Can I See the Stars?

Clear skies are essential for astronomers, but depending on where you live they may be few and far between. If you want to do some star gazing, but aren't sure if the weather will cooperate, take a look at the clear sky clock (http://cleardarksky.com/csk/). All you need to do is click "find a chart" and enter your location (or chose a state then city). What you'll see is a chart telling you all sorts of weather predictions, but the most important one is the cloud cover. Above is a clear sky chart for Kitt Peak, AZ, and you want to look at the top row of boxes to see if the sky will be clear. The color of the box at a given time tells you if there will be clouds in the sky (white), or if the sky will be clear (dark blue). So it looks like the sky will be cloudy before midnight Saturday, and then crystal clear the next day and a half. Below the chart there will be a description of how to read the chart and what the colors correspond to exactly. The chart is usually very accurate and astronomers use it all the time while observing. So the next time you want to go to a local star party, but aren’t sure if you should bother going because it might be cloudy, take a look at the clear sky chart before you head out.

Department Store Telescopes

Have you been looking up at the stars recently and thought about purchasing your own backyard telescope? Have your kids put telescope on their holiday wish list? Do you want to learn how to take photos of astronomical objects? If you answered yes to any of the above questions, then I have one piece of advice for you: don't buy a department store telescope! Yes they are inexpensive and promise to show you beautiful images of the moon and planets, but they are more hassle than they are worth. I've had many friends and family members purchase these telescopes, struggle with their kids for hours in the back yard trying to see something with it, only to package it up the next day and toss it or re-sell it. Why are these telescopes so "bad"? Well, bad is really a poor choice of words. They are usually refracting telescopes designed to look at large bright objects, and they do a good job of that. One of the main complaints I get from people is that the images look blurry, so they try to magnify the image by inserting a higher magnification eyepiece, in hopes of getting a clearer view. What they don't realize is that magnification only blurs the image more. Theses telescope are small (usually a few inches wide) and only collect so much light. Magnifying that light is not going to make things more clear or brighter, its going to enlarge a small dim region, and likely make it look darker than before. The image you see will never look like the one on the box, guaranteed. The second complaint I hear is that they are difficult to "point", as in, even if you think you have it aimed at the moon, you can't see anything. This is a problem with all small, non-computerized telescopes, and can get really frustrating really quickly. My best advice here is to be patient and try to learn your way around the sky. Point the telescope towards the moon and practice lining it up by looking at the stars with your eyes, then through the telescope, and adjusting as necessary. Practice makes perfect with this. Lastly, you must remember that we live on a moving rotating sphere, and therefore, when you point your telescope at an object, it will only stay in your field of view for a short time before you have to readjust. This is true for all telescopes, unless you have one that "tracks".

So, I very much encourage you to buy a backyard telescope, and I don't want a bad experience with a cheap scope to detour your love of astronomy! You can still acquire an excellent, easy to use telescope for a few hundred dollars. Check out websites like http://www.celestron.com/ and http://www.meade.com/ and do your research! Ask friends in a local astronomy club what they suggest, or attend a telescope buying seminar. Often, local museums will offer workshops on how to purchase and operate basic telescopes for the beginner. Check these out, avoid the department store telescopes, and I promise you will love your new investment. Clear Skies!

Stars in Spiral Galaxies

Spiral Galaxy M74

When most of us think of a galaxy we think of a beautiful spiral shaped entity. Astronomers have been studying these spiral galaxies for quite some time now, and have noticed that most of the stars seem be located within the arms. To form a star, you need a giant cloud of molecular hydrogen, and other gaseous materials. The cloud will eventually collapse due to gravity and form stars, and some of those stars may even host planetary systems. Most of the material in a galaxy (gas, dust, rocks, etc.) sits in the spiral arms in the plane of the galaxy. So it makes sense that stars tend to form here; it’s where all the stuff is!  Because the spiral arms contain millions of stars, they glow very brightly in optical light. This allows Hubble, and other telescopes, to image the structure of the galaxy. M74, pictured above, is a perfect example of a spiral galaxy whose structure is illuminated by the light from many stars within its spiral arms.

Image Credit: NASA, ESA, Hubble Heritage(STScI/AURA)-ESA/Hubble Collaboration 

Curiosity Self Portraits

I'm sure many of you heard about the Mars Science Laboratory: Curiosity in the news back in August. The rover successfully survived the trip and descent to Mars, landing safely in the early morning hours on August 6th (EST). Much of the scientific community was fretting about Curiosity surviving the landing due to all of the creative engineering maneuvers that needed to go of without a hitch for the rover to survive. Thankfully everything went smoothly and we are now beginning to study the Martian surface! A young girl, who has seen many of the photos the rover has taken, asked me why it keeps taking self portraits. "Why not point the camera at the Martian surface?" she asked. "We already know what the rover looks like. It's almost like he's taking a picture of himself for Facebook!"  There is good reason for Curiosity to take pictures of itself, and that is to make sure that everything is functioning properly. We want to make sure that nothing broke during Curiosity's trip, and we also need to make sure that camera, levers, wheels, etc. are all working as they should. Once we trust that everything is working properly, we can start to move the rover and do experiments. So we expect to see many more close ups of Curiosity on Mars, just as a sort of "check-up". Below is an image of almost the entire rover sitting on the Martian surface. Everything looks good to me!

Image credit: NASA/JPL-Caltech

Is Today Affecting Yesterday?

I came across an article this morning, that’s more about quantum physics than astronomy, but it was so fascinating that I just had to share it with you all. Physicists may have discovered a way that the future can alter the past! Yup, you read that right, what you do today could affect what you did yesterday! How can this happen? Quantum physicists are studying the ideas of non-locality and causality. Non-locality is the idea that two particles can be entangled such that an action on one automatically affects the actions of another. Kind of like two train carts tied together, if I move one the other moves as well. Causality is the idea that tiny particles exist with unknown properties until someone makes a measurement of one of those properties, and these measurements can be strong (I know for sure this is true about the particle) or weak (I think this might be true).

For example, lets say you glance super quickly at an unknown street sign, then look away. You might notice that the sign had a reddish color to it (weak measurement). You look quickly again, and notice there is also some white (weak measurement). Repeat the process and eventually you might figure out that you are looking at a stop sign. Then you stare directly at it for a few seconds (strong measurement) and for sure decide that it is a stop sign. The idea of causality states that the street sign’s properties are unknown (what type of sign is it?) and the signs location is unknown (where is it?) until you look at it and decide it’s a certain one in a certain spot. So how can observing an object properties today affect it yesterday? Try this thought experiment below

A friend and I live in Upstate New York, and we live 50 miles apart. You don’t know where exactly we live, but only that our houses are 50 miles apart and that our bodies are always 50 miles apart no matter what (we are entangles that way). Now you decide you want to figure out where I currently am. You can’t do this by calling or asking me, you have to put tiny bits of information together to figure out where I am (weak measurements). Ok, so you know that I just posted this blog, and therefore, I must be somewhere where there is wifi. You just made one tiny measurement of where I am, without defining exactly where I am. There are tons of place with wifi, so I could be at any one of those places. Measurement number 2, again I’m writing this blog post , so I must be at a computer (for the sake of argument, lets assume it must be a desktop computer). So now, with two measurements, you’ve narrowed down where I am (somewhere with wifi and a desktop computer), but still don’t know exactly where I am. Let’s pretend you were able to make a whole bunch of other measurements and finally figure out that I am at the local library, 10 miles from my house. Now that you’ve made a solid measurement of where I am, you have fixed me in place, and thus fixed my friend in a place exactly 50 miles away from me. Since I am 10 miles from my house, my friend must also be 10 miles from her house (because we are always 50 miles apart). But how did she get there? Sometime in the past, she must have drove from her house, to a point 10 miles away from her house. But we didn’t know or decide that she was 10 miles from home until we figured out where I was located, just now. The act of deciding that I am 10 miles from my house right now, put my friend 10 miles from her house, and thus altered the past in such a way that caused her to drive 10 miles away from her house sometime in the past. So my action of being at the library today, had an affect on what my friend did in the past, or in other words, the future (today or tomorrows actions) had an affect on what happened yesterday!

So what does this all mean? Are your actions today changing the past? Well, physicists aren’t really sure. They think they see this occurring for special particles that are entangled together and have certain kinds of properties. It doesn’t necessarily work on a human scale. But if we understand what’s going on in the quantum world, we may someday be able to use it in the “real” world…

Here is a link to a nice article explaining this in more detail: http://physicsworld.com/cws/article/news/2012/aug/03/can-the-future-affect-the-past

Discovery of the Higgs Boson!

Back on July 4th of this year, physicists working at the Large Hadron Collider (LHC) at CERN announced that they may have a found the much sought after particle called the Higgs Boson. One of the main reasons scientists built the LHC was to look for and hopefully find evidence of the Higgs. But what exactly is the Higgs boson and why is it so important?

To put it simply, the Higgs boson and the accompanying Higgs field are the reason why objects have mass, or in other words, why we take up space. For example, an astronaut in outerspace weighs nothing, as no large body is gravitationally attracting him. But the astronaut still has mass, he still takes up space. But what entity gives him mass, since it's not gravity that is responsible.  The theoretical answer to this is the Higgs field. Physicists think that a Higgs field pervades all of empty space, and Higgs bosons fill this field. When a particle enters the Higgs field, the Higgs bosons crowd around it, making it difficult for the particle to move and thus it feels heavy or massive. Think of it like a celebrity walking into a party. Everyone at the party crowds around the celebrity, making it hard for them to move through the room and thus they feel more massive. The Higgs field interacts with different types of particles in different ways, and the reason for this is not very well understood. But, if we have evidence that the Higgs boson does exist, then we can study it and hopefully answer this and many other questions associated with its discovery!

For a great explanation of the Higgs boson, check out this Ph. D. Comics movie!

Image Credit: Ph.D. Comics

Asteroid Eros as Real Estate?

Eros

Since the only other astronomical body that humans have set foot on is the moon, few laws have been put into place governing who can own what in outer space. Believe it or not, people have tried to claim full ownership of astronomical objects. A man by the name of George W. Nemitz actually tried to claim the near-Earth asteroid Eros as his property! Here's the story: Nemitz worked for a company which helped construct the Near-Earth Asteroid Rendezvous Probe Shoemaker, which landed on Eros in 2000. Nemitz claimed that since he helped build the spacecraft, he could claim ownership of whatever body it landed on, under the Homestead Principle. This principle states that if you discover a new piece of land that is not owned by another person or government (and I'm sure law makers were implying a piece of land on Earth), and you make use of it in some way, you can claim ownership. Thus, Nemitz dubbed Eros as a "spacecraft parking facility" and mailed NASA a $20 parking ticket for landing their spacecraft on "his" asteroid! Can you believe that? To Nemitz's dismay, NASA refused to pay the parking ticket, and a court judge dismissed his case. 

Image Credit:NEAR PRoject, NLR, JHUAPL, Goddard SVS, NASA

How Big is the Universe?

To put it bluntly, the universe is absolutely huge! The study of Cosmology, or how the universe was created and how it has evolved, has revealed some very interesting facts. We now know that the universe is expanding at an increasing rate, and that the universe seems to be roughly uniform. The approximate size of the visible universe is 10^24 miles wide! That's 1,000,000,000,000,000,000,000,000 miles! The image below represents what we believe the universe looks like. Every white spec in the image represents a galaxy, and there are over 350 billion of them! But notice how uniform it looks; there doesn't appear to be any distinct clumps of matter, its all equally spread out. This is somewhat expected  via the current cosmological theories, but also curious. Why should the universe be uniform? What properties of the beginning of the universe lead to this result, and how precise must they have been produce a uniform universe? Cosmologists are working hard on answering these questions, as astronomers continue to probe the most distant parts of the universe!

 Image credit: atlasoftheuniverse.com

Galaxy Superclusters

We live in the Milky Way Galaxy, a beautiful spiral armed galaxy filled with hot gas and young stars.

Did you know that many galaxies, including the Milky Way, actually formed in clusters? Galaxy clusters are groups of 30 or more galaxies that are all gravitationally bound to each other. Galaxy clusters nearby one another can form a supercluster of galaxies, though they may not all be gravitationally bound, just spatially coincident with each other. The Milky Way is part of the Local Group, which contains roughly 40 galaxies. This group is a sub-portion of the Virgo supercluster, which contains over 2500 galaxies within 100 million light years of us! These clusters contain spiral galaxies, like the Milky Way, but also elliptical galaxies which are disk shaped collections of older stars. Some popular clusters you may have heard of are the Fornax cluster, which also lies inside the Virgo supercluster, and the Coma cluster, which is a separate cluster of over 1000 galaxies located over 300 million light years from us. The image above shows some of the superclusters of galaxies in the Universe, with the Virgo cluster at the center. Each white dot is an entire galaxy, so those white regions throughout the image are collections of hundreds of galaxies! 

Image Credit: R. Powell

What Does An Astrophysicist Do?

Apologies for the hiatus in posts these last few weeks, life and work have been very busy. Since I've been swamped with so much work, I thought I'd take the time in this post to describe what  an astronomer or astrophysicist does on a daily basis.

When you think of life as an astronomer, the first thing that comes to mind is telescopes and star parties. You imagine the scientists out late at night staring through their telescopes and taking notes about what they see. While this part of the job, astronomers have much more to do. Graduate students and professors in astronomy spend most of their time teaching, doing research and applying for grant money. They teach or assistant teach college courses, and are constantly writing proposals to different organizations asking for money to fund their research. But what does "doing research" actually mean? In astronomy, research can mean one of three things: taking images with a telescope  and analyzing them using a computer (observational astronomy), writing computer programs to simulate interactions between objects in outer space (theoretical astronomy), or building telescopes, cameras, and detectors for astronomers to use (instrumentation). The first two require you to sit at a computer most of the day and  write computer programs to perform certain tasks. Observational astronomers also spend a lot of time applying for observation time on both space and ground based telescopes. If their proposals are accepted, they receive images from the telescope that they can then analyze to understand the physics and properties of the objects they are looking at. Theoretical astronomers are more like physicists or mathematicians.  They think of a situation that might occur in outer space, write down all of the physics equations  that govern the system, and write computer programs to simulate what's going on. Then they can compare their results with real observations to see if they are correct! The last group of astronomers spend most of their time in labs, building and testing devices for other astronomers to use. This is a more hands on job, and takes just as much engineering skill as it does astronomy knowledge. If it weren't for these people building nice cameras and telescopes, astronomers would be out of a job!

Aside from doing actual science, astronomers spend a good amount of time writing papers about their findings, doing community outreach, and presenting their work at conferences and colleges around the world. Being an astronomer is a lot of work, but also a lot of fun. It's a fast paced and never ending job, and there is always more to learn about outer space!

How Old is that Star?

Determining the age of a star is not as easy as you might think. Since we can't ask a star how old it is, we have to guess the stars age by its appearance. And just like with humans sometimes looks can be deceiving! 

 

There are many ways to determine the age of a star, and today we will discuss stellar models. Like we've discussed before, stars can be placed on an Hertzsprung-Russel (HR) diagram. To do this, you need to measure the stars brightness, or luminosity, and you also need to know what type of star it is. Is it a big, hot blue star,? A cool, small, red? Somewhere in between? Astronomers can determine this by looking at a star's spectrum, or distribution of light, with a telescope. Once we know these two things, we can place the star at the proper position on the HR diagram. Astronomers have been hard at work modeling how stars form, and how their size, temperature, and brightness changes as they age. They have developed paths or lines that are placed on the HR diagram which show a stars path on the graph as it ages. There are models for before the star has reached the main sequence, and after. Basically what you do, is place the star on the HR diagram, see which line it is closest too, and that tells you the stars size and age. Here is an example of how this works. The graph above shows brightness vs. temperature, and models (solid lines) for stars of different masses. Stars, in theory, follow one solid line path going right to  left as it ages. The star represents the spot on the diagram where some arbitrary star's properties are. Based on its position, the star is probably about 4 times the mass of the sun, and about 200,000 years old! This is before it has started hydrogen burning, and is still a "baby" star. You can follow the same method with different models and estimate the age of a star that is burning hydrogen, or on its way towards death.

Discovery of Uranus' Rings

We have discussed before that all the gas planets in the solar system have rings.  Even through a small telescope Saturn has visible rings, but Jupiter, Uranus and Neptune do not. So how did astronomers discover their rings in the first place?

Hubble image of Uranus and its rings

The rings around Uranus were discovered in 1977. Astronomers knew that Uranus was going pass in front of a distant star in the night sky, from Earth's perspective. They pointed their telescopes to towards the planet each night, and expected to see the planet block the light from the star only when the star was directly behind the planet. What they actually observed was the star flickering right before and right after is passed behind the planet. This meant that there must be some unseen object near the planet blocking the starlight! The only plausible explanation was that Uranus has very thin, dim rings that are not visible from telescopes here on Earth. In 1986, Voyager flew by Uranus and imaged the rings for the first time, proving  their existence. Since then, we have discovered rings around Jupiter and Neptune in similar ways.

NASA Missions Extended

 

Artists conception of Spitzer, Planck and Kepler (left to right)

Astronomers received some great news a few days ago. Three major space telescopes, Kepler, Spitzer and Planck, have had their missions extended! This is great news, as astronomers will obtain more data and hopefully make some big discoveries! But what can we do with these telescopes?

The Kepler Space Telescope is an optical telescope has been actively searching for exoplanets. It looks at the same region of the sky 24/7, and measures the brightness of 150,000+ stars. If one of them dims for a short period of time, it might be due to a planet crossing in front of the star and blocking the light. Kepler has already found over 2000 potential exoplanets in the last 2.5 years of operation, and it's funding has been extended until 2016

The Spitzer Space Telescope is an infrared telescope that has been operating since 2004. For the telescope's detector to work properly, it needs to be kept extremely cold. Unfortunately, the cryogenics which keep it cool have run out, but the detector still functions, and some science can be done with the telescope. Astronomers have used Spitzer to look at young stars, distant galaxies, and many other objects that are "hidden" behind giant clouds of gas.  It will continue to operate for another two years.

Planck is a jointly funded NASA and ESA telescope which has been operational for about three years. It's a space based microwave/radio telescope whose main purpose is the study the cosmic microwave background. This is the first light emitted by the universe after the Big Bang. It will help us understand how the universe began by observing it right after it was born. Astronomers also use Planck to study distant galaxies, and objects in our solar system.

Image Credit:  NASA/JPL-Caltech

Finding the Planets

Today, we take a more observational approach to our astronomy lesson which will require you to go outside tonight and look at the stars. If  you've taken a look at the sky lately, you might have noticed a few extra bright objects up there. These bright objects are not really large stars, they are actually the planets in our solar system! Three of the planets (Venus, Mars and Jupiter) are visible just after sunset right now (assuming skies are clear where you are!) To find the planets, start by looking west. You should see two very bright objects in a straight line fairly low in the sky, brighter than any other stars around them. These are Venus (brightest one) and Jupiter! Once you've found them, turn around and look east. There should be another bright object in the sky that has a distinct red hue to it. That is Mars! Below are some images from Sky & Telescope magazine showing you where the planets are in relation to other stars and the moon. (Even though they say April 2nd they are about right for any day this week)

If you happen to have a telescope, or an observatory near by, take a look at these planets. If the night is very clear, you might be able to see the four Galilean moons of Jupiter or even the polar ice caps on Mars! It's really a spectacular sight!

Kepler's Third Law

The final law, Kepler's third law, is one of the most useful relations in astronomy. It states that the period of time it takes a planet to orbit the sun, squared (that's period*period), is proportional to its distance from the sun, cubed (distance*distance*distance). Or, as astronomers would say: P^2=a^3, where P is period and a is semi-major axis (i.e. distance).  The graph above shows the period and orbital distance of some planets in our solar system. The line going through all the points corresponds to the spot where P^2=a^3. The fact that all the planets fall on this line means that Kepler's third law is correct, and that we can predict the orbital time if we know the orbital distance, or vice versa. This relationship can be applied to most objects orbiting a larger object in space. Astronomers use it to estimate the period of exoplanets orbiting stars, and stars orbiting galaxy centers. 

And there you have it! Kepler's three laws of planetary motion!

Image Credit: Kevin Brown, Reflections on Relativity

Kepler's Second Law

Kepler's second law states:  The line joining the planet to the Sun sweeps out equal areas in equal intervals of time. 

 

This law is often referenced as the "law of equal areas" . So what does it mean? In the diagram above we have a planet going around the sun (or any star) following an elliptical path (as the 1st law states). When the planet is at point A, we draw an imaginary line towards the star. The planet continues to orbit the star, and lets assume one month passes. The planet is now at point B, and we draw another imaginary line towards the star. The area shaded in blue is the imaginary triangle in space that is created by the two lines we drew. We can calculate the area of this triangle because we know the length of the two lines we just drew. Now we repeat this scenario for when the planet is at points X and Y, and again it took the planet one month to go from point X to point Y. Notice that it traveled a much shorter distance on its orbit, and that the imaginary triangle we made is a lot thinner. But, again we know the length of the lines we drew, and if you calculate the area of this green triangle, you should get exactly the same amount as for the blue triangle! So in one month, the planet sweeps out a path of equal area!

Why is this the case? When the planet is closer to the star, it feels a stronger gravitational force from the star. The star sort of whips the planet around the corner closest to it, and has a weaker effect when the planet is farther away. All planets that orbit their host star in an ellipse will follow this rule.

Kepler's First Law

Johannes Kepler was a very famous astronomer. He was one of the first astronomers to understand the physics behind our solar system and how objects orbit one another. If you ever take a course in astronomy, one of the first concepts you will learn about is Kepler's three laws of planetary motion. Today I introduce Kepler's first law of planetary motion.

 

Kepler's first law: Planets orbit the sun in an ellipse with the sun at one foci .

With the technology and telescopes that we have today, it's easy to show that planets follow a squished circular shaped path around the sun called an ellipse . But how did Kepler know? Back in the early 1600's, astronomer and physicist Tycho Brahe took very precise measurements of the position of Mars in the sky. At the time, astronomers believed that all planets orbited in a circular path with the sun at the center. Assuming this is true, Brahe calculated where he expected Mars to be located in the sky throughout the year. To his surprise, the position of Mars never matched his prediction! He then gave Kepler the task of figuring out why the data and predictions did not match. Kepler discovered that if you model the Earth and Martian orbit using ellipses with the sun at one foci, Brahe's predictions would match up perfectly with his observations! We can quantify how "squished" the circle is using a parameter called eccentricity. An eccentricity of 0 means the planets path is a perfect circle. An eccentricity of 1 means that the planets path is a straight line. Planets orbit with eccentricities between 0 and 1, and most of the planets in our solar system have an eccentricity of <0.1 i.e. almost circular. This law is universal, which means it can be applied to extrasolar planetary systems as well as our own.

Van Allen Belt

Earth is surrounded by a large magnetic field caused by a molten iron core deep inside the planet. It's very similar to the bipolar magnetic field produced by a bar magnet, just on a much larger scale. The field lines extend out one pole, wrap around the earth, and re-enter at the other pole, creating a magnetic barrier around Earth. The Van Allen Belt is the part of this barrier, where most of the high energy particles aimed towards Earth are collected and safely grounded at Earth's poles. It sits about 20,000km above Earth's surface, well within the orbit of the moon. There are actually two Van Allen belts, an inner and outer one, which trap different types of particles.

This is a great thing for humans on Earth, but it poses big problems for satellites, telescopes, and space travel. Telescopes and satellites that travel through the Van Allen belt can be easily damaged by this highly concentrated radiation. This is why most satellites orbit within the belt, and most space telescopes have orbits that do not cross the belt, or cross through it once to get to a further destination.  The Van Allen belt is also a big problem for astronauts. Without special equipment, humans can not safely pass through the belt, as they would instantly be poised by the radiation. Special protective equipment from astronauts and the space shuttle was developed so that astronauts on the Apollo missions could travel safely to the moon and back.

Space Weather

CME March 7th, 2012

The sun has been very active lately! It's reaching the peak of its 11 year sunspot cycle, and therefore solar storms and flares are more prominent. You probably heard about the giant solar flare that smacked into Earth early yesterday from your favorite news channel, but there are many places on the web where you can get information that's a bit more detailed than what your news anchor says. One of my favorite places to visit is SpaceWeather.com. Here you can find all sorts of information about the sun, solar storms, solar flares and other space weather related things. It also shows you a daily picture of the sun in case you are looking to view sunspots. There's information about the speed of the solar wind and any types of flares that are headed our way. Today, the solar wind is hitting us at 296 km/s (that's 662,000 miles per hour!) You can also check the site to see when objects such as the international space station will be visible in the night sky.

 

Measuring Temperature with Light

If you have ever read a news article or scientific paper on a star or group of stars, the author may have given a temperature for that star. But how do they know how hot the star is? There are many methods that astronomers use to estimate the temperature or all sorts of objects, but the simplest way is just to look at light! 

  

Astronomers assume that objects such as stars, planets, etc. in space emit like blackbodies. A blackbody is an object that emits a majority of light over one small wavelength range that directly corresponds to its temperature. Let's take the sun as an example. The image above is a blackbody curve for our sun, where the vertical axis is amount of light emitted and the horizontal is the wavelength or color of light. This graph says that the sun emits most of its light around ~0.5um (yellow) and not much at other colors. Emitting mostly at yellow means you have a temperature of ~5800 Kelvin. If you emit most of your light at shorter wavelengths, then you are hotter. If you emit more light at longer wavelengths then you are colder. Graphs like this can be made for any object just by observing it through different filters with a telescope. This method works best for objects that emit light in the UV, optical, and Infrared, and with one simple equation astronomers can calculate the temperature of an object based solely on its color. We can't always use this method measure the temperature of objects that emit in the x-ray or radio, because this light is usually not caused by heat, but by other mechanisms.

Humans emit most of their light in the infrared, which is why we glow fun colors in pictures taken with infrared cameras. Based on this fact, we can figure out that humans have a temperature of ~310 kelvin, or 98F. So this method works both on Earth and in space!

Image Credit: Quantumfreak.com

The Sun Today and Every Day

The Solar Dynamics Observatory (SDO) launch in early 2010 and has been studying the sun ever since. SDO focuses on understanding solar storms and the sun's magnetic field, and how all this affects us here on Earth. You can check the SDO website and see what the sun looks like every day! Today we can see a few sun spots and prominences. What will the sun look like tomorrow? We'll have to wait and see!

Image Credit: SDO

Happy Leap Day!

 

 Today, February 29th 2012, is leap day! Every four years an extra day is added to the calendar in February to make up for the fact that one full year is actually ~365.25 days.  But why is it defined this way and what does astronomy have to do with it?

Throughout history, many changes to our calendar have been made so that the seasons and solstices occur on roughly the same dates every year. Since the 16th century we have been using the Gregorian calendar system, which defines one year to be 365days, and one leap year to be 366 days. Every four years we have a leap year, except for years which are divisible by 100 and not divisible by 400. So, for example, the year 2000 was a leap year (divisible  by 100 and 400) but the year 2100 will not be a leap year, because it's not evenly divisible by 400. If you do the math, this results in the average number of days in a Gregorian year to be 365.2425 days. This coincides with amount of time it takes the Earth to go around the sun once (~365.2425 days). This makes sense, but Earth's orbit does not stay in the exact same place in space year after year. This slight shift in Earth's orbit is called precession. This results in a tropical year (the time it takes to go from the exact time of the winter solstice one year to the next) to occur on a 365.24219 day schedule.  So in general thing line up nicely, but actually, we are overestimating  by a tiny amount. If we want the seasons to line up correctly, we will have to make an additional one day correction every ~26,0000 years.  This also doesn't include other astronomical changes to the Earth that occur on even longer timescales, but during your lifetime you shouldn't notice any change between seasons and the dates they occur on.

Core Collapse Supernova

Crab Nebula Supernova SN1054 remnant

When stars much bigger than our sun reach the end of their life, they often experience huge explosions called supernova. They leave behind beautiful supernova remnants like the ever popular crab nebula (pictured above). But why do these stars die in such violent ways? The answer lies deep inside the star.

Stars spend most of their life fusing Hydrogen in their core, which is what makes them shine so brightly. After a star uses up a good amount of its hydrogen, it can start burning heavier elements such as helium, oxygen, carbon, and silicon. It continually burns heavier elements, creating onion like shells of elements on the core, until it gets to iron. At this point, the core is so hot that the light it releases is able to break apart elements down to its constituent protons, neutrons and electrons, essentially undoing the creation of heavy elements that the star just spent its whole life doing. The pressure in the core that's holding up the now "puffy" star begins to decrease and eventually the star implodes on itself. The in fall of material eventually bounces off the now super dense core, creating a shock wave outward. If the shock wave has enough energy, it will burst through the surface of the star, as what we call a core collapse supernova explosion! It essentially blows the star apart, leaving behind only the super dense core, now called a neutron star.

Image Credit: NASA/HST

Beating Extinction

Last ADYK we discussed extinction due to clouds of dust and gas in outer space. When we view objects like the pillars of creation in visible light, the stars are blocked by the pillars of clouds.  To beat the extinction, astronomers look at the infrared light coming from that region, which is able to pierce through the clouds revealing the hidden stars! Infrared light has a longer wavelength, so it's able to travel further and through more material before it gets absorbed or scattered. This is because most of the gas and dust particles are smaller that the wavelength of infrared light.  The concept is similar to that of radio waves. We use radio waves on Earth to transmit information because the wavelengths are very long, on the order of meters. So for the radio waves, things like people, buildings and trees appear "small" or on about the same size scale as the waves are. Therefore, the waves can travel pretty far before they are disrupted. Shorter waves, like millimeter long waves, wouldn’t travel very far on Earth because they are smaller than the objects they must travel past.  Going back to our pillars of creation, infrared waves emitted by the stars are longer than the size of the gas and dust, thus the light can travel through the clouds. The picture above is taken in infrared light, and we can now see all the stars that were previously hidden behind the clouds!

Image Credit: ESO/VLT

Extinction Astronomy Style

When I hear the word extinction, I think of the dinosaurs and endangered animals. Astronomers have meaning for this term too, and it doesn't involve dinosaurs in space or anything like that!

When astronomers point their telescopes towards the stars, they have to look through not only Earth's atmosphere, but also any gas and dust between us and the star in outer space. Since stars form out of big clouds of mostly Hydrogen gas, astronomers often find themselves looking through thick "space clouds" to try and see stars. These clouds can make the stars appear dim, and sometimes block the light completely! This dimming/blocking of starlight is called "extinction" or "reddening". Stars emit all colors of the rainbow, and even many types of light that we can't see with our eyes. These space clouds tend to preferentially block blue light, making stars appear more red than they actually are. This is why extinction is sometimes called reddening. Above is a picture of the Pillars of Creation taken in visible light with the Hubble Space Telescope. This image shows giant clouds of Hydrogen gas, behind which many stars are forming. We can't see the stars though, because the gas cloud is extincting them and blocking them from our view. Tune in next time to learn how astronomers beat this difficult problem and see these hidden stars!

Image Credit: NASA/HST

Apparent vs. Absolute Magnitude

Last ADYK we discussed the magnitude scale and how astronomers use it to quantify how bright a star is. But there's a little more to this whole magnitude idea. Think about this scenario… The sun is very bright, about -27 magnitude, and very big in the sky. What would the sun look like if I moved it very far away? The sun would still emit the same amount of light, but it would look much smaller and dimmer on the sky. I would no longer say it's magnitude -27, but rather some larger (dimmer) magnitude. In other words, stars that are close are going to appear brighter and therefore have a lower (brighter) magnitude. So how do astronomers correct for this distance bias? They have two different magnitude definitions: apparent and absolute magnitude. Apparent magnitude is the one we discussed last time. It answers the question "how bright does that star appear to be in the sky?". Absolute magnitude corrects for the fact that stars are different distances from Earth, and answers the question "If I assume that all the stars are the same distance from Earth (often assume 10parsecs), how bright does the star appear to be?" Absolute magnitudes allow you to directly compare the light output of two stars without worrying about the fact that they might be different distances away. With some basic algebra, you can switch between the absolute and apparent magnitude of a star, as long as you know how far away it is. Both of these magnitude scales are used by astronomers and are very handy when you are trying to observe or compare the properties of two stars.

Image Credit: http://mrscreath.edublogs.org/2011/12/01/hr-diagram-day-2/

The Magnitude Scale

If you've ever listened to a group of amateur or professional astronomers talk, you've probably heard them say something like: "Yeah, I should be able to image that star, it's magnitude 4." But what does magnitude 4 mean? In astronomy, we use a magnitude scale to define how bright stars and other objects are in the sky. To make it super confusing, the magnitude of a source can be a positive or negative value, and larger positive numbers mean the source is dimmer. You can thank Hipparchus for this, he was the first to catalog the brightness of stars, defining magnitude 1 as the brightest stars in the sky and magnitude 6 as the dimmest. Since then, astronomers have come up with equations to calculate the magnitude of stars, so that the system is not based on how good your eyesight is. The magnitude system is defined such that a difference of 5 magnitudes equals 100 times brighter or dimmer. So how much brighter is star A at mag=2 than star B at mag=3? By definition, 1 magnitude difference equals ~2.5 times as bright, so star A is 2.5 times brighter than star B.

 With today's telescopes, we can see stars that are as dim as about mag 30. Without a telescope, our eyes can't see anything dimmer than magnitude 6. The chart below shows you some common sky objects and how bright they appear. Don't forget, the bigger the number the dimmer the object!

Tidal Locking

You've probably seen a full moon many times during your life, but have you ever noticed that it always looks exactly the same?  The Earth and the moon are tidally locked to each other, which means that the same side of the moon always face Earth. This can happen when you have a small body close to a large body, and gravitational interactions cause the small objects orbit and rotation to synchronize. Let me explain. Intuition tells most people that if you always see the same side of the moon, then the moon must not be rotating on it's axis. But this is not true! You can convince yourself of this by doing a little demo with your hands. Hold up your right hand and make a fist, then point the fingers of your left hand toward it. Now move your left hand around your right, such that the tips of your fingers always point to your right fist. You'll quickly find that you have to rotate your left hand to do that! The moon goes around the Earth once every ~28 days, and it rotates on its axis once every ~28 days as well. This causes the same side of the moon to always face Earth! Planets that are close to their host stars can be tidally locked in the same fashion, and so can two stars. Many moons in our solar system are known to be tidally locked to their host planet, and astronomers speculate that many known exoplanets are tidally locked to their host stars.

RR Lyrae Stars

Globular Cluster M15 which contains RR Lyrae stars

When we hear the word star, we think of a big flaming ball of gas like our sun. Our sun is a "typical" star, but there are many other types of stars in our galaxy. An example of a different type of star is an RR Lyrae star. These stars belong to a class of different types of variable star, or stars that change their brightness periodically over time. RR Lyrae stars are found in globular clusters, and are more aged and contain less heavy metals than the sun. Reactions in the star's core cause the star to physically pulsate periodically in size, temperature and brightness. They change brightness on the order of days. RR Lyrae stars are being studied by many astronomers so that we can understand and accurately predict the brightness changes of these objects. 

Image Credit: Efrain Morales Rivera

A Supercritical Exoplanet

One of the main goals in searching for exoplanets is to find one similar to Earth. Astronomers are beginning to find planets that are roughly the same size and weight as Earth, but are quickly discovering that these planets have few other similarities to Earth.  55 Cancri e is an excellent example. This exoplanet is roughly 8 times the weight of Earth, and a little less than twice the size. The image above shows Earth and the exoplanet to scale, though the drawing of 55 Cancri e is just an artists idea, we have no idea what it really looks like. The two planets are comparable enough to call 55 Cancri e a "Super-Earth". One major difference between Earth and 55 Cancri e is that it sits much closer to its host star than Earth does to our Sun. For comparison, 55 Cancri e is 26 times closer than Mercury is to the sun, and Mercury is 3 times closer to the Sun than Earth! Observations with the Spitzer Space telescope suggest that the planet is not rocky, but actually made of lighter elements, including water! Since the exoplanet is so close to its host star, it is extremely hot. This means that any elements are in a "supercritical" state, or in other words they are in a liquefied gaseous state. Here on Earth we have super critical water near heat vents, and liquid rocket fuel is super critical when ignited. Essentially, this planet is oozing with  super hot material! Definitely not a place I'd want to live!

Image Credit: NASA

Ebb and Flow

GRAIL A and B are lunar satellites launch by NASA that will be studying the gravitational field of the Moon (see GRAIL). The spacecrafts just arrived at the moon on December 31st 2011 and January 1st 2012. To get the general public involved in the mission, NASA decided to hold a competition for elementary school students in which they proposed new, more creative names for GRAIL A and B. The winners are a class of fourth grade students from Montana, who came up with the names "Ebb" and "Flow". Ebb means to move back or away (like a receding tide), where as flow means to move forward, like a flowing stream. The Moon's gravity is what causes the tides to occur, and since GRAILS primary mission is to study the Moon's gravity and how it affects Earth, these names are quite appropriate. Keep an eye out for other space related competitions that you can participate in on the NASA website: www. NASA.gov

Image Credit: NASA

Dragonfish Star Cluster

The Dragonfish star cluster is a group of very massive stars that are embedded in a thin bubble of gas from which they formed. This cluster was recently discovered using the Spitzer Space Telescope, and further studied using the New Technology Telescope in Chile. It's name comes from the fact that the shell of gas (bottom middle) resembles the snarling mouth of a dragonfish. This cluster is made up of many massive stars, some of which may even be 100x the size of our sun! The region around the fishes eye (bright star in the middle) contains more gas and could still be forming stars. Stars this massive don't live very long, so it's likely that star formation in this region won't last very long, as a supernova explosion could blow away most of the material in the next few million years!

Image Credit: NASA/JPL-Caltech/GLIMPSE Team/Mubdi Rahman

Voyager Golden Records

Voyager Golden Record (left) and the case it's contained in (right)

In 1977, NASA launched a pair of telescopes called the Voyager Space Telescopes. They were designed to travel to the edges of our solar system and beyond, and send back as much information as possible along the way. Since astronomers knew that these telescopes would be leaving the solar system, they wanted to have something on board signifying the telescopes origins, just in case they were picked up by an alien species some day! So onboard these telescopes are two gold plated records called the Voyager Golden Records. The records contain greetings from Earth in many languages, images of various places, and different iconic sounds. Directions on how to build and use a record player are etched on the case that holds to records. The star like symbol shows some of the nearest and brightest stars to Earth. This was placed there to help any alien species pinpoint Earth's location in space. The Voyager Spacecrafts are just now leaving the solar system and have a long way to go before they reach another planetary system.  If you'd like to see some of their content, check out this website: http://spaceplace.nasa.gov/voyager-to-stars/