Neptune up all night

¡SkyCaramba! Weekly astronomy blog for the week ending August 25, 2012!

The farthest of the eight objects now considered to be true planets orbiting the sun is at opposition this week. On August 24, Neptune will be up all night. Most people will consider this the best chance to see it all year.

The blue gas ball called Neptune takes 165 years to orbit the sun. Last year, it completed one orbit since its discovery. Neptune’s discovery and its remaining undiscovered for more than two centuries before happened because of accidents.

Galileo saw the planet while observing Jupiter in 1612 and 1613 and mistook it for a star. He thought the star had moved from one night to the next, but he continued tracking and observing Jupiter. Drawings of what he saw, including Neptune, still exist. Neptune moved out of his telescope’s field of view and that’s the last he noted of it. French astronomer Jerome Lalande saw Neptune in 1795 but also thought it was a star. John Herschel, son of Uranus discoverer William Herschel, saw Neptune in 1830 and also thought it was a small blue star.

In 1845, it had been more than a half century since William Herschel’s discovery. Astronomers in various locations made calculations showing where they believed Uranus should have been throughout its orbit. But it appeared in slightly different places. A logical explanation was that some other planet must be out there tugging on Uranus gravitationally. In 1846, Johanne Galle used calculations that appeared to show where the yet unknown stranger must be. He found Neptune.

It turns out, nobody who calculated where the new planet must be had calculated correctly. Purely by luck, Galle used calculations that directed him to a region of the sky where a planet actually happened to be. It’s no longer thought that Uranus even went off course. Observations weren’t perfect, so calculations that predicted where Uranus should have been weren’t perfect either.

If you want to see Neptune and distinguish it from the stars around it, you’ll need a good telescope, a very still atmosphere, and a dark sky. You can probably see it with binoculars, but don’t count on being sure which dot it is. If you can magnify it by 100x, it will look like a bigger dot than the distant stars. You should use 200x or greater to see the planet’s disk. The wider your scope, the better.

I highly recommend using planetarium software to find Neptune. And try to look when Neptune isn’t in the sky at the same time as the moon. The moon is new and then waning this week, so it’s a pretty good time.


More sites to find out about observing Neptune: