Planetarium Stuff
Published on Apr 14, 2006 at 6:53 pm.
2 Comments.
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I have always liked going to a planetarium. Growing up, trips to the planetarium allowed me to learn the night sky in a way that I could not have otherwise done. A knowledgeable person would point out stars and constellations on the dome of the planetarium, time could be sped up and slowed down to see the motions of the planets, and you could see what the sky would look like without light pollution (something that growing up in Houston, Texas, was hard to fathom). So, I thought that perhaps a planetarium blog entry might be in order.
First of all, since I wanted to talk about more than one planetarium, I figured that it would be useful to know the plural of the word. The word obviously comes from Latin, and having had several years of Latin, I knew that the plural should be “planetaria,†if normal Latin conventions are used. However, I often have also heard “planetariums†used as the plural of the word. So, I naturally decided to look in the dictionary. Much to my consternation, I find that both words are listed as the plural of planetarium! Now, if that isn’t silly. Microsoft Word seems to think that the plural is planetariums, but the majority of people that I personally know who are in the planetarium field (planetarians, they call themselves) use planetaria as the plural. Since planetaria also fits with my own reasoning from knowing the Latin root of the word, that is what I will use.
So, now that we have the grammar down, what exactly is a planetarium? Put simply, a planetarium is a device that shows what the sky looks like. Planetaria in some form have been around since ancient times. We don’t know who came up with the first one, but there are stories that the Arabs used to have tents with small holes punched through the material. Inside, the tent during the daytime, you’d see a representation of the night sky. There were also devices such as astrolabes that could be used to show the relative orientation of stars, the Sun, Moon, etc in the sky at different times of the day. One might think of these as handheld planetaria. A more modern version of this would be software that lets you see on your computer screen what the sky would look like at night. This is universally called “planetarium software.†Interestingly, many modern planetarium projectors use computers to drive them, and the software so used is also called planetarium software, even though it only superficially resembles the planetarium software that shows visualizations of the sky. Personally, I use planetarium software on both my desktop computer and on a laptop that I can take into the field. Also, I have planetarium software on a PDA that has turned into one of the most useful programs that I have ever put on that device. Anyone who plans on going out observing, especially any amateur, should think about putting planetarium software on a PDA (if you’ve got a PDA, that is!). You would not believe how often that you use it if it is available.
Related to a planetarium is an orrery. Most of you have probably seen an orrery, but had no idea what it was called. An orrery is, simply put, a model of the Solar System. It usually has the Sun in the middle, and the planets positioned in their proper positions around the Sun. The planets can then be repositioned to show their motion around the Sun. A mechanical orrery has gears and motors to move the planets about in the proper speed. So, an orrery would be a sort of working model of the Solar System. I have seen some very complex ones that even had moons around the various planets. A few that I’ve seen have even incorporated projectors to shine the relative planetary positions onto a screen. That makes such an orrery very close to a planetarium.
But, what I really wanted to talk about was not planetarium software, but rather what I think of as actual planetaria: i.e. planetarium projectors inside specially built buildings. This is what I think of as a planetarium. There is a certain mystic to the large domed room with the strange machine in its middle. I don’t know how long such planetaria have existed. The first large precision planetaria seem to date to early in the Twentieth Century, with the construction of such a device by Carl Zeiss in 1924. I have heard that less sophisticated devices existed before that, but for now we’ll just attribute the first modern planetarium device to Zeiss. Essentially, such a device is a powerful lamp situated inside a hollow ball. The ball has holes drilled in its surface to represent stars. The larger the stars, the larger the hole is drilled. This star ball is then place inside a room with a domed ceiling. However, the star ball is very expensive to make. It can’t be done on an assembly line, so it must be done one at a time by a craftsman. Also, drilling precision holes in a spherical shape is quite difficult and time consuming. Until the invention of computer controlled machining, even a template was not possible. So, that made construction of the planetarium ball very expensive. Also, you can’t drill holes for planets on a ball like that since they move around. That meant that in addition to the large star ball, the planetarium projector also needed a separate mechanism to show the planets. This usually consists of a light source and a set of individually controlled mirrors. The mirrors are geared to turn together, much in the way that the orrery works, projecting a dot onto the planetarium ceiling at the proper place to represent the planet. But, since the planet projector is not on the star ball itself, the positions of the planets will be slightly off. This effect is minimized by making sure that the ceiling onto which the stars and planets are projected is located many times the diameter of the ball away from the projector itself. Also, the image on the ceiling will be misshapen to an observer sitting far from the star projector. These are known issues, so a well designed planetarium has the seating clustered near the star ball in the center of the room. Planetaria designed as public theaters, though, often cram as many seats as possible into the space, resulting in a poor view for anyone not near the center of the theater.
The Zeiss planetaria were a fantastic success. However, they were quite expensive, so only a few were built. These were associated with major museums in large cities, and even then they could only be built if some generous benefactor donated a large sum of money to the museum to build the planetarium. Armand Spitz, an amateur astronomer and astronomy populizer, decided to design a less expensive planetarium that would be affordable to colleges, schools, and smaller museums. Spitz was convinced that a planetarium could be used as a fantastic tool for education. He developed a design for a planetarium projector consisting of a dodecahedral ball of flat plates. The ball looked sort of funny, but the holes for the stars drilled in the flat plates were easy to produce from a template. This cut down costs. This new planetarium design eventually took off, and these smaller, less expensive, planetaria started popping up all over the country. His company still exists, but they eventually switched production to the more traditional spherical star ball. A college that I used to teach at had a planetarium with a Spitz projector. It was absolutely wonderful to teach astronomy using a planetarium.
Of course, technology has continued to advance. It is now possible to have a computer screen and a fish-eye lens that can project onto the dome of the planetarium anything that is shown on the screen. This has some advantages over the old star ball. For one thing, the star ball is limited to showing what the sky looks like from Earth (Granted, if you know how to use it, then you can show the sky from anywhere on Earth, any day, any time of day, any year, and I have done this.). The computer screen can show the sky from anywhere in the universe that the computer has enough data to generate a sky view. You can even simulate “flying†from one star system to another. You can also highlight and zoom in on certain things, something not possible with the star ball projector. One disadvantage, though, is that for most of the computer generated views, the stars don’t quite look right. For one thing, to make a brighter star, these projectors usually use bigger dots (especially the earlier ones). In the sky, the stars all look the same size, just different brightness. This is more what the sky looks like using a star ball. Still, the more modern computerized projectors seem to be overcoming this limitation.
While I normally think of the planetarium as a place to see the stars, you can do more with it. Basically the planetarium building is a room with a high domed ceiling. The ceiling is reflective so that you can see the stars better, and this makes the entire ceiling basically a giant projection screen. So, you can also show movies and slide shows in the planetarium. It also is a place where you can see laser shows. Sadly, these seem to be more common uses than showing the sky. The last few planetarium shows that I have been to didn’t even really mention the stars on the ceiling one time all during the show! In fact, the shows were little more than fancy slide shows with some cool narration. This misses out on the entire reason for having a planetarium in the first place!!!!
The other problem seems to be that most planetarium shows produced now-a-days seem aimed at elementary school kids. While I have no problem with planetarium shows aimed at young children, and I believe that it is essential to get them interested in science early on, I also think that it is a mistake to only aim at the young ones. We are losing children from the sciences in middle and high school. When asked why they didn’t want to study science, a group of high school students a few years ago replied that it was because they thought that science was boring, irrelevant, and only for kids. Clearly something is horribly wrong here. I can’t imagine anything less boring. I see science involved in all aspects of my life, so it is far from irrelevant. And as for being only for kids, I guess that I am young at heart, but still … . So, perhaps we should have some of these programs aimed at middle and high school, and even some aimed at adults. I think that we are missing out here.
I wish that we had a planetarium at my college so that I could put together some planetarium shows that used the unique capabilities of the planetarium projector and the planetarium experience. Alas, planetaria are still expensive to build and to maintain, so we aren’t likely to get one anytime soon (if ever).
-Astroprof
Richard Everiss on March 4, 2007 at 3:21 am: 1
Hi
Why not build a planetarium at your college? With the move to digital there are secondhand starballs around that could bring the stars to students relatively cheaply. I can help you with ideas as I have just built a planetarium for our community in Yorkshire England (www.yorkshireplanetarium .co.uk)
Just a thought.
Astroprof on March 4, 2007 at 9:17 am: 2
Thanks for the comment. Even an inexpensive star ball requires money for maintenance and money for a room to house it. We almost had a planetarium several years ago, but internal and exteranal politics caused the governing board to vote to leave a planetarium off of the long range plans for the college. Since then, all money has gone towards building a new campus for the college. I am afraid that if we did get a planetarium, they’d put it at the new campus, not the one where I am. But, it might be worth investigating how much a used star ball would cost. Who knows …?