29P Schwassmann-Wachmann 1

The August 2003 Outburst

As recorded in amateur CCDs

Juan Lacruz, sep 2003




Introduction. 1

The outburst of August 2003. 1

The Larson Sekanina filter 2

Coma analysis. 3

The Outburst’s light curve. 5

The sequence. 6

Useful information about 29/P. 6

Other references, 6



Discovered on January 17th  1929 by Schwassmann and Wachmann at Hamburg at magnitude 11, but rapidly faded to magnitude 16. Later on, observations were pre-discovered of the comet at outburst to magnitude 12 in 1902.

Has been seen at 6 returns to perihelion (1908, 1925, 1941, 1957, 1974 & 1989) but, in reality, its almost circular orbit - eccentricity 0.045 - means that its distance from the Sun hardly varies. The comet has a perihelion distance of 5.77AU and a period of 14.9 years; thus its orbit is almost circular outside that of Jupiter. However, both the eccentricity and the period have decreased steadily over the last century, the period from 16.44 years and the eccentricity from 0.15.

Studies of the light curve over the years have shown that outbursts of the kind observed at discovery are common. It occurs at least once a year, despite the fact that the comet is at a heliocentric distance where most objects are inactive or barely active. The magnitude is about 17 in quiescence, but has risen to 9.4 in the largest known outburst. The mechanism of the outbursts is unknown, but their pattern is fairly consistent with the formation of an intense stellar nucleus and a rise in brightness over a few hours or days. The coma expands and forms spiral jets, before fading slowly. The mechanism of the outbursts is currently unknown.

The outburst of August 2003

This outburst was first notified to Observadores_cometas list by Ramón Naves on August 23rd   2003 and then notified to comets-ml list by Diego Rodriguez on August 25th 2003 :

29P in outburst on August 24.050 at 12.9 mag with well defined nucleus and spiral structure within coma.

29P/Schwassmann-Wachmann 1
0029P C2003 08 24.05046 22 36 18.12 -03 34 40.0 12.9 N 213
0029P C2003 08 24.05153 22 36 18.10 -03 34 40.1 12.9 N 213

0029P C2003 08 24.96788 22 35 53.16 -03 36 16.7 13.0 N 458
0029P C2003 08 24.97252 22 35 53.04 -03 36 17.0 13.1 N 458

0029P C2003 08 25.11207 22 35 49.13 -03 36 32.5 13.0 N 442
0029P C2003 08 25.11402 22 35 49.07 -03 36 32.7 13.0 N 442

The observers have measured the brightness in a 10”x10” arc seconds diameter
Photometry with the USNO A2 catalog (in R band)

Diego Rodriguez
code 458
Ramon Naves
Code 213
Albert Sanchez Caso
Code 442

On September the 4th the comet continued active so I decided to take a high resolution (1.16 arc sec per pixel) series of pictures of it with the idea of imaging the coma structure. The night of September the 5th  I started a series of 60 sec. exposures, I was able to take 13 frames before the sky became overcasted. Note that the stars are elongated because the images have been stacked, using Astrometrica, centering on the comet’s nucleus using the speed and position angle as calculated from the orbital elements.

The above image illustrates the current outburst the comet is undergoing, two jets are visible, one at a PA of about 209 deg and another  at a PA of 152 (north is up, east is left).

No spiral structure is apparent, however a few days ago it was detected by other observers, suggesting that the outburst somehow has destroyed such structures, in the second picture of the composite (The sequence) such spiral structure is quite obvious.

The Larson Sekanina filter

To boost the contrast of the jets it’s usual to apply a Larson-Sekanina filter which shows the gradients of luminosity in both, radial and angular displacements. The filter has been applied to the previous picture, the jets are readily evident,

The jet to the south west is curved to the south east, the other jet however seems straight, this suggest that they are probably of a different composition.

A rotational gradient process by Sebastian Hönig done on the same picture

Coma analysis

The following picture is a false colour rendition with an estimate of the coma size encircled, the diameter exceeds  72 arc sec, note that the comet’s nucleus is not the centre of the coma, there’s a noticeable shift of the coma to north east, the north west side of the coma is less dense than the rest.

(north up, east left)

The coma profile shows the asymmetry and allows a better estimation of the coma size,

The decay to the right (west) is quite sharp, the coma size in this section is about 60 pixels which gives 96 arc. sec. diameter.

If we look at the South-North section

(South is left) We can see the slow raise from south to north and the sharp drop past the nucleus, some field stars are apparent, the coma size can be estimated in 70 pixels or about 112”.

The Outburst’s light curve

The following light curves have been elaborated with the CCD data acquired by the Spanish amateurs contributing to the mail list cometas-obs, available at  :


The magnitudes have been measured in a standar photometric aperture of 10”X10” reducing in this way the dispersion of the results. Here you’ll find a  description of the 10x10 method .


From the light curve we can see a sudden increase in brightness starting the 22-23 august, in less than two days the magnitude raises from 15.2 to 12.9, around 2 magnitudes, the maximum is the day 24 when a slow decay, lasting around one week fades it back to normal magnitude.

For comparison purposes, the following picture shows the light curve of the outburst in August 2002, the raising edge is not well covered but we know that on July the 30th it was at 15.2 mag. We can see a similar relaxation in about one week time.


The sequence


The following composite shows the evolution in terms of mangitud and visual aspect, at the maximum the coma is very bright and concentrated, two days later we can appreciate spiral details developing in the coma, one week after the maximum the comet is fading and an extended coma can be seen with two jets developed, fifteen days after the maximum the comet is back to normal.


Useful information about 29/P

29/P great activity, (Diego Rodriguez)

Observadores de cometas

Seichii Yoshida

View orbit


Other references,


Herbert Raab for Astrometrica and the excellent track & stack facility.


Thanks to :


All the amateurs contributing with their CCD photometry to the Observadores de cometas list.

Sebastian Hönig for his rotational gradient process.

Gerald Rhemann for the second picture of the composite.


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