Time: 5:00 AM
Brief
Pluto received "demotion" back in 2006 to dwarf planet status; a term to classify solar system bodies "more massive than asteroids, but different than the known planets". See more about that here.
http://solarsystem.nasa.gov/planets/profile.cfm?Object=Dwarf
Based on the info provided in the above link, Pluto has a 17ยบ orbit inclination with the ecliptic, which I will talk about a little more in the detailed section. If in a planetarium, with software which shows the solar system from afar, we would see something similar to image one below, with all orbits showing. Because of the small zoom size, I didn't label the inner planets, yet did for the outer ones and Pluto to make clear of where the latter's orbit is in relation to the rest; it is different, to say the least!
Detailed
The definition of a dwarf planet is complex, as defined by the International Astronomical Union:
"a celestial body in direct orbit of the Sun that is massive enough that its shape is controlled by gravitational rather than mechanical forces (and thus an ellipsoid in shape), but has not cleared its neighboring region of other objects".
At over 3 billion miles away, Pluto wasn't discovered as a planet originally until 1930. One of its other orbital characteristics includes a perihelion [to the Sun] that is much closer than its aphelion: measured in astronomical units, which I mentioned in early entries as about 93,000,000 miles, Pluto has an aphelion and perihelion of 48.9 and 29.7 a.u.'s respectively.
Image two brings us back to Earth, seeing Pluto zoomed out before dawn. It has become separated enough from the Sun to see further out of atmospheric pollution. At only 14th magnitude however, a telescope of at least 10" is recommended to gather enough light. Pluto is very small, and far enough away that not much Sunlight reflects off of its surface and back to our eyes. As shown in the image, its orbit puts it far from the ecliptic plane, in comparison to how we have seen other planets' orbits so far. Where descending node is shown, with the arrowhead, look to the right and notice that where Pluto's orbit crosses the celestial equator is at a point in the sky far north of the ecliptic. It is because of this, that although moving very slowly with a revolution of almost 2 1/2 centuries in duration, Pluto changes declination quickly from one constellation to another for some parts of its orbit.
*click on images to enlarge: courtesy of Starry Night Pro Plus, version 6.4.3, by Simulation Curriculum Corp. |
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