Our only option to see the big picture

Perhaps you have read several of my previous posts, and I hope you have gotten some idea of why Chile is one of the best places in the world for astronomy.  For this reason, I have been thoroughly enjoying the experience (Thanks: Fulbright, U de Chile, ALMA, Yale) to live in Santiago this year, and work at the University of Chile and ALMA.  So why, you might ask, would I leave the astronomy-mecca that is Chile, and travel 7000 miles to seclude myself on top of this mountain in the Spanish Sierra Nevadas, where we happen to have been stuck in a snowy cloud for several days?

Sometimes we're above the clouds (at 3000 m elevation), and conditions are great for observing.  The sunsets are gorgeous too.

The telescope I am using is called the 30 meter telescope at the Institut de Radioastronomie Millimétrique (IRAM).  "30 meters" is the size of the telescope dish, and IRAM is an international research institute with headquarters in Grenoble.  Besides the fact that when I applied to use the 30m telescope, I was encouraged by the potential trip to Spain and a week of what I was told would be incredible cuisine, I wanted to use this telescope because it is one of the largest single dish telescopes that observes at the frequency at which carbon monoxide (CO) emits light.  This frequency of light is not necessarily what most people think of as "light".  If you looked at the CO in a star forming region with your eyes, you would see nothing, because the gas and dust are not hot enough to emit light at visible wavelengths.  However, the gas that forms stars is just barely hot enough (still, it is very very cool, only about 10-20 Kelvin, or degrees above absolute zero) to emit some radiation with wavelengths of about 1 millimeter.

They were actually observing through this.

 The IRAM 30m telescope is designed to detect this kind of light.  Why no shiny mirror? Don't you need a dome? How can you keep observing even when it's cloudy outside?  Radio and mm telescopes are slightly different than optical telescopes because the longer wavelengths of light don't need such a perfectly smooth, shiny mirror surface in order to be reflected and focused.  Also, the weather (as we obviously have wind, rain, snow here) doesn't do significant damage to the surface of the antenna.  And, we are lucky that we can observe even if it's cloudy or somewhat humid (although we have to be careful with the telescope if water, snow or ice accumulate) because radio wavelengths of light are longer than a typical water molecule, and therefore just pass right through (radio wavelengths can also pass through you and me, think about it).  Similarly, we can observe radio wavelengths during the day, because the light of the sun doesn't compete with our observations.  Very convenient... 

Check out these icicles on the telescope.  Skiers beware.

In fact, ALMA is also a "mm/sub-mm" observatory, and it can detect similar emission as IRAM.  But, the IRAM telescope is 30 meters, and the largest ALMA antenna is 12 meters.  With its many 12 meter antennas, ALMA has a large "collecting area" (think of it as many buckets scattered through the desert collecting falling photons), and it is very sensitive to faint light.  This is because the sensitivity of a telescope depends on its size, and with an array, the areas of all of the antennas contribute to the total sensitivity. 

Another important concept in observational astronomy is that the spatial scale to which a telescope is sensitive depends on the distance between any two points of the telescope.  In other words, an array of telescopes with large distances between any two telescopes (a.k.a. baselines) is sensitive to very small details. However, it is difficult for an array like ALMA to also be sensitive to the larger information (they don't want the antennas too close that they might collide).  For this we need single dish telescopes, where we can consider the infinitesimally small distance between any two contiguous points to tell us the bigger picture of what we are observing.

The receiver, behind the telescope dish, is where some magic happens.  Millimeter-wavelength light is converted to a frequency that a computer can process, and we can measure how much light we have received.

The heavy lifting (i.e. moving the telescope) is done with monster motors like these, inside the telescope mount.

Eventually, ALMA will incorporate a "compact array" and several single dish telescopes, at the same time as it functions as a large array that spans several kilometers, and we will have the best of both worlds.  But, for now, there is a bit of an art to carefully combining observations from a telescope array (we used an array in California called CARMA) and a single dish telescope like IRAM.  This combination magic will be my project after my observations end, so that hopefully we can make a pretty picture, and even more importantly understand the details of star formation on many levels.