1) Problems with the plate

Forums Website News and Help Update to member pages 1) Problems with the plate

Dominic Ford

1) Problems with the plate solver

We’re aware that the plate-solving software is producing a high rate of false matches currently.

I’m surprised by this, as we’re using <astrometry.net> with mostly default settings, and it is supposed to be quite robust against finding spurious matches. However, I’ve told it that we have no prior information about the field-of-view of each image, so it’s searching for matching star patterns from a full range of length scales, from 30 degrees right down to 2 arcminutes. Consequently, the database of star patterns it’s using is extremely large: about 30 GB of data.

My guess is that we’re getting spurious matches because there are an awful lot of possible star patterns that an image can spuriously match when we’re checking it against so many possibilities. The sky is quite large when you look at it with a 2 arcmin field-of-view.

As for finding Jupiter in Pavo – well, astrometry.net looks only at stars, and knows nothing about planets. This is no more surprising than some of the meteor spectra which are also getting erroneous fits. In general, I would not expect planetary images to get successfully plate-solved as they wouldn’t contain enough stars.

At some point, it would be nice to improve this, and once we do so, it should be possible to retrospectively update the plate solutions of old images (at the cost of a few thousand hours of computation time). However, fiddling with this is likely to be a large project, and I’m not volunteering to do it imminently.

2) The sky map

Note that the sky map only shows 400 images at a time. You should see a message at the top along the lines of: “Showing latest 400 of 2568 observations. Older observations have been omitted to avoid excessive processing time.” Note that it also cannot show images which haven’t been plate solved, for obvious reasons.

You really don’t want it to try to display thousands of images at the same time.

If your image isn’t showing up, you probably need to make your search criteria more specific.