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What is the farthest thing I can see with my own eyes, and the farthest thing I can see with an amateur telescope, and the farthest-away thing the biggest telescopes on Earth can see?

The most distant object visible to the naked eye is M31, the Andromeda Galaxy, at about 2 million light-years. This is the nearest large galaxy to us, and a very bright one at that. I can't say for certain the most distant object that you can see with an amateur telescope because the size of such telescopes can vary a lot, and because it depends on the detector that you have attached to it (like your eye, film, or an electronic CCD). But you can definitely see galaxies beyond the Local Group, even with your eyes.

If you use a detector such as film or a CCD, you can increase the exposure time, i.e. the length of time that light from the object you are observing is collected. It's like the shutter speed of a camera: slow shutter speed = long exposure time. The exposure time for your eye is fixed at a fraction of a second, not very long. With film or a CCD, you can expose for minutes or even hours, and detect distant galaxies.

The most distant object known and observed with a large optical telescope is the quasar PK 1247 +3406, at a distance of 5000 megaparsecs, the time when galaxies first began to form. The most distant event ever observed with any telescope would be the Cosmic Microwave Background Radiation, light which is a remnant of the Big Bang.

Submitted by Ben (Maryland, USA)
(June 8, 1998)

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Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA