Of the five planets visible with the naked eye, Mercury is the closest to the sun, so it is the most difficult to observe. Mercury's tight orbit means that it never deviates more than 28 degrees from the sun as viewed from Earth.

And because you have to look close to the sun to see it, you need to use extreme caution when observing it through any optical aid. Viewing the sun—even for an instant—without a proper solar filter can cause irreversible eye damage.