Comet Close Approach

Factual Questions
1

I have heard that the coma of a comet can become as large as the Sun, and the tail much much longer than the sun’s diameter.

I remember Comet Hale-Bopp around 15 years ago. I thought it was fairly bright, but nothing that made me say “wow.” If Hale-Bopp had its closest approach to Earth at 1/100 of its actual closest approach, which was 1.315 AU, it would have come within just less than 2,000,000 km, which is around 5 times greater than the average distance between the Earth and the Moon. What would it have looked like for us then as it approached and receded?

2

It would have been a “great” comet.
As it was Hale-Bopp was seen by more people than any other comet in history (of course, there were a lot more people around…). Some past Great Comets were so bright that they could be seen during the day. It’s hard to say how big and bright it would have appeared, but an approach that close would have made it spectacular (and probably caused a lot of panic).

Some information here: Great comet - Wikipedia
and here: SkyEye - Comets