Posted on by Amy Shira Teitel

Astronomers Find the Most Supermassive Black Holes Yet

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For years, astronomer Karl Gebhardt and graduate student Jeremy Murphy at The University of Texas at Austin have been hunting for black holes — the dense concentration of matter at the centre of galaxies. Earlier this year, they made a record-breaking discovery. They found a black hole weighing 6.7 billion times the mass of our Sun in the centre of the galaxy M87.

But now they shattered their own record. Combining new data from multiple observations, they’ve found not one but two supermassive black holes that each weigh as much as 10 billion Suns.

“They just keep getting bigger,” Gebhardt said.

An artist's impression of the black hole at the centre of the M87 galaxy. Image credit: Gemini Observatory/AURA illustration by Lynette Cook

Black holes are made of extremely densely packed matter. They produce such a strong gravitational field that even light cannot escape. Because they can’t be seen directly, astronomers find black holes by plotting the orbits of stars around these giant invisible masses. The shape and size of these stars’ orbits can determine the mass of the black hole.

Exploding stars called supernovae often leave behind black holes, but these only weigh as much as the single star. Black holes billions of times the mass of our Sun have grown to be so big. Most likely, an ordinary black hole consumed another, captured huge numbers of stars and the massive amount of gas that they contain, or be the result of two galaxies colliding. The larger the collision, the more massive the black hole.

The supermassive black holes Gebhardt and Murphy have found are at the centres of two galaxies more than 300 million light years from Earth. One weighing 9.7 billion solar masses is located in the elliptical galaxy NGC 3842, the brightest galaxy in the Leo cluster of galaxies 320 million light years away in the direction of the constellation Leo. The other is as large or larger and sits in the elliptical galaxy NGC 4889, the brightest galaxy in the Coma cluster about 336 million light years from Earth in the direction of the constellation Coma Berenices.

Each of these black holes has an event horizon — the point of no return where nothing, not even light can escape their gravity — 200 times larger than the orbit of Earth (or five times the orbit of Pluto). That’s a mind-boggling 29,929,600,000 kilometres or 18,597,391,235 miles. Beyond the event horizon, each has a gravitational influence that extends over 4,000 light years in every direction.

The illustration shows the relationship between the mass of a galaxy's central black hole and the mass of its central bulge. Recent discoveries of supermassive black holes may mean that the black holes in all nearby massive galaxies are more massive than we think. This could signal a change in our understanding of the relationship between a black hole and its surrounding galaxy. Image credit: Tim Jones/UT-Austin after K. Cordes & S. Brown (STScI)

For comparison, the black hole at the centre of our Milky Way Galaxy has an event horizon only one-fifth the orbit of Mercury — about 11,600,000 kilometres or 7,207,905 miles. These supermassive black holes are 2,500 times more massive than our own.

Gebhardt and Murphy found the supermassive black holes by combining data from multiple sources. Observations from the Gemini and Keck telescopes revealed the smallest, innermost parts of these galaxies while data from the George and Cynthia Mitchell Spectrograph on the 2.7-meter Harlan J. Smith Telescope revealed their largest, outmost regions.

Putting everything together to deduce the black holes’ mass was a challenge. “We needed computer simulations that can accommodate such huge changes in scale,” Gebhardt said. “This can only be done on a supercomputer.”

But the payoff doesn’t end with finding these massive galactic centre. The discovery has much more important implications. It “tells us something fundamental about how galaxies form” Gebhardt said.

These black holes could be the dark remnants of previously bright galaxies called quasars. The early universe was full of quasars, some thought to have been powered by black holes 10 billion Solar masses or more. Astronomers have been wondering where these supermassive galactic centres have since disappeared to.

Gebhardt and Murphy might have found a key piece in solving the mystery. Their two supermassive black holes might shed light on how black holes and their galaxies have interacted since the early universe. They may be a missing link between ancient quasars and modern supermassive black holes.

Source: McDonald Observatory Press Release.

Where Have All the Quasars Gone?

Posted on by Jon Voisey

Thankful Astronomer

The Milky Way from Earth. Image Credit: Kerry-Ann Lecky Hepburn (Weather and Sky Photography)

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Typically, I’ve been known as the Angry Astronomer. But since it’s Thanksgiving here in the US, I figured I should take a break and remind everyone that there’s a lot to be thankful for.

I’m thankful for our galaxy. Aside from being quite nice to look at, its collective (but weak) magnetic field, and the pressure from all the stars within it, protect us from the shock of plowing through the intergalactic medium as well as intergalactic cosmic rays.

I’m thankful for quantum mechanics. While it wasn’t the most fun course I’ve ever taken the fact that particles often behave as waves, giving rise to atomic orbitals, is what makes up the discreet absorption an emission spectra. Without this astronomers wouldn’t be able to determine the composition of stars from great distances.

I’m thankful for Newton’s third law; that one about equal and opposite forces and all that. It’s what lets the moon create tides. This may have had important effects in stabilizing our axial tilt and making life feasible on the planet in the first place. It’s also what allows us to detect planets around other stars through the “wobble method” and exoplanets are just cool.

I’m thankful for the immensely pristine vacuum that exists just beyond our atmosphere. Its existence allows astronomers to test theories at some of the lowest densities imaginable.

I’m thankful for neutron stars and black holes which allow astronomers to test theories at the highest densities imaginable.

I’m thankful for the supernovae which produce these objects and seed the universe with the heavy elements necessary to make planets, people, pineapples, and platypi.

I’m thankful that we’ve had the relatively close supernova (SN 1987a) to study. While I’d love to have another one in our own galaxy, I’m thankful we haven’t had one too close, or that directed a Gamma Ray Burst our way. With all the other issues we face from the universe, another Ordovician extinction just doesn’t sound too fun.

I’m thankful for dark matter. It may be a huge headache for astronomers trying to figure out what it is, but even if we can’t see it, it’s still like the Force: It binds the galaxies together.

I’m thankful for the Sun. Its nearly 1400 watts per square meter pours energy onto our planet, making all life possible, Creationist claims and ignorance aside.

I’m thankful for our atmosphere. It’s generally pretty breathable and it does a great job of blocking out that cancer causing UV. If only it would lighten up and let some more IR through so we didn’t have to send telescopes to space to study this region of the spectrum.

I’m thankful for this lump of rock, third from the Sun, we’re all riding on. It the grand scheme of things, it’s just a pale blue dot, but that’s home. And it’s not so bad.

So what is everyone else thankful for?

Posted on by Amy Shira Teitel

Do-It-Yourself Guide to Measuring the Moon’s Distance

The Moon. Photo credit: NASA.

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When the distance from the Earth to the Moon comes up, the common figure thrown around is 402,336 km (or 250,000 miles). But have you every wondered how astronomers got that figure? And how exact it really is? There are a couple of ways you can measure the distance of the Moon that don’t require lasers or any instruments. All you need are your eyes, a clear sky, and someone else willing to stand outside all night with you. 

There are two ways to measure the distance from the Earth to the Moon on your own: using a Lunar eclipse and using parallax. Let’s look at eclipses first.

The phases of a Lunar eclipse. Photo credit: Keith Burns for NASA/JPL

The Ancient Greeks used Lunar eclipses – the phenomena of the Earth passing directly between the sun and the Moon – to determine the distance from the Earth to its satellite. It’s a simple matter of tracking and timing how long it takes the Earth’s shadow to cross over the Moon.

Start with the few knowns. We know, as did the Ancient Greeks, that the Moon travels around the Earth at a constant speed – about 29 days per revolution. The diameter of the Earth is also known to be about 12,875 km or 8,000 miles.By tracking the movement of the Earth’s shadow across the Moon, Greek astronomers found that the Earth’s shadow was roughly 2.5 times the apparent size of the Moon and lasted roughly three hours from the first to last signs of the shadow.

From these measurements, it was simple geometry that allowed Aristarchus (c. 270 BC) to determined that the Moon was round 60 Earth radii away (about 386,243 km or 240,000 miles). This is quite close to the currently accepted figure of 60.3 radii.

You can follow Aristarchus’ method in your own backyard if you have a clear view of a Lunar eclipse. Track the movement of the Earth’s shadow on the Moon by drawing the changes and time the eclipse. Use your measurements to determine the Moon’s distance.

Lunar parallax: the moon as observed from Italy and China at the same time during a lunar eclipse. Photo credit: measurethemoon.org/wordpress

For the second method, you’ll need a friend to help out. The Ancient Greeks also knew about parallax, an object’s apparent change in position when seen from two different viewpoints. You can experience parallax by holding a pen out at arm’s length and looking at it with one eye at a time. As you switch between your left and right eye, the pen will appear to move back and forth.

The same thing can be seen on a giant scale. Two observers in different parts of the world (at least 3,200 km or 2,000 miles apart) will see the Moon’s position as different from where calculations say it should be in the night sky.

To find the distance of the Moon from the Earth, you and a friend stand 3,200 km apart and each take a picture of the Moon at exactly the same time. Then, compare your images. The Moon will be in a different spot, but the background stars will be in the same place. What your images have given you is a triangle. You know the base (the distance between you and your friend), and you can find the angle at the top (the point of the Moon in this triangle). Simple geometry will give you a value for the distance of the Moon.

It might be a little more labour intensive than searching the internet, but determining the Moon’s distance yourself is sure to be more fun! If you really want to get involved, check out International Measure the Moon Night on Dec. 10, 2011. Join participants around the world who register their own events and share their images and observations!

A graph showing which parts of the world have the best chance of measuring the moon's distance using these two methods. Regions in red can see full eclipses while regions covered in red bars are best suited to measurements using parallax. Photo credit: measurethemoon.org/wordpress
Posted on by Jason Major

Asteroid 2005 YU55: See It For Yourself!

Passage of of 2005 YU55 near Altair from 6:03 p.m. – 6:12 p.m. EST (11:03 – 11:12 UTC)

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It’s already been stated several times here on Universe Today that 2005 YU55, a 400-meter-wide roughly spherical asteroid, will not pose any threat to Earth as it passes by on Tuesday, November 8… even though it will come within 80% of the distance to the Moon. Many experts have come forward to state this fact, including Don Yeomans of JPL’s Near-Earth Object Observation Program and Lance Benner, a radio astronomer with the Deep Space Network in Goldstone, CA.  But it will still be a notable event, being the first time since 1976 such a large object will pass so closely by our planet. So, with the eve of YU55’s approach upon us, let’s turn our curiosity toward another aspect of this cosmic visitation: how can we see it?

Unfortunately there are a couple of factors working against the casual observer being able to witness YU55’s pass. One: it’s a dark object. A very dark object. 2005 YU55 is a C-type asteroid, which means it is composed of carbonaceous material and is thus effectively darker than coal, reflecting less than 1% of the sunlight that it receives. It probably won’t be brighter than magnitude 10. (On the backwards-ranked scale of apparent magnitude, 6 is the limit of best visibility to the average human eye, while -1 or 0 would be a very bright star. Jupiter is about -3 right now, while the full moon would be -12.7. In a typical suburban neighborhood 3 or 4 is the limit of naked-eye visibility.)

And two: the Moon will be close to full on the night of the 8th, and YU55 will be headed in its direction. That sure won’t help visibility.

But, should you be located in a dark area, and should you have a 6″ or larger telescope at your disposal, you may want to give a go at spotting the asteroid that’s caused quite a fuss over the past few months for yourself. It won’t be a simple task, but it’s not impossible – and to help you out teacher, writer and astronomy enthusiast David Dickinson has posted an article about it on his blog, Astro Guyz.

Here’s an exerpt:

Closest approach to Earth occurs at 11:29 UTC/06:29 EST at about 202,000 miles distant, placing it high to the southwest for observers on the US Eastern Seaboard. At its closest approach, 2005 YU55 will glide along at one degree every 7 minutes, easily noticeable after a few minutes of observation at low power. I plan to target selected areas with my GOTO mount, sketch the field, then watch for changes. I may also take some wide-field piggyback stills with the DSLR, but mostly, this one will just be fun to watch.

Visually tracking a Near-Earth asteroid can be thrilling to watch; for example, I’ve actually seen 4179 Toutatis years ago show discernable movement after tracking it for a few moments in the eyepiece!

– David Dickinson

Wide field finder of 2005 YU55 from sunset until 8:30PM EST.

The asteroid will pass through the constellations Aquila, Delphinus, and Pegasus as it heads westward. Interestingly, 2005 YU55 passes within a degree of Altair centered on 6:07:30PM EST only 27 minutes after local sunset, and also makes a very close pass of the star Epsilon Delphini during closest approach. These both make good visual “anchors” to aim your scope at during the appointed time and watch. Keep in mind, the charts provided are rough and “Tampa Bay-centric…”

On an approach as close as this one, two factors muddle the precise prediction coordinates of the asteroid; one is the fact the gravitational field of the Earth will change the orbit of 2005 YU55 slightly, and two is that the position will change due to the position of the observer on the Earth and the effect of parallactic shift. Many prediction programs assume the Earthly vantage as a mere point in space, fine for positioning deep sky objects but not so hot for ones passing near the planet. A good place to get updated coordinates is JPL Horizons website which lets you generate an accurate ephemeris for your exact longitude latitude and elevation.

David goes on to add:

2005 YU55 will pass our Moon at 8 AM Universal Time on November 9th at a distance only marginally closer than it did the Earth, at 140,000 miles. Interestingly, it also transited Sun on November 3rd as seen from the Moon, but would have appeared <1” in size, a tough target for any would-be lunar-based observer. Its next close predicted passage of the Earth won’t be until 2056 at nearly 3 times the distance.

__________

Excellent information… many thanks to David for sharing with us! (You can read the full article on his website here.) And if you do witness the pass of this asteroid and somehow manage to get some photos of it, you can share them on the Universe Today Flickr group… they may be featured in an upcoming article!

Read more about 2005 YU55’s close pass by Earth tomorrow.

Charts and excerpts by David Dickinson, created with Starry Night and Paint.

 

Posted on by Ray Sanders

World Space Week ( Oct 4th – 10th ) — Join the Fun!

World Space Week - October 4th - 10th, 2011. Image Credit: World Space Week Association

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What is World Space Week?

Founded in 1981, World Space Week Association is one of the world’s oldest space education organizations. As a partner of the United Nations in the global coordination of World Space Week, WSWA recruits and supports a worldwide network of coordinators and participants. WSWA is a non-government, nonprofit, international organization, based in the United States.

World Space Week is an international celebration of science and technology, and how each benefits the human condition. In 1999 The United Nations General Assembly declared that World Space Week will be held each year from October 4-10, commemorating two notable space-related events:

The annual kick-off date of October 4th corresponds with the October 4th 1957 launch of the first human-made Earth satellite, Sputnik 1.

The end date of October 10th corresponds with the October 10th 1967 signing of the Treaty on Principles Governing the Activites of States in the Exploration and Peaceful Uses of Outer Space, including the Moon and Other Celestial Bodies.

Here’s some information from their F.A.Q on how you can participate in World Space Week, either by volunteering or by attending an event.

Where and how is World Space Week celebrated?

World Space Week is open to everyone – government agencies, industry, non-profit organizations, teachers, or even individuals can organize events to celebrate space. WSW is coordinated by the United Nations with the support of WSWA and local coordinators in many countries.

What are the benefits of World Space Week?

WSW educates people around the world about the benefits they receive from space and encourages greater use of space for sustainable economic development. WSW also demonstrates public support for space programs and excites children about learning and their future.
Some of the other benefits include promoting institutions around the world that are involved in space and fostering a sense of international cooperation in space outreach and education.

How can schools participate?

This event is ideal for teachers to promote student interest in science and math. To encourage participation, World Space Week Association gives various educational awards each year.

Sign at NASA's Johnson Space Center announcing World Space Week. Photo Credit: NASA/WSWA

What can I do for World Space Week?

If you’d like to become involved with WSW you can:

  • Volunteer for World Space Week Association
  • Organize an event directly
  • Help expand and coordinate World Space Week
  • Encourage teachers and students to do space-related activities
  • Become a Volunteer
  • Hold an Event During World Space Week

    • If you hold an event, be sure to add your event to the World Space Week calendar and tell the media and your regional WSW coordinator about your planned event. You can also order World Space Week posters and display them in your community.

    If you’d like to find a World Space Week event in your area, visit:http://www.worldspaceweek.org/calendar_2011.php

    You can learn more about World Space Week at: http://www.worldspaceweek.org

    Source: World Space Week Association

    Posted on by Nancy Atkinson

    ALMA Opens Her Eyes — With Stunning Results

    ALMA's first light: a view of the Antennae Galaxies. Credit: ESO

    There’s a new telescope in town that just opened up for business. It’s the long awaited ALMA, the Atacama Large Millimeter/submillimeter Array. Although it is still under construction, the science teams have released the first “early science” image, showing a pair of interacting galaxies called the Antenna Galaxies. ALMA’s view reveals a part of the Universe that just can’t be seen by visible-light and infrared telescopes. “From the formation of the first galaxies, stars, and planets to the merging of the first complex molecules, the science of ALMA is a vast spectrum of investigation,” said Tania Burchell, the ALMA Public Information Officer at the National Radio Astronomy Observatory, on today’s 365 Days of Astronomy podcast.

    A composite image combining images of the Antenna Galaxies from ALMA and the Hubble Space Telescope. Credit: ESO, Space Science Institute

    Currently, about one third of ALMA’s eventual 66 radio antennas are built and operational. The antennas are positioned just 125 meters apart on the Chajnantor plateau in northern Chile. This extremely dry and high desert sits over 5,000 meters (16,500) feet above sea level. This puts ALMA higher than any other telescope array on Earth. At this elevation, the temperatures hover around freezing all year round, and the air pressure is half that at sea level. Cold temperatures combined with little air is perfect for telescopes like ALMA.

    “Even in this very early phase ALMA already outperforms all other submillimetre arrays,” said Tim de Zeeuw, Director General of ESO, the European partner in ALMA. “Reaching this milestone is a tribute to the impressive efforts of the many scientists and engineers in the ALMA partner regions around the world who made it possible.”

    Historically, collecting, focusing, and imaging millimeter and submillimeter waves has been very tricky, Burchell said.

    “These waves are so large that mirrors cannot focus them, and their frequencies are too high for off-the-shelf receiver technologies to process,” said said. “The warmth of a telescope’s own electronics is enough to ruin the weak cosmic mm signals that, by the time they reach us, sputter in at about a billionth of a billionth the power of a cell phone call. And as an added torment, humidity itself broadcasts at these frequencies, turning most skies into a glare of millemeter/submillimeter light.”

    But ALMA is radically different from visible-light and infrared telescopes. It is an array of linked antennas acting as a single giant telescope, and it detects much longer wavelengths than those of visible light. Its images therefore look quite unlike more familiar pictures of the cosmos.

    Compare images of the Antenna Galaxies, from ALMA and the Very Large Telescope:

    A comparison of the views of the Antenna Galaxies, from ALMA and the VLT. Credit: ESO.

    ALMA’s view reveals the clouds of dense cold gas from which new stars form. This is the best submillimeter-wavelength image ever made of the Antennae Galaxies.

    Massive concentrations of gas are found not only in the hearts of the two galaxies but also in the chaotic region where they are colliding. Here, the total amount of gas is billions of times the mass of our Sun — a rich reservoir of material for future generations of stars. Observations like these open a new window on the submillimetre Universe and will be vital in helping us understand how galaxy collisions can trigger the birth of new stars. This is just one example of how ALMA reveals parts of the Universe that cannot be seen with visible-light and infrared telescopes.

    Learn more about AlMA in this video:

    ALMA Opens Its Eyes

    Sources: ESO, 365 Days of Astronomy, NRAO

    Posted on by Nancy Atkinson

    How to See a Supernova From Your Backyard This Weekend

    The timing couldn’t be better. A new supernova, named PTF11kly, which was discovered on August. 24, 2011 is continuing to brighten and should be visible to backyard astronomers this weekend using just a pair of binoculars. It’s not quite naked-eye material but this is an exciting opportunity for amateurs (as well as the pros!) to view a supernova first-hand. Of course, if your backyard is full of light, the best option is to go to an area with darker skies, and you’ll be able to see it much better. Astronomers say PTF11kly will likely continue to shine for some time, and be at its brightest on about Sept. 9, 2011.

    In this video Peter Nugent, an astrophysicist from Lawrence Berkeley National Labs explains just how to find this star that exploded about 21 million light years away.

    Posted on by Jason Major

    Finding Phobos: Discovery of a Martian Moon

    Phobos, one of the two natural satellites of Mars silhouetted against the Martian surface. Credit: ISRO
    Mars Express images of Phobos from January 9, 2011 flyby

    If someone were to ask you when fear was first discovered, you could tell them August 11, 1877. That’s when, 134 years ago today, Asaph Hall identified Phobos, the larger of Mars’ two moons. But even though it’s named after the Greek god of fear, there’s nothing to be afraid of…

    Continue reading “Finding Phobos: Discovery of a Martian Moon”

    Posted on by Nancy Atkinson

    Now Available: 30 Free Lectures by Noted Astronomers

    We just received a note from Andrew Franknoi and the Astronomical Society of the Pacific that they are making available, free of charge, 30 audio and video podcasts from talks given by distinguished astronomers on the latest ideas and discoveries in the field. Speakers include:

    * Frank Drake, who began the experimental search for intelligent life among the stars,
    * Mike Brown, who discovered most of the dwarf planets beyond Pluto (and whose humorous talk is entitled “How I Killed Pluto and Why it Had it Coming”),
    * Natalie Batalha, project scientists on the Kepler Mission to find Earths around other stars,
    * Alex Filippenko (national professor of the year) on finding black holes.

    Recent topics added to the offerings include: multiple universes, Saturn’s moon Titan (with an atmosphere, rivers, and lakes), our explosive Sun, and whether we should expect doomsday in 2012.

    The talks are part of the Silicon Valley Astronomy Lectures, jointly sponsored by NASA’s Ames Research Center, the Astronomical Society of the Pacific, the SETI Institute, and Foothill College.
    They are available via the web and ITunes. For a complete list and to begin listening, go to:
    http://www.astrosociety.org/education/podcast/

    Posted on by Matt Williams

    What are Active Optics?

    Active Optics
    Keck Telescope

    For astronomers and physicists alike, the depths of space are a treasure trove that may provide us with the answers to some of the most profound questions of existence. Where we come from, how we came to be, how it all began, etc. However, observing deep space presents its share of challenges, not the least of which is visual accuracy.

    In this case, scientists use what is known as Active Optics in order to compensate for external influences. The technique was first developed during the 1980s and relied on actively shaping a telescope’s mirrors to prevent deformation. This is necessary with telescopes that are in excess of 8 meters in diameter and have segmented mirrors.

    Definition:

    The name Active Optics refers to a system that keeps a mirror (usually the primary) in its optimal shape against all environmental factors. The technique corrects for distortion factors, such as gravity (at different telescope inclinations), wind, temperature changes, telescope axis deformation, and others.

    The twin Keck telescopes shooting their laser guide stars into the heart of the Milky Way on a beautifully clear night on the summit on Mauna Kea. Credit: keckobservatory.org/Ethan Tweedie
    The twin Keck telescopes shooting their laser guide stars into the heart of the Milky Way on a beautifully clear night on the summit on Mauna Kea. Credit: keckobservatory.org/Ethan

    Adaptive Optics actively shapes a telescope’s mirrors to prevent deformation due to external influences (like wind, temperature, and mechanical stress) while keeping the telescope actively still and in its optimal shape. The technique has allowed for the construction of 8-meter telescopes and those with segmented mirrors.

    Use in Astronomy:

    Historically, a telescope’s mirrors have had to be very thick to hold their shape and to ensure accurate observations as they searched across the sky. However, this soon became unfeasible as the size and weight requirements became impractical. New generations of telescopes built since the 1980s have relied on very thin mirrors instead.

    But since these were too thin to keep themselves in the correct shape, two methods were introduced to compensate. One was the use of actuators which would hold the mirrors rigid and in an optimal shape, the other was the use of small, segmented mirrors which would prevent most of the gravitational distortion that occur in large, thick mirrors.

    This technique is used by the largest telescopes that have been built in the last decade. This includes the Keck Telescopes (Hawaii), the Nordic Optical Telescope (Canary Islands), the New Technology Telescope (Chile), and the Telescopio Nazionale Galileo (Canary Islands), among others.

    The New Technology Telescope (NTT) pioneered the Active Optics. Credit: ESO/C.Madsen. Bacon
    The New Technology Telescope (NTT) pioneered the Active Optics. Credit: ESO/C.Madsen. Bacon

    Other Applications:

    In addition to astronomy, Active Optics is used for a number of other purposes as well. These include laser set-ups, where lenses and mirrors are used to steer the course of a focused beam. Interferometers, devices which are used to emit interfering electromagnetic waves, also relies on Active Optics.

    These interferometers are used for the purposes of astronomy, quantum mechanics, nuclear physics, fiber optics, and other fields of scientific research. Active optics are also being investigated for use in X-ray imaging, where actively deformable grazing incidence mirrors would be employed.

    Adaptive Optics:

    Active Optics are not to be confused with Adaptive Optics, a technique that operates on a much shorter timescale to compensate for atmospheric effects. The influences that active optics compensate for (temperature, gravity) are intrinsically slower and have a larger amplitude in aberration.

    . Credit: ESO/L. Calçada/N. Risinger
    Artist’s impression of the European Extremly Large Telescope deploying lasers for adaptive optics. Credit: ESO/L. Calçada/N. Risinger

    On the other hand, Adaptive Optics corrects for atmospheric distortions that affect the image. These corrections need to be much faster, but also have smaller amplitude. Because of this, adaptive optics uses smaller corrective mirrors (often the second, third or fourth mirror in a telescope).

    We have written many articles about optics for Universe Today. Here’s The Photon Sieve Could Revolutionize Optics, What did Galileo Invent?, What did Isaac Newton Invent?, What are the Biggest Telescopes in the World?

    We’ve also recorded an entire episode of Astronomy Cast all about Adaptive Optics. Listen here, Episode 89: Adaptive Optics, Episode 133: Optical Astronomy, and Episode 380: The Limits of Optics.

    Sources: