Monday, July 13, 2015

Spotlight on Pluto!

For likely the last time in our lifetime, in less than 24 hours, a space probe will be visiting an unexplored planet for the first time. Tomorrow morning, New Horizons will pass a few thousand miles from the surface of our "ninth planet" Pluto. Even though it was demoted to a dwarf planet about 10 years ago, wife Melinda is sitting across the room and she wouldn't take kindly to calling it anything other than a planet!

The first thoughts of "Planet X" came from observed perturbations in the orbit of the outer planets in the late 1800s. Percival Lowell started the first extensive search from Arizona's own Lowell Observatory in Flagstaff. Hired to do the search was Illinois-born and Kansas farm boy Clyde Tombaugh, who eventually located Pluto in February, 1930. At the time, it marked the outermost, mysterious edge of the solar system, forty times the Earth's distance from the sun at over 3 billion miles (4.5 hours for radio signals to reach Earth from New Horizons!).

My first exposure to it was when I was hired as an observing assistant at the University of Iowa's 24" telescope in 1973. The previous year it had been observed by graduate student Linda Kelsey as her master's thesis, and I remember observing it visually a few times over my years there. It is a non-trivial object to observe - it is faint, about 100 times too faint to be seen in binoculars, and as a planet, it also moves. This combination means you need very good finder charts and a decent-sized telescope. Fast forward to about 20 years ago and with a borrowed 16" telescope and good finder charts, I followed it for a couple nights, showing it to the public at the Grand Canyon Star Party. But, of course, it only looked like a faint little star - only identifiable as Pluto from its motion from night to night.

Then fast forward to now. With Pluto in the news and a break in the monsoonal circulation, I decided to set up the C-14 in the back yard to try imaging it. The weather cooperated Friday and Saturday, allowing me to obtain images over an hour for each night (dodging clouds each night too), using the finder chart that Sky and Telescope provided a month or two ago. Given the light pollution in the Midtown area of Tucson, I wasn't sure what to expect, but I was barely able to starhop to where I thought the field was and took 3 minute exposures. With the temperatures in the low 90s, I used in-camera noise reduction to reduce my hot pixels, so it took an hour to take 10 of those 3 minute exposures each night. In the cropped images above, knowing now where to look, you can see the slightly blurred image of Pluto as it moved nearly 4 arcseconds in that hour.

Otherwise, I was unsure how to display the movement from night-to-night, so I have 2 possibilities, both presented here. At left I used the method I use to make anaglyph 3D images (though this doesn't make a very good 3D image!). I rotated and aligned the stars atop each other, then do the little Photoshop magic, making one image of Pluto Cyan (11 July, UT), the other red (12 July). In the image at right, the images were nearly aligned, but keeping the stars as close doubles. The singular images are the pair of Pluto images. The high temperatures and light pollution resulted in some color gradients, but otherwise I'm surprised how apparent Pluto appears in these shots from town. These images show nearly the entire frame from the C14 telescope with the APS sensor of the Canon XSi - in case you haven't spotted the images of Pluto, they are down in the lower left corner.

EDIT: After reading John's comment below, I rethought my plan not to make a gif to display the image pair. I thought I'd lost my gif-making program in a disk crash, but found another program to do it. So here it is at right, the two images blinking back and forth, just as Clyde Tombaugh discovered them (with his blink comparator) back 85 years ago. And John was right - it is a pretty dramatic demonstration of showing the motion over the course of 24 hours. As mentioned above, there is a significant gradient between the images, likely caused by shifting the field the second night to better center on Pluto.

 It was cool to be able to image it with my own equipment in the light-polluted environs of Tucson. What is also interesting is that the nearly 90 arseconds/day of motion against the distant stars (about 3 weeks of time to move the distance of the moon's apparent diameter!) is NOT due to Pluto's motion, but rather the rapid motion of the Earth in its inner solar system orbit.

So New Horizons will have its closest approach about breakfast time Tuesday, but it will be too busy taking data to send photos back in real time. I read that only one percent of the close approach data will be sent back immediately, the rest coming in over the following weeks and months. The other fact is that it is moving so fast to get there in a reasonable length of time (only 9 years total travel time), it will zip past it very quickly, about 9 miles per second. This will be no orbital mission, but rather a flyby that won't last long... Once past Pluto there are thoughts to pass other Kuiper Belt Objects, but I don't believe that has yet been yet finalized.

Until now, images have been released pretty much as soon as they come in and interestingly, amateur data reducers can manipulate the images and release them as fast as NASA! For instance, this afternoon, I found a couple stereo pairs (Using the cross-eyed method) assembled by Bill Davis of Oklahoma City, shown at left. I found this on the Spaceweather website, which for now also includes a Pluto gallery. To see the images in 3D, cross your eyes slightly to view the left image with your right eye and vice versa. You should see a center image that displays Pluto as a round globe. Another of my favorite websites would be that of Emily Lakdawalla, who blogs regularly about various spacecraft missions, and should be a regular read for anyone interested in the solar system. She provides the right amount of technical data and interpretation in normal language that is easy for most to understand.

And, of course, the New Horizons mission has its own website, so you can check it for the latest data yourself! Have fun - we'll learn some spectacular things the next few days!


John Dolby said...

Nice pic's of Pluto from your back yard! I'm glad to have modernized with go-to and don't have to point "in the blind" anymore. Although I suppose it doesn't have the same quaint feel to it. Anyway, as for ideas about how to display the two shots, an animated GIF really works great for simulating the old-fashioned blink comparator. No add-ons required for your web visitors. There are free animated GIF creators online and Photo Shop does it. Ah, but I don't think I need to tell you any of that, so I'm assuming that you dismissed the animated-GIF option for other reasons. Hey, the old "cross-eye" 3-d works well, too; at least for some of your fans, like me.

John Dolby said...

No. Wait! That's genius! (Head-slap) I like what you did there, even better than an animated GIF. How did you come up with that "slight shift" technique? That's as clever as a blink comparator! I must confess that I didn't scour your pictures before my last comment. But seeing Pluto as a single dot while all the other ones are double.... That's the best thing I've seen since the New Horizons close approach!

I think your blog is the only way you and I could ever have a conversation. I'm always about three days behind your logic. I need a few days to let it soak in. And then when I finally get it, you're off on a new topic. I just can't keep up.