My Observation: What happens next?

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This work by Mike Tomlinson/Liverpool Telescope is licensed under Creative Commons Attribution Non Commercial Share Alike 4.0 International

Just before sunset, the telescope systems start up. If the weather is OK, the telescope's enclosure will open by itself, and observations will start. As it is still quite bright at sunset, the telescope takes data that will be used to calibrate the observations taken during the rest of the night.

Once it gets dark enough, it will start trying to take observations for you and all the other astronomers who have made requests.

All through the night, the computers at the telescope make decisions about which observation to do next. So, whenever one has finished, it chooses the best one to do next from the huge list of requests.

It starts by working out which could be observed. To decide this, the scheduler asks a set of questions:

• Is the object high enough above the horizon?
• Will it stay high enough all the way through the exposure time of the observation?
• Can the observation be finished before the end of the night?
• Is the sky dark enough for this observation?
• Is the "seeing" good enough for the observation?
• If the observation needs the very best conditions, is it a night with no clouds at all?
• If it has to be done at a special time (like a point in an orbit, or when a variable star is very bright), is the time right?

Requests with "yes" answers to all these questions will be moved on to the next stage. This narrows down the list of observations to only those possible right now. These are then ranked using a special computer code called an algorithm. The observation with the highest rank is then observed, and the process starts again.

The rank given to each observation depends on a few things:

• Slew Time: It takes time for a telescope to move and get into position for an observation. This could be several minutes, depending on how big the telescope is and how far across the sky the next object is away. Requests with quicker slewing times are given a higher rank since they won't cut into the available observing hours as much. This means the telescope isn't moving back and forth across the sky all night.
• Height Above the Horizon: If the object is going to be further above the horizon later in the night, it might be better to wait, so the rank number is lowered a bit until then.
• Priority: Higher priority observations are given a boost to their ranking.
• Completion: Big science projects that need lots of observations over many nights, or even months, are also given a bit of a boost as otherwise completing them might be difficult.

The overall rank for each possible observation is then compared, and the one with the highest rank is observed.

Because it starts again with the full list every time rather than planning the whole night in one go, the telescopes can take observations that have only been requested. This is very useful for trying to learn more about things that change very quickly or unpredictably, such as exploding stars like supernovae or gamma-ray bursts.

It also means that whenever you make your request - even in the middle of the night - the telescopes will start trying to observe it straight away.

As the Sun rises, the dome closes by itself. Another computer program carefully all the calibrates data using the special observations taken earlier that night.

The data files for your observation are copied to The Schools' Observatory website. They are ready for you to download and explore.

Sometimes, you might have been unlucky, like your image being taken through a small, unexpected cloud. You may also notice some quirks in the image. You may wish to resubmit your request and try again in these cases. Go to your observation list and click on the resubmit button ( ).

Sometimes, you might need to wait a while for your observation, or it might not be possible for it to be completed in time for you.

Observing conditions can change frequently, even during the course of a single night. Many things need to be thought about before an observation can be taken.

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Credit

This work by Liverpool Telescope/The Schools' Observatory is licensed under All rights reserved

Here are a few things that may help you understand why you might not be lucky with your observations:

• Seasons and Weather: Nights are longer in winter than summer, making it seem like a better time to observe. However, the winter weather is often worse, so it is still down to luck. And it's not just rain and ice that can make it unsafe for the telescope to open. There's the air temperature, humidity, pressure, wind speeds, etc., to take into account as well.
• Across the Sky: As the Earth spins each day and orbits around the Sun each year, the part of the sky that can be seen changes. We use coordinatesto help work out if something can be seen at a certain time. These can help us to plan an observation. Some objects may only appear in the sky at a specific point in the year and for a limited time.
• Sky Brightness: The fainter something is, the harder it is to observe, especially if the sky is not really dark. Things like the Moon and twilight can make the sky too bright to see the faintest objects.
• Seeing: "Seeing" is what astronomers call the "blurring" of images by the atmosphere. The amount of blurring changes and requests that need the sharpest possible images can only be done at certain times. The telescope measures the quality of the seeing all the time, so it will take observations that need to be good only when conditions are right. This means that requests which ask for the best conditions have more competition in the "ranking". If slightly poorer quality is OK, it is easier for the telescope to fit the observation in.
• Long vs Short: Observations that take a long time to carry out are more challenging for the telescope to fit in than those that are quick. So, observations with long exposure times might take longer to get observed.
• Priority: To help the telescope decide which observations are the most important to finish, all requests are given a "priority". For research astronomers, the priority is decided by a committee that thinks about what science is being done and which requests are the most exciting and important. For your observations, we use priority to boost observations that a lot of people want to get done. We also give those who haven't used the telescope much a bigger chance to get their first observations done quickly. However, this is only used together with all the other factors - lower priority observations might still be done first if all of the other conditions are better for them.

The simplest thing to do is to try again! If you are sure the observation is exactly what you want, click the resubmit button ( ) to your list of observations.

But if your observation was hard for the telescope to take the first time, it might be just as hard now, so you may want to try something different. In this case, go back to Go Observing and see what you might change.

For example, you might find a similar object that is easier for the telescope to fit in (check the coloured "Visibility" bars).