Many stars are visible at night, even without using a telescope or any other optical device. Stars are, in general, larger than planet Earth, but in certain stages of their evolution, they can be smaller. Due to the large distance, they appear as tiny dots. Often, these dots consist of two (a binary system) or more stars. Not all stars emit visible light and not all starlight can reach us.
There are many approaches that we can take to find bright stars in a starry sky image. In this recipe, we will look for local maximums of brightness, which are also above a threshold. To determine brightness, we will convert the image to the HSV color space. In this color space, the three dimensions are hue, saturation, and value (brightness). The OpenCV split() function image values in a color space into the constituent values, for example, hue, saturation, and brightness. This is a relatively slow operation. To find maximums, we can apply the SciPy argrelmax() function.