Monday, January 27, 2014

Astronomical Observing - Actually Getting Data

Sunset view from 2.1 Meter catwalk.
So after days of writing about cirrus, humidity, and telescope shut downs, I figured it was time to write about the glories of when it works.  It looked a bit cloudy to start the night, and we were wondering how it would go.  But the worst of the clouds have moved through.  We've been chugging along well so far (fingers crossed for more) and hope that more clouds won't come along until after sunrise.

So what are we doing up here, anyway?  We are looking at asteroids, for the most part.  We are getting image data (in a handful of colors) of the Trojan asteroids of Jupiter.  These are a population of asteroids that orbit the sun at the same distance as Jupiter, gravitationally influenced to stay in two groups, 60 degrees in front and behind Jupiter's orbit.  These objects have not been extensively studied, and may hold some keys to the early formation of the solar system as a whole.

Example of our data.  Asteroid highlighted by green circle.
So here we are, getting data on as many of these asteroids as we can.  And the observing program will go on for the next few years, since we need to look at a large number of asteroids in order to draw meaningful conclusions - at least for this study.

Our data roughly looks like this sort of thing.  An image showing stars and our target asteroid.  The telescope has been commanded to compensate for the rotation of the Earth, so the stars look like nice points, even after a long exposure.  The asteroid is moving at a different rate, however, so if you add the various images together, you can see that it has moved relative to the background stars.  So it looks a bit like a smudge or streak, here.  (The 'wavy lines' are not real, they are artifacts of the data and quickie reduction done for this example.)

Jupiter - Always fun, and amazing
Of course, the 'seeing' isn't always perfect.  Even on a nice night like this one, intermittent clouds can go by.  When that happens, we spend a little time on some very bright targets, until we can go back to taking our regular data.  This is what astronomers call 'having fun.' 

Image Credit:  Shot from catwalk, Andy Rivkin @asrivkin on twitter, example of data from our run, and same for Jupiter.

Sunday, January 26, 2014

Astronomical Observing - Dealing With Weather

An (old) picture of the 2.1 Meter Telescope with lightning.
Ah, yes.  Can't write a series of posts about observing without mentioning the weather.  It is particularly appropriate right now - since I have time to write this post because weather has shut down the telescopes.

We'd hoped for clear skies tonight.  The forecast was for no clouds, and reasonable seeing conditions.  But sometimes it just isn't that easy.  When the weather is obviously bad, say you have lightning like in the picture, you know you won't be getting any data.  It is a very black and white situation.  When you have heavy clouds, or it is raining, that is also straightforward.  You can easily see that the conditions are simply not conducive to observing.  But there are less obvious factors that are just as important.

One of these factors is wind speed.  Most telescopes cannot be open in relatively high winds (say 45mph in some places) as this can damage the telescope and is a safety issue.  Wind is something you can feel, of course.  You may not know exactly how fast the wind is blowing, but you can look at a wind gauge and assuming it is working properly, it will tell you if it is safe to open or not.  Mostly.  The wind is not always steady, of course, and it can change value or direction, or there may be sudden wind gusts.  It can be much harder to determine what is or isn't safe under those conditions.  So it is possible to be sitting inside the dome on a clear night, unable to open, because the wind is occasionally gusting a bit too fast for comfort.  That can be a little frustrating.

Sky Chart predicting clear skies ... and high humidity.  At least for a while.
Another factor is humidity.  This factor is particularly frustrating, and is the reason we are closed at the present moment.  The issue in this case is not that we can't see the sky, but as with wind, that there is a possible issue with the telescope.  It isn't a safety issue, but rather that under the right conditions, water can condense right onto the telescope mirror.  This is very bad for the telescope, and could damage the mirror.  One way to avoid this is not to open the dome if the humidity is high outside, but that is not always a perfect indicator of dew formation.  Condensation (dew) is also a function of the air temperature, the temperature of the telescope, wind speed, and more.  To add to the frustration, humidity is highly variable across short distances.  It is possible that one telescope on the mountain is just fine to open, while another is not.

Bright Jupiter in a haze of humidity.
It isn't particularly obvious how humid it is outside until you look up and see the fuzz of light around the planet Jupiter.  As in this sky shot, the sky is pretty clear, but pretty much straight up (in the center) is a bright spot with haze around it.  That is Jupiter, and the haze is water in the atmosphere.

So here we are sitting under a clear sky, unable to open.  Adding to the frustration is the constant checking.  I am the sort of person who is uncomfortable with gray area.  I want it to be cloudy or not.  Raining or not.  Constantly checking the humidity, (and getting four numbers for four different instruments) is maddening.  Hopefully things will improve later, the sky charts says they might.  But our little corner of the mountain, well, who knows.

Image Credit:  2.1 Meter in lightning from  NOAO/AURA/NSF.  Clear Sky Chart from Kitt Peak Clear Sky Chart.  Sky Shot from  Kitt Peak National Observatory.

Friday, January 24, 2014

Astronomical Observing - To Find a Telescope

Approach to 2.1 M. Dome
Long before going to the mountain, the observer has to create an observing proposal and apply for time on a telescope.  Time can be found on some telescopes by applying to an open, national program, or (if you have the right partners), can be obtained from consortia who own their own telescopes, and have a certain amount of guaranteed time for their specific observers. 

The telescope needs to be a good match for what you want to do.  Telescopes vary in size (light gathering power) and each has its own unique suite of instruments.  Some observations can only be made with the largest and most sensitive telescopes that exist.  But getting time on one of these is difficult - it is very expensive, competitive, and if you do get time, it won't be much.  If you need a lot of nights, or if you have relatively bright targets, then a somewhat smaller telescope is what you need.

At least for the time being.

Base of the 2.1 Meter Telescope Dome
I've written in the past about the uncertain fate of the telescopes on Kitt Peak.  I mentioned that some of the most amazing and productive astronomy telescopes on the planet may be shutting down.  Several smaller, mid-sized, and older telescopes at Kitt Peak and elsewhere are being divested in favor of a small number of larger, newer ones.  This in itself is not unexpected, but as an educator, it is my personal concern that changes like this will make it harder for certain groups to get observing time - like graduate students, early career astronomers, astronomers from non-traditional backgrounds and minority institutions, and those with smaller programs.

2.1 Meter Telescope
Another complication is that, what with time at the biggest 'scopes being so competitive, they won't give time to a project that can physically be accomplished someplace smaller.  If there are no such telescopes left, then a host of important observing programs just won't get time.

This is not to suggest that there will be no smaller telescopes, but open time will become very scarce.  An observer will have to forge the right partnerships with other scientists involved in telescope consortia to get telescope time.  And this is less likely, and more difficult for the groups I mentioned above.

Our project this week is one that requires many nights - we need 300ish, relatively bright asteroids, and can get about 50 in a decent week of observing nights.  This means it will take a few years to apply for time each semester, do the observations, and iterate until having reached the necessary number of targets.  The 2.1 Meter Telescope at Kitt Peak Observatory is a perfect fit, with the right instrument (CCD imager) and the right amount of light gathering power.  So the first stop is here.

BUT this is one of the telescopes slated for shut down.  After next semester, it will no longer be available, in spite of being one of the most important workhorse telescopes on the mountain.  Hopefully it will be picked up by a consortia, but there is no guarantee that we will get time here even if it is.  So it is most likely that further work will be accomplished elsewhere ...

Image Credit:  All my pictures except the large 2.1 Meter Telescope shot, which is from     NOAO/AURA/NSF

Thursday, January 23, 2014

Astronomical Observing - Hitting The Mountain

Telescopes tend to be on mountains, far away from the lights of cities, spurious electronic signals, and above the bulk of dust and atmospheric water that can interfere with certain observations.  They also tend to be in places with good weather, of course.  This combines to put optical observatories in some very lovely places, i.e. scenic mountaintops that are sun-splashed in the day and capped by diamond skies at night.

Many observatories are very high and remote, and it can be a hassle getting there.  But it is always worth the trip, even just from a sight-seeing point of view.  Kitt Peak National Observatory is not so terribly high nor far from habitation, and the desert (if you like that sort of thing, which I do) is wonderful to drive through.

It is one of the perks of astronomy, just traveling to observatories.  There is something thrilling in taking a turn on a winding mountain road and suddenly seeing the brilliant white dome of a telescope come into view.  It feels magical to me - a place for looking deep into the darkness, and learning what's out there.

The drive up is always filled with a mix of hope and apprehension.  Working in visible and near visible wavelengths of light means you are at the mercy of the weather.  And even in places where it is "always" sunny, well, it isn't.  You have in your hands (or in your notes or your computer hard drive) the list of objects you hope to observe, but it is just a plan, an idea.  What you really end up doing will be based on weather and other considerations, like how the telescope and your chosen instrument are behaving.

So you take a few nice deep breaths of mountain air to clear your head, and then walk on up to the dome to see what the night has in store.  (And as for us, the first night went great, a dozen targets observed, and no time lost even when the water cooler insisted on leaking for an hour after we replaced the bottle on top.  Always nice when the telescope isn't the problem for the evening ...)