Live from the Hubble Space Telescope
UPDATE # 1
Welcome to "LIVE FROM THE HUBBLE SPACE TELESCOPE", a project developed by the Passport to Knowledge team.
Over the next three months, you will receive a unique perspective on the Hubble Space Telescope (HST). Through this maillist, you will receive regular Field Journals from the men and women who operate this unique facility. You will hear from the astronomers and space researchers who use the extraordinary power delivered by the HST to make exciting discoveries. These behind-the-scenes reports will provide insights in the day-to-day work required to make this NASA facility a success, including the broad diversity of skills needed.
But this time, you won't just be watching....you'll be participating in the mission. For the first time ever, the Space Telescope Science Institute has dedicated three full orbits (~4.5 hours) of telescope time towards the K-12 community. In December, students and educators debated what objects to observe with our precious HST time. Together we reached a consensus that Pluto and Neptune would be our targets. We will make the observations in early March. When the data comes down, it will belong to K-12 classrooms and Passport to Knowledge. Presently, the Hubble Space Telescope crew is busily preparing for these observations.
LIVE FROM THE HUBBLE SPACE TELESCOPE (LHST) includes two live television programs scheduled for March 14 and April 23 (each runs page Teacher's Guide which will be available shortly. This document details a variety of hands-on science activities designed to integrate with the online and television resources.
A dedicated online archive is rapidly coming together. It includes the complete collection of Field Journals, biographies of HST's people, an image gallery, a collection of classroom projects and much more. This "continuous construction" Web site is found at http://quest.arc.nasa.gov/livefrom/hst.html
As LHST evolves, special activities will be scheduled. For example, in March we will provide students and educators an opportunity to email questions to the HST team where each question will receive a personal answer. A series of special Web Chat and CU-SeeMe sessions with HST folks will be scheduled. As details emerge they will be announced on this updates-hst mailing list.
Presently, we plan to publish these email updates about once per week. The frequency will increase as we get closer to making our own observations with the HST in March.
If at any time you wish to stop receiving these electronic mailings, send an email to listmanager
In the message body, write these words: unsubscribe updates-hst
We hope that LIVE FROM THE HUBBLE SPACE TELESCOPE will prove to be an exciting learning resource for you and your students.
Thanks for your interest,
We are starting a regularly scheduled chat time online. Our goal is to gather some feedback from folks about this project or to address some of your concerns. We are particularly interested in chatting with teachers who are planning to use this LHST material with their classes, but everybody is invited.
For now, several project members (Jan and Marc) will be loitering online each Tuesday from 3:00-4:00 PM (Pacific time). Please try to join us if you can. If the time is bad, please send email to Marc and suggest an alternate time.
If you plan on viewing the television programs live or on tape, now is a good time to begin planning how you will do this. In the past, this has been a significant obstacle for many participants, so we suggest that you should actively explore options as soon as possible.
Your first action should be a call to the local PBS station. Find out if they will be carrying the programming live or delayed. They can tell you their schedule. If they are not planning to air the shows, consider organizing a teacher phone campaign to inform your local station of your educational wishes. Now is the timeframe that many stations are planning their March/April schedules and it often doesn't take many calls to capture their attention.
If that does not work, you will have to get creative. The LHST programming will also be broadcast over NASA Television. Many cable companies normally carry this station (its the one with live Shuttle mission coverage). Some may be willing to carry NASA-TV just for these special events. Other avenues to try include instructional television systems, community colleges or anyone with access to a satellite dish. During an earlier project, one excited teacher convinced a local satellite retailer to temporarily install a free dish at the school. Also, NASA-TV is normally sent via digitized video over the Internet using CU-SeeMe and MBONE technology. This option preserves the live aspect of the programming, but Internet video suffers from reduced video and audio quality.
Finally, if you cannot obtain the programming live, consider asking any of the resources above to tape the programs for you and provide them shortly after the broadcasts. NASA will also provide the programs on videotape for a modest fee. More information will be announced about this option in the future.
Dr. Clyde Tombaugh, who discovered Pluto in 1930, celebrates his 90th birthday on February 4th. Around February 23, we've arranged to meet with Dr. Tombaugh and present him with some special birthday cards. Please consider joining us in the activity below.
Have your students research Clyde Tombaugh's background and the discovery of Pluto. Use your library resources and online resources. You will find a commentary entitled Clyde Tombaugh's Blinking Persistence here (that is vol one-a) Also you'll find other related info on the discovery of Pluto here
THEN.....Chose to do one or more of the following:
We would like to have all student work sent to:
by ****Friday, February 9****.
The Passport team will see to it that all items are delivered to Dr. Tombaugh during a special presentation. We, in fact, are hoping to arrange video clips that will be incorporated into one of the live telecasts.
If you would like to include a group photo of your class and note about your school, etc. please do so. If you use a digital camera, please print out the photo and also include it on the diskette containing student work as described below.
Please send both **print copies** and diskettes with student work. If possible we would like to share your student work online at our web site. If you use computer based applications to produce student work, please save to diskette, and label appropriate filename/application/etc. information or send separate note detailing format information. (Note: We will not include individual student names or their email addresses as per concern about this type of information accessible on the net.)
The BIG DECISION has been made for the "Live From HST" project. There will be two orbits going to Neptune, and one to Pluto. Our goal for the Pluto observations will be to take a picture that closely duplicates one of the pictures taken earlier with HST. The next step in this process will be to provide a precise plan of observation to STScI (Space Telescope Science Institute).
The first step in planning this observation is to decide on the instrument and its configuration. There are two imaging cameras on HST that we could use, WFPC2 (Wide-Field Planetary Camera 2) and FOC (Faint Object Camera). You might think that from the name we would pick WFPC2 but that's not the case. There is one fundamental tradeoff between the two cameras that makes the decision easy. The pixels that make up an image with each camera are of very different sizes between WFPC2 and FOC. The FOC has smaller pixels than WFPC2 and will capture the maximum resolution image possible with HST. The WFPC2 was built to take picture over a wider area of "sky" and had to sacrifice resolution to get more area.
Having decided to use the FOC, the next step is to decide on which filters must be used. These filters select a limited range of color somewhere between the ultraviolet and visible parts of the spectrum. We have time in a single orbit to take a picture in two colors. There is a long list of possibilities that I won't list here but I've decided on F410M and F278M. These "codes" indicate the type and color of filter. M stands for medium and refers to the width of the filter in wavelength (other possibilities are N for narrow and W for wide). The number refers to the wavelength of light near the center of the filter. 410 means 410 nanometers or 4100 Angstroms and corresponds to what we'd call blue light. 278 nm or 2780 Angstroms is ultraviolet light that we can't see with our eyes.
I've chosen these to be the same as the filters used in the previous observations. Why did we chose these originally? Well, we need to take one picture at a wavelength that has been thoroughly studied in the past. A great deal of work has been done on the appearance of Pluto in blue light, some of which I've done myself. So, the choice of F410M was an attempt to get a picture that can be directly compared to previous work. The choice of F278M was a compromise. Going further and further to the far UV becomes more interesting because Pluto might look dramatically different. However, our sun doesn't actually put out that much light in the ultraviolet so the amount reflected from Pluto drops dramatically as we go to shorter and shorter wavelength. F278M is about as short in wavelength as we can go and still get a decent picture in the time we have.
So, are we done? Well, not quite. We've chosen the filter, now we need to decide how long to integrate in each filter. The FOC is carefully designed to take images of faint objects. You might think that Pluto is a faint object but in fact it's quite bright. Before you can take a picture you must first calculate exactly how bright Pluto will be as seen by the camera. The FOC can see faint stuff but it takes pictures by literally counting the photons as then come in. For an object like Pluto, we must ensure that the camera doesn't have to count any faster than about 1 photon/second in the brightest pixel on Pluto. That's pretty slow. Using the previous observations, I know that the count rate will be about 8-10 counts/second. To keep from damaging the instrument, we must put in a neutral density filter (sort of like using sunglasses) to make Pluto appear dimmer.
With this slow count rate, we will need to integrate on Pluto as long as we can. We have 1 orbit to do this. An orbit is nominally 94 minutes long but during half of this the Earth is in the way and we can't see Pluto. To make the observation the telescope is moved to point at Pluto. As soon as the earth is out of the way it begins looking for guide stars to lock onto and keep the telescope pointed at Pluto. This step takes about 12 minutes. We now have about 40 minutes left before the earth blocks our view again. It turns out that we can get two 15 minute exposures packed into the viewing time and that's what I've put into the schedule.
There is one exciting thing about these pictures. We have the benefit of seeing the previous pictures and using them to modify the experiment. The first time we did this we had to compute the brightness of Pluto without any example to follow. Since there are always some uncertainties involved we had to choose a conservative amount of neutral density to ensure that Pluto wouldn't appear too bright. Well, looking at the numbers yesterday I found that we can use less neutral density than before. This means we will collect 4 times as many photons in these pictures as was done before and thus we should have pictures with less noise.
Now that we know how the observations will be done the next step is to decide when to observe. We've been told by STScI that the observations will be scheduled for the weeks of March 4th or March 11th. During that two week interval, I've calculated when Pluto will show the same side as seen during the other pictures. Those previous pictures were taken at 15, 112, 203, and 289 degrees east longitude. This is a list of when these geometries will repeat.
longitude UT date and time priority ------------------------------------------- 203 1996/03/04 06:11:23 #2 112 1996/03/05 20:56:22 #6 15 1996/03/07 14:14:40 #4 289 1996/03/09 02:51:56 #8 203 1996/03/10 15:29:13 #1 112 1996/03/12 06:14:15 #7 15 1996/03/13 23:32:36 #5 289 1996/03/15 12:09:55 #9 203 1996/03/17 00:47:15 #3
I've chosen longitude 203 as the highest priority because there is an interesting bright spot in the south polar regions and because there are some differences between the visible and UV images. This longitude shows up three times during the two weeks and have been assigned the highest priorities. I suspect that one of these three times can be scheduled but just in case, I've ranked the other times as well. Why do we need a list at all? Why can't we just say when we want the observation to be done?
Well, one of the worst problems plaguing precise scheduling of HST observations is the South Atlantic Anomaly (SAA). This is an area over the South Atlantic Ocean off the coast of South America where the Van Allen Radiation Belts dip closer to the atmosphere due to the shape of the magnetic field of the Earth. If HST is used to take pictures during the passage through this area, the images become contaminated with radiation noise. For any object in the sky, there is roughly 6-7 hours each day where you cannot observe the object because you are in the SAA when the object is not blocked by the earth. Thus there is a 30-40% chance for a random time to be impossible to schedule because of the SAA passage. By providing a number of possible times, we can be sure that at least one of these can be scheduled free of the SAA.
So, now all this information has been distilled down and transmitted to STScI where the observation plan will be further refined. If all goes well, we just sit back and wait for our data. You might be interested to know that doing all this work and planning took me about 2-3 hours and slightly longer than that to write it all down. Of course, I've got the advantage of having worked at STScI for 3 years learning all this stuff. If you've never worked with HST before, developing an observational plan could take weeks of work.