Galaxy10 SDSS

Galaxy10 SDSS is a dataset contains 21785 69x69 pixels colored galaxy images (g, r and i band) separated in 10 classes. Galaxy10 SDSS images come from Sloan Digital Sky Survey and labels come from Galaxy Zoo.

These classes are mutually exclusive, but Galaxy Zoo relies on human volunteers to classify galaxy images and the volunteers do not agree on all images. For this reason, Galaxy10 only contains images for which more than 55% of the votes agree on the class. That is, more than 55% of the votes among 10 classes are for a single class for that particular image. If none of the classes get more than 55%, the image will not be included in Galaxy10 as no agreement was reached. As a result, 21785 images after the cut.

The justification of 55% as the threshold is based on validation. Galaxy10 is meant to be an alternative to MNIST or Cifar10 as a deep learning toy dataset for astronomers. Thus astroNN.models.Cifar10_CNN is used with Cifar10 as a reference. The validation was done on the same astroNN.models.Cifar10_CNN. 50% threshold will result a poor neural network classification accuracy although around 36000 images in the dataset, many are probably misclassified and neural network has a difficult time to learn. 60% threshold result is similar to 55% , both classification accuracy is similar to Cifar10 dataset on the same network, but 55% threshold will have more images be included in the dataset. Thus 55% was chosen as the threshold to cut data.

The original images are 424x424, but were cropped to 207x207 centered at the images and then downscaled 3 times via bilinear interpolation to 69x69 in order to make them manageable on most computer and graphics card memory.

There is no guarantee on the accuracy of the labels. Moreover, Galaxy10 is not a balanced dataset and it should only be used for educational or experimental purpose. If you use Galaxy10 for research purpose, please cite Galaxy Zoo and Sloan Digital Sky Survey.

For more information on the original classification tree: Galaxy Zoo Decision Tree.