August 9/10 Meteors

The plan was to get myself outside last night and start my 2015 Perseids visual observing campaign. Unfortunately, there were other showers going on in Tucson with rain occurring off and on all night long. My SALSA3 camera system was running and did manage to pick up 3 meteors between the clouds. In short, I can’t personally add much to what the Perseids were up to last night.

Luckily it can’t be cloudy everywhere and others were able to observe the Perseids. Observers from around the world reported observations to the International Meteor Organization. These reports show a shower that is already producing ~25 Perseids per hour. This number comes with the caveat that it is valid for those observing from very dark skies, with no obstructions to their vision and the Perseids radiant overhead. Most observers will be observing under lesser conditions and will see fewer meteors.

In addition to visual observers, automated electronic surveys have also been watching the sky. Up in Canada, the Canadian Meteor Orbit Radar (CMOR) detects small meteors. In many cases, these meteors are smaller and fainter than those visible to the average backyard meteor watcher. A map of the sky from ~17 UT on 2015 August 10 shows a number of active showers. At least for very small particles, the Perseids are not the most active shower. The Southern Delta Aquariids (SDA) appear more active than the Perseids (PER) and the Northern Delta Aquariids (NDA) are a little less active than the Perseids. This will change over the next 2 nights.

 

equatorial_cmos_radar_20150810

Map of meteor radiant locations for 2015 August 10 at ~17 UT from Western Ontario, Canada. Meteors were detected by the Canadian Meteor Orbit Radar (CMOS). Credit: The University of Western Ontario Meteor Physics Group.

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While radar was good at picking up very small meteors, all-sky fireball cameras are excellent at seeing the very largest meteors. What we call fireballs. NASA has a number of cameras set up to “triangulate” the observation of fireballs and determine their original orbits around the Sun. There are 4 groups of cameras in NASA’s All Sky Fireball Network including 3 in the Tucson area that I was somewhat involved in setting up. Even thought the Tucson cameras were hampered by the same rain and clouds that I was at home, the other camera groups detected a number of fireballs. Of the 21 fireballs, 14 of them were Perseids. At least at the large end of the meteor ‘spectrum’ the Perseids are dominating the night sky.

orbital_fireball_20150810

Orbits of fireballs detected on the night of 2015 August 10 UT by NASA’s All Sky Fireball Network. Most of the orbits are similar because most of the fireballs are Perseids. Credit: NASA All Sky Fireball Network/NASA Marshall.

Here come the 2015 Perseids!

The Perseids are one of the 2 annual showers worth getting up early for. This year the peak will occur on the morning of August 13. The Moon will not be a problem this year allowing for a wonderful meteor watching opportunity.

From the International Meteor Organization’s 2015 Meteor Calendar:

The Perseids produced strong activity from an unexpected primary maximum throughout the 1990s, associated with the perihelion passage of their parent comet, 109P/Swift-Tuttle, in 1992. The comet’s orbital period is about 130 years. Further enhanced activity ahead of the usual maximum was last seen in 2004. Recent IMO observations (see HMO p. 145) found the timing of the mean or ‘traditional’ broad maximum varied between λ⊙ ∼ 139.◦8 to 140.◦3, equivalent to 2015 August 13, 01h30m to 14h00m UT. Jeremie Vaubaillon anticipates from theoretical modelling that the dust trail from the comet’s 1862 return should pass closest to the Earth (the separation is about 0.00053 astronomical units, only 80 000 km or so) at 18h39m UT on August 12, although the activity levels are uncertain. Enhanced rates, if they happen at all, may persist for several hours around this potential peak. Plus of course, neither this prediction, nor the nodal crossing time given in the box above, are guarantees of what will occur! New Moon on August 14 means whatever happens, dark skies will prevail for checking on it. Sites at mid-northern latitudes are more favourable for Perseid observing, as from here, the shower’s radiant can be usefully observed from 22h –23h local time onwards, gaining altitude throughout the night. The August 12 peak time especially favours Asian longitudes, while the August 13 near-nodal part of the ‘traditional’ maximum interval would be best-viewed from North American sites, assuming either takes place when expected. All forms of observing can be carried out on the shower, though regrettably, it cannot be properly viewed from most of the southern hemisphere.

Additional information can be found on the American Meteor Society’s webpage at Perseids 2015: the Amateur Guide.

The best time to look will be after about 1-2 am on the night of August 12/13. Meteors will appear to radiate from the constellation of Perseus in the northeast sky.

Over the past few years, the Perseids have peaked with zenithal hourly rates (ZHR) of 68 (in 2014), 109 (in 2013), 122 (in 2012), 58 (in 2011), 91 (in 2010), 173 (in 2009), 116 (in 2008) and 93 (in 2007). These are the rates that would be seen under perfectly dark skies, with no Moon and with the radiant overhead. In reality these conditions are never really met especially if you live anywhere near a city. Still observed rates of 20-40 meteors per hour are possible even under suburban skies.

The Perseids were produced by Comet 109P/Swift-Tuttle which orbits the Sun once ever ~135 years. This comet was discovered by American astronomers Lewis Swift (Marathon, New York) and Horace Tuttle (Cambridge, Massachusetts) in July of 1861. During that return the comet reached a bright 2nd magnitude and developed a tail up to 30° long. The comet returned late in 1992 and brightened up to 4th-5th magnitude. Based on our updated knowledge of Swift-Tuttle’s orbit it is now known that the comet was also seen in 1737 and likely seen in 188 AD and 69 BC.

Back in 1992, Tim Spahr and I used the Catalina schmidt to take a photographic image of Comet Swift-Tuttle (seen below).

Comet Swift-Tuttle observed with the University of Arizona Catalina Schmidt in 1992. This is a scan of a photographic image taken by Tim Spahr and Carl Hergenrother. Credit: Carl Hergenrother/Tim Spahr.

The SALSA3 meteor shower camera has been monitoring the sky every night this summer. Though the weather in Tucson can be hit or miss during the Summer Monsoon season, last night was completely clear allowing SALSA3 to detect 43 meteors with 12 of them being Perseids. These numbers also highlight that there are many other, albeit more minor, showers active as well (such as the Southern Delta Aquariids). The SALSA3 camera system is only sensitive to meteors about 3rd magnitude or brighter (about what you would expect from inside a city like Tucson). Observers under darker skies would have witnessed many more meteors during the course of the night. The Perseids will be getting more active with every night. Right now the shower is producing about 10-20 meteors per hour during the second half of the night. That number will go up to 60-120 per hour by Thursday morning.

Obs Date(UT)     Time    TOT SPO ANT PER SDA SIA ERI KCG Oth
SAL 2015-08-09  09h 14m   43  14  0   12  6   2   4   1   4

SAL - SALSA3 camera in Tucson (Carl Hergenrother)
VIS - Visual observations from Tucson (Carl Hergenrother)
Time - 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 - Antihelions
PER - Perseids
SDA - Southern Delta Aquariids
COM - Southern Iota Aquariids
ERI - Eridanids
KCG - Kappa Cygnids
Oth - other minor showers

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Dec 15-21 Meteors

Last weekend the Geminids reached there 2014 peak. As it usual for this annual shower, they did not disappoint. Observers from around the world reported their Geminid counts to the International Meteor Organization (IMO). As of today (12/21/2014), 105 observers from 28 countries reported 10,360 Geminids to the IMO. A graph of the Geminid ZHR can be seen below.

Geminids2014_ZHR

Rather than a smooth rise, peak and fall, the 2014 Geminids produced at least 3 maxima between mid-December 13 and late December 14. The two highest datapoints correspond to ZHRs of ~160. These rates are a bit suspect since they are based on very few Geminids (hence the large error bars). A more reasonable ZHR peak for this year’s shower appears to be ~130 per hour. This fits in well with the high end of Geminid ZHR rates over the past few years (134 per hour in 2013, 109 in 2012, 198 in 2011, 127 in 2010, 120 in 2009, 139 in 2008, 122 in 2007 and 115 in 2006).

Video meteor watching here in Tucson has been hampered by bad weather over the past week. In addition to a few almost completely clouded out nights (12/17 and 12/18), many nights saw heavy dew and some ground fog form. Still the rapid decrease in the Geminids is apparent as video detected rates fell from 139 on the night of the peak (12/14) to 18 on the 15th and then only a single possible Geminid over the next 5 nights.

Sometimes refered to a major shower, the Ursids are a rather fickle shower prone to outbursts but usually very weak. This year’s Ursids were on the weak side with only ~1 per night being reported by my camera system.

Obs Date(UT)     Time    TOT SPO ANT GEM HYD COM URS Others
SAL 2014-12-21  09h 29m   27  21  2   1   -   1   1    1
SAL 2014-12-20  12h 01m   29  25  1   0   -   1   1    1
SAL 2014-12-19  09h 30m   12  8   1   0   -   0   0    3
SAL 2014-12-18  01h 51m   1   1   0   0   -   0   0    0
SAL 2014-12-17  02h 26m   1   1   0   0   0   0   1    0
SAL 2014-12-16  06h 26m   8   3   0   0   2   0   1    2
SAL 2014-12-15  11h 54m   51  18  4   18  3   1   1    7

SAL - SALSA3 camera in Tucson (Carl Hergenrother)
VIS - Visual observations from Tucson (Carl Hergenrother)
Time - 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 - Antihelions
GEM - Geminids
HYD - Sigma Hydrids
COM - Comae Berenicids
URS - Ursids
Others - other minor showers

Dec 13/14 Geminids Recap

Last night marked the probable peak of the 2014 Geminids. Here in Tucson, we had rain during the day (0.27″) and it was looking iffy as to whether the night would remain clear of clouds and fog. I spent 1h 15m outside between 10:17 and 11:33 pm local time. Though it was very muggy and it sounded like it was still rainy as condensation dripped off the house, the night turned out to be a good one for meteor watching. I was consistently seeing 12-14 Geminids every 15 minutes so just under 1 per minute (with a limiting magnitude of ~6.1).

My camera system had an even better night as it detected 179 meteors of which 139 were Geminids over the course of the night. That is a new record for my meteor camera system having beaten the peak night of the 2010 Geminids by 20 meteors. I will try to get a video from my camera online shortly.

Geminid activity rapidly falls off after the peak. Observers may still be able to see a good number of Geminids tonight though rates will be 1/4 to 1/2 what they were last night.

The International Meteor Organization (IMO) maintains a “live” graph showing the rate of the Geminids as reported by visual observers around the world.

Obs Date(UT)     Time    TOT SPO ANT GEM HYD COM Others
VIS 2014-12-14  01h 16m   71  6   -   65  -   -     -   LM=6.0-6.1
SAL 2014-12-14  12h 41m  179  21  7  139  2   2     8

SAL - SALSA3 camera in Tucson (Carl Hergenrother)
VIS - Visual observations from Tucson (Carl Hergenrother)
Time - 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 - Antihelions
GEM - Geminids
HYD - Sigma Hydrids
COM - Comae Berenicids
Others - other minor showers

Here Comes the Geminids!

Tonight is one of the best nights of the year to see a meteor as the Geminid meteor shower is predicted to reach its 2014 peak. The Geminids are one of two annual showers (the other being August’s Perseids) that are almost guaranteed to produce high rates of meteors (at least one every few minutes or better).

The International Meteor Organization (IMO) maintains a “live” graph showing the rate of the Geminids as reported by visual observers around the world.

How To See Them

This year the Geminids will be near peak intensity on Saturday night/Sunday morning, December 13/14. From a dark, moon-less sky, the Geminids have consistently produced peak rates of ~100 meteors per hour. According to the IMO, the Geminids reached ZHR rates of 134 per hour in 2013, 109 in 2012, 198 in 2011, 127 in 2010, 120 in 2009, 139 in 2008, 122 in 2007 and 115 in 2006. Note, these rates assume ideal observing circumstances that are rarely achieved. Dark sky observers may see rates that approach the ZHR values. Most of us observing under light polluted skies will see lower rates (perhaps much lower for city dwellers or observers watching before 10pm).

Unlike most showers that can only be observed in the early hours of the morning, the Geminids radiant rises as early as 7 pm and a good number of meteors can be seen by 10 pm. The radiant is nearly overhead at 2 am and it still well placed for the rest of the night. This year the Last Quarter Moon (located close to a brilliant Jupiter) will hinder Geminid watching after midnight. The shower can still be observed after Moonrise though fainter meteors will be washed out. It helps to keep the Moon out of your line of sight.

As the name implies, the Geminids appear to radiate from a point in the constellation of Gemini. More specifically from a point just to the north of the bright star Castor, the northern star in the Castor-Pollux pair. During the evening Geminids will be coming out of the northeast. By the middle of the night the radiant will be close to overhead and meteors will be raining down on all sides.

In general it is best not to look directly at the radiant. Meteors are easier to see by looking 30 or more degrees from the radiant (for reference 10 degrees is the width of your hand at arms length). The key is to look up and regardless of where you look you should see quite a few Geminids.

2014_Geminids

The night sky for December 13 at 11:00pm local time over Tucson. The Geminid radiant is shown as a yellow circle with Geminid meteors radiating away from it. Chart produced with Stellarium.

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Sky brightness matters when it comes to seeing most meteors and the Geminids are no exception. As always, the darker the sky the better. If you are located in a place with pitch black skies (mountaintops, middle of the desert, national parks) rates can be as high as ~100 per hour. In rural areas near small towns rates will be a bit lower and probably in the 80-90 per hour range. In the suburbs rates will vary depending on how close to a major city you are but you should expect rates of 20-50 per hour. In a major city rates will be very low though 2-10 per hour should be seen.

To increase your chance of seeing the Geminids find a spot with a clear view of the sky. Any obstructions (trees, buildings, etc.) can block some of the meteors. Also find a spot where lights (streetlights, security lights, etc.) aren’t shining in your eyes. This will allow your eyes to dark adapt and you will be able to see fainter, and more, meteors. The most important thing to remember is to get comfortable when observing. A lawn chair is perfect for reclining back and taking in the sky. Remember that it is cold this time of the year in the Northern Hemisphere so bundle up. It does not take much time, especially when relatively inactive, to start freezing.

Where They Come From

The Geminids were created by an enigmatic object named (3200) Phaethon. For starters Phaethon is an asteroid and only displayed what might be considered cometary activity for a few days in 2009. But meteor showers are created by comets and nearly all comets have orbits that carry them at least as far from the Sun as the orbit of Jupiter. Yet Phaethon only travels out to a distance of 2.4 AU, roughly half the distance to Jupiter’s orbit. Based on its orbit it is hard to call Phaethon anything but an asteroid.

Phaethon2014

Image of Geminid parent body (3200) Phaethon by Jean-Baptiste Kikwaya on 2014 November 27 with the Vatican Observatory VATT 1.8-m.

So what is Phaethon?

1) Phaethon could be a comet whose original orbit evolved into its current one after many millennia of close approaches with the inner planets. The probability of this happening is extremely low. Some models of the formation of the Geminids require the shower particles to be released over many centuries to millennia which is consistent with the behavior of a comet. Then again…

2) Phaethon may be a Main-Belt comet. Main-Belt comets are objects that originate in the outer Asteroid, or Main, Belt. Since they contain a sizable fraction of volatile ices, they can occasionally exhibit cometary activity. Four of these objects have been observed to display cometary activity in the Main Belt. Since they start on asteroid orbits, it is not too difficult for one of them to find itself on an orbit similar to Phaethon. Or behind door #3…

3) Phaethon is an asteroid that broke up in the past. There is evidence to suggest that Phaethon is just the largest piece of a ancient break-up. In fact, two additional asteroids that may once have been a part of Phaethon have been found, (155140) 2005 UD and 1999 YC. According to Peter Jennisken’s book “Meteor Showers and Their Parent Comets”, the Geminids can be explained by the break-up of Phaethon just after perihelion many orbits ago. Since Phaethon gets to within 0.14 AU (14% of the Earth-Sun distance), perhaps it split from the stress of intense solar heating. BTW, this scenario does not rule out Phaethon as a ice-rich Main-Belt comet.

The recent discovery of additional asteroids related to Phaethon points to scenario 3 as the most likely origin of the Geminids. If true, the Geminids were not the result of long-term cometary activity like most meteor showers but were created in a discrete event or events when Phaethon split or shed smaller pieces. The Daytime Sextentids and perhaps the very minor Canis Minorids were created by even older break-up events.

Though Phaethon has behaved like an asteroid since its discovery in 1983 it has been observed to ‘burp’. Near its perihelion, the asteroid is sometimes visible in near-Sun images taken with the STEREO spacecraft and occasionally appears to elongate as if it had a short tail and brighten. Analysis by David Jewitt and Jing Li (UCLA) found that Phaethon did release some surface particles. Due to intense heating (perihelion is 0.14 AU from the Sun or 7 times closer than the Earth is) some of the rocks on the surface may have fractured producing a cloud of dust which was knocked off the surface by solar radiation pressure. In effect, it is a rock comet. Still this event was very short-lived and produced a minimal amount of debris. So these type of events should not have been large enough to create the Geminids by themselves.

I penned a guest post on Phaethon for Dr. Dante Lauretta (PI of NASA’s OSIRIS-REx asteroid sample return mission) back in 2013. You can read it here.

Whether Phaeton is a traditional comet, a volatile-rich asteroid, an asteroid that split into pieces, or a ‘rock comet’, the result is going to be one of the best astronomical shows of the year. So go out and enjoy the show!

August 11-20 Meteors

The Perseids peaked on the night of August 13 UT. Though the monsoon was still cranking and clouds were aplenty, 36 PER were detectedby the SALSA3 camera system.

Visual reports to the IMO show a peak ZHR of ~68. This is the true rate of the shower after correcting for the effects of the Moon-lit sky and the height of the radiant. Since 2007 the peak ZHR of the PERZ have ranged from 58 to as high as 180. 2014’s ZHR of 68 is the 2nd lowest of the past 8 years.

per2014overview

ZHR Live chart for the 2014 Persieds. Credit: International Meteor Organization.

Obs Date(UT)    Time   TOT SPO ANT CAP PER SDA ERI ATR KCG BAR MPR UCE
SAL 2014-08-20 07h 07m  25  17  3   -   3   1   -   1   0   -   -   0
SAL 2014-08-19 00h 36m  2   1   1   -   0   0   -   0   0   -   -   0
SAL 2014-08-18 03h 23m  4   2   1   -   0   0   0   0   1   -   -   0
SAL 2014-08-17 02h 22m  7   5   1   -   1   0   0   0   0   -   0   0
SAL 2014-08-16 04h 43m  16  8   1   -   4   0   0   1   1   -   1   -
SAL 2014-08-15 01h 12m  4   1   0   -   2   0   0   0   1   -   0   -
SAL 2014-08-14 07h 27m  42  9   4   -   20  0   0   1   4   -   3   -
SAL 2014-08-13 03h 10m  40  1   0   -   36  0   2   0   0   -   1   -
SAL 2014-08-12 02h 18m  22  2   1   0   16  1   0   1   0   1   0   -
SAL 2014-08-11 02h 12m  16  3   0   1   8   0   0   1   1   1   1   -

SAL - SALSA3 camera in Tucson (Carl Hergenrother)
VIS - Visual observations from Tucson (Carl Hergenrother)
Time - 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 - Antihelions
CAP - Alpha Capricornids
PER - Perseids
SDA - Southern Delta Aquariids
ERI - Eta Eridanids
ATR - Alpha Triangulids
KCG - Kappa Cygnids
BAR - Beta Arietids
MPR - Mu Perseids
UCE - Upsilon Cetids

August 9-10 Meteors

The past two nights have been a mix of meteor showers and rain showers. Luckily the sky has been clear enough, long enough to still catch one or two dozen meteors per night. Even with the patchy coverage, you can see that the Perseids are the most active shower. Visual observers for the IMO are reporting ZHRs between 20-35. Rates should reach between 60-120 by the middle of the week. Over the past few years the Perseids have peaked at ZHRs of 109 (2013), 90-120 (2012), 58 (2011), 91 (2010), 140-180 (2009), 116 (2008), and 93 (2007). We’ll have to wait and watch to see what this year’s Perseids have in store though the nearly Full Moon will hamper the number of Perseids that can be seen.

The Perseids (PER) will peak on Wednesday morning August 13 UT. Bob Lunsford as written an excellent guide on how to observe this year’s Perseids for the American Meteor Society here.

 

Obs Date(UT)    Time   TOT SPO ANT CAP PAU PER SDA SIA ERI ATR KCG BAR MPR
SAL 2014-08-10 04h 55m  23  7   0   2   1   9   0   -   2   1   1   0   0
SAL 2014-08-09 03h 15m  13  4   1   1   0   4   1   0   0   0   1   1   0

SAL - SALSA3 camera in Tucson (Carl Hergenrother)
VIS - Visual observations from Tucson (Carl Hergenrother)
Time - 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 - Antihelions
CAP - Alpha Capricornids
PAU - Piscis Austrinids
PER - Perseids
SDA - Southern Delta Aquariids
SIA - Southern Iota Aquariids
ERI - Eta Eridanids
ATR - Alpha Triangulids
KCG - Kappa Cygnids
BAR - Beta Arietids
MPR - Mu Perseids