I think you'd want a focal length of 700-1000 mm, and the cheapest way to get that would be a basic Newtonian reflector of 100 mm aperture. Examples: Meade Polaris 114mm, Celestron PowerSeeker 114EQ, Orion SkyQuest XT4.5. There are brackets available to mount a smartphone on any telescope.

Before trying to track ISS, practice acquiring easy targets such as the Moon, the Pleiades, etc. Then use Heavens Above to predict ISS passes visible from your location. After you collect your evidence and your hyper-skeptical acquaintance rejects it, you can still use the scope to enjoy the planets and a few dozen star clusters, nebulae, and galaxies.

On the other hand, maybe you don't need a telescope. ISS is visible to the naked eye, is silent, and appears to move almost as fast near the horizon as it does overhead. Seeing it disappear as it enters Earth's shadow could be persuasive.

I think you'd want a focal length of 700-1000 mm, and the cheapest way to get that would be a basic Newtonian reflector of 100 mm aperture. Examples: Meade Polaris 114mm, Celestron PowerSeeker 114EQ, Orion SkyQuest XT4.5. There are brackets available to mount a smartphone on any telescope.

Before trying to track ISS, practice acquiring easy targets such as the Moon, the Pleiades, etc. Then use Heavens Above to predict ISS passes visible from your location. After you collect your evidence and your hyper-skeptical acquaintance rejects it, you can still use the scope to enjoy the planets and a few dozen star clusters, nebulae, and galaxies.

On the other hand, maybe you don't need a telescope. ISS is visible to the naked eye, is silent, and doesn't appear to slow down as much near the horizon as aircraft do. Seeing it disappear as it enters Earth's shadow could be persuasive.

I think you'd want a focal length of 700-1000 mm, and the cheapest way to get that would be be a basic Newtonian reflector of 100 mm aperture. Examples: Meade Polaris 114mm, Celestron PowerSeeker 114EQ, Orion SkyQuest XT4.5. There are brackets available to mount a smartphone on any telescope.

Before trying to track ISS, practice acquiring easy targets such as the Moon, the Pleiades, etc. Then use Heavens Above to predict ISS passes visible from your location. After you collect your evidence and your hyper-skeptical acquaintance rejects it, you can still use the scope to enjoy the planets and a few dozen star clusters, nebulae, and galaxies.

On the other hand, maybe you don't need a telescope. ISS is visible to the naked eye, is silent, and appears to move almost as fast near the horizon as it does overhead. Seeing it disappear as it enters Earth's shadow could be persuasive.

I think you'd want a focal length of 700-1000 mm, and the cheapest way to get that would be a basic Newtonian reflector of 100 mm aperture. Examples: Meade Polaris 114mm, Celestron PowerSeeker 114EQ, Orion SkyQuest XT4.5. There are brackets available to mount a smartphone on any telescope.

Before trying to track ISS, practice acquiring easy targets such as the Moon, the Pleiades, etc. Then use Heavens Above to predict ISS passes visible from your location. After you collect your evidence and your hyper-skeptical acquaintance rejects it, you can still use the scope to enjoy the planets and a few dozen star clusters, nebulae, and galaxies.

On the other hand, maybe you don't need a telescope. ISS is visible to the naked eye, is silent, and appears to move almost as fast near the horizon as it does overhead. Seeing it disappear as it enters Earth's shadow could be persuasive.