Here's why:
1. Earth's Curvature: The Earth's curvature limits the maximum distance between telescopes, as the Earth's surface curves away between them. This makes it difficult to maintain a stable alignment for interferometry, especially at longer wavelengths.
2. Atmospheric Turbulence: The Earth's atmosphere constantly distorts light, making it difficult to combine images from telescopes that are far apart. This distortion is called "seeing" and is worse at longer wavelengths.
3. Logistics and Cost: Building and maintaining a network of telescopes across vast distances is extremely expensive and logistically challenging.
4. Earth Rotation: The Earth's rotation means that even if telescopes are fixed in place, they will move relative to each other over time. This can make it difficult to maintain the alignment needed for interferometry.
Current Limits:
* Optical/Infrared Interferometers: The largest optical/infrared interferometers on Earth, like the Very Large Telescope Interferometer (VLTI) in Chile, have baselines (distances between telescopes) of up to 200 meters.
* Radio Interferometers: Radio telescopes can be placed further apart due to the longer wavelengths of radio waves. The Very Long Baseline Array (VLBA) in the United States has baselines of up to 8,600 kilometers.
Future Possibilities:
* Space-based Interferometers: To overcome the limitations of Earth-based telescopes, astronomers are increasingly looking to space. The Space Interferometry Mission (SIM) and the James Webb Space Telescope (JWST) are examples of space-based telescopes that use interferometry to achieve higher resolution.
* Adaptive Optics: Adaptive optics systems are being developed to compensate for atmospheric distortion, allowing telescopes to be placed further apart.
In conclusion: While Earth's curvature, atmospheric turbulence, and logistics pose challenges, there are ongoing efforts to push the limits of interferometry, with space-based telescopes and advanced technologies offering exciting possibilities for the future.
