Ever since we realized that an object from the sky could actually cause a mass extinction event like the one that killed off the dinosaurs, science fiction authors and doomsday conspiracists alike have frequently reminded us of the danger. But the reminders are not totally uncalled for, as there is a very real probability that such an object, commonly called a NEO (for Near-Earth Object), could at some point collide with the Earth, wreaking havoc as no man has ever seen. So what do we do? A lot of methods have been discussed for somehow avoiding the disaster if a comet or an asteroid were discovered on collision course with Earth, but any one of them requires us to know about it in advance. If you don’t know the punch is coming, it’s hard to block it right? Now imagine it’s dark, the big guy doesn’t glow very much (despite all the steroids) and there’s an unknown amount of big guys running around punching randomly in all directions…

Well the Pan-STARRS telescopes on Hawaii will enable us to spot very dim, moving objects, kinda like the NEOs we just described above. It will do this by surveying the night sky around 4 times a month with unprecedented sensitivity and the highest resolution digital camera ever built. Like the Wikipedia article explains, it will consist of four 1.8 meter (in diameter) telescopes and it will perform astrometry and photometry, largely meaning that it will measure the position and movement of the objects as well as their brightness. Enough to determine if the big guys are coming for us and how big they might be.

So far I’ve spared you of a lot of the details about the telescope as it quickly gets a bit tangled up in astronomy lingua, but I’m going to leak this one to you, explaining it afterwards: The telescope will be able to image objects down to an apparent magnitude of 24. Now the magnitude scale is one of those things that only astronomers use, and while it can be a bit hard to grasp at first, it’s an important thing to know if you’re ever going to read about a telescope or anything astronomy related in general. First of all, apparent magnitude is really nothing but a measure of how bright an object looks in the night sky, but with a few twists. For example it’s logarithmic and its backwards.

In astronomy you tend to get REALLY big numbers, or at least really big leaps in numbers, and brightness is no exception (eg. its around 4*10^26 Watts for the Sun), but if you take the logarithm of the number, you get a much nicer, more understandable number (like -27 for the Sun). The scale is reverse for historical reasons, meaning that the brighter an object is, the lower the magnitude is. For example the apparent magnitude of the full moon, which is 450.000 times less bright than the Sun, is -13 and the apparent magnitude for the dimmest objects visible by the naked human eye is around 6.

So let’s get the apparent magnitude of 27 for the Pan-STARRS into perspective. It must be able to observe really faint objects, as 27 is a lot larger than that of the faintest objects visible to unaided humans. Faintest objects visible with binoculars are around apparent magnitude 10, and Pluto, the former planet, has a maximum (that is, maximum brightness and minimum apparent magnitude) of 14. It’s when talking about Plutos smallest moons, Nix and Hydra, that we’ll encounter an apparent magnitude of 23. Notice that the Hubble telescope is able to see down to an apparent magnitude of 30 in visible light, but there’s a subtle difference, namely that Pan-STARRS will survey almost the entire sky, and really fast. With Hubble you’d have to know where to look to see Plutos moons. With Pan-STARRS you’d actually be able to discover them without knowing they were there.

It can’t be a surprise to anyone that surveying the night sky with an 1.4 GP (GigaPixel) camera 4 times a month will create an abnormally large amount of data to analyse for NEOs and other faint celestial objects. In fact, it’s expected that the system will produce around 10 TB (TeraBytes, 1.024 GB) of data each night! This will of course require an unseen data processing mechanism and an 1 PetaByte database. A nice article has been written about that in Computerworld, if you’re interested in that kind of stuff.

Just in case anyone should actually still be reading this, I wanted to mention that this telescope is not only useful for looking at and finding things in our own solar system. The project has a number of use cases far beyond the Solar System neighborhood. In addition to the expected findings of a lot of variable stars and eclipsing binary star systems that will help determine the distances to nearby galaxies better, it is actually expected that Pan-STARRS could find a lot of new exoplanets by measuring small changes in the brightness as the planet moves in front of the star or due to microlensing of the planetary system. In other words, this will not only be an important tool for protecting Earth against the great dangers from the sky, but also a great scientific tool for learning a lot more about the Universe that we live in!