how far can you see with a telescope

Theoretically, a telescope can see infinitely far. However, in practice, the distance you can "see" is limited by several factors:

1. Light’s Properties and the Expansion of the Universe:

• Finite Speed of Light: Light, even from the most distant objects, takes time to reach us. The further away an object is, the longer the light has been traveling. We are essentially looking back in time as we look further out.
• Expansion of the Universe: The universe is constantly expanding. This means that the objects we see are also moving away from us. This expansion causes the light from very distant galaxies to be stretched to longer wavelengths (redshifted), making them fainter and harder to detect.
• The Cosmic Microwave Background (CMB): This is a remnant of the Big Bang. It’s a faint afterglow of the universe’s early hot state. We can "see" the CMB, but it’s a signal, not a visible object in the traditional sense. It’s a limit to what we can detect.

2. Limitations of the Telescope and Observation:

• Telescope Size (Aperture): Larger telescopes (larger lenses or mirrors) gather more light and are able to see fainter, more distant objects. This is the most important factor in determining how far you can see.
• Atmospheric Conditions: Earth’s atmosphere can blur and distort the images you’re trying to see. This is called "seeing." Telescopes on mountaintops (less atmosphere) or in space (no atmosphere) have a significant advantage.
• Light Pollution: Artificial light in the night sky makes it harder to see faint objects.
• Observing Time: The longer you observe an object, the more light you can collect and the fainter an object you can see.
• Detector Sensitivity: The more sensitive the sensors (e.g., CCD cameras) on the telescope, the fainter the objects you can detect.
• Wavelength of Observation: Telescopes can observe at many different wavelengths. Some wavelengths (like infrared) can penetrate dust clouds better than visible light and therefore allow us to see further. Some wavelengths are also easier to detect than others.
• Object Brightness: The intrinsic luminosity (brightness) of an object greatly affects how far away we can see it. A very bright galaxy will be detectable at much greater distances than a faint one.
• Object Size: For an object to be visible, it must, after enough distance, at least a certain threshold size relative to the aperture of the telescope itself.

Summary:

• The most distant individual objects we can "see" are extremely far away – galaxies whose light has been traveling for over 13 billion years.
• The observable universe extends to the edge of what we can see (based on the expansion), which is about 93 billion light-years across.
• "Seeing" is a process of detecting electromagnetic radiation (primarily visible light, but also radio waves, infrared, ultraviolet, X-rays, and gamma rays) that has traveled across immense distances.
• The practical limit to how far any individual telescope can see is dictated by its size, the quality of its optics, the atmospheric conditions, and the sensitivity of its instruments.

It’s more accurate to talk about the "observable universe" or the distance to the farthest objects detected rather than a simple number. Understanding these factors provides a more complete answer.