Saturday night/Sunday morning October 20/21. These positions do not change greatly day to day so the listed coordinates may be used during this entire period.

The following radiants are expected to be active this week:

The Northern Taurids (NTA) are now active from a large radiant centered at 02:40 (040) +19, which lies in central Aries, eight degrees southeast of the second magnitude star Hamal (Alpha Arietis). The radiant is best placed near 0200 local daylight time (LDT), when it lies highest above the horizon. Maximum activity is not expected until November 13, so current rates would be 1-2 per hour, no matter your location. Meteors from the Northern Taurids strike the atmosphere at 29km/sec., which would produce meteors of slow velocity.  You must face in the general direction of the north and south Taurid radiants in order to tell them apart.

The Southern Taurid (STA) radiant is currently located at 02:48 (042) +11. This position lies near on the Cetus/Aries border, very close the the fourth magnitude star Mu Ceti. This radiant is best placed near 0200 local daylight time (LDT), when it lies on the meridian and is located highest in the sky. Maximum occurred on October 9th, so rates would now be near two per hour when the radiant lies high in the sky. With an entry velocity of 29 km/sec., the average Southern Taurid meteor would be of slow velocity.

The Orionids (ORI) reach maximum activity on mornings of October 21st and 22nd. The radiant is currently located at 06:20 (095) +16, which is in the northeastern Orion, four degrees west of the second magnitude star Alhena (Gamma Geminorum). The radiant is best placed for viewing near 0500 when it lies on the meridian and is highest above the horizon. At this time of night one should be able to count at least 20 shower members per hour from rural locations. Good rates can actually be seen any time during the morning hours. Orionid meteors are equally well seen either side of the equator. With an entry velocity of 67 km/sec., most activity from this radiant would be swift. This display does not have a sharp peak so activity seen after moon set after the 22nd should be good. Unfortunately the moon will begin to interfere late in the week.

The Epsilon Geminids (EGE) are active all month long with low hourly rates. Even at maximum activity only three shower members per hour are expected. Recent research by the IMO has indicated an earlier maximum of October 15th, rather than October 19th. The radiant position is currently located at 06:56 (104) +28. This position lies in northern Gemini, four degrees northeast of the fourth magnitude star Mebsuta (Epsilon Geminorum). The radiant is also best placed during the last dark hour before dawn, when it lies highest above the horizon in a dark sky. Rates would be near two per hour as seen from the northern hemisphere and less than one per hour as seen south of the equator. With an entry velocity of 70 km/sec., most activity from this radiant would be swift.

The Leonis Minorids (LMI) are active from October 16-27 with maximum activity occurring on October 23rd. This radiant is currently located at 10:36 (159) +37, which places it in northeast Leo Minor, four degrees northeast of the fourth magnitude star Beta Leonis Minoris . The radiant is best placed just before dawn when it lies highest in a dark sky. This shower is better situated for observers situated in the northern hemisphere where the radiant rises far higher into the sky before the start of morning twilight. At 60km/sec., the average Leonis Minorid is swift.

As seen from the mid-northern hemisphere (45N) one would expect to see approximately ten 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 five per hour as seen from rural observing sites and one per hour during the evening hours. Locations between these two extremes would see activity between the listed figures. Rates during the evening hours are reduced this week due to moonlight.

The list below presents a summary of the expected activity this week. Rates and
positions are exact for Saturday night/Sunday morning, but may be used all week.

Northern Taurids (NTA) – 02:40 (040) +19   Velocity 29km/sec
Northern Hemisphere – 2 per hr   Southern Hemisphere – 2 per hour

Southern Taurids (STA) -02:48 (042) +11   Velocity 29km/sec
Northern Hemisphere – 2 per hr   Southern Hemisphere – 2 per hour

Orionids (ORI) 06:20 (095) +16   Velocity 67km/sec
Northern Hemisphere – 20 per hr   Southern Hemisphere – 18 per hour

Epsilon Geminids (EGE) 06:56 (104) +28   Velocity 70km/sec
Northern Hemisphere – 2 per hr   Southern Hemisphere – <1 per hour

Leonis Minorids (LMI) – 10:36 (159) +37   Velocity 60km/sec
Northern Hemisphere – 2 per hr   Southern Hemisphere – <1 per hour

Clear Skies!
Robert Lunsford
American Meteor Society

Meteor Activity Outlook for October 13-19, 2012

The following is a slightly edited version of Bob Lunsford’s excellent weekly summary of meteor activity. The original version can be found at the American Meteor Society’s site.

Meteor activity in general increases in October when compared to September. A major shower (the Orionids) is active all month long with many minor showers. Both branches of the Taurids become more active as the month progresses, providing slow, graceful meteors to the nighttime scene. The Orionids are the big story of the month reaching maximum activity on the 22nd. This display can be seen equally well from both hemispheres which definitely helps out observers located in the sporadic-poor southern hemisphere this time of year.

During this period the moon reaches its new phase on Monday October 15th. At this time the moon is located near the sun and is invisible at night. As the week progresses the waxing crescent moon will enter the evening sky but will not interfere with meteor observing. The estimated total hourly meteor rates for evening observers this week is near four for observers located at mid-northern latitudes and three for observers in mid-southern latitudes. For morning observers the estimated total hourly rates should be near twenty from the mid-northern hemisphere and thirteen from the mid-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 (the area of the sky where meteors appear to shoot from) positions and rates listed below are exact for Saturday night/Sunday morning October 13/14. These positions do not change greatly day to day so the listed coordinates may be used during this entire period.

The following radiants are expected to be active this week:

The center of the large Southern Taurid (STA) radiant is currently located at 02:24 (036) +10. This position lies near on the Cetus/Aries border. The fourth magnitude star Xi 2 Ceti lies two degrees southeast from the center of the radiant. The radiant is so large that Southern Taurid activity may also appear from eastern Pisces, Aries, northern Cetus, northern Eridanus, and western Taurus. This radiant is best placed near 0200 local daylight time (LDT), when it lies on the meridian and is located highest in the sky. Maximum occurred on October 9th, but rates remain near maximum levels of three per hour for a week after this date. With an entry velocity of 29 km/sec., the average Southern Taurid meteor would be of slow velocity.

The Orionids (ORI) are producing 3-5 shower members per hour during the last few hours before dawn, when the radiant lies highest in the sky. The radiant is currently located at 06:00 (090) +16, which is in the northeastern Orion, eight degrees northwest of the brilliant first magnitude orange star Betelgeuse (Alpha Orionis). Orionid meteors are equally well seen either side of the equator. With an entry velocity of 67 km/sec., most activity from this radiant would be swift. Maximum activity is predicted to occur on the 22nd when hourly rates should be near twenty.

The Epsilon Geminids (EGE) are active all month long with low hourly rates. Even at maximum activity only three shower members per hour are expected. Recent research by the IMO has indicated an earlier maximum of October 15th, rather than October 19th. The radiant position is currently located at 06:27 (097) +29. This position actually lies within the borders of Auriga, just east of the faint star Kappa Aurigae. The radiant is also best placed during the last dark hour before dawn, when it lies highest above the horizon in a dark sky. Rates would be near two per hour as seen from the northern hemisphere and less than one per hour as seen south of the equator. With an entry velocity of 70 km/sec., most activity from this radiant would be swift.

Studies of the IMO’s video database by Sirko Molau and Juergen Rendtel has revealed a radiant active in Lynx this time of year. Earlier visual observations of this activity placed the radiant in eastern Auriga. Therefore the radiant is known as the Psi Aurigids (PSA). This radiant is active from October 8-18, with maximum activity occurring on the 12th. The radiant drift is not well established as positions jump around quite a bit during its ten day activity period. At maximum the radiant is located at 07:36 (113) +47. This position lies in a remote area of central Lynx. The nearest bright star is second magnitude Castor (Alpha Geminorum), which lies fifteen degrees to the south. This is a weak display and even at maximum activity rates would most likely be less than one shower member per hour, no matter you location. With an entry velocity of 68 km/sec., most activity from this radiant would be swift.

Studies of the IMO’s video database by Sirko Molau and Juergen Rendtel has also revealed a radiant active in Ursa Major this time of year. The October Ursae Majorids (OCU). are active from October 15-20, with maximum activity occurring on the 16th. At maximum the radiant is located at 09:36 (144) +65. This position lies in western Ursa Major, near the faint star 23 Ursae Majoris. This area of the sky is best placed during the last hour before morning twilight, when it lies highest above the horizon in a dark sky. At maximum activity rates would most likely be 1-2 per hour. Due to the high northern location of this radiant, these meteors are not well seen from the southern hemisphere. With an entry velocity of 54km/sec., most activity from this radiant would be medium-swift.

The Leonis Minorids (LMI) are active from October 16-27 with maximum activity occurring on October 23rd. Hourly rates would be less than one this week. This radiant is currently located at 10:16 (154) +38, which places it in northern Leo Minor, two degrees northwest of the fourth magnitude star Beta Leonis Minoris . The radiant is best placed just before dawn when it lies highest in a dark sky. This shower is better situated for observers situated in the northern hemisphere where the radiant rises far higher into the sky before the start of morning twilight. At 60km/sec., the average Leonis Minorid is swift.

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

The list below presents a summary of the expected activity this week. Rates and
positions are exact for Saturday night/Sunday morning, but may be used all week.

Southern Taurids (STA) – 02:24 (036) +10   Velocity 29km/sec
Northern Hemisphere – 3 per hr   Southern Hemisphere – 3 per hour

Orionids (ORI) 06:00 (090) +16   Velocity 67km/sec
Northern Hemisphere – 4 per hr    Southern Hemisphere – 4 per hour

Epsilon Geminids (EGE) 06:27 (097) +29   Velocity 70km/sec
Northern Hemisphere – 2 per hr   Southern Hemisphere – <1 per hour

Psi Aurigids (PSA) 07:36 (114) +47 Velocity 68km/sec
Northern Hemisphere – <1 per hr Southern Hemisphere – <1 per hour

October Ursae Majorids (OCU)  – 09:36 (144) +65   Velocity 54km/sec
Northern Hemisphere – 1 per hr Southern Hemisphere – <1 per hour

Leonis Minorids (LMI)  – 10:16 (154) +38   Velocity 60km/sec
Northern Hemisphere – <1 per hr Southern Hemisphere – <1 per hour

Clear Skies!
Robert Lunsford
American Meteor Society

 

Live Interview on Comet 168P/Hergenrother

In 15 minutes (5 pm PDT, 6pm MDT, 7pm CDT, 8pm EDT) I will be interviews by Peter Lake and the guys at iTelescopes.net. The interview will be carried live on Youtube. I’ll post the link and try to embed the video below.

Follow

Get every new post delivered to your Inbox.

Join 104 other followers