Observing Challenges

Four little telescopes, all in a row



So I am, once again, at the Paranal Observatory, observing with the Very Large Telescope Interferometer (VLTI). VLTI uses multiple telescopes to synthesize a single, larger telescope - one of a size that is far beyond what is practical to build by itself. For example, we are able to configure our telescopes to act like a telescope more than 100-m in diameter - something that would be nice to have but is not economically feasible.

We are in the process of commissioning a new instrument for VLTI called PRIMA - I'll save you the pain of what the acronym means and cut to the practical impact of it: PRIMA allows us to observe two objects simultaneously. It effectively lets the VLTI behave like an interferometer, times two. This setup lets us do a couple of tricks - first, it will allow us to look at things fainter than we normally can, by using one of the two channels to lock up the optics on a bright star, while the second channel stares at something dim. Second, PRIMA will let us measure the angle between those two objects to an unprecedented level of accuracy, something south of 100 microarcseconds.

Twilight - getting ready to observe Hmmm... a microarcsecond: this is a pretty daunting science-type term. How small is such a measure? Well, let's put it this way: if you & your friend are standing on opposite sides of a soccer pitch (or football field) - about 100 meters - it's the angle subtended by the apparent distance that one of his hairs grows in a second, as viewed by you.

Pretty cool, huh? But here's the catch: VLTI is a rather complicated beast, and PRIMA makes it all that much worse. So, we shipped PRIMA out to the site last August, and we've been working to get it functioning ever since. It'd been expected that there would be an extended period of commissioning to shake out all the bugs (think of it as a test flight regime for a new aircraft), but some times the observing runs associated with commissioning can be a challenge when new & exciting optomechanical system do new & exciting - and unexpected - things. So at times we're left scratching our heads. ("Huh? The star separator did what?")

The moon and Venus in conjunction This particular observing run has been like that. We fix one thing and something else breaks or misbehaves. It's currently day 4 of 10 - and things overall are only getting better - but it's turning into a long haul. We'll be ready for the bus in a week! However, as we like to say (and first attributed to Albert Einstein), if we knew what we were doing, it wouldn't be research...

[nb. tip 'o the hat to The Blog Doctor for tips on image posting in Blogger.]

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