The Cards

Q: How Can I Obtain Additional Copies of Cosmic Decoders?

A: Cosmic Decoders is available for purchase by anyone through the Society's AstroShop.

Q: How and Why Did You Pick the 52 Images of Deep Space Objects and 12 Telescopes that are Depicted on the Cards? What Makes Them So Special?

A: To begin with, we wanted our card games to have four "suits" (like a standard deck of cards), so our images had to come in four categories. Once we agreed on the four categories of Deep Space Objects that would best help players learn about the variety of objects in space (and lend themselves to the best pictures), we then set about narrowing down our choices by looking over the many "galleries" of astronomy pictures now on the web. If you want to see some of the major galleries we looked at, click here.

Once we got to that point, we confess that picking the images was not (pardon the expression) an exact science. We first assembled a series of pretty images that demonstrated the science points we wanted the cards to make. (Our gallery search had yielded over a hundred such images from the world's biggest telescopes!) For our final group of 52 Deep Space Object images, we simply picked pictures we and our test audiences liked best. Different people could have picked many different objects. We apologize, therefore, if we left out any of your favorites.

Overall, we wanted the pictures to show some visually arresting examples of each type of object. So, for example, among star death nebulae, we wanted to show a nice variety of both planetary nebulae (the "death shrouds" of smaller stars) and supernova remnants (what remains after the explosion of larger stars). Among galaxies, we wanted to show different shapes (spiral, elliptical, and colliding galaxies) and different sizes (from giant to dwarf galaxies). In addition, we wanted to show images from several of the most important telescopes, both on the ground and in space. So, in addition to the Hubble Space Telescope images, you will also see pictures from the European Southern Observatories Very Large Telescope, the Chandra X-ray Observatory, and many other major telescopes around the world.

For the 12 telescope cards, we wanted to show a range of telescopes at the forefront of astronomy research, and at the same time, include some that captured the images of Deep Space Objects we chose. Some of these telescopes are on high mountaintops on the Earth, while others orbit our planet in space. Also, we wanted to show telescopes that gather more than just visible light, the light our eyes can see. So the cards show several instruments for collecting "radio static" from space (or radio waves), x-rays, and infra-red rays (or heat rays). See the Learn More About Telescopes section for more information about telescopes that collect invisible types of light.

Q: Where Can I Find More Pictures Like These?

A: If you want to see some of the major galleries we looked at, click here.

Q: Are the colors on the pictures real?

A. The answer to this question is not simple, and depends on the instruments with which the image was taken. A few of the pictures in our card set show cosmic objects as seen not with visible light, but other kinds of waves (radio waves or x-rays) that our eyes cannot see. In these cases, the colors are added as a kind of code - colors could show different types (energies) of x-rays, for example, or they could show where radio waves are stronger or weaker in the sky. It is best to read the detailed captions on the web that go with each image to see what the colors mean. To find these captions, go to our section "More Information and Web Links for the Images Depicted on the Cards," and for each card, click on the link provided under "Where on the Web is the Image?"

The majority of the images on our cards are taken with telescopes and cameras that record visible light. So you may ask, are those colors real? We don't mean to sound like lawyers, but that depends on what you mean by "real."

When astronomers take pictures of astronomical objects, they don't do it with a simple camera - like the ones we use for home snapshots. The process is a bit more complicated and usually involves several exposures that are later combined to make the image that is published. Often each exposure is taken using a filter to highlight a specific type of feature in the object we are interested in. A filter selects one narrow set of colors and keeps all others out. Different colors can tell us about different processes going on in nebulae, star clusters, or galaxies.

For example, hydrogen gas, when excited, glows in a pinkish red color. Clouds of excited hydrogen often mark star-forming regions in galaxies. So to highlight such regions, one exposure of a galaxy might be taken with a particular red filter that only lets through the hydrogen color. Another excited gas (oxygen, say) may glow in a different color, so a different filter is used to highlight those regions rich in excited oxygen. Astronomers may combine several single-color images taken with different filters and produce an image that looks "full color." Thus, not all colors in the object may be present in such an image, but only those highlighted by the filters chosen for the individual exposures.

In other cases, all the filters being used might let pass various shades of red. Then, to distinguish the results from different filters more clearly, astronomers may choose to artificially change one or two of the red images to a green or a blue. This helps clarify what is happening in the object, but now takes us even further from what you might consider "true color."

Again, we recommend reading the detailed captions for each image by following the "Where on the Web is the Image?" links if you want to know what colors are being captured and how and why the image may have been enhanced or changed.

For a nice graphic description of how the Hubble Space Telescope team creates their color images, visit their web site at: http://hubblesite.org/sci.d.tech/behind_the_pictures/

Q: Since there are no 1-hour photo developing machines in space, how are images taken with telescopes in orbit?

A: Telescopes like the Hubble Space Telescope don't use cameras with film. Instead, images are recorded on sensitive electronic detectors, devices similar to (but better than) what is now used in home camcorders and digital cameras. They are called CCD's - charge coupled devices. They convert each pixel (picture element) of light in an image into a flow of charge (or current or electricity). The amount of electricity at each spot tells you how much light hit the detector. And unlike undeveloped film, the results can be "beamed" back to Earth. Plus these devices are much more sensitive than film ever was, and thus can record much lower levels of light - something that is very important for astronomy where objects are so far away, they look very dim even in large telescopes.

Q: How Do Astronomers Know How Far Away or How Big the Objects on the Cards Are?

A: Measuring distances to objects out in space is one of the most challenging parts of modern astronomy. After all, you can't just send a graduate student out there with a tape measure. Most of the objects astronomers are interested in are, in fact, so far away that we may never be able to visit them. Nevertheless, if we want to figure out how big they are, how much energy they give off, or what groups of objects they are part of, we first need to know how far away they are located.

One way to measure distances is to look at relatively nearby objects in space from opposite sides of the Earth's orbit. (In the same way, surveyors can measure distances across a wide river, by sighting from two different locations along the river's bank.) One nice bonus we get from living on Earth is a free trip around the Sun every year. This means that the Earth's position in its orbit in the spring is roughly twice the distance between the Earth and the Sun, or 186 million miles from its position in the fall. So in those two seasons we see the universe from two different vantage points some 186 million miles apart.

To understand how this method works, note that you get a slightly different perspective on the world from your right and left eyes. Try holding up a finger in front of your face and then close one eye and then the other several times in a row. What do you see? Note that each time you close an eye the finger "shifts" relative to the background. The closer the finger (or cosmic object) is to you, the greater the shift. (Try it! Starting with your finger at arm's length, repeat the experiment above, but this time slowly move your finger closer and closer to your face as you close and open each eye.) In the same way, we see nearby objects in space shift (very slightly) from the Earth's fall and spring vantage points. By measuring this so-called shift, or "parallax," we can determine the object's distance. However, this method only works for objects that are not too far away. It gets astronomers "started," so to speak, in measuring cosmic distances, but is actually not directly useful for most of the Deep Space Objects on our cards.

Another way astronomers try to measure distances is by searching for "standard candles" (or standard bulbs in modern terms) among cosmic objects. Standard bulbs are bright objects of a known luminosity (i.e., "built-in" brightness). Imagine you are in a dark auditorium or arena and are trying to get yourself oriented. Luckily, someone has installed some light bulbs around this giant space, and the staff turns a few of them on. If all the bulbs are 100-watt bulbs, say, then they will all look the same if you see them from close up. But the further you get from a source of light (like a bulb), the dimmer it will look. (Distance, after all, makes all lights look dimmer.)

This means that if a bulb looks bright to you, it must be nearby. If a bulb looks very dim, it must be way on the other side of the auditorium. But being able to judge the distance of a bulb from how it bright it looks can only work if ALL the bulbs are the same. If some bulbs are 10 watts, others 100 watts, others 250 watts (and you don't know which is which), then how bright a bulb looks will depend not only on distance but also on which "built-in" wattage bulb it is.

Stars and galaxies in the universe are (alas) not standard bulbs. They come in a wide range of built-in brightnesses and so how bright they look from Earth is not a clear indication of their distances. Astronomers have spent the last century trying to identify objects out there that are (more or less) standard bulbs. For example, a certain type of exploding star (called a Type Ia supernova) generally has the same brightness. The brightest elliptical galaxy in a cluster of galaxies is often roughly the same built-in brightness. When we observe such an object, how bright it looks to us will give us an indication of its distance.

Another type of star is also a big help in finding distances. "Variable stars" are stars whose light output changes with time - they get a little brighter, then a little dimmer, and then brighter again. (The most commonly used variable stars like this are called "cepheids," after the constellation in which the first one was discovered back in 1784.) These slight but regular changes in the star's brightness can take less than a day, several days, and, in some cases, several weeks.

It turns out that the built-in brightness (the "usual" brightness) of such a star is related to how long the variations take. The shorter the time to vary, the less bright the star. (This is not obvious, but had to be figured out from information about many such stars.) Measurements of the time for one cycle of getting brighter or dimmer for a variable star can then be used to tell astronomers how bright the star really is. It's as if the flashing rate of a twinkling bulb on a Christmas tree were related to its wattage. Slow flashing bulbs are high-wattage, but fast flashers are low wattage. Measuring the time for flashing (which is easy to do), tells us the wattage (which is hard to know from far away.) This is not generally true for flashing bulbs in store windows, but IS true for variable stars. You can essentially read off the "wattage" of the star from how long it takes to vary. Once we have the built-in brightness of a variable star, we are in good shape. Comparing how bright the star really is and how bright it looks from Earth helps to tell us its distance.

Because many star clusters and galaxies have such variable stars in them, we have used these "flashing" stars to measure distances to many objects in our galaxy and in other nearby galaxies. But this technique requires astronomers to be able to make out one individual star within a galaxy - something that gets harder and harder to do as the galaxy is farther away and begins to look like a smudge of light even in large telescopes. Luckily, we have other methods of establishing distances to far away galaxies (that are a bit technical beyond the scope of this brief web page.)

In such ways, astronomers have been able to determine how far away stars, nebulae, star clusters, and galaxies throughout the universe are and have been able to show how things are organized on the largest of scales.

For a somewhat more technical introduction to how astronomers measure distances, see the UCLA web site, The ABC's of Distances: http://www.astro.ucla.edu/~wright/distance.htm

Q: Can I really see the star cluster M92 without a telescope? Isn't M13 the visible globular in Hercules?

A: Yes, M13 is the more famous of the globular clusters found in this constellation. But M92 is visible to the naked eye too; although not from the city, because of all the "interference" from city lights that shine directly or reflect their light into the skies. Astronomers call this light pollution. It's one of the main reasons that observatories are in such remote mountaintop locations. But if you are out camping, say in the Tetons, or if you simply live in a more rural setting with no bright lights shining into the sky, look at Hercules again. If M13 is along his right thigh, M92 is under his left foot. (Note: Both can be found using binoculars if they are not visible with the unaided eye.) So even though many sky watchers know M13, we thought the little beauty that is M92 deserved some notoriety as well. Click here for more information about M92.

Q: I Have a Question about One of the Objects Pictured on Your Cards. How Can I Get More Information?

A: Click here to be taken to the sections that provide information links for each of the images depicted on the cards. Many other questions about the Deep Space Objects or telescopes on our cards will be answered by following those links.

Q: I Have a Question about Something Else in Astronomy. Where on the Web Can I Ask an Astronomer a Question (or a Dozen Questions)?

A: Click here to go to our general web resources page, where there is a list of "Ask an Astronomer" web sites.

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The Games

Q: What Other Games has the Family ASTRO Team Produced?

A: To date, four Family ASTRO take-home activities have been produced. Click here to view them all. In addition, all our Family ASTRO kits and games are available for purchase to anyone through the Society's AstroShop.

Q: In Build a Galaxy, what happens if the first card turned over from the deck is a Telescope Card?

A: In both Build a Galaxy and Telescope Trouble, if the first card turned up is a Telescope Card, put it back in the middle of the deck and turn over a new card to start the discard pile. (See page 12, item #3 in your Cosmic Decoders Manual.)

If you have a question about the Cosmic Decoders Card Set that is not listed here, or about Cosmic Decoding in general, please contact us at astro {at} astrosociety.org.

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