Event Date: September 14th/October 4th* (see after image 1)
Time: 9:00 PM
Brief
We know that Pluto can be challenging to find as a result of being a magnitude as dim as the dimmest stars through most amateur telescopes. However, just for the sake of curiosity, have you ever observed its field? Since Pluto moves very slowly, at a rate slightly less of 1.5º each year against the stars (360º/248 years), we can successfully use a field about one-sixth that size (1/4º) to try to track it. Under the darkest of skies, this size field being of magnitude somewhere between, 260-270x, is just enough to see Pluto as a dim "star". Although only looking a tiny amount of space, let's label a few stars so to see how slowly Pluto is actually moving. Since it is now picking up speed very gradually in prograde, being long past its opposition, it is a good test.
The first image shows Pluto centered, with a star at the edge of the field labeled. Since this marks the radius of the field, the two are 1/8º (about 7 or 8 arc-minutes) apart. The star that I picked is just slightly brighter than Pluto.
Time: 9:00 PM
Brief
We know that Pluto can be challenging to find as a result of being a magnitude as dim as the dimmest stars through most amateur telescopes. However, just for the sake of curiosity, have you ever observed its field? Since Pluto moves very slowly, at a rate slightly less of 1.5º each year against the stars (360º/248 years), we can successfully use a field about one-sixth that size (1/4º) to try to track it. Under the darkest of skies, this size field being of magnitude somewhere between, 260-270x, is just enough to see Pluto as a dim "star". Although only looking a tiny amount of space, let's label a few stars so to see how slowly Pluto is actually moving. Since it is now picking up speed very gradually in prograde, being long past its opposition, it is a good test.
The first image shows Pluto centered, with a star at the edge of the field labeled. Since this marks the radius of the field, the two are 1/8º (about 7 or 8 arc-minutes) apart. The star that I picked is just slightly brighter than Pluto.
The second image shows us jumping ahead by 20 evenings*. Notice how the star has moved by about the 7 arc-minutes since then.
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| click on images to enlarge: courtesy of Starry Night Pro Plus, version 6.4.3, by Simulation Curriculum Corp. |
Detailed
Image two's celestial path of Pluto shows two things: it quickly picks up speed in prograde motion during the last 10 days; the inclination of Pluto's orbit has it curve towards the star rather than go more in a direct line. Since Pluto's orbit inclination is 17º, with a slope almost always changing against the ecliptic, we see this unusual curve shape that we would hardly see with any of the "classical" outer planets: Mars through Neptune. Also, during the 20-day span shown, the star moved only about halfway across, if keeping Pluto centered, Therefore, if we say that Pluto moved about 8 arc-minutes over almost 3 weeks, that it moved a little under 3 arc-minutes a week. Regardless of number accuracy, this brings me to the point of getting familiar with Pluto's field: if you study and get to know it well one night, you will see almost the identical field with it centered a week later, using the same eyepiece. Granted, we get the Moon in the way for that part of the sky every month for a week or so. Therefore, try this exercise during weeks when the Moon is crescent or new, as is the case this week as a waning crescent; it will not rise until hours after Pluto gets too low and eventually sets.
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