M101 Mosaic Report

Report for M101 Mosaic Observing day on 8th May 2007

Aim

The whole observing night (0830 - 1259 UTC) of 8th May was dedicated to obtaining images to create a mosaic of M101 (a spiral galaxy).

The sessions were booked up by myself and advertised on the website to users who wanted to be involved in the project; users then booked sessions by email requesting which ever session they wanted.

I gave each school three Right-Ascension and Declination co-ordinates to observe, told them which filters and exposure time to use and provided them with a grid of images so they see/could check which portion of the galaxy they were observing. I also provided software instructions for The GIMP on the M101 webpage so they could make their own “mini-mosaics” with their images.

It was my intention to process the images as they were taken and produce a timeline of the mosaic in it’s different stages so users could see it’s progress. This was hampered however due to the slow availability of FITS files.

Comments

Observing

On the whole the actual observations went very well - all the users knew where to point the telescope and what exposure time they should use. There were a few issues with users being unable to expose their last image because they lacked sufficient time; this was mostly due to problems with the telescope at the beginning of their session. Some users reported the telescope took some time to give them control. These issues compromised some parts of the final mosaic in terms of image quality but was of course through no fault of the users.

Processing

The final mosaic was not as good as I had initially hoped, for a number of reasons:

1. Light from the Moon degraded the finer detail that is present in the galaxy, particularly in the dimmer regions of the spiral arms. It also created a lot of noise in these darker regions. This project was very experimental and the Moon only hindered the image quality and did not effect any of the collaboration methods that we were also testing.
2. This particular galaxy has a slightly lower surface brightness than some of the better known galaxies such as M51. Combined with the effect of the Moon, the images were not as contrasting as I hoped.
3. Because this was a large mosaic of 9 images, the observing time that was available was spread thin over the whole galaxy and only a maximum of 4 images were achieved for each portion of the galaxy. Unfortunately, to achieve some of our better images, many more observations are needed for each portion in order to improve the signal-to-noise ratio.

However, considering the quality of the images we did get - I am pleased with the quality of the final mosaic that we managed to achieve.

Evaluation

Lessons for the future…

Thankfully, all of the issues raised above can be accounted for and avoided.

1. To get around this point is simple - we simply book these nights when we know there is no Moon. We may find that we can run some projects that may not be affected by the Moon so much such as asteroids so we can still space them around the month a bit.
2. M101 was a nice galaxy to do, it just requires more time to get more observations. But if we are restricted to one day of observations we can choose a brighter galaxy such as M51 that we know works well and looks good even in the dimmer regions.
3. If we ran these large mosaic projects over more than one day, then we will obviously be able to get more images of each portion to improve the quality of the final mosaic. If however, we choose to keep them as one-day projects only, we can look at imaging smaller galaxies that require fewer images. This way, we can get more observations of the galaxy.