Question: I wanted to inquire about Neptune’s close approach to Earth on September 5th of this year. From the information that I have read, it seems that it will at its’ most visible to Earth. What parts of the world will it be most visible at? Will it be visible in the Northern Hemisphere (i.e. Spain)? — George
Answer: Indeed Neptune will be at perigee, or closest approach to Earth, in September of this year. Note also that Neptune will be at opposition, positioned directly opposite the Sun in the sky, during this period. Because Neptune’s orbit is pretty far out in the solar system, though, its apparent size and brightness do not change very much from other points in its orbit, so the slight brightness increase due to perigee will be difficult to notice. This event will be visible from almost anywhere in the northern and southern hemisphere, but to be able to distinguish Neptune from a star requires the aid of a telescope or very good binoculars from a dark observing site.