Frequently Asked Questions

Questions about Stargazing and Observing

Questions about the Observatory

Questions about the telescope

General astronomy questions

Questions about CAS

1) Where are the North Star and Big Dipper?

Ok, first you have to figure out where north is and face that way. (Hint: Fuertes is on the eastern edge of NORTH Campus. In which direction is the Arts Quad? Further hint, if it's early in the evening: where did the Sun set, and what's the relationship between that direction and north?) Once you're facing north, look up not quite halfway between the horizon and directly overhead. There will be a medium-bright star situated in a somewhat empty area of the sky. That's Polaris, the North Star. The Big Dipper, which is only part of the constellation Ursa Major (the Big Bear), will be somewhere nearby—where, exactly, will depend upon the time of year and time of night, but it is always above the horizon (it is "circumpolar") as seen from Ithaca. The two stars that form the edge of the bowl of the Big Dipper farthest from the handle point almost but not exactly at Polaris.

By the way, Polaris is not always the North Star. In fact, at times there is no "North Star". The Earth spins like a top, of course, but a wobbling top. Over a cycle of 26,000 years, the North and South Poles point towards different directions in the sky; this is called precession. About 4000 years ago, a star in the constellation Draco (the Dragon) was the North Star; in some 13,000 years, the very bright star Vega in the constellation Lyra (the Lyre) will be it.

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2) Where is / Can we look at [insert your favorite object here]?

It depends upon several things: 1) what time of the year is it? 2) what time of the night is it? and for planets and the Moon, 3) where are they in their orbits about the Sun? (Orbit around the Earth, in the case of the Moon...) Some constellations, like Orion and Gemini, are winter constellations—by mid-to-late spring they're setting nearly at sunset, and in the summer the Sun is in the same section of the sky so they can't be seen at all from the Earth's surface. Conversely, Scorpius and Sagittarius are summer constellations, and not visible in the winter. For faint objects (i.e., almost all star clusters and galaxies), the glare of the moon can wash them out. Thus, at nearly full moon it may be too bright, even out in the country-side, to see something that's up in the sky.

The planets of course move around the Sun over the course of months or years; they therefore change their position in the sky each night. (This is, in fact where the name derives from: the Classical Greek word planetes means "wanderers.") You thus have to determine where a planet is in the sky for a given night, and then determine whether that section of sky is visible on said night.

(There are of course more mundane considerations, such as if the object is behind a tree, a building, or—especially in Ithaca—clouds. And on public observing nights, sometimes it just gets too busy at Fuertes to take special requests.)

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3A) Why are there two times on the observatory clock, and why is one wrong?

3B) How do you keep the telescope pointed?

3C) What's the spinning thing inside the telescope mount?

The "wrong" time on the clock shows the sidereal time, which is which "line of celestial longitude" (the technical term is "meridian of right ascension") is passing overhead. We define a "day" to be the time it takes the Sun to complete one circuit around the sky. Since the Earth is constantly moving in its orbit around the Sun, this period is longer than the time taken for Earth to spin once around its axis by around 4 minutes. As a result, a particular meridian of right ascension is overhead 4 minutes earlier each successive day, so sidereal time gains 4 minutes a day relative to clock time. (This is why the constellations change with the seasons: over time we're looking out at different sections of the sky.) At the start of an evening's observing we use the sidereal time to calibrate where the telescope is pointing. There is a "right ascension calibration wheel" on the telescope column, consisting of two disks with graded tick marks—vaguely reminiscent of a sundial, except it's flat and vertical. We set this based on the current sidereal time. When we've been moving the telescope around for a while and we want to double-check where we think we're pointing (e.g., if we think we're at a target based on what we see in the eyepiece, but the target isn't there...), we consult that wheel.

Now, if we were just to point the telescope at something and did nothing further, the object would move out of the field of view within a minute because of the Earth's rotation. There is a clock drive mechanism inside the central column of the telescope that keeps the telescope tracking along with the apparent motion of the heavens. It is entirely mechanical, and is in effect a big grandfather clock: there is a weight inside the column, and we have to crank it up about once an hour. The spinning thing is simply a pair of weights that is part of the clock drive; if we see that they are no longer spinning (and haven't been looking in the telescope for the last few minutes), we know we have to wind up the clock drive! (At that point we also have to reset the right ascension calibration wheel.)

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4) How many galaxies are there?

Waaaay more than anyone had the remotest idea about as of 1990.

Based on then-existing sky surveys, the answer around 1990 would've been something like, "There could be several hundred million galaxies." Then came the Hubble Deep Field, one of the most important images to come from the Hubble Space Telescope. In December, 1995, the telescope was pointed at an "empty" patch of sky (i.e., no visible galaxies and only a couple of dim stars) and over ten days took 342 images at various wavelengths. The resulting composite image showed over two thousand galaxies, a result that completely stunned everyone. It was followed by the Hubble Ultra Deep Field (HUDF), released in 2004. There, in a field of view only 1/10 the area of the full moon, were some 10,000 galaxies. Furthermore, they were all extreeeemely distant galaxies. One of the nearest galaxies in the image is about one billion light-years away (i.e., the light from it, moving at 186,000 miles each second, has taken one billion years to reach us); some of the furthest galaxies in the image could be well over 10 billion light-years away, and so some of the earliest galaxies to form. Extrapolating from the HUDF, the lower bound on the number of galaxies is now on the order of 120 billion. It's safe to say that that number can be raised with improved observational instruments.

In August 2009, after the final repair mission, Hubble reimaged part of the Ultra Deep Field in infrared light, seeing galaxies even further away: it is estimated that those galaxies show how conditions were in the universe only 600 million to 800 million years after the Big Bang, the beginning of the universe. The successor to Hubble, the James Webb Space Telescope, which is scheduled to be launched in 2014, will take even more sensitive pictures in the infrared and thus be able to study such early galaxies in more detail.

A good recent book on the HUDF and its implications for cosmology, written for general audiences, is Jeff Kanipe's Chasing Hubble's Shadow: The Search for Galaxies at the Edge of Time (New York: Hill and Wang, 2006).

(By the way, until the 1920s it was not even known whether there was only ONE galaxy: our Milky Way. Objects like the Andromeda Galaxy were known as "spiral nebulae," i.e., things within our galaxy that had spiral structures instead of looking like glowing gas clouds. The nature of such objects was a matter of deep controversy, and there was a famous "Great Debate" in 1920 about them. The excellent myth-debunking Bad Astronomy website has more information and pointers to details about this controversy.)

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5) How do you find stuff in the telescope?

The field of view in the main telescope is too narrow to use for finding anything. We have to zero in on an object over a multi-step process called "star-hopping."

We begin by consulting the books of detailed star charts to find a chart that has both the object we're going to look for and a starting object—some fairly bright star—on the same page. Next, we get the starting object centered in the small "finder" telescope that's attached to the main scope. We then alternate moving slowly along the north-south and east-west axes, going from star to star as depicted on the chart (and consulting the chart repeatedly!), until we get to the object we're looking for, or close enough that we can pan along in the main telescope if the object is too faint to be seen reliably in the finder. We only move along one axis at a time because we would get immediately lost (unless we were very experienced and the next target were very close by!) if we tried to go diagonally.

(This leaves out a couple of details of the process, such as moving the dome so that the object in question is visible through the slit!)

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6) What do things like "M42" and "NGC 205" mean?

These are catalog numbers referring to various objects (luminous gas clouds, star clusters, galaxies) in the sky. "M-objects" are on a list drawn up by Charles Messier, an 18th century French astronomer. He was trying to find comets, but he and his assistant Pierre Méchain kept finding various faint fuzzy things. At first annoyed by these repeated false alarms, he eventually realized that these were apparently different types of "deep-sky objects" and published a list giving the locations in the sky of said fuzzy things as a service to other astronomers. Messier published a couple of revisions over his lifetime; a few posthumous entries were added, bringing the total to 110. Messier of course did not know the actual natures of most of the objects he saw, and neither did any other astronomer of his day.

NGC stands for "New General Catalog." It is a much larger catalog of objects, first published under the editorship of John L. E. Dreyer in 1888, that covers both the Northern and Southern hemispheres—Messier could only list objects visible from France, and his telescope was less powerful. The NGC has been revised, and several supplements have been added over the decades. In addition, a few other catalogs of various types of astronomical objects have been published; these go beyond visible-light objects (e.g., the 3rd Cambridge Catalog of radio sources).

In the late 1970's, someone noticed that there is a window of about 10 days in late March when it is theoretically possible to see all or nearly all the objects in the Messier catalog in a single dusk-to-dawn viewing session. This is called a "Messier Marathon," and it has become a very popular activity for amateur astronomy clubs. For more information on Messier marathons, click here. We have attempted a couple of marathons in recent years; you can read about the relative success of those efforts here.

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7) What do these names like "Delta Orionis" mean? Why is it "Orionis" and not "Orion?"

Some stars have their own proper names, like Rigel (in Orion), Vega (in Lyra), or Polaris (in Ursa Minor). These are either prominent, bright stars, or they occupy particular places in the constellations. (For example, two fun star names are Zubenelgenubi and Zubeneschamali, Arabic names meaning "The Southern Claw" and "The Northern Claw," respectively; the stars are in Libra, the Balance. Libra used to be part of Scorpius, the Scorpion; these stars were its two claws.)

Most stars, however, don't have special names. For those such stars visible to the eye, we use a system developed by Johann Bayer in the 17th century. He ranked stars in constellations in order from brightest to dimmest, using letters of the Greek alphabet: Alpha is the brightest star of a constellation, Beta the second brightest, etc. When the Greek alphabet has been exhausted, numbers are used. This latter system was devised by the 17th century British astronomer John Flamsteed, who assigned numbers even to stars that Bayer had given letter designations; most people only use the Flamsteed numbers for stars that do not have proper names or Greek letters.

As to why it's Orionis rather than Orion, etc.—these are just the genitive (possessive) cases of the Latin names/words for the constellations. Thus, "Delta Orionis" is "4th brightest star of the constellation Orion." While you need to learn Latin for the details (and it's very useful to know Latin, so you should consider it!), for nearly all the constellations the rules are: 1) if the name ends in "a" (Lyra, Andromeda,...), the genitive will end in "ae" (Lyrae, Andromedae,...); 2) if the name ends in "us" or "um" (Cygnus, Cepheus, Scutum,...), the genitive will end in "i" (Cygni, Cephei, Scuti,...); 3) anything else (Orion, Virgo,...) is likely a "3rd declension noun," which indicates a sort of kitchen-sink situation re whether/how the base portion of the noun changes—simple answer is, memorize the genitive versions.

By the way, there's a very simple reason why very few stars have proper names—there are waaaay too many! Under ideal (pre-Industrial Revolution) conditions, about 6000 stars are visible to the unaided eye. In even a modest telescope, there are tens of thousands visible, and millions visible in the largest research scopes.

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8) Have you ever seen a UFO?

If you mean, "Have you ever seen an alien spaceship?", there are no such things as UFOs. If you feel that that needs a more detailed reply, click here.

Now if, instead, you were really asking, "Have you ever seen moving lights in the night sky?" then, sure, tons of times. In most such cases, these were planes or helicopters—the blinking, differently-colored navigation lights and especially the jet/helicopter sounds are good giveaways! In all the other cases (i.e., steady silent light moving fairly quickly, usually in a more or less easterly direction), they were some sort of human-launched satellite—there are now a large number of satellites orbiting the earth, and it's a lot more common nowadays to see them going by than it was in the 1960s.

Occasionally, one can see a very bright light in the sky that fades in out of nowhere, moves a bit, and fades out again over the course of a few seconds. While these can seem mysterious the first time one sees them, they are just reflections off satellites. Such occurrences are called Iridium Flares. Iridiums are a set of several dozen satellites in low-earth orbit, launched and maintained by the Iridium LLC Consortium, to support mobile communications. They each have three large antennae, which are always pointed at certain angles relative to their direction of travel. These antennae are, in effect, big mirrors in orbit. Once you know the satellite's orbit and the angle of the Sun, it's straightforward (if somewhat involved) trigonometry to determine when someone at a given ground position can see the Sun's light momentarily reflecting off these antennae as the satellite goes by, and how bright the reflection will be. You can click here to find when Iridium Flares or passes of the International Space Station and the Hubble Space Telescope might be visible from Ithaca over the next ten days.

Sometimes, people have mistaken planets for UFOs. Venus and Jupiter, and even one or two stars, are bright enough to be visible in the daytime if you know exactly where to look, especially with binoculars, and though they are stationary points of light they will sometimes appear to be slowly moving (an optical illusion psychologists call the autokinetic effect). Also, if the geometry is just right, some Iridium Flares are visible during the daytime—and those do move!

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9) Have you ever met Steve Squyres? Can you get his autograph? How about Jim Bell?

In the 1970s and 1980s, this question would've been about Carl Sagan. Yes, some of us have met Profs. Squyres and Bell; a couple of us have even worked for them. They are both very nice gentlemen, and really good teachers and public speakers. They are also incredibly busy and are going to be so for many years to come, given how long the two Mars rovers have lasted and the amount of data that the rovers have returned. We don't ask for their autographs. We request that you don't, either, unless you and they are both at a public book-signing.

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10) How powerful is this telescope?

There's no single quantity as the "power" of a telescope. You can, however, ask about its magnification, or its ability to gather light, or other specific capabilities.

Magnification depends on which eyepiece we have in. A telescope's magnification is determined by dividing its length by the focal length of the eyepiece being used. The Fuertes scope is 15 ft. long, which is 4572mm. We normally use a 32mm or 26mm eyepiece for observing; these give magnifications of just under 143 and 180 times the apparent size in the sky, respectively. We have several other eyepieces all the way down to a 9mm, for a magnification of 508; the smallest eyepiece we tend to use is a 12mm, which gives a magnification of 381.

The tradeoffs of higher magnification are: 1) a narrower field of view; and 2) less light coming into the eyepiece, so it's harder to see details. The contrast when using the 12mm eyepiece is a lot less than when using a 26mm or 32mm eyepiece. Thus, for the types of viewing we can do with this telescope (especially given the light pollution around Fuertes), the lower magnifications are actually better most of the time. In Fall 2005 we acquired a wide-angle 40mm eyepiece, which lets in a lot more light, and in which the full moon will just barely fit.

Some people ask, "How far can the telescope see?" Stated that way, the question is pretty meaningless—we're really just looking towards infinity and sometimes there are things in the way.:) Stated instead as "What's the farthest object you can see with the telescope?", then the issue is, how bright is an object vis-à-vis its distance—we can't see the (former) planet Pluto, within our own solar system, much less tiny asteroids that come within a few million miles of the Earth, but we can see quite a few galaxies trillions of times further away because they shine with the light of hundreds of billions of stars. We have regularly seen galaxies in a group called the Virgo Cluster, estimated to be spread between 40 to 60 million light-years away; for some of its galaxies, dinosaurs were still around when the light began coming here.

The most commonly cited "farthest object" visible with a telescope in our size bracket is the quasar 3C 273, also in the constellation Virgo. It is something like 2.5 billion light years away; when that light began coming here, the only lifeforms on Earth were bacteria that did not even have cell nuclei. In May 2009 we confirmed that it is visible from Fuertes (at least, if the North Campus lights are off!). We haven't tried looking for any other quasars; they are likely all too faint for this telescope, even if every light in Tompkins County were turned off.

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11A) Why are the dome lights red?

11B) Can we take pictures?

11C) Why do you get upset when we use our cell phones?

Human eyes are least sensitive to red light. By using red lights, we can have enough illumination to do things like read the star charts or not trip over the ladder supports while still retaining some dark adaptation so we can see things in the telescope. Full dark adaptation takes over 40 minutes; any sort of bright or flashing lights will knock out the dark adaptation. (If we have to go downstairs, you may notice that we sometimes keep a hand over one eye, to conserve some of the dark adaptation we've built up.) Hence, we take an extreeeeemely "dim" view of visitors who do any sort of flash photography, whip open their brightly-lit cellphones, etc.

If you would like to take pictures, there are several options. First, if your camera or whatever can do long exposures, consider doing an existing-light picture using only the red lights. This will be a much more dramatic and interesting picture than something done with flash! Second, if you can hang out until closing or can come back another night as we're starting, you can take pictures while we have the white light on. Finally, if your parents or out-of-town friends are here for their one and only visit ever to Fuertes, you're all about to leave, and you reaaaally need to take a picture right now, please ask us first, so we can warn others and turn away/cover our eyes before you use any flash!

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12) Which eyepiece do I look through?

You want to look through the one in the center of the main barrel of the telescope. The smaller telescope mounted on the side of the main one is a finder scope—we use it to home in on what we're aiming at. (You can, of course, peek through the finder scope as well, if you want to see the difference; the view will be substantially different.) You may find it difficult to look through only one eye. Some observers prefer to leave both eyes open (instead of squinting the other shut), and covering the non-observing eye with their hand. Also, some people who wear glasses find it better to take them off before looking in the scope; others prefer to keep their glasses on.

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13) Were the pictures across from the sign-up table taken through the telescope?

A few were; not many. Some are clearly labeled as predating Fuertes Observatory (e.g., the sketches of Mars from 1909; the observatory wasn't built until 1917 or 1919—the sources contradict each other—and the telescope wasn't installed until 1923). Many require better resolution than is obtainable in our telescope, or equipment that we don't have (e.g., the pictures of the Sun with the Sun's disk blocked out).

A couple of pictures, such as the one of Halley's Comet during its 1986 pass, were taken here. We once had darkroom facilities, although the equipment therein was really obsolete by today's standards; due to environmental concerns (chemical runoff would go straight into Beebe Lake), those facilities have been shut down. In the past few years we began building a CCD camera "by kit" so as to be able to do digital photography. That project was never finished before the technology we were then using became itself obsolete, although we did get as far as taking an image of Mars as a first test. The real problem with photography from Fuertes is, of course, the amount of light pollution around Ithaca and North Campus in particular.

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14) What discoveries were made here?

None, unfortunately. Even when it was built, the Fuertes Observatory was not state of the art. Its primary purpose was for teaching skills necessary for naval navigation and civil engineering surveying. See the history of Fuertes for further information; or ask Shianne, our resident expert on the history of Cornell observatories, if she's around some night when you're visiting.

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15) I heard there's another observatory on campus. Is it better/worse?

The Astronomy Department maintains a small observatory, named the Hartung-Boothroyd Observatory, a few miles outside of town. It is not open to the public; it is used primarily for the training of astronomy majors, to give them some experience in "driving a 'real' telescope." Like all research telescopes, it is primarily computer-driven: to aim it, one sits in a control room in front of a screen and gives commands to a computer that moves the dome and telescope. (Large motions in "declination", i.e., latitude, are done by hand, however.) Also, most observing on that telescope is not done by looking through an eyepiece. Instead, the incoming light is gathered by a CCD (charge-coupled device)—a digital camera; again, just like all research telescopes. There is a way to use eyepieces on the telescope, but that feature is very rarely used.

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16A) Are you an astronomy student/professor?

16B) Do you work here?

16C) How can I join CAS?

A couple of us are astronomy students; most are not. None of us work here; we are all volunteers who do this because we love looking at things in the heavens, and we enjoy learning about the topic and sharing that knowledge with the public. (As in the original meaning of amateur, "One who does something for the love of it.") If you also think looking at star clusters and galaxies is cool, then by all means join us! Just talk to any CAS member during viewing hours.

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17A) Who owns this place?

17B) How much is this telescope worth?

Cornell University owns all the facilities on its campus, including this building and the equipment in it. The Astronomy Department is the unit within Cornell that is in charge of maintaining the building and the telescope.

While it is possible to put some dollar figure on the telescope, based on its initial purchase cost and computing inflation since then, it really is priceless—they literally do not make them like this anymore!

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18) How do you move/open the dome?

On the wall just below the dome, to the left as you enter from the stairs, is an electric motor that rotates the dome. It is the only aspect of observing that is not muscle-powered. (There is, however, a photograph from the 1920s, just after the installation of the telescope, that shows a chain & pulley system where the motor now sits!) When we need to rotate the dome, we use a cable control to operate the motor. (The motor was replaced a few years ago; before that it used to make a very loud noise when it started up, which used to startle people.)

We would not want to open the entire dome—in case of precipitation, it would be very difficult to close it in time to prevent water damage to the telescope. Thus, there is only a small slit that is openable. Like everything except the dome motor, it is hand-operated; you can see a wheel at the bottom-right of the dome-slit. When we open or close for the night, we rotate the dome so that the slit is due south (opposite the stairs), climb the tall ladder on that side, and hand-crank the wheel.

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19) If the stars are so far away, how do you know if they're still there?

The short answer: we don't, of course; but it's a VERY safe bet.

Because light travels at a finite speed, everything you see is always a little bit back in time: the stars, your cat, the teacher in class, etc. For anything except astronomical objects, the disparity is on the timescale of microseconds because lightspeed is so fast (just under 300,000 kilometers, or 186,282 miles, per second). For astronomical objects, however, the distances back in time quickly become significant. Once beyond the solar system, you are looking years into the past: hundreds, thousands, or millions of years. The light from the next star over, Alpha Centauri, takes over four years to reach us; meanwhile, the Pleiades star cluster, a winter favorite in the constellation Taurus, is estimated to be about 440 light-years away, so Shakespeare was in grade school when that light left. The farthest object visible to the naked eye, the Andromeda Galaxy, is about 2.5 million years away at lightspeed: a few species before modern humans in evolutionary terms. (Keep in mind that this is "next door" on the scale of the universe: if our galaxy is Ithaca, the Andromeda Galaxy is Dryden!) Some of the galaxies in a huge galaxy cluster in the spring constellation Virgo are on the order of 60-65 million years away by light, so the light you see from some of them started its journey while the dinosaurs were still around! (In terms of the above Earth distance analogy, this is still only the equivalent of going from Ithaca to Rochester!)

On human timescales, a million years is long enough for lots of things to happen—all of recorded human history is only about six thousand years, after all, and Homo sapiens has only existed as a species for less than 100,000 years in total. The timescale of the universe and of stars, however, is so much vaster that a million years is hardly anything. Here's the arithmetic: 1) A human who lives 76 years will live for approximately 40 million minutes. 2) Our Sun, a completely run-of-the-mill star, has been around about five billion (=five thousand million) years, and it is only about halfway through its expected lifespan. 3) One 40-millionth of 10 billion is 250. So, 250 years is about the same to the life of a star as is one minute to a human being's life. If we say (to make the arithmetic simpler) that the whole of recorded history is 5000 years, that's the equivalent for a star of 20 minutes in a human life. Now think: of all the people you walk past in any particular 20 minutes, regardless of their ages, how many of them usually drop dead during that timespan? In the same way, we should expect stars to be just as stable and stick around—they are, and do.

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20A) Are you SURE there's something there? I'm not seeing a thing!

20B) What's averted vision?

If one of us assures you that we've got something in the telescope (and it's not obviously big and bright, like the Moon...) but you can't see anything, there are two possibilities for what's going wrong. (Assuming the telescope hasn't gotten knocked out of alignment, of course!)

The first thing to check is that you're looking down the center of the view. The field of view for the various eyepieces is actually pretty narrow, especially for the "wide-angle" eyepieces. If you look even a little off-center you'll find yourself staring at the inside of the telescope. The easiest way to center your view is to make a ring around the edge of the eyepiece with your thumb and forefinger, then put your eye up to the center of the ring you made.

The second thing is to use averted vision. The retina has two basic kinds of receptor cells: rods and cones. Cones process color, but they don't work well for low light-levels. Rods work in low light, but they don't do color. Since cones are more useful for humans from an evolutionary standpoint (e.g., being able to tell by color there's a tiger in those bushes waiting to pounce...), the center of your field of vision—where you're looking straight ahead—is mostly cones. The biggest concentration of rods is along a ring a little ways away from your center of vision. Therefore, your best seeing ability at night is a bit off-center; looking at something this way is called averted vision.

There is a third thing possible, which unfortunately is not practical: jiggling the view. Your brain is very good at noticing something moving through the visual field. (Evolution again: that tiger in the bushes waiting to pounce becomes obvious if it paces...) So, a very faint smudge that's difficult to pick out from the background, like a galaxy, will likely pop out at you if it's moving through the field of view. When we have multiple visitors waiting, though, we simply can't take the time to jiggle the view for each person. For showing galaxies to members of the public, we therefore stick to ones that are bright enough that jiggling shouldn't be necessary.

Finally, remember that it takes practice to pick out faint fuzzy things if you don't know what you're looking for. So don't get discouraged—come on back another night to get some practice!:)


(Oh, yes: absolutely none of the above will help in the least if you've just texted your friend "im @ obs, c u l8r" on your brightly-lit whatever—you just finished blinding yourself for the next hour!!)

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21A) Why are stars different colors?

21B) I'm told stars are different colors but they almost all look white to me...

21C) Why aren't there any green stars?

All objects give off electromagnetic energy as a function of their temperature. Most of the time this energy is not in visible light; for example, plants and animals give off energy in the infrared, which is "below" (infra) red light. Objects that are in certain temperature ranges give off energy at wavelengths we can see (red, yellow, blue...), while even hotter objects emit energy at wavelengths too short for us to see: ultraviolet (ultra="beyond, above"), X-ray, etc. (Think about turning on a metal burner on an electric stove with the dial all the way up. It starts off cold; soon you can feel the heat/infrared, and as it gets hotter you can begin to see it glow red. It might get up to an orange with a hint of yellow, depending on the stove. For obvious safety reasons it won't get any hotter, but an arc-welding flame is white-hot to blue-hot.)

Now, an object does not emit energy at only a single wavelength/color—in other words, it's not "4000 degrees = red / 4010 degrees = orange / 4020 = yellow," or anything like that. Instead, an object emits energy over a range of wavelengths; this is called black-body radiation. So, stars that are cool (relatively speaking!) emit a lot of their radiation around red wavelengths, with some towards the yellow and a bunch down in the infrared. Betelgeuse, one of Orion's shoulders, is one such star you can easily see during Nov.-Mar. (Betelgeuse is so huge that in late 2009 astronomers were actually able to image features on its surface!); Antares in Scorpius the Scorpion is another one, visible during June-Sept. Stars about as hot as our sun (ca. 6000 degrees Centigrade/11,000 Farenheit) give off most light around yellow wavelengths; and really hot stars like Sirius (about 50,000 deg. C) give off mostly blue and ultraviolet.

The relative mix of colors that a star emits as its black-body radiation varies with temperature. A star that's hot enough to give off a lot of green light also gives off a lot of blue, red, and yellow light as well. When you look at such a star, your eye integrates (blends) all that color information together, so it comes out white. Hence, no green stars.

As for why most stars look white, this has to do with the structure of your eye. The retina has two basic kinds of receptor cells: rods and cones. Cones process color, but they don't work well for low light-levels. Rods work in low light, but they don't do color. When you're looking at stars it's obviously a low-light situation, so you're using almost exlusively rods. Thus, unless a star is giving off nearly all its visible light in, say, the red, enough that your cones can tell your brain, "Yo—red, dude!", you're basically only getting rod info, i.e., black + white. (To the extent that there appears to be a bluish tinge to the white, you're seeing the background glow of the sky.)

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22) Wow, this is SOooo cool; how can I become an astronomer?

First off, we're glad you agree that astronomy is cool—we certainly think it is!

To be a professional astronomer, you need good math and physics grades, of course—but then, everyone should know something about math and physics!:) Depending on what part of astronomy most interests you, you'll also need to study other subjects: meteorology for planetary atmospheres, geology for asteroids and planetary surfaces, and so forth. (Oh, and astronomy courses in general, too.:)

However, you don't need to become a professional astronomer in order to do astronomy, either just because you like it or because you want to contribute to science. Thanks to the Internet, dirt-cheap computing power, and the availability of relatively inexpensive telescopes with excellent optics, we are now in a new Golden Age™ for amateurs to contribute to astronomy. So, it's possible to have a "regular" career in some other field and contribute to astronomy on the side.

There are two reasons why amateurs can help professional astronomers. First off, there are not enough professional astronomers and research telescopes/satellites to scan the entire sky all the time. Thus, amateurs tend to find most comets, lots of asteroids, and a lot of supernovas (exploding stars) in other galaxies. Amateurs are also the only group with enough time and numbers to keep track of variable stars (stars that change in brightness). As the American Association of Variable Star Observers (AAVSO) says about itself:

Membership in the AAVSO is open to anyone—professionals, amateurs, and educators alike—interested in variable stars and in contributing to the support of valuable research. Professional astronomers have neither the time nor the telescopes needed to gather data on the brightness changes of thousands of variables, and amateurs make a real and useful contribution to science by observing variable stars and submitting their observations to the AAVSO International Database.

The second reason amateurs can help professional astronomers: as hard as this might be to believe, there aren't enough computers to analyze all the data that come in. Also, there are some tasks like shape recognition and classification where computers are really lousy while humans are superb. These have led to multiple projects where you don't even need to know math/physics/etc. to help: the two most famous such are the SETI@Home and the Galaxy Zoo projects. You can read a bit more about the SETI@Home project here, and you can read a bit more about the Galaxy Zoo project here.

So, there are a lot of ways you can contribute to astronomy--go for it!:)

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Tell me about the SETI@Home project, please.

SETI stands for "Search for ExtraTerrestrial Intelligence." Radio telescopes scan the skies in multiple radio bandwidths. If a section of radio data appears to have some sort of structure to it instead of being a generic hiss, that might be a potential radio signal generated by another civilization. (Obviously, false alarms caused by Earth aircraft, satellites, cell-phones, etc. need to be weeded out first! There are also other naturally-occuring regular radio signals, caused by pulsars, that need to be eliminated as well.)

There is a lot of radio data to go through, more than professionals have the computing power to analyze. SETI@Home was developed as a way to let the public help with the analysis. In effect, it creates an immensely big and powerful computer made up of thousands of small personal computers, each analyzing tiny chunks of radio data.

SETI@Home simply needs you to 1) leave your home computer turned on and connected to the Internet, and 2) download some software that connects your computer to the project. At the times when your screensaver would kick in as the computer goes idle, the software starts up the SETI@Home application: it requests a chunk of data from the project (taken from radio telescope surveys of the sky) and analyzes it for a possible signal from a civlization elsewhere in the galaxy. So far they haven't found anything; but there is a HUGE amount of data to be processed, on a scale that really wants a few million computers working in parallel for years to get through. So, here's something you can do to help even while you're asleep!:)

(Several other computationally-intensive projects, modeled after SETI@Home, have started up, including a search for large prime numbers...)

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Tell me about the Galaxy Zoo project, please.

Galaxy Zoo is a project to classify galaxies, using thousands of volunteers around the world to look at pictures. It is like the SETI@Home project in that it involves using thousands of people's computers in parallel, but it differs because you, not your computer, are directly doing the analytical work.

Galaxy Zoo arose from the Sloan Digital Sky Survey project. SDSS is a automated survey of one quarter of the entire sky that has to date resulted in over a million images of galaxies. There is no way the professionals could ever sort through that many pictures; and computers are really stupid when it comes to image classifcation. In contrast, people are superb at identifying features in images because of how evolution has shaped brains over the last few hundred million years. So, the professionals enlisted the help of everyday people around the world. You sign up, go through a short tutorial on how to do a basic classification of a galaxy (is its shape spiral/round/other, how many arms does it have if it's spiral, etc.), and have at it.

GalaxyZoo has been VERY popular. Over 250,000 people have participated, and their work has already led to several very interesting discoveries; Hanny's Voorwerp (pronounced "FOOR-vurp") is the most striking example. Hanny van Arkel is a young Dutch teacher who heard about the first phase of the Galaxy Zoo project and signed up to help. About a week after she began helping to sort images of galaxies she did the equivalent of winning the lottery: she classified a galaxy then noticed something weird on the image, and posted it to their feedback forum asking, "What's the blue stuff? Anybody?" Turned out not only didn't anyone know, it was something nobody'd heard of before: it's a galaxy-sized cloud of gas, glowing very strongly in only certain colors (to a human eye it would be bright green, but the original image had been false-color and thus blue), apparently being lit up by the galaxy near it in the image, and has a huge empty hole through it. The object became known as Hanny's Voorwerp (Dutch for "object"), and Ms. van Arkel is now a minor astronomy celebrity and has acquired a part-time side job as an astronomy outreach educator.

An animation, taken from a Powerpoint presentation, gives a very simple explanation of the Voorwerp in lay person's terms, based on what is known as of January, 2010. Meanwhile, an explanation at the Galaxy Zoo site has a few of the technical details behind the animation. The Hubble Telescope is scheduled to take some images of the Voorwerp in 2010, and several astronomers are including it in their research programs. Ms. van Arkel maintains a website about developments in the Galaxy Zoo and the Voorwerp, remains an avid volunteer with the project, and as of Sept. 2009 became one of the moderators of a new forum for astronomy outreach and gender equality issues in the sciences, the She Is An Astronomer forum.

Less spectacular but just as noteworthy are the "Green Peas." These are a group of small round galaxies all more or less the same distance away on the galactic scale of things, and all of which look greenish—i.e., like peas. Now, green is not a color one sees in stars, much less galaxies (here's an explanation of star colors); so a few people who'd noticed the things (including Hanny van Arkel) also posted to the feedback forum, which made others keep a better watch out for them, and made them notice others, and... Thanks to the members of the "Peas Corps," there's now a first paper in the peer-review process (as of Sept. 2009). While the paper was written up by the pros, it lists these amateurs as contributors. The Peas appear to be a new subclass of galaxies with very high levels of star formation. Their green color comes from having a huge amount of a particular type of ionized oxygen. When oxygen is ionized in a certain way, it gives off the specific color of green light seen in these galaxies and nothing else. This type of ionization tends to occur in gas clouds where new stars are being formed; that these entire galaxies appear green implies that there is a LOT of star formation going on in them.

In late 2009, several related projects were added to the Galaxy Zoo; the entire suite is now whimsically called "The Zooniverse." One project asks people to look for supernovas (incredibly bright exploding stars) in galaxy images. A second project asks people to run simulations of merging and interacting galaxies: you're given an image of two interacting galaxies and several simulations, and if one or more of the simulations look at all like the image, you can play around to see if you can get them to look more like the image. In this way, astronomers hope to understand better the dynamics of galaxy mergers. (A stunning composite image of various interacting galaxies in the Galaxy Zoo is at the Astronomy Picture of the Day [APOD] website for Oct. 26th, 2009—the "letters" in the name at lower right are unaltered images of interacting galaxies, by the way.:) More projects will almost certainly be added to the Zooinverse in coming years, giving members of the public ever more opportunities to help professional scientists.

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ZZZ) Why don't you believe in UFOs? Don't you think there's intelligent life on other planets?

Those are two completely different questions. To answer the second one first: while there is no evidence as yet of any life, never mind intelligent life, elsewhere in the universe, we certainly hope that there is. As the saying from the film Contact goes, "If there weren't, it would be an awfully big waste of space." There are ongoing efforts to listen for signals from extra-terrestrial civilizations; you can aid these efforts by joining the SETI@home Project.

Re the first question: once you get some conception of the size of space, it is obvious that the idea that multiple small-scale (20-60 meter) "manned" spacecraft have, during the last 50-odd years, repeatedly come to this particular planet in this particular mediocre out-of-the-way planetary system, is ludicrous to the point of being delusional. Space is just tooooooooooooooo big for a ship to carry sufficient provisions and fuel to traverse interstellar space, slow down to do detailed exploration, speed up to go home, and slow down again when it gets there. The scale is beyond anything whatsoever in human experience.

Here's one way to view the size of things. One of the most famous pictures from the Hubble Space Telescope is an image called "The Pillars of Creation," a very small portion of the Eagle Nebula, in the constellation Serpens Cauda (the Snake's Tail). The section visible of the leftmost column is estimated to be approximately the distance from our solar system to the next star over, Alpha Centauri. At the top of the column are a few tiny pimple-like protrusions. On that scale, each of those is over 2500 times as wide as the distance from the Earth to the Sun. The two Voyager probes, the fastest human-made objects ever until the New Horizons probe was launched in January, 2006, have taken over thirty years to go less than 1/25th the width of one of those protrusions—and this was with over 99% of their initial mass being used as a propulsion system that was immediately discarded.

Another way to get an appreciation for the scale of things, in a visceral, personal way, is to do the Sagan Memorial Planet Walk downtown from the Commons out to the Sciencenter out by Route 13, a little more than a mile. (And the Sciencenter is a cool place to visit in any case.) On the Planet Walk's scale, the stele for the next star, Alpha Centauri, would be in Honolulu! So think how long it would take you to walk non-stop to Hawaii (ignoring such details as having to walk on water for the last 2000 miles...); and remember that in traversing the Planet Walk at a typical walking speed, you are doing the equivalent of going some 15-20 times faster than the speed of light! (Sunlight takes over 5 hours to reach Pluto. Time yourself to walk from the Sun stele to the Earth stele; light needs about 500 seconds to go from the Sun to the Earth, so divide 500 by your time to get your "solar-system hyperdrive" velocity.)

If you try to bring up "Well, so what about warp-drives like on Star Trek?", here's a Trek example. The book The Making of Star Trek (Stephen Whitfield & Gene Roddenberry; repr., NY: Ballantine Books, 1986) states that the fastest safe speed for the ship, warp six, was 216 times the speed of light; going faster risked serious structural damage. This would make for a 7-day transit time to Alpha Centauri, the nearest star—a little longer than an Atlantic crossing would take for a steamship like the Titanic (had it not sunk, of course...). One episode takes the Enterprise to a mining outpost on the planet Rigel 12. The star Rigel is estimated to be something like 800 light-years away. This means that if the Enterprise went straight from Sol to Rigel at top speed with no stops or side trips at all, it would have taken nearly four years of their "five-year mission" just for one episode (never mind getting back!).

For an excellent discussion about the engineering challenges for real interstellar travel, read Paul Gilster's Centauri Dreams: Imagining and Planning Interstellar Exploration (NY: Copernicus Books, 2004). Gilster does a serious, detailed technical analysis of the issues involved in sending an unmanned probe to Alpha Centauri on a human-lifetime scale (75-100 years), and shows, based on interviews with experts in the various fields involved, where current technology stands compared to what would be needed. Gilster maintains a Centauri Dreams website with updates on space science issues and relevant technological innovations, to foster discussion about when interstellar probes might become feasible.

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