Neptune and William Lassell

Posted by Anonymous
on Tuesday, October 10, 2006

Today marks the 160th anniversary of Neptune's discovery by English astronomer William Lassell. Lassell also discovered Ariel and Umbriel, satellites of Uranus;  Triton, a satellite of Neptune; and Hyperion, a satellite of Saturn. William Bond and George Bond also independently discovered Hyperion.

William Lassell was a Liverpool businessman-turned-astronomer who had made his fortune in brewing. 

If you would like to take a look at Neptune, by midevening on October nights, binoculars will let you pick out the planet. The eighth planet glows at magnitude 7.9 and lies approximately midway between Iota Capricorni and 29 Cap. Another star lies in Neptune's vicinity, but it's a magnitude brighter than the planet and shouldn't cause confusion. In fact, you can use this star to track Neptune's motion.

Grab a pencil and notepad, and mark the positions of all the objects visible through binoculars between 4.3-magnitude Iota Cap and 5.3-magnitude 29 Cap — then jot down the time and date. Repeat this process over a couple of nights, and you'll easily notice Neptune's motion. A digital camera with a zoom lens can perform the same feat: Make a 5-second exposure each night with the camera's ISO speed setting at its highest value.

Telescopes show little of Neptune beyond its tiny blue-gray disk. Even though it's 4 times Earth's diameter, Neptune lies 2.75 billion miles away and so appears only 2.3" across.

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