Q&A With Dr. Harry Ferguson
Astronomer, Space Telescope Science Institute

Anthony Zeller
Savage, MN

The Hubble Deep Field project showed how the telescope can be used to view the end of the visible universe. Would a bigger, better telescope be beneficial to see that end even better or is there no need because astronomers can see all that there is to see?

Also, what is the length of time for the lifecycle of a supernova?

Dear Anthony,
As another astromer, Rachel Dewey, once said while discussing ground-based radio telescopes, "bigger is always better." A larger telescope would allow detailed studies of objects we can only barely glimpse now. Perhaps the greatest change, however, would occur if the telescope were optimized to see in the infrared rather than in the optical. The redshift of light emitted by very distant objects implies that the optical light we observe now was emitted in the ultraviolet, but as Harry Ferguson discusses on the main web page, intergalactic hydrogen throughout the universe absorbs far-ultraviolet light. Because of this effect, the Hubble Deep Field discussed on the TV program only saw back to when the universe was about 2 billion years old. To see further we will need to build a large space-based infrared telescope. Fortunately, NASA is considering building just such a telescope, which is presently referred to as the Next Generation Space Telescope.

A major reason that astrophysicists have had a difficult time modelling supernovae is that there are many different timescales which are important in understanding these impressive objects. But supernovae will be discussed on the second show in the series, so let's leave this question for just a couple of days.

Take care,
A. F.

Name and City Withheld

1. Why are there so many double stars?

2. The Deep Space Hubble image is wonderfully beautiful. What enhancements are done to create this image? Does the image reflect the impositions of any "ideal" galactic shapes onto indistinct fuzzes? It seems so clear that it is hard to believe that a lot of assumptions weren't made in its presentation...if we can see that far back so clearly, then surely the horizon must be much further back...

1. A binary system is the only gravitational system made up of equal partners that has stable orbits. Quasi-stable orbits are feasible in a hierarchical system, like the solar system where the sun dominates. But put three or more equal objects together and not only do the orbits quickly become chaotic, but often one of the objects is often thrown out by the other two! As a result we can expect triple and quadruple stars to be rare. Computer simulations of star formation show that the angular momentum in a collapsing gas disk will frequently produce an instability that results in two separate bodies forming. But we don't yet really understand the difference between the initial conditions that led our sun to be a single star while so many of theirs are binaries.

2. I'm glad you enjoyed the Hubble Deep Field image. We do live in a very beautiful universe. And that really is the point; there were very few enhancements made in producing the image. It is a fairly accurate representation of what your eye would see if only it were as sensitive as the instruments at the back of Hubble Space Telescope. There were only two slight fudges: 1) the red filter used in the image is actually a bitter further red than the eye can see (it is in the near infrared), and 2) we used a new technique called "drizzling" to reduce the blurring effects of the large pixels in the Wide Field camera. But this is a very mild enhancement (it was developed precisely to insure that we would NOT introduce any artifacts into the galaxy images). We made no assumptions about the shapes of the galaxies. But you are right, we are not quite seeing to the "edge of the universe." See Harry Ferguson's introduction for a discussion of this question.

A. F.

Jeff Daniel
Vista, CA

Suppose theoretically, you could bore a 12" diameter hole all the way through the earth. Then you drop a 10 lb. cannon ball down the hole. My question is, what would happen? Would it come out the other side of the earth or would it settle in the center of the earth or would it just stay suspended above the hole? Thank you. I think PBS is great.
Take care
Jeff

Hi Jeff,
Well you first want to drill the hole right along the earth's axis of rotation, or else have the earth stop spinning, because otherwise the ball will hit the side of the wall on its way down, since the rotational velocity of a point in the earth is proportional to its distance from the center. But forgetting that complication, and assuming you've completely evacuated the hole, then the ball would just oscillate up and down. It would rise to the surface on the other side of the earth and then fall right back to the point from which you dropped it, and it would go one doing this forever. You see the ball is in orbit. In fact, when an object, like the space shuttle, is in orbit it is falling towards earth, but it is moving so fast to one side that it misses the earth and just keeps on falling. In this case, the cannon ball is on a radial orbit, and it misses the earth because you kindly moved the earth out of the way!

Cheers,
A. F.

Jan McCulloch
Owosso, Michigan

I've been looking up all of my life (46 years worth) but have never been financially fit for a telescope for deep-space viewing. I am now in that position and already have the 35 slr I want. What is a good, dependable telescope for someone who has unpolluted viewing from their own back deck? This scope will be with me and my husband for the rest of our lives and there are too many to choose from for a real novice like me.

Thanking you in advance!

Hi Jan,
I suggest that you contact a local skygazing group, and join them on one of their outings. I am sure that many of the people on the trip will be glad to let you look through their telescopes and discuss with you the pros and cons of the model they chose. This way you will be able to chose a telescope that is well suited to your needs.

Happy observing!
A. F.

Carter Rhodes
Atlanta, GA

I was "out to lunch" during the time the astronauts were repairing the Hubble telescope. The 1st episode said that a flaw in the optics impaired the telescope. Can you elaborate *just* a little (unless it's way too technical); but more, can you say that since the repairs, the telescope is now operating as it SHOULD have to begin with, or is it going to remain compromised?

Bravo to this little gem of a series! And to those astronomers!

Hi Carter,
When the primary mirror of the Hubble Space Telescope was being polished, a mistake was made in the measurement of its shape. As a result the focal "point" of the telescope instead became a focal "line". The best focus point for the light reflected from the telescope now depends on whether the light has been reflected from near the edge of the mirror or from near the center. In a well polished mirror, all the light focuses at a single point independent of where it hits the mirror.

Fortunately, the corrections that have been made work wonderfully. In fact, the telescope now works better than the original designers of the Hubble Space Telescope thought it would! The error in the primary mirror makes building new instruments for HST slightly more complicated than had the primary been polished correctly in the first place, but the real effect on the final performance of the telescope is minor.

I'm glad you are enjoying the series. We are living in what must be one of the golden eras of astronomy.

All the best,
A. F.

Al Cook
Sarasota, Fl

Is it possible to orbit a second Hubble telescope and sync it with the first to take advantage of the longer baseline for greater distance observation, or is the vlba only usable with radio telescopes? If the first half of the above is possible, are there plans afoot to build a second? Al

Hi Al,
Unfortunately, it is not feasible to make HST part of an interferometer. However, there are plans to build a space-based optical interferometer, which will have a span of 10 meters, and thus will have angular resolution several times better than HST. In the longer term, a much larger space-based interferometer may be built to search for planets about other stars. Both of these interferometers will probably have their mirrors attached to a single support structure. We have yet to develop the technology that would allow free-flying optical interferometric elements (in the radio the job is much easier as the wavelengths are thousands of times larger); however, if we do perfect such technology we might someday be able to image the planets in other solar systems.

Cheers,
A. F.

Matt Keye
Dove Canyon, California

Is there a way to go faster than the speed of light?

Hi Matt,
As far as we know, nothing moves faster than the speed of light in a vacuum (light moves more slowly in a medium like glass). We do know that were it possible to travel faster than the speed of light, then time travel would also be possible. So, perhaps the fact that we don't have tourists from the 24th century popping in all the time means that mankind will never find a way to make faster-than-light travel practical.

Take care,
A. F.