Neptune to complete first revolution since discovery on 13J uly

Neptune, the eighth planet in the solar system, is set to complete its first revolution of the sun since its discovery in 1846. The blue-hued planet will complete its first orbit around the sun on 13 July at 03:06 IST when it reaches approximately the same heliocentric longitude 329°.1020 as at the time of its discovery, R C Kapoor of Indian Institute of Astro Physics says.

To get a glimpse of the planet with a moderate size telescope, one needs to point toward Capricornus and Aquarius constellations between the stars Delta Capricorni and Lambda Aquari to be precise, experts say.

Neptune is also the first planet found by mathematical prediction rather than by observation. Certain unexplained deviations in the orbit of Uranus after Neptune's accidental discovery on 13 March, 1781, led astronomer William Herschel, to believe that there was some unknown body farther out.

The mathematicians – Englishman John Adams and Frenchman Urbain Le Verrier independently analysed the discrepancies in the observed and calculated positions of Uranus and predicted in 1845, the mass and orbit of the body that could be responsible for the deviations.  

The planet was discovered on 23 September, 1846, by Johann Galle and Heinrich d'Arrest from Berlin Observatory very near the predicted position.

In addition to its 13 satellites, Neptune has a thin ring system that was discovered in 1984. The planet has a near circular orbit and an atmosphere mainly made up of hydrogen (80 per cent), with helium (19 per cent) and methane (1 per cent) , and a very small admixture of other compounds.