Call for Comet Tail Images

Comets act like giant wind socks. They travel through the very tenuous solar wind that constantly flows outwards from the Sun at hundreds of km per second. Ions from comets join the solar wind flow, and we can observe the ions remotely as the ion or plasma tail. Changes in solar wind flow speed and direction cause changes in the appearance of the tail.

In most cases, unfortunately not. Although spacecraft solar wind data is more precise and accurate than information that we obtain from comet images, comets provide a free source of information on solar wind conditions.

Spacecraft such as SOHO and STEREO also provide valuable comet images when possible, but these facilities can’t image comets far from their usual look directions.

Images! Wide-field to narrow field, from all camera types from DSLRs to dedicated CCD imagers all are welcome. Please contribute as many as you can. If you took several images in one night, please send them all in, as ion tails are constantly changing. To extract the maximum amount of information, we need as many images as possible of these comets. When comets are not circumpolar, we need data from observers located at all longitudes to attempt to keep a continuous record of solar wind conditions.

Any images contributed will not be used for any commercial gain, but purely for scientific research. The contribution of all who donate data to this study will be acknowledged in subsequent scientific publications in peer-reviewed journals.

We do plan to construct movies of tail features using contributed images, and may post some such movies on our website, with a list of those who contributed data. If you do not wish your images in such movies to be placed on a webpage, then please do state this clearly and we will of course honour your request.

Any images contributed will not be used for any commercial gain, but purely for scientific research. The contribution of all who donate data to this study will be acknowledged in subsequent scientific publications in peer-reviewed journals.

We do plan to construct movies of tail features using contributed images, and may post some such movies on our website, with a list of those who contributed data. If you do not wish your images in such movies to be placed on a webpage, then please do state this clearly and we will of course honour your request.

First, we identify the starfield in the background of your images, using astrometry.net

This provides us with the scale and orientation of your images, allowing us to compare your data to those obtained by other observers. Once this is done, we have an automatic estimate of the time when your image was obtained.

If you have provided information on your location and time at which the images were taken, we use these to constrain parallax effects for comets near Earth, and to aid the timing of the image in the rare case when the starfield is not recognized automatically.

We then use our specially-written IDL software to map your image onto the comet’s orbital plane, and the image is then analyzed semi-automatically. From each image, we use the positions at several points along the ion tail axis to infer solar wind speeds at the comet during a period of up to several hours before your image was taken. Sequences of images from single and multiple observers help us improve the accuracy of these results.

As the data collection builds up, we gather a valuable resource detailing the solar wind conditions at the comet. These results are then compared to simulations of the solar wind based on solar data, to test how well these computer models reproduce conditions in the inner solar system. Where possible, these solar wind speeds are compared to those obtained by spacecraft nearby.

Periods when major disturbances appear in the tail, such as kinks, clouds, and disconnection events, are analyzed in more detail, using different techniques. Features are traced from image to image, and, where possible, a map of speeds and directions of tail features is built up.

In many cases, JPEG or PNG are fine. If you have raw format images, they can of course be very useful.

If you contribute a mosaic constructed from several images, please let us know so that we can take this into account when analyzing the data.

If you are providing images from a digital camera, please ensure that your time and date settings are correct so that EXIF data can be used when possible.

FITS files in some cases can be more difficult for us to process; please email us with questions about contributing files in this format.

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