The annual Perseid meteor shower occurs when debris from Comet Swift-Tuttle intercepts the Earth at a high velocity (59 km/s, 133,000 mph). This debris is somewhat diffuse, so we see activity for many days on either side of the peak. Like most meteor showers, this is named for the constellation its members appear to originate in: Perseus.

Shower Summary

This is a composite image of 96 meteors collected between sunset on August 11 through sunrise on August 12. Since the images were collected over many hours, the radiant of the shower is not in a fixed location. However, because most of the meteors occurred between 2am and dawn, and because the radiant's high declination means it doesn't move fast, most of the meteors appear to point back to the same general area of the sky - just above the left center of the image. Note also that meteors farther from the radiant tend to make longer trails, since they have a smaller component of their velocity towards the camera.

We had a strong monsoonal weather pattern here during August, and many nights have been cloudy. Fortunately, the peak nights of August 11/12 was clear, although the Moon interfered somewhat. In this composite, the Moon has been digitally removed.

Long string-like images are stars or planets captured as they traveled across the sky over many hours. Jupiter can be seen trailing across the sky in the lower right corner. Bright star trails are evident for Capella, Aldeberan, Debeb, Vega, and Altair.

Update: the shower continued very strong on the night of August 12/13 (along with clear skies), and I recorded an additional 115 Perseids. Mouse over the image at left to see a composite of the two nights, showing a total of 211 meteors. Also, we've set up a new allsky camera on the roof of the Denver Museum of Nature and Science, replacing the old mirror-based camera that was removed while the Museum did roofing work and added a large solar power system. The night of August 12/13 saw the first new data from the Museum in a long time, and it is of excellent quality. Here is a composite of the night's meteors, showing 149 separate events. Note how much brighter the Denver night sky is than that over Guffey!

Selected Fireball Videos

• 2009.08.12 00:33:50 MDT - very long trail, nearly overhead
• 2009.08.12 02:02:49 MDT - long trail with slight terminal explosion
• 2009.08.12 05:09:16 MDT - caught in morning twilight
• 2009.08.12 22:09:56 MDT - under Denver's light pollution; note mag -4 Venus rising at the left
• 2009.08.12 23:35:56 MDT - slight burst near endpoint
• 2009.08.13 02:26:53 MDT - note faint persistent trail
• 2009.08.13 05:41:48 MDT - in the dawn sky, passing close to the Moon

Perseid Time Distribution

This graph plots the distribution of meteors on August 11/12 and on August 12/13. Local sunrise was at UT 12:15, with twilight starting about UT 11:15. The strong peak of activity at 08:15 on August 12 was previously predicted, and is the result of a debris filament shed by Comet Swift-Tuttle in 1610 (an important year in the history of astronomy, being when Galileo reported his discovery of Jupiter's four large moons, Ganymede, Europa, Io, and Callisto).

The hourly rate as given is normalized from 15-minute sampling bins, and is not corrected for either zenith position or camera sensitivity. Visual rates were higher than this.

Visual observations submitted to the International Meteor Organization strongly suggest a broad outburst of activity on August 13 between UT 5:00 and 7:00. This is weakly seen in the Cloudbait data, but nowhere near as strongly as seen in the IMO data.

Broader Shower Activity

All 211 meteors in the above composite Cloudbait image (both nights combined) are Perseids, seen here in red. Also captured, but filtered from the composite, were 15 Alpha Capricornids (yellow), 14 Kappa Cygnids (green), 17 Southern Delta Aquariids (magenta), and 63 sporadics (blue). Some of the sporadics are probably associated with one of the currently active showers, mainly the Perseids, but were simply too short or too badly located on the sky to determine their radiants with enough accuracy to positively identify them. The radiants can be determined much more accurately when meteors are caught on more than one camera, but this data is all from a single camera, and radiants are simply estimated by projecting each meteor path backwards and determining if it crosses a known radiant active on that particular date.