Friday, November 8, 2013

Eight Great Telescopes That Aren't Hubble

The Hubble Space Telescope has successfully become the most famous telescope in the world. It has maintained this popularity through many years of operation, repeated news events surrounding the telescope, and promotion through sharing its imagery with the public through various venues on the internet. It's so well known that any time an average member of the public sees a detailed astrophoto they're more likely than not to ask if it's a Hubble image.

But Hubble isn't the only great telescope out there. In fact, while it is still a very valuable instrument contributing much to current science, its capabilities have in many ways been eclipsed by other instruments. After all, the Hubble was conceived and designed when an Apple II computer, running at 1MHz with an 8 bit processor and about 128KB of RAM was a serious work computer. So, while we recognize and accept the greatness of Hubble, let's have a look at some other telescopes that have been eclipsed by its popularity.

The Chandra X-Ray Observatory

Chandra X Ray Observatory Satellite
The Chandra X-Ray Observatory was one of Hubble's sister scopes in NASA's Great Observatories program. While Hubble was designed to cover the visual and near-infrared part of the electromagnetic spectrum, Chandra covers X-Rays. One of the great advantages of Hubble was that it was outside the atmosphere, eliminating the effects of the air on its images. In Chandra's case, getting outside the atmosphere is critical, x-rays don't penetrate our atmosphere to any degree. A ground-based x-ray telescope would be blind.

Despite coming from the same overall program as Hubble, the Chandra has gotten far less notoriety. Its images are no less beautiful, and are arguably more scientifically valuable since much of what Hubble does could be reproduced with other instruments. The same can't be said of Chandra.

The Spitzer Space Telescope

Spitzer against an infrared sky in space
Spitzer was also part of the Great Observatories program. It is the full-featured infrared complement to Hubble. Infrared is another part of the electromagnetic spectrum that is interfered with by the atmosphere far more than visual light. High altitude observatories can get above enough of the atmosphere to do IR observation from the ground, but getting into space is far better.

Infrared observations are especially important compared to visual light because IR wavelengths penetrate gas and dust better than visual wavelengths. On top of that, the effects of red-shift--light being shifted to lower frequencies by the expansion of the universe--means that to observe the visual light emissions of far away objects in space we need to look for infrared light here. It's been red-shifted out of the visual light spectrum entirely. Observations of the early universe rely on IR telescopes. This is why the new large space telescope, the Keck, often hailed as "Hubble's replacement", is being designed to work in IR wavelengths.

Aside from its scientific value, Spitzer also produces images of great beauty and wonder. Like Chandra, it has lived in Hubble's shadow for over ten years now.

The Great Observatories were originally rounded out by the Compton Gamma Ray Observatory. Its stabilization systems broke down after years of operation, and it was brought back down into the atmosphere for destructive re-entry. The remaining Great Observatories are still working today to produce valuable new science.

Fermi Gamma Ray Telescope

Fermi satellite image, a box with wings.
Fermi is the successor and advancement over the Compton Gamma Ray Telescope. Like the Compton, it is an orbital telescope. It observes the highest energies of radiation in the electromagnetic spectrum. It's been in operation for over five years as of the time I write this, and is extending its mission time in space. We hear about Hubble all the time, but this telescope has been working away in space, revolutionizing science for five years. Have you heard of it? (If you read a lot of astronomy magazines and journals like I do, you almost certainly have--if you get information from less specialized sources, you've could easily have missed it or forgotten about it even if you saw a short segment on it somewhere.)

Fermi was originally called GLAST after its main instrument, the Gamma ray Large Area Space Telescope. Once again, this telescope is designed to see things that Hubble can't see. Rather than looking as small, specific parts of the sky it scans the entire sky every three hours. It is used to image particles that are travelling just under the speed of light, the most energetic particles in the universe. This allows us to study physics in ways that we can't reproduce in laboratories on Earth. You think the Large Hadron Collider is powerful? The physics powerhouses that Fermi studies make LHC look like a pop-gun!

Large Binocular Telescope

large binocular telescope with doors open, showing dual telescopes inside.
Before Hubble, the Palomar Hale Telescope got all the press. It was the "200 inch telescope", the biggest in the world for a long time. Even after the Bolshoi Telescope was built, many Americans (at least) still thought Palomar was the largest. (Though the Bolshoi has always had problems that kept it from having the best performance. However, it is still used and is being upgraded again.

Today, the relatively unknown Large Binocular Telescope sports a pair of mirrors, each 331 inches in diameter! That means each mirror has over 2.7 times the light collecting area of Palomar's Hale telescope. Together, it's about five and a half times the light collecting area. But, as they say in the commercials, that's not all.

The Large Binocular Telescope uses adaptive optics (AO). This is a means of flexing the optical surfaces of the telescope to get the best possible image. The adaptation happens in real time, allowing the telescope to eliminate much of the problems from observing from the ground, rather than in space. In essence, if we'd had working adaptive optics back when Hubble was being designed, we would have already had ground-based telescopes that can see as well or better than Hubble! If we'd gone ahead with launching a telescope into space (still a good idea), then we would have had to build a telescope even more amazing than Hubble to justify the extra cost and effort (Hubble cost as much or more than a huge ground-based observatory project.)

But, reality is that we pulled together all the parts to build adaptive optics into ground based observatories after the commitment had already been made to Hubble. So now we have many ground based observatories that can out-perform Hubble, the Large Binocular Telescope among them.

The South African Large Telescope

SALT Observatory in daytime
The South African Large Telescope is the largest telescope in the southern hemisphere. Now, space telescopes like Hubble, Fermi, Spitzer, and Chandra don't care about hemispheres, but here on Earth you can only see so much of the sky from any place on Earth. It has roughly four times the light collecting area of Palomar's 200 inch (5.1m) Hale telescope. Its main mirror is a segmented mirror. Whereas the LBT has two mirrors that work side by side as two optical trains, the SALT telescope has 91 individual mirrors that all work together to form one big mirror, creating a single image. The mirrors are all made to work together through careful alignment using laser calibration. Also, rather than tracking the sky like other telescopes, the telescope stays fixed in place, while the instruments attached to the telescope track to capture the light from the object being observed.

The Magellan Telescopes

The Magellan Telescope buildings at night, lit by ambient light
Image by Krzysztof Ulaczyk
The Magellan Telescopes are a pair of telescopes that each use a single 6.5 meter mirror. They can work together, like the telescopes in the LBT, or they can work independently. Their large reflecting surfaces are made up of a single mirror, rather than a lot of smaller mirrors put together to act as a single mirror, like SALT. The mirrors are not a single large thick slab, like the Palomar Hale Telescope, however. They have hollows inside, they've got a honeycomb-like structure inside that supports the reflecting surface without being solid. Each mirror has well over 1.5 times the light collecting area of the Hale telescope, and, like the LBT, they are equipped with adaptive optics to clean up the image.

The Keck Observatory

The twin Keck Telescope Domes
Hubble's launch ended up being delayed, then, once it was launched, it had optical defects that budget cuts had eliminated the tests to catch (the back-up mirror, which still sits here on the ground, was perfect, so it's not like it would have cost a lot to solve the problem if it had been caught.) This meant a further delay while corrective instruments were designed and a half-billion dollar Space Shuttle mission to perform repairs was mounted. During that time, work on ground-based observatories did not stop.

The Keck Observatory was the great project that brought together so many of the advancements from the time between the start of work on Hubble and Hubble reaching its scientific potential. It used segmented mirrors to produce a collecting area far greater than the Palomar and Bolshoi telescopes. It added adaptive optics, as well as a second advancement to the optical train, active optics.

Active optics are similar to adaptive optics, in that they make adjustment to the optics of the telescope in real time to make a better image. Active optics, however, primarily correct environmental problems from being on the ground, rather than correcting problems with the image caused by the atmosphere (which is the purpose of adaptive optics.) Active optics correct for the pull of gravity on the mirrors changing as the telescope moves to follow objects across the sky. It corrects for changes in temperature, mechanical stresses on the mirrors, and so on.

Active optics keeps the mirrors within the telescope's main reflector as perfect a reflector for the telescope as possible. Then adaptive optics kick in later to clean up the effects of the atmosphere. The result is that the Keck can produce more detailed images than Hubble.

On top of that, Kick added a second telescope that can combine with the first to work like one really huge telescope. This not only increases the light collecting area, but the apparent aperture size of the telescope. That allows for resolution of finer detail (whereas increased collecting area allows the detection of fainter objects.)

Gran Telescopo Canarias

GTC over a cloud deck at sunset
Image by Christoffer H. Støle
The GTC is an 11.4 meter telescope in the Canary Islands. Like Keck and SALT, it has a segmented mirror. It is one of the most active telescopes in modern science, and it produces stunning images, like Hubble.

Atacama Large Millimeter/submillimeter Array

The ALMA radio telescopes under a starry sky
Image by ESO/B. Tafreshi (
ALMA will soon be the most powerful telescope. Period. It doesn't even see in light, or infra-red. Instead, it sees electromagnetic radiation in the part of the spectrum in radio waves, just below the IR part of the spectrum. Just as IR can see through gas and dust better than visible light, ALMA can see through it better than IR. Where other scopes can only see cloudy things, ALMA can look inside the clouds to see what's inside. It can see stars that are beginning to form, for example.

While the far longer wavelengths it observes in would normally mean that it has to give up high detail and positional accuracy to do so, ALMA spreads its reflectors, radio telescopes that all work together as a single instrument, across 16km to get the aperture necessary to get even higher detail than the most detailed visible light and IR telescopes.

ALMA is the result of many millimeter/submillimeter wave projects coming together into one larger, more capable system. Many countries worked together and committed resources to create ALMA. As I write, ALMA is still in development. It is already producing amazing images that no other telescope in existence can make. If you're looking for a telescope that may steal Hubble's crown as the most talked about telescope, ALMA is a good bet. You can get in before the rush, and start spreading the word.

Future Telescopes

There are several more great telescopes on the near horizon, including the Giant Magellan Telescope and NASA's James Webb Space Telescope. Not to mention at least two other giant telescopes in the works.

Hubble will remain useful for as long as it continues to function. Originally, its retirement was planned to come about as a return to Earth via the Space Shuttle. That's not going to happen now, the present plan is to send up a robot spacecraft to guide it to a destructive re-entry. No matter how its life ends, its place in the history books is secure. What's important is to remember that it's not the only game in town.

Tuesday, August 13, 2013

The Sky and What You See in Astronomy

Seeing is the term astronomers use to describe the condition of the atmosphere and the things we look at in space when stargazing. The atmosphere over us is very active, changing from moment to moment. This is why we see the stars twinkle, and why we can see things with our eyes when we learn to see actively that we wouldn't see otherwise.

We live in the lowest part of the atmosphere, even those of us living at high altitude. Within that lower portion there are many layers that swirl and churn invisibly over our heads. That activity becomes visible when we look at light that passes through it, especially light that comes from a "point source", that is, a star.

Each of these layers has a different temperature. The temperature differences affect how they interact at the boundaries between layers. If you've ever seen a layered fluid, with each layer a different color, as you might get in a layered drink, this is similar to the layers in the atmosphere.

A layered cocktail in a glass.
Image courtesy of Morpheus1703
In the case of a drink in a glass, the layers are static. There's no wind, no forces pushing them one way or another. They lay quietly one on top of the other. In the atmosphere, however, the layers are constantly in motion. Heat radiating from the ground, accumulated from the daytime sunlight, rises from below. Winds blow. And each time that narrow line of light that we see coming from a star passes across the boundary between two layers, its straight line path is disturbed.

Refraction is the word for that disturbance. It's the same effect that we use in lenses to focus light. The ordinary type of telescope that people think of, that has a large lens facing the sky and a small lens near your eye is called a refractor telescope because it uses refraction to create its image. Its lenses are made of glass that doesn't change shape much, which refracts light by only so much--no more no less. The atmosphere, however, is like a lot of liquid lenses all flowing over and around each other, constantly changing shape and position.

Seeing is the word used in astronomy to describe how good or how bad the atmosphere is affecting the view of the sky outside the atmosphere. When we say the seeing is good, we're saying that the air is relatively still, the images are steady. When we say the seeing is bad, we're saying the turgid atmosphere is making it hard to see a clear image of the astronomical objects we're looking at.

Seeing can be different at different times of the night, of course. Once the ground has cooled hours after sunset after a sunny day, the seeing can improve dramatically. Or if the weather becomes still. The hours after midnight are the best for seeing in most places. But we can't all choose to engage in our hobby at that time if we have responsibilities in the morning.

The effects of seeing on a view of the Moon's surface, which appears to swim before our eyes in this animated image.
Image courtesy of Philipp Salzgeber
Fortunately, we have a built in solution. Our eyes have been built to actively adapt to differences in seeing conditions. Normally we use that without thinking about it when viewing normal terrestrial objects under varying conditions of lighting, at different distances, of different colors and materials. We learn to make out objects in shadow when we're standing in sunlight, see differences of texture where there's not much difference in color or lighting is low enough to hide detail. We adjust naturally between something held in our hands to objects in the distance. But many of these conditions don't exist when we're doing astronomy.

Everything is infinitely far away so far as our eyes are concerned, when we're doing astronomy. The difference between the Moon, at a mere quarter million miles or about four hundred thousand kilometers, and the Andromeda Galaxy, which is eighty trillion times further away than the Moon, is indistinguishable to our eyes. Everything might as well be equally far away. Our eyes can't distinguish details using the means that we normally use distance to give us cues when we're looking at things on Earth.

There is no apparent color for most things in space, with a few exceptions. At that, any color that does exist is pale and washed out by daytime standards. If we see color, it is usually more a matter of contrast between colors of objects that are near each other with significant differences.

We need to learn a new set of cues for actively seeing with our eyes for astronomy. It's not difficult, it just takes a little awareness and practice. Knowing what's happening is part of the solution. Aside from color and distance, we have to look hard to see many of the differences in lighting in astro objects, textures are subtle. Instead, we have to learn to use our eyes to "capture" images during moments of good seeing among the bad.

Relaxing the eye is key to capturing those moments of clarity. If we're straining to see, we're focusing entirely on the image we see now, trying to pick out detail. Instead, we need to relax and take our time, hanging over the eyepiece for a while, waiting for that moment of clarity to come.

The changing of the atmosphere can enhance as well as degrade the image we see, either with our eyes, or through the telescope. If we're waiting for that moment, relaxed, when it comes our eyes will "capture" those moments of superlative clarity. Sure, it's really happening in the brain, where all the image interpretation and processing is happening.

This is why the mount of the telescope becomes so important. It needs to be there for our eye, silently doing its job, keeping the telescope on the object we're viewing. We can't be stressing about the fact that the thing we're looking at is sliding out of view. We can't be using our built-in image processors to compensate for a wobbly, weak, or shaking mount--we want to save that capacity for dealing with the thing we can't do anything about, the cylinder of atmosphere that lies between the end of the telescope and the edge of outer space.

So, remember:
  1. You can get your eyes used to seeing with as much skill as night as during the day, but it'll be unfamiliar at first, and will take a little practice.
  2. You need to relax, and take your time at the eyepiece (even if there's a line of people waiting to look behind you. Take your moment and make it count. I guarantee, you're not going to be there as long as you fear you have been.
  3. The support for the instrument needs to be stable, reliable, and out of your mind when you're at the eyepiece.
  4. The atmosphere is going to do what it's going to do. Even if it is wild, and the image is bouncing around in the scope, there will still be occasional moments when the object you're viewing snaps into clarity. The difference between good seeing and bad is how long you have to wait for that to happen, and how long those moments of clarity last.

Image of the Moon during eclipse, with stars in the background of the image.
Your eyes can't tell that the stars are a few hundred million times as far away, except for Saturn to the lower left of the Moon, which is only 3,500 times as far away as the Moon.
Image courtesy of Ragesoss
We're lucky to live in a world like this. We don't need to have a view of space to live. Our atmosphere could support us perfectly well as we are, and have constant cloud cover over the entire planet. We could live in a world where the only things we're aware of in space are the Sun and the Moon, and those only as hazy lights in the clouds. Stars, planets, nebulas, and galaxies could all be completely abstract things to us in daily life. They'd be nothing more than scientific oddities, discovered by chance with the invention of radio. Instead, we have an atmosphere that allows us to look directly into the infinite when local conditions permit. We can see the wonders of the universe, the greatest physics laboratory ever, by just looking up. With simple, inexpensive instruments we can get views of these objects that bring their natural detail and beauty into our view.

A few objects show enough to even the unskilled eye to be magnificent. The Moon, Saturn, Jupiter. Other objects require a little more from us to meet them halfway. The Orion Nebula, Hercules Cluster, Andromeda Galaxy are relatively bright objects with details strong enough to enjoy easily, and there are several dozen more like them. Those object prepare us, and our eyes, for the next level. When we want more.

The good news is, that as your viewing skills increase, each dimmer, more subtle level of objects that you learn to appreciate has even more objects. From a handful of objects to a couple of dozen, we go to a few hundred. Once we have trained our eyes to appreciate those, objects such as the Black Eye Galaxy, M65 and M66, and the Little Dumbbell, we reach a point where there are not merely hundreds, but thousands of objects waiting for us to see them and appreciate their beauty. A lifetime pursuit opens up.

Many amateur astronomers specialize in a particular type of sight they seek, over the course of a season or for a few years. I myself spent a couple of years collecting new galaxies that I had seen. I shifted from that to globular clusters. First, in our own galaxy, then to those visible in other galaxies. Double stars and nebulas of particular types have also been among my "current interests" at different times of my life and under different sky conditions. The eruption of Mount Pinatubo in 1991, and the dust it put into the upper atmosphere, brought my galaxy-seeking to an end at that time, and for a few years afterward. That was when I shifted to globular clusters, which "shine through" the dust better than the faint details of a galaxy's halo.

That was also one of the times it struck me how lucky we are to have the sky that we have. Frustrating as it can be at times, our atmosphere is a wonderful thing, and our first gateway to the universe.
The night sky with stars viewed behind the silhouette of a tree bare of leaves.
Image courtesy of Michael J. Bennett

Friday, February 8, 2013

Planetary Nebulas

Planetary nebulas are one of my favorite objects in the sky to observe. The way they look, and the way they respond to magnification, make them unique among the different types of nebula.

The Owl Nebula, M-97
The Owl Nebula doesn't look so dramatic in my telescope as in this image, but it's still one of my favorite objects in the sky.

Nebulas, or, more properly, nebulae, are cloudy-looking objects in the sky. The word nebula is Latin for 'mist', 'cloud', or 'fog'. There are a lot of different types of things that look like a patch of cloud or fog in the sky. To give a brief list, there are reflection nebulas, emission nebulas, supernova remnants, and planetary nebulas. Each is different, and looks like a bit of cloud in a modest sized telescope. Even galaxies were once considered nebulas, before it was discovered how far away they are, and that they're made of stars like the Milky Way.

Planetary nebulas were given their name by William Herschel. He was trying to build a fairly comprehensive catalog of things in the night sky that aren't stars. He included a description of them in the Philosphical Transactions of the Royal Society, Volume 75 starting on page 263. You can read it, without pestering your local reference librarian, thanks to Google Books.

He chose the name because, though he knew they were nebulas, he also noticed that they tended to be somewhat round and that when magnified their brightness across their visible surface they tended to act like the illuminated disk of a planet, rather than like the other nebulas he had been observing. Sometimes it's implied that the name was given out of a mistaken sense that the objects have something to do with planets, but that's clearly not the case.

Stellar Remnants

Today, we know that planetary nebulas are made up of material that's been cast off a star when it goes from being a giant star (like a red giant) to being a white dwarf star. When this happens, the outer parts of the star that aren't involved in the nuclear reaction of the star (which happens at the core of a normal star) are blown off into space by bursts of energy from the core. The core collapses to form the white dwarf, the outer areas of the star, usually called the "atmosphere", though it's nothing like our atmosphere except that it happens to be the outer part of the star just as the atmosphere is outside the solid and liquid part of the Earth.

There are two basic types of planetary nebula, spherical and bipolar. The spherical ones appear to be stars that have blown off their atmosphere in a fairly uniform fashion.

Abell 39, a classic example of a spherical planetary nebula.
Abell 39 is a perfect example of a spherical planetary nebula.

Bipolar planetary nebulas are ones where the material appears to be spread into two halves on opposite sides of the original star. Usually, each side looks like a mirror of the other half. One of the mysteries of planetary nebulas is why this happens, and how some of these beautiful forms come into being.

The Dumbbell Nebula, M-27
One of the brightest bipolar nebulas in the sky, the Dumbbell Nebula.

The bipolar nebulas appear to take on a wide range of shapes. In some cases, probably in many of these cases, the nebulas themselves are the same shape as each other, but look very different when seen from different angles. Dr. Bruce Balick has a great web page on this that includes lots of other information about planetary nebulas.

Seeing Planetary Nebulas for Yourself

Many planetary nebulas are bright enough to be seen easily. A few can be seen by eye, but they don't look as spectacular that way. The Helix Nebula is the closest known planetary nebula, and it can be seen by eye about 1/3 of the size of the Moon (when I look at it, it actually looks closer to half the size of the Moon, but that's probably just an optical illusion.) But it's very dim, because its light is spread out over such a large area. It looks more like a slightly light patch of sky than like a nebula.

The Helix Nebula, a nearby planetary
The Helix Nebula is visible by eye but it's not this dramatic and colorful.

Binoculars do a great job of bringing it out and making it look brighter. You still won't see what the Hubble Telescope sees, but it will be worth your while.

A modest sized telescope will bring out detail in about another one or two dozen planetary nebulas in the sky. The Dumbbell, above, shows its "apple core" shape to even a small telescope at low magnifications.

The Future of Our Sun

Present thought is that our own sun will create a planetary nebula of its own in the far future, several billion years from now. First it will become a red giant by puffing up its outer parts, then the core will collapse and the outer gases will be blown off into the space around it.

I've heard mixed predictions of whether the resulting planetary nebula would be visible from within the solar system. Since the Earth will be destroyed during the red giant phase of the Sun, unless a future project relocates it somewhere to move it outside the space that the Sun will swell up into as a red giant, it'll be pretty much an academic question, anyway.

I recently gave a talk on Planetary Nebulas to the Nevada County Astronomers. You can see the slides from my talk on my website.

Monday, February 4, 2013

Dr. Stephen Robinson to Speak in Folsom, Feb 19

Dr. Stephen Robinson in a Shuttle cabin spacesuit

Astronaut Dr. Stephen Robinson will be speaking at Three Stages at Folsom Lake College on Tuesday, February 19th. He's the veteran of four flights on the Space Shuttle, including the Return to Flight mission of the Discovery, and one of the final missions in ISS assembly aboard the Endeavour.

He's logged over 48 days in space on those missions, and over 20 hours of time spent on space walks.

He's also somewhat of a "local", he completed his undergraduate work at UC Davis, and did his graduate study at Stanford.

I'm sure this will be a very interesting talk, and it's not every day we get an astronaut out this way to give a presentation, so I recommend you check it out!