Undersampled images are a common issue in astronomical observations due to several factors related to the limitations of imaging systems and the nature of astronomical data collection:

1. Resolution and Detector Size: The resolution of an image is determined by the size of the detector's pixels relative to the angular size of the objects being observed. If the pixel size is too large compared to the detail of the object, the image can become undersampled, meaning that fine details are not captured accurately.

2. Telescope Optics: The optics of a telescope, including its aperture and focal length, play a crucial role in determining the resolution of the images it can produce. If the optical system is not perfectly matched to the pixel size of the detector, undersampling can occur.

3. Atmospheric Conditions: For ground-based observations, the Earth's atmosphere can blur images, a phenomenon known as seeing. This can lead to undersampling if the detector cannot capture the blurred details effectively.

4. Nyquist Sampling Theorem: According to the Nyquist theorem, to accurately capture all the information in an image, the sampling rate (or pixel size) must be at least twice the highest frequency present in the image. If this condition is not met, undersampling occurs, leading to aliasing and loss of information.

5. Cost and Technological Constraints: High-resolution detectors with small pixels can be expensive and technologically challenging to produce. As a result, there might be a trade-off between cost and resolution, leading to undersampling in some cases.

6. Field of View Considerations: Sometimes, astronomers prioritize a wider field of view over higher resolution, which can lead to undersampling. This is especially true in surveys where covering large areas of the sky is more important than capturing fine details.

Addressing undersampling often involves optimizing the balance between detector design, telescope optics, and observational techniques to ensure that the maximum amount of information is captured from astronomical sources.