A. The traditional answer is five planets: Mercury, Venus, Mars, Jupiter and Saturn. These are easily visible with the naked eye.

There's at least one more. The Earth is clearly and easily visible with the naked eye. You have to look down.

Moreover, Uranus is visible to the naked eye. The ancients didn't happen to spot it. It is just visible, and you really need to have a very dark sky site, and it helps if Uranus is at opposition, and it really, really helps if you know where to look. It can be as bright magnitude 5.5, as dim as 6.0.

The days of the week are attributed to the seven astronomical objects known to the ancients. They include the Moon and the Sun.

• Sunday
• Moonday
• Marsday
• Mercuryday
• Jupiterday
• Venusday
• Saturnday

By contrast, we get Earth Day just once a year.