I don’t know how fast asteroids travel, so lets just say it’s moving at an “average” speed and it’s large enough to wipe out all life on earth. Would this asteroid be visible to the naked eye for any significant amount of time before impact? Hours, days, weeks? Nighttime only, or daytime as well? I’m doing research for a sci-fi story and can’t seem to find an answer to this. Thanks in advance to anyone who can help.