Questions and Answers for the
National Science and Technology Week Program


ASK A SCIENTIST

These questions were submitted by students and the public as part of the NSF-sponsored National Science and Technology Week. Answers were provided by various NOAO staff members.

  1. Do you study constellations?
  2. Who was the first person to discover a planet?
  3. Why do planets need sunlight?
  4. Is the news about the new planet true?
  5. How many miles away are the stars (NOT our sun)?
  6. Are there more than nine planets in our solar system?
  7. Can we travel our of our galaxy?
  8. What planets in our solar system are the hottest?
  9. Is is possible that we will be able to live on Mars?
  10. Why does the sun look larger at sunrise and sunset than at other times of the day? When are we closest to the sun?
  11. If you had a blank check what top five priorities would you set for the space program in the next few years? In other words, what do you think is the most important work that astronomers are doing now?
  12. How much could be realized in, say, the next twenty years if funding were not an issue?
  13. How does NOAO get its funding and would you say that the money situation is improving or worsening? Vice President Gore is supposedly a big supporter of the space program and related spending. Has any of that been realized? How do you think we can improve public support for spending?
  14. What is the most important recent discovery in Astronomy? New Planets?
  15. What is the most exciting project that you have been involved in?
  16. Do you believe that as astronomy gets more and more specialized it will be harder to gain public support for projects? The space race seemed to rally public support but it must be harder to reach people with less tangible or sensational discoveries?
  17. How much do you think we are capable of discovering? How far will we get in the next, say 50 years?
  18. What are you working on right now?
  19. I am trying to decide between medicine and astronomy as a career. Any advice?

1. Do you study constellations?

No - I study how stars are born and how they live in galaxies other than our home galaxy, the Milky Way. The Milky Way is that faint, fuzzy band of light you can see when the sky is dark and you are not too close to a lot of lights. The Milky Way is made up of billions of stars so far away they have blurred together into the cloudy band you see. Our Sun is just one of those billions of stars. The Universe contains billions of galaxies. Many galaxies look like pinwheels and are called spiral galaxies. The Milky Way is a spiral galaxy. Other galaxies look like basketballs, footballs, and cigars. We call those galaxies elliptical galaxies. But all these galaxies are made up of individual stars, like the stars you see in the night sky. By studying stars in these distant galaxies, I hope to better understand how our entire Universe was born and how it has changed since it was born.

2. Who was the first person to discover a planet?

There are nine planets in our Solar System: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto.

The planets closest to Earth (Mercury, Venus, Mars, Jupiter, and Saturn) were discovered so long ago that no one remembers who saw them first. These planets are bright in our night sky and can be easily seen without binoculars or telescopes. Their positions in the sky change quickly from night-to-night. The stars you see also change their positions from night-to-night but only by very small amounts, too small to be seen easily naked eye unless you lived for hundreds of years. The planets move so fast that ancient humans would have noticed these changes after only a few nights or weeks. So, we believe these planets have been known for thousands of years and probably tens of thousands of years.

Right now, the planet Venus is the brightest star in the northwestern sky right after sunset. If you watch it from night-to-night, you do will notice it has a slightly different position in the sky every night.

The three more distant planets (Uranus, Neptune, and Pluto) are too faint to be seen without binoculars or telescopes. Uranus was discovered in 1781, Neptune was discovered in 1840, and Pluto was discovered in 1930. The man who discovered Pluto is named Clyde Tombaugh. He is still alive and lives in Las Cruces, New Mexico.

3. Why do planets need sunlight?

All the planets we know about orbit around stars, which give off light. The further away from the star a planet is, the fainter the star appears. From Pluto, the Sun looks like a very bright star, not the big yellow disk we see from Earth. This light is most important for living things, like animals and plants on Earth. Without light, all living things would die. Only the Earth is known to contain life, although some scientists think there is life on other planets orbiting around other stars.

4. Is the news about the new planet true?

Yes! In fact, there are six new planets, but none of them are part of our Solar System. All six planets revolve around other stars. Three of these new planets revolve around a type of dead star called a pulsar. The other three planets orbit around other stars which are very similar to our Sun (think of them as our Sun's cousins). None of these planets is like the Earth, our home, and none of them is likely to contain life. Astronomers are very excited about these new planets and hope to find planets like the Earth very soon. To read more about these new planets, see the April 1996 issue of "Astronomy" magazine.

5. How many miles away are the stars (NOT our sun)?

The stars are so far away that we don't measure their distances in miles, but in "light years." A light year is the distance that light travels in one year. We know that the speed of light is 186,000 miles per second, and there are about 31,536,000 seconds in a year. So light travels a distance of 5,870,000,000,000 miles in one year. The nearest star, Proxima Centauri, is 4.2 light years away. Proxima Centauri is too faint to be seen with the naked eye, or even binoculars. It is a small, cool, dim, red star whose mass is just a fraction of the Sun's. It can be seen with a small telescope in the southern hemisphere.

Another way to think about the distance of the stars is to compare it to the distance of the Sun from the Earth (about 93 million miles, or 150 million kilometers). It takes light 8 minutes to reach the Earth from the Sun, and it takes light 4.2 years to reach the Earth from Proxima Centauri. That means that Proxima Centauri is 276,000 times further from the Earth than the Sun is. And that is just the nearest star; most are much further away. The furthest stars that are part of our galaxy are about 100,000 light years away.

6. Are there more than nine planets in our solar system?

So far, we know of only nine planets in the solar system. Astronomers have searched very hard to find additional planets beyond the orbit of Pluto, but no more have been found.

We do know that our solar system contains objects that orbit the Sun further out than Pluto - the Oort Cloud of comets, discovered by astronomer Jan Oort. Sometimes one of these comets gets "nudged" by the gravity of another comet or a passing star, and its orbit is shifted so that it travels into the inner part of the solar system. Then we see the object as a comet in the sky. But we can only see it when it is relatively close to the Sun. Then, the sunlight causes some of the comet's surface to sublime (to change from a solid like ice to a gas), and the gas reflects a lot of sunlight, causing the comet to look bright. Comets in the Oort Cloud are too faint to be seen even with the largest telescopes.

7. Can we travel out of our galaxy?

The Milky Way, our galaxy, is enormous, so big that it takes light 70,000 years to travel all the way across the galaxy - and light travels 186,000 miles every second! If we could travel at the speed of light (which we can't) it would take 4.2 years even to reach the nearest star, Proxima Centauri. If we could build a spaceship which could travel at 1/10 the speed of light, it would take 42 years to reach Proxima Centauri. So if human beings are ever going to travel to the stars, we will have to do so in very large ships, and spend our lives, our childrens' lives, and our grandchildrens' lives, even to reach the nearest stars.

Right now, the space ships we build for humans stay in the vicinity of Earth, just above the atmosphere. We know we can build ships to take us to the Moon, because we did it once, but we have no ships like that now. Now we build robot spacecraft to explore more distant parts of the Solar System, like the Galileo spacecraft that is now orbiting Jupiter. Some of the earliest spacecraft that explored the outer planets are just now leaving the vicinity of our Solar System and beginning to explore interstellar space. Maybe someday we will build robot spacecraft to visit the nearby stars.

If we could build a spaceship, though, that could travel great distances quickly, there is no barrier at the edge of the galaxy to keep us inside - we could travel out to intergalactic space.

8. What planets in our solar system are the hottest?

The hottest planets are those closest to the Sun. Mercury is only about 36 million miles from the Sun, and its surface is very hot - maybe up to 850°F when the planet is closest to the Sun. Venus is only 67 million miles from the Sun. It is a very hot planet, both because it is close to the Sun and because its atmosphere traps the heat from sunlight. Its surface temperature has been measured over 800°F. Mars is a cold planet, with temperatures usually below freezing (but it can get up to 70°F on a summer day). Pluto is extremely cold (-369°F).

The giant planets Jupiter, Saturn, Uranus, and Neptune don't have surfaces like the smaller planets do. They are made mostly of hydrogen and helium gas. These planets are very cold at the tops of their clouds, because they are so far from the Sun and receive little sunlight. But they may be very hot inside. The heat inside comes from the slight contraction of the planet with time. We know that Jupiter is hot inside, because the top of its atmosphere is warmer than it should be at Jupiter's distance from the Sun.

9. Is is possible that we will be able to live on Mars?

Your question is very interesting but also very hard to answer because it asks about the future.

A century ago, nearly nobody thought we could leave the Earth or even land on the Moon but we did land in 1969. We had several probes go to Mars and more are on their way in the next few years. The next step would be to land people on Mars before thinking about living there. With our present technology it is possible to get people to Mars and back but it would take at least 2 years. Nobody has been in space that long and effects about spending so much time in space are being studied right now. Also, we do not know how fast technology will improve or even jump so that it would be possible to go to Mars faster.

Of course, getting to Mars is just the first step. Living on Mars is another one. People cannot live on Mars without special protection. If you go to the library and find a book about the planets, especially Mars, it will tell you that the gravity on Mars is smaller than on Earth (not a big problem), and that there is only a very, very thin atmosphere. Also, Mars is further away from the Sun (1.5 Astronomical Units) than the Earth (1 Astronomical Unit from the Sun) and Mars gets less energy and warmth from the Sun. Without atmosphere we cannot breath and we would not be protected from harmful cosmic rays, the solar ultraviolet radiation, and the deadly cold like here on Earth. We would have to build confined domes that are pressurized and have breathable air. There has been no life found on Mars. This means, we will have to bring all our food. We need resources to build domes. Maybe some mining would be possible on Mars but we would have to build machinery first (or maybe we could send robots).

You see, we seem to know what all has to be done and some of it we already know how to do. But other things would right now just be too complicated or too costly.

I am convinced that sometime in the rather far future we will be able to live on Mars. But do we want to spend the resources and do we want to live on Mars?

10. Why does the sun look larger at sunrise and sunset than at other times of the day? When are we closest to the sun?

Photographs of the sun taken close to the horizon at sunrise and sunset and high in the sky around noon showed that the sun is not larger when it is close to the horizon. Most people agree that we think it is larger because there are many objects close to the horizon (houses etc.) with which we can compare the image of the sun, but we cannot do this when the sun is high up in the sky. By the way, the same effect also occurs with the moon. Furthermore, close to the horizon the images of the sun and the moon are distorted by the Earth's atmosphere. They are not round anymore but tend to be compressed in the vertical direction. This might be an additional factor that makes us think that the sun and the moon look larger close to the horizon.

The Earth is closest to the sun in January, and it is furthest away from the sun in July. The difference in the apparent size of the sun is only 3.3%, between January and July, which is a very small effect. Remember that the season's are not generated by this effect but are due to the inclination of the Earth's rotation axis by about 23 degrees.

11. If you had a blank check what top five priorities would you set for the space program in the next few years? In other words, what do you think is the most important work that astronomers are doing now?

Note that by saying "next few years", you constrain my answer to existing instrumentation on space observatories. It takes about 4 years to plan a servicing mission on any low orbit satellite (like the HST) and it takes almost a decade to plan an entirely new mission. Experiments on-board high altitude aircrafts, like the defunct Kuyper Airborne Observatory or the new SOFIA (Stratospheric Observatory For Infrared Astronomy), or even short- lived rockets have however, a higher turn-around rate. Still, the next few years in space astronomy will focus on existing and projected missions as developed, in large part, in NASA's program of four "Great Observatories" to be launched before year 2000. The Compton Gamma Ray Observatory (CGRO) was the second "Great Observatory" launched by NASA in April 1991. The first was NASA's Hubble Space Telescope, deployed from the Space Shuttle Discovery exactly a year before, and reserviced in 1993 to correct for optical aberrations in the primary mirror. The others still to be launched are the Advanced X-ray Astrophysics Facility (AXAF) and the Space Infrared Telescope Facility (SIRTF). Each telescope will be sensitive to a broad region of the electromagnetic spectrum (CGRO: Gamma rays, HST: optical and infrared, AXAF: X-rays, and SIRTF, near and far-infrared). NASA also launched the Cosmic Microwave Background Explorer (COBE) in 1989 which provided very accurate limits on the diffuse infrared and microwave radiation from the early universe which gave unprecedented support for the Big Bang model for the formation of our universe.

The top priorities for the Great Telescopes were:

CGRO: Understand the process of energy transfer in the universe and lead to a better understanding of the nature of astronomical objects that produce very high-energy radiation.

HST: Provide extremely high-resolution imaging and spectroscopy of nearby and distant objects mostly in the optical. The observatory will be retrofitted with an infrared camera and a long-slit spectrograph in 1997.

AXAF: Study X-ray background radiation from the universe at early times and provide high-resolution imaging of galaxy clusters to help understand the distribution and amount of matter in the universe, and study the formation process of hot stars and stellar remnants in our galaxy.

SIRTF: Provide imaging and spectroscopy in the 3-180 microns wavelength regime. The major SIRTF science themes are: the detection of protoplanetary and planetary debris disks, the search for brown dwarfs and giants planets, detection of ultraluminous galaxies and active galactic nuclei, and provide deep surveys for the study of the early universe. A similar mission called ISO (Infrared Space Observatory) was launched in Nov 95 by the European Space Agency.

Because astronomy is cursed by a severe funding crisis, it is very important to convince tax payers and Congress that we are tackling grand questions and not only focusing on very specific minute issues. There are crucial areas of research which fulfill both the merit of attracting the public eye and address key scientific issues and it's those of the search for extraterrestrial planets and the nature of very distant galaxies, or probing the beginning of the universe. The director of the HST has already recognized the latter has a main scientific priority for the 90s and allocated very large amounts of HST time to image very deep field of galaxies both in the Northern and Southern hemisphere.

On a short term basis, I think the unlimited amount of money you would give me would be best used by hiring more scientists to work on these fundamental issues and new data. These new data are being collected at a rate much too high for our capacity to analyze and understand them. By their complementary nature, it is very important to ensure that ground- based astronomy is adequately equipped to follow on discoveries made in space. For example, HST (and soon ISO and SIRTF), is showing pictures of merging galaxies close to their formation era but our largest telescopes are just barely able to get spectra of them (to infer their distance and study evolution of the stellar population).

I would also start planning for the next generation space instruments which will not fly in space but actually reside on the dark side of the moon.

12. How much could be realized in, say, the next twenty years if funding were not an issue?

A lunar observatory would be conceivable within the next twenty years. A second, larger HST, could also see the light. However, under more realistic constraints, I believe the focus will be on building large ground-based telescopes to study faint objects which require long exposure times. Adaptive optics, even though it is restricted to small fields of view, makes ground-based astronomy a lot more competitive.

13. How does NOAO get its funding and would you say that the money situation is improving or worsening? Vice President Gore is supposedly a big supporter of the space program and related spending. Has any of that been realized? How do you think we can improve public support for spending?

NOAO gets its funding from the National Science Foundation (which is independent from NASA.) Money for the NSF is allocated directly at the Congress level. I am actually not aware of the specifics of VP Gore's space science program, so I can't comment on it. To receive more money from Congress, I think we must convince the public that advancement of pure science goes hand-in-hand with cultural and financial prosperity of a nation. I wrote a short article on this when I was a graduate student. I'll be happy to give you a copy next week. Astronomy is also a national asset for scientific leadership, a source of international pride, and provides resources for general scientific literacy.

14. What is the most important recent discovery in Astronomy? New Planets?

The discovery of new planets is indeed very interesting but it didn't come as any big surprise: it merely confirmed what all of us expected, that smaller non-shining bodies ought to orbit and gravitate around a larger central mass, i.e. a star. Their discovery was just a matter of time. These new planets, found to orbit either around normal stars like our Sun or around "pulsars" (small, rapidly rotating, and very dense stellar objects), could never harbor organic life because of the harsh environment at their surface. Their discovery is thus, to some extent, somewhat academic. The discovery of life on the other hand, either via detection of intelligent radio signals or more likely spectroscopic detection of organic structures, will be truly phenomenal even though, like the recent discovery of new planets, we believe that technology is our only limitation to finally detecting the presence of other life in the Universe. In my mind, one of the most exciting recent discoveries comes from HST pictures of colliding galaxies at very large look back times (the Hubble Deep Field) and the detection of massive compact halo objects (MACHOs) in our own galaxy. The former shows a very early stage of galaxy evolution that we had never been able to probe before; the latter uses micro-lensing theory to address the "mass problem" in spiral galaxies.

15. What is the most exciting project that you have been involved in?

For my thesis, I showed that our local extragalactic environment is part of a bulk flow (with respect to the ensemble of the universe) which moves at very high speed (300 km/s) over a fairly large region of space. We call that the coherence length of the flow. If this length keeps increasing, as one of my NOAO colleagues has recently proposed based on his NOAO observations, we may have to revise our most fundamental theories about the formation of structures in the universe. This is therefore a most important problem for cosmologists.

16. Do you believe that as astronomy gets more and more specialized it will be harder to gain public support for projects? The space race seemed to rally public support but it must be harder to reach people with less tangible or sensational discoveries?

While specific questions get indeed very specialized, the fundamental motivations for the support of astronomy will always remain: where do we come from? How did the Universe form? How do stars evolve and how is this linked to the emergence of life?

What is key is to convince the public that support of astronomy is conducive to a healthy, creative and leading nation. To make that connection is not necessarily obvious.

17. How much do you think we are capable of discovering? How far will we get in the next, say 50 years?

I believe we'll have observatories on the Moon. We'll probably be able to see all the way to the first visible moments of the Universe (the so-called era of recombination when the Universe became transparent), black holes will have been "seen", and I bet that we will have found a solar system similar to our own.

18. What are you working on right now?

My current work involves the measurement of large-scale structure streaming velocities (the bulk flows I alluded to above) and the formation, evolution, and dynamics of spiral galaxies. In particular, I try to measure the amount of dark matter in these galaxies, study their stellar populations and dust distributions, and, by combining various observational pieces of information that I collect on different telescopes around the world, I try to understand the process or processes by which they form and evolve.

19. I am trying to decide between medicine and astronomy as a career. Any advice?

I will put a copy of the FAQ in the mail to you today, along with a few other materials you might find interesting. I think you have an interesting and difficult decision ahead of you, medicine or astronomy. You might consider the job market in both professions to help you decide. I don't know statistics for medicine, but the job market for research scientists, including astronomers, is bleak. Funds for medical research are currently being given higher priority than astronomical research in our federal budget. On the other hand, I never discourage anyone from becoming an astronomer (or an artist, truck driver, or lawyer) if that is what they really want to do! Being a practicing physician is a much more service oriented position than research astronomer - you might consider your thoughts on that point. And, one final thought, astronomy is one of the few professions which has a strong amateur component. There are thousands of amateur astronomers in the world, some with quite sophisticated telescopes and observatories in their backyards. It occurs to me that you can be a physician and an amateur astronomer, but not an astronomer and an amateur physician.

Page created and maintained by Suzanne H. Jacoby (outreach@noao.edu)
Last Updated: 11 June 1996
Artwork by students of the Satori School, Tucson, Arizona

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