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Key dates

2007 December 21/22:
Ursid shower outburst,
Ursid MAC mission (proposed).

A chrismas comet(h)!
Parent comet 8P/Tuttle
visible in evening sky,
+5.7 magnitude in Pisces.

Report your observations:
Report your observations of 8P/Tuttle to: pjenniskens [at]

Information for media:
Media inquiries should be directed at the NASA Ames Public Affairs Office: rachel.l.prucey [at]

Ursids at a glance

Date: 2007 December 22
Peak time: peak at about 20 - 22.2 h UT (= 12 h a.m. - 2.2 h p.m. Pacific Standard Time).
Width: 5 - 8.5 hours above half the peak rate

Peak rate: ZHR perhaps 40 - 70 per hour
Meteor brightness: mostly faint meteors?
Shower radiant: constellation Ursa Minor (Radiant at RA = 218.3, Decl. = +75.5)
Entry speed: Vinf = 35 km/s; Vg = 33.52 km/s

Visible from: N. Europe, N. Asia, Arctic
[see flux applet for visibility from your location]

98 percent illuminated, in Taurus, high in the sky

Best viewing direction:
Best viewing: Keep Moon out of field of view (best to block behind obstruction such as telephone pole, then watch whole sky), avoid city haze that scatters moonlight
Best direction: North
Best time: Early evening and early morning when the Moon is low in the sky

Important because:
Hard to see meteor shower outburst that only occurs when the parent comet 8P/Tuttle returns (due January 2008). Old dust that holds clues to how cometary dust weathers the space environment.

Public interest:
The Ursid shower is very hard to observe from the ground, but can be detected with intensified cameras and low-light-level cameras that adjust to the bright Moon background light.

A more direct way to participate in the mission is by observing the parent comet 8P/Tuttle with your telescope and CCD camera when it makes its favorable return in December of 2007 and January of 2008. More information.

More information:
General tips on observing meteor showers from the American Meteor Society and the International Meteor Organization.

Photo credit:
Banner photo shows Earth from the perspective of the approaching Ursid meteoroids, and the orbit of 8P/Tuttle as shown by the Orbit Viewer applet orignially written by Osama Ajiki (AstroArts) and modified by Ron Baalke (JPL).

8P/Tuttle - Image Of The Day

Where is 8P/Tuttle now (from: Heavens Above)?


2007 Dec 31 - IAU Telegram Ursid report

2007 Dec 24 - We are preparing for the next mission (Jan 3, 2008):
the Quadrantid Multi-Instrument Aircraft Campaign

Ursid Shower Highlights

Ursid spectrum
2008 Jan 13 - A composite of four video frames (slightly displaced for clarity) of the meteor spectrum of the 12:42:44 UT Ursid as observed from Fremont Peak Observatory by Peter Jenniskens.

First reports

Initial reports from ground-based observers in Europe seem to confirm that an outburst of Ursids happened close to the predicted peak time. First reports from very few observations put the rate around ZHR = 25/hr, predicted was 40 - 70/hr. The peak time may have been around 21:15 UTC, predicted 20.0 - 22.2 h UTC. The Ursids appear to have been bright. The picture is still very sketchy. Keep tuned - Peter Jenniskens.

Ursid meteor
2007 Dec 23 - Klaas Jobse, Dutch Meteor Society captured these two Ursid meteors from Oostkapelle, the Netherlands [click for larger image]. The Ursids appeared at about 20:30 (-2) and 20:34 (-1) UT. Camera used is a Canon 400 D with 16mm Zenitar F4 lens. The image is a composite of 7 30-s expsorues.

Radio MS counts
2007 Dec 23 - Global-MS-Net observer Jeff Brower of Vancouver, Canada, reported these radio forward meteor scatter counts (at 61.260 MHz), suggesting a peak around 20:30 UT.

2007 Dec 23 (0h UT) - The International Meteor Organization's live website reports a peak rate around ZHR = 25 /hr, albeit based on few visual observations. This rate is much higher than normal Ursid shower activity, confirming that an outburst did occur.

2007 Dec 22 (21:23 UT) - "So far captured 25 URS mean mag. +1.2 and 16 SPORADICS with mean mag. +1.4. The rates picked up a few hours ago, the latest 10 minute radio plot looks decend, may mean the peak was around 21:15 UTC, or is just a temporary drop." - Ilkka Yrjola, Finland.

radio MS data
Radio MS reflections recorded by Esko Lyytinen of Helsinki, Finland, on December 22. Time in UT. The period of outburst activity is marked.

2007 Dec 22 (21:01 UT) - " The weather here got cloudy this evening after I got the first (quite bright) Ursid into my video camera. I heard that Ilkka has it yet clear and has captured a number of Ursids. My radio data seems to been climbing clearly up. Let's see how will it behave." - Esko Lyytinen, Finland.

Ursid meteor

2007 Dec 22 (12:42:44 UT) - Brian Murahashi and Jim Albers captured this bright -5 magnitude 12:42:44 UT Ursid fireball (see below) from an observing site in the Santa Cruz Mountains, California.

Ursid train
Ron Dantowitz and Ari Atinizian at Fremont Peak Observatory.

2007 Dec 22 (12:42:44 UT) - Ron Dantowitz (Dexter and Southfield Schools), student Ari Atinizian (Dexter School), and Peter Jenniskens (SETI Institute) observed from Fremont Peak Observatory and captured the spectrum of a bright -4 magnitude Ursid meteor at 12:42:44 UT in the hours before the peak. The observing interval was from 06:00 to 14:20 UT, with dawn arriving before the onset of the outburst.

Ursid train Ursid train
Peter Jenniskens points to two comets visible in the sky in small telescopes on the night of the Ursid shower maximum, December 22, 2007.


2007 Dec 20 - Ursid story.

2007 Dec 20 - The International Meteor Organization has set up a quick-look page to collect visual observations of the 2007 Ursid shower from ground-based observers worldwide.

2007 Dec 20 - Video podcast on how to observe the Ursid shower courtesy of NASA Ames.

2007 Dec 18 - The 2007 Ursid shower prediction paper offprint is now available (courtesy Chris Trayner, editor JIMO).

2007 Dec 16 - The Geminid shower peaked Dec. 12 - 15 and produced this peculiar video of a not-so-bright Geminid leaving a persistent train. This series of photos was taken with a Canon 400D (16mm f4 Zenitar) digital all sky camera, each 44 seconds exposed at ISO 1600, by Klaas Jobse / Dutch Meteor Society. More pictures at

2007 Dec 14 - Comet Tuttle's rotation period has been determined.

2007 Dec 13 - Feature story on the Ursid meteor shower predictions.

prediction model
Figure: Location of 8P/Tuttle dust ejected between AD 700 and 900. The Earth moves from Right to Left through the cloud of debris on December 22.

2007 Dec 11 - The prediction paper has been accepted for publication in the Journal of the International Meteor Organization, and is now in press.

2007 Dec 10 - Results from the Aurigid Multi-Instrument Campaign were presented at the American Geophysical Union Fall Meeting in San Francisco today.

2007 Dec 10 - Ursid Meteors 2007 announcement IAU Telegram.

2007 Dec 02 - Latest shower outburst predictions point to 2 to 8.5 hour half-peak duration shower with peak rate of about ZHR = 40 - 70 Ursids/hr at 20.0 - 22.2 UT (most likely around 21.4 - 22.2 UT), Dec 22, if seen under ideal circumstances.

2007 Nov 30 - Ursid MAC mission has been given the green light.

2007 Nov 12 - Ursid comet to travel over M33 galaxy on night of Dec 30 17h UT - Dec 31 00 UT.

2007 Nov 03 - Ursid comet now magnitude +12.1, with 3.5 arcminute sized coma, in reach of 0.2-m reflectors according to data listed in International Comet Quarterly.

2007 April 22 - Ursid comet recovered at +20.3 magnitude by Carl W. Hergenrother using the 1.54-m telescope at Catalina Observatory, Arizona ( IAUC 8848).

URSID MAC mission statement: Measure the size distribution and spatial distribution of a cloud of debris that travels with the parent comet 8P/Tuttle to develop a prediction model for this uncharted stream of meteoroids, which is a satellite impact hazard, and to compare to the freshly ejected dust observed in astronomical observations of the comet.

Big old comet the size of Halley returns

Orbiting just outside of Earth is a big old, but seemingly whimpy, comet the size of comet 1P/Halley. This comet called 8P/Tuttle, some 15 km (10 miles) across, is suspected to be a captured Oort cloud comet and is now in a very stable 13.6-year orbit. It has been revolving the Sun now for many tens of thousands if not hundreds of thousands of years. The comet spews as much vapor as does comet Halley, but even in the very favorable upcoming return it makes just barely naked eye visibility because, unlike comet Halley, it does not create a big cloud of smoke. Instead of fine sand and dust, this comet ejects solid matter the size of pebbles and course sand grains that fall appart over time.

Some of this dust evolves into Earth's path and creates the Ursid meteor shower of December. By finding out the age of the shower, and the age of the comet, we can learn how the properties of comet dust change in the inner solar sytem due to collisions with the dust grains of the zodiacal cloud and space weathering effects from solar and cosmic radiation.

Could lead to unusual meteor shower

In December of 1945, a new meteor shower was discovered, active in the days around December 22nd, by meteor astronomers at Skalnate Pleso Observatory in what is now the Slovak Republic. The shower was initially known as the "Umids", some called it "Becvar's shower", but over time it came to be known as the "Ursids". The IAU has adopted the popular name "Ursids", even though the IAU's nomenclature rules would make these the "Ursae Minorids".

At the time, the shower was unusually active and it took until the year 2000, before it was discovered why: the Earth traveled through old dust trails of parent comet 8P/Tuttle ejected in the return of AD 1405 and 1392. This had happened in 1945 and again in 1986, and the predicted return in 2000 was confirmed by observations (see figure below). In all these years, the comet itself was far from the Earth, close to its furthest point along the comet orbit. Astronomers Peter Jenniskens and Esko Lyytinen [paper] showed that the trail of meteoroids took 600 years to evolve its node inwards from where the comet crossed the ecliptic plane (just outside of Earth's orbit) into Earth's path itself. During those 600 years, the dust stayed clumped, and moved in an orbit slightly longer than that of the comet, trapped in the 7:6 mean-motion resonance rather than the 15:13 resonance of the comet, so that after 600 years, the dust delayed the comet by half an orbit.

Radio MS data previous return

Counts of radio reflections during the Ursids in the years around the previous return of the comet to the Sun. 2007 is equivalent to the year 1993. Data: Ilkka Yrjola, Finland.

More unusual Ursid activity: Starting in 1993, Finnish amateur meteor astronomer Ilkka Yrjola of Kuusankoski, detected additional Ursid outbursts that were wider, with a Full-Width-at-Half-Maximum duration of about 8 hours (see figure). These outbursts coincided with the return of comet 8P/Tuttle to perihelion on 1994 June 25. The cause of these outbursts remains unknown.

location of 8P/Tuttle dust

Location of 8P/Tuttle dust ejected between AD 600 and AD 1500. Note how the model explains the aphelion outbursts, but does not account for outbursts at the time when the comet returns. Calculations by Esko Lyytinen and Markku Nissinen, Helsinki, Finland.

Will we see the outburst again this year? Models for ejection of dust in the past 1400 years don't think so (click on figure above for higher resolution version). On the other hand, these models can not explain the outbursts in 1993 and 1994. Indeed, the dust from those outbursts could be much older. The comet has been around for tens or hundreds of thousands of years and the dust could be very old.

The Ursid MAC mission

The Ursid MAC mission will set out to measure if there is an Ursid outburst with the imminent return of the comet and measure the dust size distribution and morphology to compare with astronomical observations of the comet itself.

Comparing the freshly ejected dust of 8P/Tuttle with that observed as Ursids many thousands of years later could provide valuable insight into what happens to comet dust over time, when it collides with the dust particles of the zodiacal cloud and is repeatedly heated by solar radiation.

The predictions

There are no accurate models that predict the coming Ursid outbursts. Little is known about their cause. The predictions below (for December 22 in each year) are those given in Meteor Showers and their Parent Comets, a 790-page handbook on meteor showers by Peter Jenniskens and published by Cambridge University Press in 2006. That study calculated the peak time and peak rate of the Ursid outbursts based on how the planets juggle the younger dust trails around, as calculated by Esko Lyytinen. It is expected that the new observations will help to improve the predictions for future years.

 year   dE-dR Delta_a f_M Sol.Lon. (UT) ZHR
 2007  +0.082 -0.0175 1.0 270.48 20:00 29
 2008  +0.047 +0.2674 1.0 270.54 03:42 54
 2009  +0.096 +0.5435 1.0 270.38 06:00 23
 2010  +0.097 +0.8114 1.0 270.28 09:51 22
dE-dR = Miss-distance between center trail and Earth orbit (in astronomical units).
Delta_a = Position along the comet trail, expressed as the difference in semi-major axis of the original meteoroid orbit shortly after ejection compared to that of the comet(in astronomical units).
f_M = Dilution factor due to spreading of the grains.
Sol. Long. = Solar longitude (J2000) of peak of shower.
UT = Universal Time (hours:minutes).
ZHR = peak Zenith Hourly Rate of the outburst, number of meteors visible to a naked eye observer under good observing circumstances and when the radiant of the shower is in the zenith.

Calculate the rate of meteors at your site

What is the best location for viewing the 2007 Ursid shower? Well, this is not an easy shower to see. There will be a full Moon and the peak is over Europe and Asia, not over the United States. Still, you can calculate the answer yourself with the handy FLUXTIMATOR Java Applet below (courtesy of Peter Jenniskens and David Nugent). Choose the shower, the date, and a nearby location. Check your timezone carefully. The applet then calculates the expected shower rate.

The applet also allows you to see the difference between staying downtown or moving out into the countryside to a dark and clear location. All rates were calculated by taking into account the Moon light, which is pretty bad during the Ursids.

Disclaimer: Make sure that Java is enabled. The duration, peak activity and time of the peaks are based on recent numerical models and past Ursid outburst observations, and may be in error by several hours in peak time, and an unknown amount in peak rate.


NASA Ames Research Center missions website

Aurigid MAC mission website

Further reading on Ursid shower (Chap. 16)

Campaign Highlights

+2007 Dec 21 - Quadrantid MAC mission approved. Quadrantid MAC (Jan. 03-04) will for the first time map the flux profile of the annual Quadrantid shower under nearly unchanged observing conditions throughout the night. The data will be used to determine if the shower could have been created in 1490 AD.

+ 2007 Dec 20 - We learned this morning that our alternative to do a shorter flight from the East coast during this Saturday's Ursid shower is a no-go. Our request proved too short notice to make it work. The good news is that the issue that doomed the Ursid MAC mission appears to have been solved and chances are increasing that the January 3 Quadrantid MAC mission will proceed as planned. We are waiting for a go/no-go decision.

+ 2007 Dec 18 - It is still uncertain whether the mission will proceed as planned.

+ 2007 Dec 16 - Participant Ron Dantowitz reports that spectrographs have been tested: Six fields of view, largest is 40 deg x 30 deg x 11 megapixels with 6 pixels between the sodium doublet. Other FOVs are wide and narrow, with low res for metals and higher resolution and f/0.8 fast lenses. Gratings have max exposure to the higher orders. Helium, neon, and sodium sources were tested.

+ 2007 Dec 14 - Mission patch arrived today.

+ 2007 Dec 13 - Scheduling issues prevent us from moving ahead as planned.

+ 2007 Dec 13 - DLR Cosmic ray exposure counter for Ursid MAC mission arrived today at SETI Institute.

+ 2007 Dec 12 - Ames visitor clearances approved.

+ 2007 Dec 10 - The mission follows conveniently one week after the AGU Fall Meeting in San Francisco (Dec. 10 - 14), where results from the Aurigid MAC mission will be presented.

flight path

Follow the shaddow keeps the aircraft in 14 hours of darkness. The graph shows the Earth as seen from the perspective of the approaching Ursid meteoroids on December 22, 2007, at the peak of the anticipated Ursid outburst.

The Ursid MAC mission is dedicated to observing the December 22, 2007, Ursid shower outburst from altitude, where the Moon is mostly out of the picture, and where the low extinction near the horizon creates a large surface area for counting meteors and for measuring spectra for meteoroid composition.

flight path

Nighttime areas on Earth on Dec 22.

The proposed flight plan would take off from NASA Ames Research Center in California in the early morning hours of December 22, when it is still dark, then fly north-west to stay in darkness. The plane would then fly north to Alaska, over the arctic and Canada, and back to NASA Ames, where we would land just after sunset. This provides for a 14 hour period of darkness.

flight path

First draft flight path

The direction to the Moon (azimuth and elevation) for the flight path shown above is depicted in the graph below. Click on picture for a larger version.

flight path

Elevation and azimuth of the Moon for the flight path shown above. Data: Jim Albers, Lockheed Martin.

A privately owned Gulfstream GV aircraft has been made available for this mission, providing a total of 10 windows to the shower for 14 participating researchers and volunteers.

Confirmed participating scientists are from NASA Ames Research Center, the SETI Institute, Lockheed Martin, Caltech, and the Dexter and Southfield Schools:

portrait Flux

Principal Investigator Dr. Peter Jenniskens is a research scientist with the Carl Sagan Center of the SETI Institute. He is an expert on meteor showers and author of the 790-page book " Meteor Showers and their Parent Comets". He has earlier led an observing campaign to explore the Aurigid shower. He will participate in near-real time flux-measurement team. Other participants will include experienced meteor observer Robin Gray of Nevada.

portrait Models

Meteor astronomer Jeremie Vaubaillon of Caltech, an expert in meteoroid stream modeling, will operate a digital camera to capture Ursid meteors. His Aurigid MAC result was selected as Astronomy Picture of the Day.

portrait Spectroscopy

Juergen Wolf, SOFIA scenior scientist from DLR, at NASA Ames will field test in meteor shower observations a prototype camera for the SOFIA Airborne Observatory.

portrait Spectroscopy

Ron Dantowitz, director of Clay Center Observatory at the Dexter and Southfield Schools, and a student from Dexter School (Ari Atinizian) will deploy CCD cameras for meteor spectroscopy of relatively bright Ursids to study how the meteoroids break and release their volatile minerals.

portrait Size distribution

Jim Albers and Michael Koop of Lockheed Martin will operate a set of low-light-cameras to measure the magnitude distribution of Ursid meteors.

portrait Spectroscopy

Rick Rairden of Lockheed Martin will focus on the near-UV part of meteor spectra, which are difficult to detect due to the properties of the aircraft windows.

portrait Imaging

Ed Schilling, branch chief of the NASA Ames video and graphics branch will lead an effort to image the meteor shower using state of the art HDTV cameras.

portrait Cosmic rays

Dr. Guenther Reitz head of the Radiation Biology Department of the Institute of Aerospace Medicine of the German Aerospace Center (DLR) in Cologne, Germany will focus on measurements of the radiation exposure by cosmic rays in high aircraft flight altitudes.


Preliminary instrument layout (v. Nov. 25)

SETI Institute logo Curator: Peter Jenniskens
Responsible NASA Official: Dave Jordan

Last update: July 01, 2008

Hosted by: The SETI Institute
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