Issue in Astronomy

Pluto's visual apparent magnitude averages 15.1, brightening to 13.65 at perihelion.To see it, a telescope is required; around 30 cm (12 in) aperture being desirable. It looks star-like and without a visible disk even in large telescopes, because its angular diameter is only 0.11". Distance, and current limits on telescope technology, make it impossible to directly photograph surface details on Pluto.

The earliest maps of Pluto, made in the late 1980s, were brightness maps created from close observations of eclipses by its largest moon, Charon. Observations were made of the change in the total average brightness of the Pluto–Charon system during the eclipses. For example, eclipsing a bright spot on Pluto makes a bigger total brightness change than eclipsing a dark spot. Computer processing of many such observations can be used to create a brightness map. This method can also track changes in brightness over time.

Current maps have been produced from images from the Hubble Space Telescope (HST), which offers the highest resolution currently available, and show considerably more detail resolving variations several hundred kilometres across, including polar regions and large bright spots. The maps are produced by complex computer processing, which find the best-fit projected maps for the few pixels of the Hubble images.The two cameras on the HST used for these maps are no longer in service, so these will likely remain the most detailed maps of Pluto until the 2015 flyby of New Horizons.

Pluto's orbital period is 248 Earth years. Its orbital characteristics are substantially different from those of the planets, which follow nearly circular orbits around the Sun close to a flat reference plane called the ecliptic. In contrast, Pluto's orbit is highly inclined relative to the ecliptic (over 17°) and highly eccentric (elliptical). This high eccentricity means a small region of Pluto's orbit lies nearer the Sun than Neptune's. The Pluto–Charon barycentre came to perihelion on September 5, 1989, and was last closer to the Sun than Neptune between February 7, 1979 and February 11, 1999 Detailed calculations indicate that the previous such occurrence lasted only fourteen years, from July 11, 1735 to September 15, 1749, whereas between April 30, 1483 and July 23, 1503, it had also lasted 20 years. The durations of the relationship vary because of the varying speed of motion of Neptune along its orbit; the relationship between the orbits themselves varies much more slowly, as Neptune's orbit precesses and otherwise evolves.

Pluto is NO LONGER A PLANET becuase Astronomers weren’t sure about Pluto’s mass until the discovery of its largest Moon, Charon, in 1978. And by knowing its mass (0.0021 Earths), they could more accurately gauge its size. The most accurate measurement currently gives the size of Pluto at 2,400 km (1,500 miles) across. Although this is small, Mercury is only 4,880 km (3,032 miles) across. Pluto is tiny, but it was considered larger than anything else past the orbit of Neptune.