The absence of visible curvature in long-exposure photographs of the night sky is not due to the Earth's flatness but rather the limitations of human perception and the specific conditions of the photographs.
When taking long-exposure photographs of the night sky, the rotation of the Earth causes the stars to appear as streaks or trails in the image. However, the perceived curvature of star trails depends on various factors, including the duration of the exposure, the focal length of the lens, and the sensitivity of the camera's sensor.
In short-exposure photographs, where the exposure time is relatively short (e.g., a few seconds), the Earth's rotation does not result in significant star trails. The stars appear as point sources, and any slight curvature is not noticeable to the human eye or in the photograph.
For longer exposures (several minutes or more), the Earth's rotation becomes more apparent, and the stars create circular or curved streaks in the image. However, the curvature may not be as pronounced as one might expect due to the following reasons:
Wide-angle lenses: Wide-angle lenses are commonly used in astrophotography to capture a broad portion of the night sky. These lenses tend to minimize the apparent curvature of star trails, making them appear more like straight streaks.
Rotation axis alignment: If the rotation axis of the camera is parallel to the Earth's rotation axis, the star trails will appear relatively straight. However, if the camera is tilted or the rotation axis is not aligned precisely, the star trails can exhibit curvature.
Perspective and distance: Stars are incredibly distant objects in space. Their apparent movement due to the Earth's rotation is relatively small compared to their vast distances, making any curvature less noticeable.
It's important to note that there is an abundance of photographic evidence, including images taken from space, that clearly show the Earth's curvature. Furthermore, numerous other observations and scientific measurements, such as satellite imagery, eclipses, and the circumnavigation of the Earth, provide strong evidence for the Earth's sphericity.
In summary, the absence of visible curvature in long-exposure photographs of the night sky can be attributed to factors such as exposure duration, lens characteristics, camera alignment, and the small apparent movement of stars compared to their vast distances. It does not indicate the Earth's flatness, as there is ample evidence from various sources that confirm the Earth is a globe.