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The notion of using an astronomical object as a telescope has inspired research, some of it very speculative. Gravitational lensing and gravitational microlensing have already been used for this: working out characteristics of the more distant body from the lensed electromagnetic radiation. Current sheets in the interstellar medium, which refract, have been used as lenses. Undoubtedly these methods will continue to develop.
The notion of using solar system bodies has been considered. I presume gravitational lensing offers too little bending to be of much use in this case. Using refraction by the atmosphere that surrounds a body has also been considered, with Earth is a prime candidate. In a transit or eclipse of a body passing behind another that has an atmosphere, a changing pattern in EMR that has passed through that atmosphere can be analyzed. Such a method might be applied to extra-solar planet investigations or other interstellar applications.
There may be clouds other than current sheets that produce the kind of refraction needed to be used as a lens, also offering possibilities.
Use of gravitational lensing to view more distant objects is sometimes referred to as a cosmic telescope. A few galaxies and galaxy clusters serve as useful lenses for specific targets: such configurations merely have to be noticed. Smaller bodies such as stars and planets are also used as lenses, but in that case, its often the lensing object that is being studied. The Sun has been suggested as a lens (solar gravitational lens or SGL) by observing from a distance beyond the solar system planets: parallel rays are focused by the Sun's gravity at about 547 AUs. As of 2023, Voyager 1 is only about 160 AU from the Sun after 45 years of travel, so such a telescope is a far-future concept at best.