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Paul H. Geithner
Paul H. Geithner
NASA Astronomer

October 14, 2004

Paul H. Geithner

Hello everyone. It's truly fun for me to be here and try to answer your questions. Most of the time I'm embroiled in the details of one of our upcoming space missions, so it's fun to break away for a moment and take the opportunity to listen to people outside of NASA and the astronomy community and talk about space and astronomy.

Liff, from Ohio writes:
Hi Paul: When I take the trash cans out early in the morning and the sky is clear. I look up at all the star's and what a site. I can pick out the big dipper and the little dipper BUT after that I'm LOST. Here is a dumb question, but remember its from someone who just takes the trash out. Do the star's stay in the same location and the world rotates to them each night or do the starts rotate with the world? I know they are in different areas of the sky due to the axis of the earth and the seasons but otherwise.

Paul Geithner
The sky is basically fixed, but as the Earth travels in its orbit around the Sun, different constellations are visible at different times of the day. The Earth takes 365 1/4 days to go around the Sun, and circle has 360 degrees in it. So, from one night to the next at exactly the same time (anytime, just pick one, but adjust for daylight saving time), the sky shifts about one degree, or about twice the diameter of the full Moon. Another way to think about it is that's about the same as 4 minutes of time each day, so a constellation in one spot at 8:00 PM one night will be in the same spot at 7:56 PM the next night, roughly speaking.

If you watched the sky all night, it would appear to rotate about the North Star, called Polaris. By chance, Polaris sits almost exactly above the geographic north pole in the sky, so as the Earth rotates, the stars appear to rotate around the North Star.

You can locate the North Star by extending an imaginary straight line through the end of the Big Dipper and the medium-bright star you run into after a few fist-widths is Polaris.

Hope this helps. Regards-

Rita, from Fort Lupton writes:
Is it possible to see Phobos or Deimos with the naked eye? Where did they get their names?

Paul Geithner
Phobos and Deimos, the two moons of Mars, are too small to be seen with the naked eye, or even most telescopes. They are irregularly shaped, and are probably former asteroids captured by Mars' gravity. Phobos is the large or the two, at about 14 miles in diameter. Deimos is only about 8 miles across. These moons were discovered by Asaph Hall in 1877. Phobos means "fear" and Deimos means "terror." The names seem to fit with Mars, the Roman god of war.

Jack, from Green Bay writes:
Hello Paul What times are the "most exciting" to watch the skies? I'm not even an amateur astronomer, but I love to gaze at the stars and would LOVE to know what I'm looking at. Jack

Paul Geithner
Each time of year has something to see. Late summer is ideal for looking at the star clusters and nebulae and galaxies in Sagittarius, and the Milky Way presents itself perhaps the best at this time. Springtime is great for viewing all 110 Messier objects in a single night. Winter is nice because the moisture level in the atmosphere is low and if the winds aloft are calm, the seeing can be great and you have Orion and Taurus to see. And autumn is when you can get the best of winter and summer in one night. The planets wander constantly (planet comes from the Greek for "wanderer"), so they vary from time to time.

Gunther, from NYC writes:
What exactly is the horsehead nebula? I don't think I understand it and/or have seen it.

Paul Geithner
It's in Orion, but you really can't see it with the naked eye. You need either a big telescope so you can gather enough light to see it with your eyes, or a camera mounted on even a modest telescope to track the movement of the sky.

Sarah, from Michigan writes:
Mr. Geithner,I live in Michigan, which provides for lots of great open skies. What do you recommend looking for at this time?

Paul Geithner
You are lucky to live somewhere dark, and hopefully seeing the Milky Way is not uncommon for you. Since my favorite planet is Saturn, try looking at that. You'll have to either stay up past midnight, when it rises in the east, or get up before sunrise and before the sky starts to brighten to see it, but if you have a telescope, you can see the rings, even at low magnification. Have fun!

Jon, from Texas writes:
Are there lots of other astronomers at NASA? Before I saw this, I completely never even realized that NASA would employee you guys... but now I know Do you help with any of the spaceships?

Paul Geithner
There are many scientists, including astronomers, working at NASA. Many more at universities and laboratories around the world compete for grants from NASA to perform new and exciting scientific investigations. Many astronomers are also supported by the National Science Foundation, or NSF. Of course there are engineers and managers too at NASA and in industry who make the tools that allow the scientists to do their jobs. NASA and its community of contractors and institutions are always looking for outstanding people to help design and build and operate spacecraft.

Richie, from Tucson writes:
What planets can be seen this month? Where are they and at what times?

Paul Geithner
Venus is currently a "morning star," shining extremely brightly under Leo's belly in the eastern sky before dawn. Jupiter is visible just before sunrise a little bit above the horizon in the east. the window of opportunity is small because it rises shortly before dawn .

Mars is closer to the sun in our view of the sky than is Jupiter, and in fact is too close to really be visible right now. Saturn rises around midnight in the east in the constellation Gemini.

Uranus is barely visible to the naked eye under the best conditions, so from the desert outside of Tucson, you might be able to just barely make it out. Uranus is in the constellation Aquarius right now, best seen in the early evening in the southeastern sky.

Mercury is too close to the sun to be seen now, and the others are not visible to the naked eye. So, Venus and Saturn are your best subjects among the planets right now.

Tony, from Illinois writes:
What constellations are the most recognizable now?

click here for larger image
Paul Geithner
In the early evening, the one I most recognize is Cygnus, the swan. It is directly overhead around 7 or 8 o'clock at night in the temperate northern latitudes (like the continental U.S.).

It's one of my favorites because it "flies" along the Milky Way, and points the say the Milky Way streaks across the sky. Next to Cygnus is Lyra, the harp, a small constellation that has one of the brightest stars in the whole sky in it, namely the blue star Vega. Further toward the western horizon is Hercules.

It looks like an "H" and has one of the nicest globular star clusters in it to look at--M13. It looks like a little fuzz ball to the naked eye, but a good telescope will really resolve it nicely. Also visible low in the southwestern sky after sunset is Sagittarius, the centaur archer.

This constellation, sometimes referred to as the "teapot" because of its appearance in the sky, is chock full of star clusters and galaxies--a feast for anyone with a good telescope. Later in the evening and into the pre-dawn hours, Orion the hunter and his dog Sirius are visible, protecting Gemini the twins from the horns of Taurus the bull, while Leo the lion lurks behind (to the north of) Gemini. Taurus rises around 9 PM and contains the Pleides, also known as the Seven Sisters, an open star cluster in its shoulder. Orion rises around 11 PM and is one of the most recognizable constellation, with its three evenly spaced stars that make up Orion's belt.

A spectacular nebula, the remnants of an exploded star, is the middle "star" in Orion's sword. Those constellations close to Polaris, the North Star in Ursa Minor (the Little Bear, or better known as the Little Dipper) are visible all the time in the mid and high northern latitudes, so constellations like Cassiopeia, which looks like a "W" and Ursa Major (the Big Bear, a.k.a. Big Dipper) can be found easily.

Fiona, from New York writes:
Which planet do you find most fascinating?

Paul Geithner
Personally, I've always liked Saturn best since I was little. My parents bought me my first telescope, just a small one from Sears, when I was 7 years old, and one of the first objects I looked at was Saturn. I've always thought it to be a beautiful and fascinating planet because of the rings.

Over the years I've observed it with my own telescopes and watched how the tilt of the rings changed with time--sometimes at a large angle so almost all of the rings were visible to when they are edge-on and essentially invisible. Of course all the planets fascinate me for one reason or another, and every time we send more missions to learn more, things get more fascinating.

Anna, from Peoria writes:
For someone without a telescope, do you still recommend watching the stars? They all look alike.

Paul Geithner
Yes, but then again I'm biased. But really, there's much to see even without a telescope, especially if you go somewhere away from the cities and artificial light. Stars come in a wide range of colors and brightnesses that are really apparent when you are looking at them from a really dark place.

The Milky Way, which is the edge-on view of our own galaxy, is stunning. And you don't need a telescope to get some great views. Some things like star clusters are best seen with binoculars, and the Milky Way is mind-blowing to see though binoculars as it resolves into countless numbers of individual stars.

Esther, from Brooklyn writes:
What is the latest with the SETI program? Is it still there? Anything exciting to report?

Paul Geithner
The Search for Extra-Terrestrial Intelligence (SETI) program is alive and well. Today it is a privately-funded, non-profit organization and it continues to search for radio signals from other civilizations. Occasionally, SETI discovers a signal that is a candidate for follow-up observing and analysis, but none have been found that come from extraterrestrial intelligent life. However, the search continues. To learn more about SETI and related work, go to

Scotty, from Lancaster writes:
What is so spectacular, Paul, about the Southern Cross? There are songs about it (see below), Universities named after it, it attracts so much attention. And can you see it from the northern hemisphere....

When you see the Southern Cross for the first time, You understand now why you came this way, 'Cause the truth you might be runnin' from is so small, But it's as big as the promise, the promise of a coming day.

Paul Geithner
That CSN&Y tune came to mind for me the first time I saw the Southern Cross. It is visible only from near and south of the equator, so you'll need to take a trip to see it. I was in Chile, in the Atacama desert on Cerro Paranal at the location of the Very Large Telescope (VLT) when I was it for the first time. It is indeed beautiful, as is the rest of the southern sky which really is chock full of stars. The Southern Cross is a medium-sized constellation and it is very obvious--you can't miss it.

Something else that was neat that I noticed when I was there was the fact that the familiar northern constellations looked upside down from the way I was used to seeing them. The other, cool thing was that I had the privilege of seeing the Zodiacal Light, which is sunlight reflected off the dust that orbits the Sun in the inner part of our solar system.

You have to be somewhere extremely dark and clear, like high up in the Andes, to see that.

Cindy, from Central Texas writes:
With the galatical photos transmitted from Hubble Telescope, the awesome NASA-sponsored website for Transit of Venus, the "X prize" mission accomplishment AND the "recovered" solar wafers, how does an astronomer with America's premier government agency, NASA, keep footing on the ground while reaching for the stars? In other words, given the elite view from above, is it possible to increase K-12 space-based curriculum? Thanks for taking the time to share your knowledge, vision and pursuits.

Paul Geithner
I've been into this stuff since I was a boy, so I feel pretty lucky to get to work in this field. I know that NASA is actively reaching out to schools to let kids know what their space agency is doing and to perhaps inspire them to pursue an interest in space exploration.

I certainly would encourage anyone interested in increasing the presence of space exploration and science in the K-12 curriculum to make a grass-roots effort to include it in your local school. One of the things I enjoy the most related to my job is when I get to talk to kids in school about the stuff I'm involved in. It really wasn't that long ago that I was in grade school myself!

Michael, from Azle,Tx writes:
How do you feel about the discovery Dark Matter?

Paul Geithner
It's a fascinating mystery to me. We are learning so much about the universe right now, that it really is a golden age in astronomy. We are also learning how little we really know and understand about our universe, and Dark Matter and Dark Energy, with together make up about 95% of everything as far as we can tell, are evidence of that.

Dark Matter and Dark Energy, frankly, are not intuitive concepts to me, and I wonder if they aren't the "Ptolemy spheres" of our time and that someone will come up with a new way of thinking about the universe that explains things better.

Bob, from Laramie, Wyoming writes:
I'm wondering how the recent X-Prize competition (and SpaceShipOne's achievements there) will influence the development of space exploration (both on a manned and unmanned or scientific basis)?

Paul Geithner
I'm really quite excited about the X-Prize success and I hope it has a real energizing effect on the exploration of space. I think privately-backed ventures into space are a wonderful thing, and we'll all benefit by more of it. I think that human flight will benefit more by this in the short term, and science will probably benefit too.

Katherine, from Phoenix writes:
I was just wondering how may months we can see the constellation of Orion in the Southern sky?

Paul Geithner
Orion straddles the equator, so it's visible from both hemispheres. Orion is basically a "winter" constellation. Depending on what time of the night you are up, you can see Orion in the eastern sky before dawn in the late summer/early fall, most of the night in the winter, and in the western sky just after sunset in the late spring/early summer.

Beverly, from Oklahoma writes:
Mr Geithner, Where and when will the meteor showers be? Thanks

Paul Geithner
One of the best and well-known meteor showers is the Leonids. It's called the Leonids because the meteors appear to radiate from a point in the constellation Leo.

It occurs in mid-November every year when the Earth flies through the dust leftover from comet Temple-Tuttle. Every 33 years or so, the Leonids really puts on spectacular a show. That's when our planet flies through a part of Temple-Tuttle's orbit that has a lot more dust in it than the rest of the orbit. The last time this happened was 2001.

I went out on a boat in the middle of the Chesapeake Bay then to get away from light and trees and watch the show, and it was truly awesome.

Still, the Leonids is one of the premier meteor showers any year and there are times when you can see literally thousands per hour--that's more than one every second! This year's Leonids should peak on November 19th, between midnight and dawn.

Michael, from Bay Shore, NY writes:
Dear Mr. Geithner, What are the chances our planet will be hit by a asteroid large enough to cause significant damage within the next 100 years? And how many of these objects is NASA currently keeping a close eye on?

Paul Geithner
We should be OK for the next 100 years or so, which makes me feel better. NASA does have program to track NEOs, or Near-Earth Objects--asteroids and comets that have orbits similar to ours or that cross Earth's path occasionally.

Many of these objects are very black, so they are really hard to image and detect. Some have been known for many years--before NASA came to be, and they are familiar. Many new ones are discovered all the time, and many of these by amateur astronomers. I'm not sure how many are tracked, but there are some 3000 or so "close approach" objects.

No need to panic for a while, as the odds of us being struck by an object in the foreseeable future, like the one that hit Earth 63 million years ago near the Yucatan that is thought to be a reason (if not the main reason) why the dinosaurs disappeared, are vanishingly small.

Rachel, from Smithtown, NY writes:
Dear Mr. Geithner, How many planets do you estimate are similar to earth in our galaxy? Ones that could perhaps support similiar life forms in terms of basic molecular makeup.

Paul Geithner
That's a question that people have asked for a long time, and one that many of NASA's missions are trying to help answer. My answer would only be a guess because we don't have enough data through scientific observations to really answer you yet.

However, we can make educated guesses based on information we've gathered so far. We know there are a few hundred million stars in our Milky Way galaxy, so depending on how many of these are "friendly" stars that don't have another star as a companion and that have long lives with stable outputs, and of these how many have planets around them, and of those how many have planets like Earth around them.

So, depending on your assumptions about these frequencies, the number could well be in the thousands or even many millions. We haven't detected life beyond our own precious planet yet, but we do know that primitive life started pretty early on Earth and thrives in some really severe environments, so I would venture to speculate that life is elsewhere, especially primitive life. But we need to explore and use science to really find out.

Bill, from Belleville, Illinois writes:
There was a comment on a Discovery Channel episode that the moon's extraordinary relectivity is due to the soil covering the moon is 60 percent glass. How did this come to be? Can the moons of Jupiter have similar composition?

Paul Geithner
The moon is made up of the same stuff that our Earth's mantle. We're pretty sure now that the Moon formed when a Mars-sized planet whacked into the infant Earth only about 200 million years after its formation.

Then, the Moon got pelted for another several hundred million years by asteroid "junk" during what some call the "Great Bombardment." So between the process of its formation and its surface being pulverized, the lunar soil has a lot of shocked material in it.

Many of the moons of Jupiter have a lot of ice in their makeup, as they probably formed by accretion of ice and dust rather than a collision. But there are some rocky ones out there too, and some really strange moons elsewhere in the solar system.

Personally, I think the 90 plus moons in our solar system are some of the most interesting places that we know of.

Dirk, from Long Beach writes:
What is the most spectacular constellation in your opinion. CAn you show a picture of it please?

Paul Geithner
That's a tough one to answer, and largely a matter of personal taste. But the first one that comes to mind when you ask that is Orion, the Hunter. It's very easy to recognize and it has a spectacular nebula in it--the Orion nebula.

Another that comes close is Sagittarius due to it having so many beautiful clusters and galaxies in it that are great to view through binoculars and telescopes.

There are some great ones in the southern sky, visible only if you are near or south of the equator, but I've only been south of the equator on two occasions, so I'm not intimately familiar with that sky as I am with the northern hemisphere. Cygnus is another personal favorite, flying along the Milky Way.

click here for larger image
click here for larger image

Theo, from Provo, Utah writes:
Paul, How does the Hubble Spacecraft help with seeing our skys? Does it track which stars are where and report back to you?

Thank you.

Paul Geithner
The Hubble Space Telescope has the advantage of being above our atmosphere, which absorbs and distorts light passing through it. With Hubble, we can take exquisite images and cleanly analyze light from other stars and planets to see what they are made of.

It operates 24 hours a day, 7 days a week. NASA controls the spacecraft, and science data is relayed back to Earth by radio waves to the Space Telescope Science Institute in Baltimore, Maryland.

There, the data is basically sorted-out and scientists the world over get to analyze it. Some of the most beautiful images make it into newspapers and magazines the world over.

Jorge, from USA writes:
What's so great about the autumn skies? better than the summer?

Paul Geithner
Each season's skies has something special. I don't think it's a matter of better as much as different. Actually, the springtime night sky is when you can go out and see all 110 Messier objects.

These are various star clusters, nebulae and galaxies that the 18th century French Astronomer Charles Messier, the premier "comet hunter" of his day, catalogued during his observations. Some clubs have "Messier parties" in springtime to see who can detect all 100 in one night.

Griffin, from Columbia, South Carolina writes:
Mr. Geithner, Thank you for participating in Ask the White House today.

Is there a favorite place in the country of your's that you really like looking at the stars at? Or a favorite star of yours?

I am a big fan of Casseopea (maybe because it is easy to pick out) Thanks and have a great day.

Paul Geithner
The most incredible sky I ever saw in this country was when I went camping with friends in the Mineral King region of the high Sierra Nevada mountains.

The countless stars visible at 12000 feet and dozens of miles from the nearest artificial light was truly moving. I also remember when I got a to go to the University of Arizona's Steward Observatory's 90-inch telescope on Kiit Peak outside Tucson, Arizona.

There's a reason there are telescopes there--what a view. And the other really memorable time for stargazing for me was not here but in Chile, in the Andes at the European Southern Observatory's Very Large Telescope (VLT). The sky was so brilliant, it literally blew me away.

Paul, from Topeka writes:
I would like to start looking at the stars but don't have any equipment. Is there any star-watching equipment I could use or build that wouldn't be too expensive? thank you.

Paul Geithner
You don't need big bucks to see a lot. Naked-eye observing from a really dark place away from lights is pretty cool. Binoculars are a great way to scan the heavens. And good telescopes don't have to be expensive.

If you try to buy something, don't be fooled by claims of magnifying power, which is poor metric of quality. Try going somewhere away from the city first and bring some binoculars and have fun, and see where that takes you from there.

Paul H. Geithner