All Plutophiles are based in America. If you go to other countries, they have much less of an attachment to either the existence or preservation of Pluto as a planet.
Figure 1: Pluto and its Moons As Seen from
Earth. The Earth-Moon System diameter is
about 770,000 km.
I have been following the voyage of the New Horizons spacecraft to Pluto (Figure 1) since its launch on January 19, 2006. It will flyby Pluto on July 14, 2015. I have already marked that day on my calendar!
I was reading the Planetary Society's blog post called "The Mapping of Pluto Begins Today" and the post mentioned that the Pluto is now large enough to form an image 3.5 pixels in width and height in New Horizons' narrow-field telescope. I thought it would be interesting to show how this calculation is performed.
To calculate Pluto's pixel width in New Horizon's telescope (Submarine Fiber-Optic Cable Trivia), you need to know the following numbers:
- Diameter of Pluto (DPluto)
- Distance of New Horizons from Pluto (RPluto)
- Size of a pixel on New Horizons' CCD (δ)
- Focal length of the New Horizons' telescope (FL)
- CCD width/length in pixels (NPixel)
The key formula used in this analysis is for the field of view (Equation 1).
| Eq. 1 |  |
where
- FOV is the telescope field of view.
- LCCD is the width/height of the CCD sensor.
- FL is the telescope focal length.
The Wikipedia has a good derivation of this formula and I will refer you there for more details.
My calculation for Pluto's pixel width is shown in Figure 2, which confirms the 3.5 pixel width statement mentioned in the Planetary Society's blog post.
Figure 2: Calculations for the Pixel Width of Pluto in New Horizon's Narrow-Field Telescope on 20-March-2015.
I am not on my usual computer, so I did not have Mathcad available. I used Smath instead, which proved to be a workable substitute for this problem.