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Hubble Space Telescope Banner


Live from the Hubble Space Telescope

UPDATE # 13

PART 1: Our Neptune and Pluto images are available

PART 2: The Hubble team will answer your questions

PART 3: Starting work on the Neptune images

PART 4: Hawks, aluminum, and math: more work on the Archive

PART 5: Program and standard stars for the catalog

PART 6: Trying to understand the changing wavelengths


OUR NEPTUNE AND PLUTO IMAGES ARE AVAILABLE

If you saw the live television program on Thursday you already know that our observations of Neptune and Pluto produced good data. After a quick first look, it appears that our images contain exciting new science information. The next five weeks promise to be interesting as we work with Planet Advocates Heidi Hammel and Marc Buie to process the data and discover the scientific significance of our images.

These Hubble pictures are available online on the Web. Go to our home pages and look in any of the following sections for the images: - Project News - Featured Events (student do research with the HST) - Photo Gallery


THE HUBBLE TEAM WILL ANSWER YOUR QUESTIONS

The opportunity to send Email questions to the men and women of the Hubble team is now available and will remain active until early May. We are grateful to the HST folks for generously volunteering their time to support this service.

This section will describe some guidelines and procedures for the process.

K-12 students and educators can Email questions to researchers, engineers and support staff. This interaction will be supported by a "Smart Filter" which protects the professional from Internet overload by acting as a buffer. The actual Email addresses of these experts will remain unlisted. Also, repetitive questions will be answered from an accumulating database of replies; thus the valued interaction with the experts will be saved for original questions. (More information about how you can directly search this database will follow later).

Tips for asking good questions

Each and every expert is excited about connecting with classrooms. But it is important to remember that the time and energy of these researchers is extremely valuable. If possible, please review the materials available online to gain an overall understanding of the basics. It would be best to ask questions that are not easily answered elsewhere. For example, "What does the Hubble Space Telescope do?" would not be an appropriate question.

We recognize that this creates a gray area about whether or not a question is appropriate. Simply use your best judgment. Since the main idea is to excite students about the wonders of science and research, please err on the side of having the students participate. If you are not sure whether or not to send a question, send it.

Some teachers have used a group dynamic to refine the questions that they email to experts. For example, after first studying HST material, students divide into groups and create a few questions per group. All of the questions are then shared, and students are given an opportunity to find answers to their classmates' questions. Those that remain unanswered are sent to the HST team.

Ideally, the act of sending questions will further engage the student in their learning. It may help to think back to an early stage of development when the 3 year old learns that repeating the word "why" can get parents to do most of the work in a conversation The wise parent will try to get child involvement by asking "why do you want to know?". The same is true in the classroom. Teachers might want to help students learn to ask good questions. Here are three questions the students might ask themselves as they submit their questions:

	What do I want to know?

	Is this information to be found in a resource I could easily
	check (such as a school encyclopedia)?

	Why do I want to know it? ("What will I do with the
	information?" or "How will I use what I learn?")

The last question is the most interesting. Student reflection on why they want to know something is a very valuable learning experience.

Logistics of sending in questions (address and format)

Questions will be accepted from now through May 7, 1996. To submit a question during these times, mail it here.

We will acknowledge and answer all questions as quickly as possible. Our goal is to provide a basic acknowledgment immediately. In most cases we should be able to provide an answer within ten days to two weeks, sometimes quicker

In the subject field, please put the letters "QA:" before a descriptive subject. Also, provide a sentence of background information to help the experts understand the grade level of your students. The following example should illustrate this idea.

TO:             question-hst@quest.arc.nasa.gov
FROM:           your Email address
SUBJECT:        QA: Hubble mission control

Hello,
I am an 8th grader from Buloxi, Mississippi. In the television program, it seemed like there were a lot of people in the control center to operate Hubble. How many people normally work in this room?

Thanks, Sophie Jackson

One question per message

If you or your class have several questions which are unrelated, we ask that you please send each unrelated question in a separate Email message rather than as one message with many different questions. While this may be inconvenient, it is important because it will help us to keep track of the questions and ensure that no question remains unanswered. Messages that do not follow this request will be unnecessarily delayed as we go through the extra step of splitting up the messages ourselves.

Twenty question limit

Any individual teacher will be limited to submitting a total of twenty (20) questions during the life of the project. Hopefully this will encourage more classroom discussion about what students want to know and will lead to research done before asking questions.

Browsing answers to questions already asked

An archive of question/answer pairs of previously asked questions will be maintained. This archive is readily available at this location.

Searching question/answer pairs

A capability to search for interesting question/answer pairs is also available via Email. The system relies on the user choosing one or more keywords related to their interest. Every existing question/answer pair will be searched to see if it contains the keywords. Messages with the keywords will be returned via Email. To initiate a search, send a mail message here.

In the message body, simply include the keywords (multiple keywords should be separated by spaces).

Receiving all question/answer pairs as they get created

A capability has been set up for those people that would like to receive ongoing Email with answers to all of the questions asked. Each night, one mail message will be sent to those interested. This message will contain a copy of every question/answer pair generated that day. If you are interested in this feature, send an Email here.
Leave the subject blank and in the message body, write the words: subscribe answers-hst


STARTING WORK ON THE NEPTUNE IMAGES

Heidi Hammel and Wes Lockwood

March 15, 1996
This is Heidi and Wes, writing from MIT on Friday afternoon. You already know me (Heidi) and Wes Lockwood is a scientist from Lowell Observatory in Flagstaff, Arizona. We have worked on Neptune data analyses together for many years. The next series of journals will document how we analyze the new LHST Neptune images. These will be analyzed right along with some of our older images, taken in 1994 and 1995. Much of the processing is the same, and we hope to include the LHST images in the paper we are writing about Neptune right now.

Today, we downloaded the images from Space Telescope Science Institute: this means we transferred them over the Internet from a disk in Baltimore, Maryland, to a disk attached to Heidi's work station at MIT in Cambridge, Massachusetts. This took about three hours! They are big images! But most of the image is just sky. The pictures on the LHST web pages were clipped out to show just Neptune.

Heidi also installed a new disk on her computer, to hold the new data and the work that we expect to do over the next two weeks. While she was doing that, Wes reviewed the work we had done the last time we were together, which was just before Christmas.

We took a quick look at our new images - they're great! The first thing we

noticed was that the clouds were very different from the way the planet looked in September. The general banded structure (the stripes, like on

Jupiter) look pretty much the same, but the brightest cloud is now in the south - not the north! That was a big surprise.

We have a lot of complicated work to do, both on these new LHST data, and the other data. So we made a To-Do list, and here it is:

* Go over previous to-do list (18 Dec 1995), and document what we have done
* Put disk directories back in order since addition of new disk
* Track down Amanda's email about HST ephemerides
* Track down Mert Davies 1994 reference for Neptune ephemeris
* Get 1994 and 1995 disk-integrated photometry from Lowell
* Refresh memory of solar cycle phase vs. Neptune outbursts - is 1994 a burst?
* Assemble planet center table 
* Assemble observation logs table 
* Write up navigation procedure

During the next few weeks, we will keep you updated on our progress as we work.

Heidi and Wes


HAWKS, ALUMINUM, AND MATH: MORE WORK ON THE ARCHIVE

Tom Comeau

March 8, 1996
I had just packed away my wife's snowboots (we're moving the end of this month) and this morning it snowed. Two inches or so, but enough to mess things up and close some of the schools.

We think the hawks are back! Last year we had a small family of red-tailed hawks that lived in a nearby park. A couple times a week they would come over onto the campus and go hunting. We'd see them perched halfway up a tree, or up on the gutters just below the roof line of the building. The female is pretty big, the male was about the size of a large crow, and the juveniles (there were one or two, we were never sure which) got to be the size of the male by the end of the summer. A couple of people think they saw the female return in the last few days. I've been keeping an eye out for her.

Today I'm doing two things at once: testing the changes I described in my last journal, and doing some database work.

The optical platters we use cost about $300 each, so we try to make sure things are working pretty well before we actually start writing data. I've been "burning aluminum" all day, and I'm pretty confident that things are working correctly. Suzanne (another DADS developer) and I have been working on this project since about Halloween, and we're both relieved to see it coming close to the end. And we're anxious to get on to the next phase of work for SM-97.

I mentioned "burning aluminum" above. I call it that because when we write to an optical disk, a laser in the drive blows little pits in a very thin sheet of aluminum trapped between two layers of transparent plastic. When we write, a high-powered laser burns out the pits. When we read, a lower-powered laser looks to see what those pits look like. Once you've burned the pits into the aluminum, it's permanent. You can't erase it, and we expect the disks to be good for at least 20 years, and maybe as much as 100 years.

CD-ROMs (and music CDs) work basically the same way, but the pits are "stamped" using a pressing machine, rather than blowing them out with a laser. The low-power laser in your CD player works the same as our optical disks drives.

To test a new version of the programs that add data to the archive, we run a standard set of test data through the system. There are about 700 files, for a total of 305 megabytes of data. That's about half of a typical CD-ROM, or about one twentieth of our big disks. It takes a couple hours to run all the data through, and that leaves me time to work on my other problem.

The database work I'm doing involves figuring out how much space we should reserve when we are making tapes to send to astronomers.

I'm trying to figure out just how big HST Datasets are. A dataset is a collection of files that together hold all the data for an image or spectrum. For WFPC-II (Wide-Field and Planetary Camera Two - the camera that takes most HST pictures) this is a pretty constant number: about 25 megabytes in 10 files. It's a pretty constant because the camera takes the same sort of pictures all the time. Each picture is four "chips" in an 800x800 array. (A typical PC screen has 1024x768 pixels -- a single WFPC-II chip is just slightly smaller, but square.) There are a total of about 40 bytes of information about each pixel, including calibrated and uncalibrated values, quality information, and other stuff. Since the size of the picture doesn't change, the size of the dataset doesn't change either.

For the spectrographs, the size of the dataset can vary a lot. This is because a single dataset can contain multiple spectra. In the case of the Goddard High Resolution Spectrograph, it can vary from just 38 kilobytes to over 300 megabytes!

But what I want is a "pretty good" estimate of each kind of dataset, and I can use that to plan how much space I'll need to retrieve a particular set of data. To get a statistical look at the data, I have this nice complicated query that gets the minimum, maximum, and average size of "Z-CAL" datasets. "Z-CAL" datasets are CALibrated science data for the GHRS. (Each instrument has a letter associated with it: U is for WFPC-II, X is for FOC, Z is for GHRS.) Once I have all that data, I can also compute the "standard deviation", which is a kind of average difference in sizes. That gives me an idea of how much variation there is in size.

Here's another example: If ten people take a test, and they all score between forty and sixty points, with an average of fifty points, that's a pretty low standard deviation. If another group of ten take the test, and half of them score about 20, while the other half score about 80, the average would still be 50, but the standard deviation would be pretty big.

When you see a large standard deviation like that, you have to decide if you're seeing different "populations". For example, if you have a test aimed at eighth graders, and you get five people who score about 20, and five who score about 80, the fact that you have a large deviation makes you wonder if maybe the five who scored 20s were perhaps second graders!

In my case, I've discovered there are two types of GHRS observations: short, small observations with one or a few spectra, and large observations that have many spectra. The "mode" I see for those observations is "RAPID", and I'll have to get one of the astronomer types to explain that operating mode to me.

That's the kind of math I do pretty regularly: Statistical analysis of the contents of the archive. I rarely need to do any calculus, though I know enough to understand how the mathematical "tools" I use work. But I do a lot of algebra, and use programs that have statistical functions.

Well, my big test is finished, and while most things are working, there are a couple of problems I need to work on. I'm going to take a break, get something to drink, and see if I can spot that hawk before I tackle them.


PROGRAM AND STANDARD STARS FOR THE CATALOG

Trisha Borgman

March 15, 1996
Good morning!
I apologize for not being able to write anything last week-- I had 2 midterms and 3 papers due, and I was barely able to come into work at all! But now things have calmed down; Spring Break is next week, and I'm finished with all of my classes.

Our observing run is coming up quickly! Since next week is Spring Break, I will actually leave for Arizona on Wednesday (my parents live in Arizona, so I'll spend a few days with them before going down to Kitt Peak) The run begins on the night of March 25, and ends on the morning of March 29. I sure hope we'll have good weather!!

Yesterday, my boss sent me a list of all the objects which we should try to observe--I believe we're going to have a meeting on Monday to plan everything out. I have never done anything like this, so I'll be learning as much as you will!!

Since we're building a star catalog, it is very important for us to be certain that the data we collect is completely accurate. I mentioned before that part of my job is to remove the instrumental "signatures" left by the telescope itself. Another very important part of building the catalog is having a separate set of stars whose photometric information is already known to compare our stars to. We therefore call the stars we're observing for our catalog "Program stars"; the stars for which the information is already known are called "Standard stars." The standard stars come from a catalog which was compiled by an astronomer named Arno Landolt. He spent several years observing around the celestial equator (the celestial equator is just like the earth's equator-- stars near the celestial equator would be almost directly overhead to a person standing on earth's equator). Stars near the celestial equator are visible to people both in the northern hemisphere and the southern hemisphere. His catalog is filled with literally hundreds of stars from this region, and are often called the "Landolt standards."

Have you ever looked at what happens to sunlight when it passes through a prism? The light separates into the colors of the rainbow, right? Well, this visible light is just a small part of what scientists call the "electromagnetic spectrum." The electromagnetic spectrum includes the entire range of waves, waves can teach us about the amount of energy a star is producing. A picture of our sun in radio waves would look very different from a picture in x-rays, and both would look very different from what the sun looks like in the visible wavelengths -- wavelengths our eyes can see.

When collecting photometric information about the stars, astronomers typically use five of what we call 'passbands': U (ultraviolet), B (blue), V (visible), R (red), and I (near- infrared). A passband, as you might have guessed, is a narrow region of the electromagnetic spectrum. In order to only study within a certain passband, astronomers have to block out the rest of the spectrum with very sensitive filters. Of course, many astronomers choose other filters, but these five are probably the most common. The first GSPC catalog included data only from the B and V filters; the second GSPC (which I'm working on) will contain B, V, and R data and will also include much fainter stars.

So what does all this have to do with our observing run? Well, when we go out to the telescope, it's important not only for us to know which "program" stars to observe for our catalog, but also which "standard" stars to use. The standard stars help us to account for atmospheric distortions. When a star is directly overhead, its light will pass through much less atmosphere than when the star is near the horizon. We therefore observe these standard stars at many positions in the sky (overhead, at 30 degrees that we can take into account the effects of the atmosphere when reducing the data from our program stars. Does this make sense? We already know what the data from the standard stars SHOULD be, so when we measure them at many positions in the sky, we can compare the differences between what the standard star data SHOULD be and what it really is. We can then take that information and apply it to our program stars.

Pretty neat, huh?

Well, I'll be sure to write more next week before I leave, and I promise to write from Kitt Peak!!

Trisha


TRYING TO UNDERSTAND THE CHANGING WAVELENGTHS

Lisa Sherbert

March 13, 1996
Today I am zeroing in on the answer to a GO (General Observer) question about why wavelengths from data taken in March 94 are off by 2 angstroms After looking at his data and seeing how little signal there was, I wondered how he could tell anything about the wavelengths associated with the individual spectra. I found that the signal improves (i.e. you could start to see features as opposed to noise) when the individual spectra are combined or co-added, i.e. summed together.

Still I was confused because I thought he was trying to compare the same feature (an absorption (usually) or emission line) in wavelength space but the data weren't taken at the same central wavelengths at all. There was hardly any overlap. It turned out he was not comparing the same feature but different features in redshift space, not wavelength space. Redshift is the amount a feature moves in wavelength or velocity, etc. due to the fact that it is moving away from us. This relates to something you may have heard of called the Doppler effect? It is expressed in terms of "delta lambda over lambda" which is equal to "v over c". Lambda (the Greek letter lambda) stands for the rest wavelength, where you expect to find the feature if it weren't moving away from you. Delta lambda is the difference in wavelength between where you found the object and the rest wavelength. "v" is velocity, the speed at which it is moving away. And "c" is, of course, the speed of light.

The General Observer) was plotting his lines of different wavelength on a redshift (or velocity) scale, then trying to fit them with theoretical profiles. What he found was that the absorption lines in the March 94 data line up at the same redshift, but the line in the October 95 data appear to be at a slightly different redshift. And that is the shift he didn't understand. But I figured out that the wavelength calibration has changed since the first data were taken. It is quite possible, probable, and hopeful that if he recalibrates his data the unexpected shift will go away.

Of course, while I am working on this problem, I also have several more that I am trying to keep on top of...but my ability or lack of ability to do more than one chore at a time is the topic for another journal.

Lisa Sherbert, GHRS Data Analyst
Space Telescope Science Institute


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