You can measure the width of the sun without a telescope. All you need are two cardboard boxes and a meter stick. You tape aluminum foil with a tiny pinhole to one box. The other box holds a card with two parallel lines 8 mm apart. Both boxes slide onto the meter stick. Aim the pinhole at the sun and a bright image appears on the far card. Slide the second card until the image fills the gap between the lines. The distance between the two cards plus a simple ratio gives you the sun's diameter. You then compare your result to the accepted value of 1,391,000 km.