Sunday Space: How and when do astronomers use telescopes?

It's a valid question; there are only a handful of very large telescopes (not to be confused with the "Very Large Telescope") in the world, so how do astronomers agree who gets to use it? Do they have to pack their bags and head to the remote Atacama Desert to observe their galaxy of choice?

To answer the latter, these days most astronomers observe remotely. Thanks to computers, the days of long cold nights, staring through a telescope are over. Most telescopes can be accessed through the internet, so astronomers here at Mount Stromlo can access huge telescopes in Chile and Hawaii from the comfort of Canberra.

Thanks to time differences, it also means that astronomers here in Australia can observe the night sky in Chile during their normal working hours and don't need to work late.

Some telescopes don't even require you to personally observe them. Astronomers can request the so called "service mode", where they give all the details to the telescope operator months beforehand.

Then, when the conditions are right, they can observe your object on your behalf and send you the data afterwards. A lot of modern telescopes and their associated science instruments are so complicated, it can often be best just to leave observing to the experts.

Other times, you may need to do some very tricky telescope manoeuvring or some complex observations - at these times, it may be better if you ask to use the telescope yourself, or even fly to the observatory and observe in person.

But what about telescope access? It turns out that not just anyone can certain telescopes. Often, telescope time is reserved for certain groups of people.

Scientists from observatories that own the telescopes, or astronomers who helped build some of the scientific equipment attached to the telescope, generally get a set aside amount of time to use the telescope. These groups can also reserve certain objects: they built the telescope, so they get first priority.

The rest of the available hours of the telescope are then open to the rest of the scientific community through what are known as "telescope proposals".

Every six months or so, telescope operators put out a call for astronomers who are interested in using their telescope in the following six months. Each astronomer then writes a proposal for why they want to use that telescope, detailing why their science will be interesting, why that telescope, and how much time.

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These proposals are collected together and looked over by the "telescope allocation committee", whose role is to rank all of the proposals based on their merit.

Often a telescope is "oversubscribed"; the number of hours requested is larger than the number available, so astronomers with the least appealing or least feasible observations are not granted time.

The rest receive their requested time (or a portion of it), and if the weather is favourable, they are able to observe and collect their scientific data. However, if you get to your night, and you get rain, you don't get a make-up night. You have to start the whole process over again!

This is one of the reasons telescopes have moved to service mode.

It can be a competitive process, but that makes a successful proposal all the sweeter.