I'm out at the VLA right now, getting ready for our observations this Thursday. I'm looking forward to the chance to talk with each of you! To make our time more productive, I wanted to give you some background information and let you know how I intend to start the telecon. These are suggestions only, and I'm happy to focus on different things if you prefer. Just let me know!
1) I'm at the Very Large Array (VLA), which is located in central New Mexico. It consists of 27 antennas, each 25 meters across (smaller than your GAVRT antenna). The cool thing about the VLA is that we can combine the signals from all 27 antennas in a way that gives us the resolution of a telescope 23 miles across! That allows me to actually make maps of Uranus. You can't do that with the GAVRT antenna, but you can measure the total brightness — which is still important!
This is a website for the VLA. It may contain some useful material for you... or not... http://www.vla.nrao.edu/
2) On Thursday, you will be observing at X-band, with a wavelength of about 3.5 cm. We'll compare your measurements to VLA data collected a few months ago at the same wavelength.
I will be observing this Thursday at a wavelength of 1.5 cm — a little different than yours.
Later this year, I'll be combining your 3.5 cm data with my 1.5 cm observations. I will create a computer model of the planet, which fits both your data and mine. Having two different wavelengths makes the model more accurate.
3) During our telecon, I thought I would discuss how the brightness of Uranus has been changing over the past 40 years. I'd like your kids to be aware of a few things going into this.
Uranus takes 84 years to go around the sun, so each season lasts 21 years!
Uranus is tilted over on its side. This creates extreme seasons — when it's summer, it's daylight all the time (for 21 years), and when it's winter, it's dark for 21 years.
From the Earth, we see different regions of the planet as Uranus orbits around the sun. We always see the part that is pointed at the sun. (That's because the Sun and the Earth are relatively close together, while Uranus is far away.)
Some of you may recall the "beach ball" exercise we did in training---it covered these points. It would be great if you could do something similar with your kids!
4) To see how the radio measurements have been changing over time, we'll use a PowerPoint presentation which the Lewis Center has e-mailed you. You may want to print it out and give each student a hardcopy. The presentation is available here Uranus Telecon PowerPoint.
That's it for now, I'll be talking to you soon!
Mark Hofstadter, Ph.D.
P.S. For those who wish a quick tour of the presentation, here it is:
Slide 1) Pictures of Uranus. The 1986 one was taken by the Voyager spacecraft as it flew by. The South Pole is pretty much in the middle of the image. The picture on the right was taken by the Hubble Space Telescope. The idea to convey is that things have been changing on the planet.
Slide 2) Just some facts to keep in mind.
Slide 3) This shows how Uranus is tilted on its side, and how the rotation axis always points in the same direction. That means that some of the time the North Pole is in the sun, and at other times the South Pole is in the sun. The Earth is much closer to the Sun than Uranus, and we never see the dark side of the planet. Sometimes (such as in 1965 and 2007) we see the Equator of Uranus. Other times, we see a pole (the South Pole in 1985).
Slide 4) These show how the brightness, as measured at professional observatories, has changed over the past 40 years. What trends do you see in the data? What might be causing the changes? Remember that our view of the planet, as well as the seasons, are changing over time. In the 1960s, and again now, we are looking at the Equator of the planet. In 1985, we were looking at the South Pole.
Slide 5) I've fit a couple lines to the data, to better show the trends.
Slide 6) I've added the first two years of GAVRT data to the chart — they are the points in red. (All observations made in a year are averaged together.) The second one was calculated by students of Rex Roettger, a teacher in Puerto Rico. I've put large error bars on that point, because I haven't reviewed Rex's procedures yet. Note how the brightness seems to have been relatively constant over the past ~10 years. Has Uranus stopped changing, or will the brightness decrease again, matching measurements made during the last Equinox (compare the 1965 data with the most recent measurements)? Nobody knows!
Slide 7) For discussion, some recent images of Uranus. The one on the left was made at the VLA. The red colors are regions bright at radio wavelengths, the green colors are relatively cool. The South Pole is the bright region on the left of this image.
The right-side image was taken from the Keck telescope in Hawaii, at infrared wavelengths. Note how the left half of the planet (which is the Southern Hemisphere, in its fall) is different than the right half of the planet (the Northern Hemisphere, which is in its spring).