The Cosmic Distance Ladder, part 2…

Let’s continue our explanation of how astronomers are able to gauge the distances to celestial objects. In my first post on this topic, we talked about how radar ranging and stellar parallax are used to determine distances in the solar system. Now we’ll continue working our way up the Cosmic Distance Ladder.

Beyond our solar system

As we leave our local planetary neighborhood, our solar system, we can still use stellar parallax up to a point. In fact, I received an email from Scott in Placentia, CA, asking “What maximum distance an object can be reliably determined by parallax measurement using the latest  technology?” As I explained to Scott in my response, it’s hard to answer that question with a single number. Ideally, stellar parallax should always work, because the stars close to us will always move at least a little bit with respect to the background stars. Unfortunately as we look at stars farther and farther away, the angle that the near-ground star moves gets smaller and smaller. As you can imagine there is going to be a point where that slight angular movement is almost imperceptible. However, technology is always improving. In 1989, the European Space Agency (ESA) launched the Hipparcos mission which was specifically designed for astrometry- determining the position and location of stars. The Hipparcos mission found the positions of nearly 100,000 stars as far away as 1,600 lightyears. Expanding on that mission’s success with new technology, another mission named Gaia is slated to launch this summer and claims to have the ability to find distances to stars tens of thousands of lightyears using stellar parallax. Some sources claim that stellar or trigonometric parallax is limited by current technology to around 1,000 parsecs or roughly 3,260 lightyears.

Examining other Suns

Once we reach that upper limit for the use of stellar parallax, where we can no longer accurately measure the angular shift of the star with reference to the background stars, we have to turn other methods for determining distances. The next technique we need to rely on is called spectroscopic parallax. Now, confusingly this new type of parallax is totally different from and unrelated from actual (stellar) parallax, it just uses the word “parallax” because it’s a technique used to find distances, like parallax. (That’s not confusing at all…) Okay, so how does this spectroscopic parallax work? Well you might remember in The Cosmic Distance Ladder, part 1… I talked about an important instrument used by astronomers called a spectrometer (a.k.a. “spectrograph” or “spectroscope”). These extremely useful devices break white light up into all the colors of the rainbow- this resultant array of colored light is called a spectrum. You’ve probably seen this phenomenon before. Well spectroscopic parallax, as the name implies, is all based on being able to take a good spectrum of a star. This is what sets the upper limit on the maximum distance of objects that we can determine using this technique; with current technology, spectroscopic parallax is limited to roughly 10,000 parsecs (1 parsec = 3.26 lightyears = 19.2 trillion miles). For distances where both spectroscopic and stellar (trigonometric) parallax can work, we generally use stellar parallax because it’s more precise- you’ll see why in a bit.

A prism is an example of a very simple spectrometer. Also known as “spectrographs” or “spectroscopes”, these instruments break down white light into its component colors and are integral to astronomers. Credit: Montana Space Grant Consortium

You might also remember in my recent post about stellar classification, that I explained how each stellar class has a spectrum that is unique to that class.So that means that if you look at a nearby B-type star and a far away B-type star, they should have the spectra that are nearly identical. The difference between the two measured spectra will be their intensity, which correlates to the brightness or luminosity of a star. But now we have to be careful because there are two types of brightness: apparent magnitude and absolute magnitude. Absolute magnitude is how bright an object actually, intrinsically is, while apparent magnitude is how bright it appears to be at Earth if you ignore the atmosphere. So basically absolute magnitude is how bright an object would be if you were at it and apparent magnitude takes into account how far away you might be from the object. Think about a lightbulb: absolute magnitude would be the physical amount of light that the bulb puts out and apparent magnitude is the amount of light you measure from the bulb when you stand on the opposite side of the room. As you can imagine, the bulb will appear less bright the farther away from it you are. Same with stars.

Now, once you’ve measured the apparent magnitude (using some sort of light collecting device) to see how bright the star appears to be, you have to figure out the absolute magnitude. This can be a little tricky and involve some guesswork, but the main tool we use is the Hertzsprung-Russell diagram.

A Hertzsprung-Russell diagram like this makes it easy to determine the absolute magnitude range of each stellar class. Credit: Swinburne University

As you can see, when you plot the H-R diagram, you can easily determine a range of absolute magnitudes that apply to each spectral class. Unfortunately that means there isn’t one right answer, so you can’t get an exact distance for the star…but you can get a pretty good range. Once you determine an appropriate value of absolute magnitude (M), you need to use some math and a mathematical formula known as the distance modulus.

Yay math!

Now that we have the apparent magnitude (m), which we measured, and the absolute magnitude (M), which we inferred from the H-R diagram because we know the star’s spectral type, we can now use both to get the distance modulus: m – M. You might ask, “How does that help?” Well if you think about it, the difference between the absolute brightness and apparent brightness of a star is determined by distance; naturally then there is a mathematical relation that proves that.

Distance Modulus formulaWoah, that probably seems like a lot of math…but it’s not so bad. The lefthand-side of the equation is our distance modulus (m – M), that gives us a dimensionless number (since neither m or M has a unit of measurement like feet or grams) that’s the difference between the absolute and apparent magnitudes. Since the lefthand-side has no units, then that means the righthand-side can’t have them either, that works out as long as we say that the 10 in the denominator is in the unit of parsecs, hence the “pc“. Then our distance (d) will be in units of parsecs and everything is balanced out correctly. So rearranging this equation to solve for the distance, we get:

Distance formulaAnd calculating that gives us the distance to the star, d. Now granted, we might need to do that for a high and low value of M, based on how we read the H-R diagram, meaning we’d get a range of distances and not a single answer, but it still gives us a much better idea than we had about these far away stars. This is why we’d choose trigonometric parallax over spectroscopic parallax for distances where both can work, but for distances beyond the reach of stellar parallax, then spectroscopic parallax is better than nothing! Somewhere “between A and B lightyears away” is much better than “really far”!

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The Cosmic Distance Ladder, part 1…

For the past few months, I’ve been spending a lot of time in my position as Manager of the UNH Observatory, in helping to prepare for the 2012 New England Fall Astronomy Festival. The event, lovingly known as NEFAF, is a family-friendly astronomy-related event that will be hosted by the UNH Physics Department in partnership with the New Hampshire Astronomical Society. As you can imagine, this is quite an undertaking, but in an incredibly exciting turn of events, we just found out that Dr. Alex Filippenko, noted astronomer from UC-Berkeley and member of the research team that won the 2011 Nobel Prize in Physics, will be giving the keynote talk at NEFAF 2012! In addition to being a highly acclaimed professor, Filippenko is also the co-author of an extremely popular astronomy textbook and a frequent contributor to the documentary series The Universe on The History Channel.

Dr. Alex Filippenko, the newly announced keynote speaker for the 2012 New England Fall Astronomy Festival to be held at the UNH Observatory.

That extremely exciting news has inspired me to do a couple of posts about the expansion of the universe, the area of research that Dr. Filippenko works on. But before we can really get into talking about that, we need to cover a very basic aspect of astronomy, but something that most non-astronomers don’t really know about. I was at a public session at the Observatory this weekend when a guest who had never studied astronomy before asked me what she thought might be an “ignorant” question: she wanted to know how exactly astronomers knew the distances to objects in space. This is by no means an ignorant question, in fact it’s a very fundamental and very involved question that really gets at the very nature of astronomy.

Astronomy by definition is an observational science. Unlike many other scientific disciplines, astronomers can’t really do experiments in a laboratory (although some do). But the stereotypical astronomer can’t throw his subject (a star or galaxy) on a lab bench and dissect it or set up an experiment to test it, so astronomers need to observe and record data. Okay, so we observe light, that tells us what something looks like, where it is, and how bright it is. Big deal, is that really that helpful scientifically. Well, not really. So we have to come up with ways to get more information from observing the light. The main way we do that is by breaking the light up in a spectrometer, an instrument that breaks light down into a spectrum of colors. This breakdown of light can reveal an abundance of new information including what the object is made up of, how hot it is, how fast and in what direction it’s moving, how old it is, and more.

The question of how astronomers calculate the distance to an astronomical object varies depending on how far away the object is. Because most of these techniques only work up to a certain distance, there is actually a progression of different approaches that astronomers use to measure distance to celestial objects. This list of methods of measuring astronomical distances is known as the Cosmic Distance Ladder (or less poetically, the extragalactic distance scale).

A graphical representation of the distance-measuring techniques that make up the Cosmic Distance Ladder. “1 A.U.” is 1 astronomical unit or approximately 93 million miles, the distance from the Earth to the Sun. A “pc” is a parsec, equal to 3.2 lightyears (206,265 A.U.) or about 20 trillion miles. “Mpc” stands for “Megaparsec” or millions of parsecs. Credit: University of Rochester

In our solar system

The first step in our exploration of the universe was to our own celestial neighborhood. The first step was precise measurement of the size scale of the solar system, which started with the determination of the distance between the Earth and the Sun. As I’ve explained before, this measurement was originally calculated via observations of transits of the planet Venus across the disk of the Sun. Early on in the 20th century, observations of asteroids also played an important role in this measurement. But today the distance from the Earth to the Sun, defined as 1 Astronomical Unit or “AU”, is measured with high precision using radar ranging. By bouncing a radar beam off another planet, usually Venus, and measuring the time that beam takes to return to Earth, scientists can very accurately determine the difference in the size of the two planets’ orbits. Using that difference and the ratio of the two orbital sizes, we can very easily calculate the distance the Earth must be from the Sun. We use a similar process even closer to home. During the Apollo missions of the late 1960s-early 1970s, astronauts deployed the lunar laser ranging experiments, arrays of mirrors that allowed scientists to measure the distance to Earth’s only natural satellite with extreme precision using lasers. This radar ranging is how we’ve calculated the distance to most of the objects in our solar system. More recently, we can also use spacecraft in orbit around other planets as a tape measure by measuring the time it takes for a signal to travel from the spacecraft to its controllers on Earth.

Another  way we can get measure the distance to the planets and to nearby stars is a phenomenon known as stellar parallax. This method is less accurate than radar ranging for planets, but is very good for stars in our local stellar neighborhood. Parallax is something you experience almost every day. Hold your thumb up at arm’s length. Close one eye, then open that one and close the other. Notice how your thumb appears to shift with respect to the objects far off in the distance? That’s parallax! Astronomers take measurements of a planet or star a two points in Earth’s orbit (6 months apart) and measure the angular shift of an object with respect to the background stars between those two measurements. Then, because we know the distance the Earth is from the Sun, we can use some basic geometry to calculate the distance to that star or planet in the foreground.

This diagram shows how parallax is used to find the distance to planets in our solar system and nearby stars. Scientists make two observations 6 months apart, measuring the angle that an object (the red dot) makes with regard to the background stars between the two observations. Then using the distance from the Earth to the Sun (1 A.U.) and some simple geometry, the distance to the object (d) can be calculated. Credit: Hyperphysics

It was using parallax, that Italian astronomer Giovanni Domenico Cassini was able to roughly calculate the distance to Mars in 1672. His calculation was a little bit off though, because instead of taking two measurements 6 months apart, he sent his colleague to Cayenne, French Guiana (on the northern coast of South America) to make observations while he stayed in Paris. Then Cassini could make the same parallax calculation using the known distance between the two observation points (~4400 miles) instead of the distance from the Sun to the Earth. This single direct measurement of the distance to Mars, which is now easily calculated and heavily used by missions such as Curiosity, actually allowed for the calculation of the distances to all the planets. Since geometry and Kepler’s Laws governed the basic ratios the Sun-planet distances, you only needed to measure one Earth-planet distance to be able to easily calculate them all. This major contribution and several others in planetary science (including the discovery of four of Saturn’s moons and joint discovery of Jupiter’s Great Red Spot) prompted NASA to name the Saturn-bound spacecraft mission after the him.

Giovanni Domenico Cassini

[To be continued…]

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Can Venus help us find exoplanets?…

This post is in response to loyal reader Jarman Day-Bohn’s question, which he left in a comment on the post “Today is transit day….”. Jarman asked:

How much do you think this [transit of Venus] will contribute to the current research experts are performing toward the study of possible earth-like planets out there? I know they were heavily using a technique measuring how much of a star’s light is blocked out by a planet to judge its size and other factors. Will this in any way help that process?

Great question Jarman, thanks for asking! Let’s look into that a little bit more.

But before we get too far into that, let’s think a little more about transits. Whether or not a transit occurs is all based on perspective. From Earth, only Mercury and Venus are interior planets- planets orbiting closer to the Sun- so they’re the only two that can we can see transit the Sun’s disk. If you were on Mars though, you could conceivably see Mercury, Venus, and Earth transits. And if you were on Pluto you could, in theory, see all eight planets transit the Sun. Remember though, as you get further away, even though more planets can be seen transitting the Sun from your perspective, you’re also getting further away, meaning the Sun is going to look smaller and smaller to you, as are the transitting planets. The Sun is only 93 million miles from the Earth (that’s really close astronomically speaking), so the enormous Sun, which is 1 million times larger in volume than the Earth, takes up a relatively large portion of the sky (~0.5 degrees). As you move further away from the Sun, its angular size in the sky will shrink. By the time you got to Pluto, which is 3.67 billion miles from the Sun, but still close astronomically speaking, our local star would look like a bright speck only ~0.01 degrees (50 times smaller than in the sky on Earth); probably something similar to the artist’s depiction below.

This artist’s depiction shows what the Sun might look like from an object, like Pluto, that’s in the solar system’s Kuiper Belt. Notice how the relatively close Sun differs from the background stars. Credit: NASA/JPL-Caltech/T. Pyle (SSC)

Now as you travel further from the Sun, let’s say to a planet orbiting another star, and look at our Sun, you could still in theory see all eight planets (and Pluto) transit the Sun, but now you’re trillions of miles from the Sun which is now just point of light in the sky, the same way other stars appear to us in the nighttime sky. The really astounding thing about looking at the other stars in our galaxy (Note: every star you see in the nighttime sky is in the Milky Way, we can’t resolve single stars in other galaxies.) is that they are so incredibly far away that no matter how large a telescope we use, we can never see the disk of the star like we can with the Sun, it just won’t have a large enough angular size. Now matter what, even through the Hubble Space Telescope, stars look like pinpricks of light that astronomers call “point sources“. Which makes actually seeing a planet transit a star, like we can see with Venus, impossible. I’ll remind you that in a previous post entitled “Baseballs, not umbrellas…” I explained the continuing search for exoplanets and covered all three of the main techniques which scientists employ to find these elusive celestial bodies around our galaxy. As Jarman indicated, the most successful and commonly used method of detection is the “transit method”. This is the method that NASA’s Kepler mission has already used to find the first Earth-like rocky exoplanet. However, since I just explained that we can’t actually see the exoplanet transitting the distant star, the only way we can detect the transit is by recording the change in light we see as the exoplanet crosses in front of the star. But again, we don’t actually “see” the transit happen, we just observe the dip in the brightness given off by the star. Similarly, if you were on a ship off the shore and someone walked in front of the lighthouse beacon, you wouldn’t be able to see the person, but you might be able to record the drop in brightness as they walked by.

This artist’s idea of NASA’s Kepler mission looking for exoplanets illustrates the main technique that scientists hope to use to find planets orbiting other stars- called the transit method- but no matter the size of the telescope we can’t actually see the exoplanets transitting the disk of the star. Credit: universetoday.com

But now let’s get back to Jarman’s actual question: can a transit in our solar system, like that of Venus, help scientists to find planets transitting other stars? It might. The transit of Venus is a well-documented and well-understood phenomenon, which scientists have been able to accurately predict and observe at least 6 times in the last 400 years. As I explained in “Looking to launch and preparing for transit…“, the transit of Venus helped us to determine the size of our solar system. And since we’ve actually been able to explore our solar system and have a very good grasp of the size of Venus and the Sun and the distances between the Earth and each of them, we can use the transit of Venus as a calibration tool in our search for extrasolar planets. For instance, scientist can say a planet like Venus, which is so big, transitting in front of a star like the Sun, which is so big, would cause a drop in brightness of this much at this distance. Then we can scale that distance out to other stars and we get some idea of what we need to look for in our search for exoplanets.

So Jarman, there’s your answer: while the spectacular crossing of Venus may not lead to groundbreaking new methods to find exoplanets, it does give us a rare opportunity to view a transit (that involves objects we know a lot about) and use that as a reference point as we continue our search!

Thanks again to Jarman for posing this question and if you, like Jarman, have a question that you’d like to have answered, please leave a comment or use the “Contact astroian” tab at the top of the page to send me an email!

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A glimpse of the transit…

Here’s a screen capture from the live NASA webcast of  visible (white) light image of the surface of the Sun. That black spot at about 3 o’clock is Venus. The other small black features are sunspots on the surface of the Sun. Some sunspots can be larger than the Earth. Credit: NASA

Hey everybody! So I hope all of you are watching the NASA live feed of the transit of Venus and seeing cool things like above.

So here is a mid-transit update of some very cool transit things.

First off, you should check out helioviewer.org a very cool website that allows you to make your own compilation of solar images or videos from a multitude of satellites and data from NASA, NOAA, ESA, and more!

Here’s another great shot in the extreme ultraviolet (EUV) from NASA’s Solar Dynamics Observatory (SDO). Again you can see the dark spot, Venus, about halfway across the Sun’s disk. You’ll notice that the EUV allows you to see a lot different detail than the visible light image above. Here we can see the solar corona, or atmosphere, as well as flux tubes (hot plasma trapped along magnetic field lines). That extremely bright region just below Venus with the massive flux tubes flowing out of it is associated with the sunspot you see in the same location on the visible light image above. Sunspots are caused by magnetic field lines on the surface of the Sun that cause a drop in surface temperature (from ~6000 K to only ~3000 K). That temperature drop causes the cooler region to seem dark compared to the rest of the Sun’s surface– hence, sunspots.

An extreme ultraviolet (EUV) image from NASA’s Solar Dynamics Observatory (SDO) of Venus transitting the Sun’s disk. Credit: NASA

And just in case that’s not enough, here’s a link to a movie of Venus’s progression during the transit from SDO, care of @Camilla_SDO.

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Today is transit day…

Hello friends, don’t forget that this evening starting around 6pm EST you’ll be able to see Venus transiting the disk of the Sun, a phenomenon that won’t occur again until 2117!!

Remember, DO NOT LOOK AT THE SUN DIRECTLY WITHOUT PROPER PROTECTION! For safe tips on how to view the transit, click here. Or to be super safe (and mobile) you can check out NASA’s live webcast of the transit from the Keck Observatories at Mauna Kea, Hawaii. That broadcast will feature UNH alumnus and thesuntoday.org creator Dr. C. Alex Young of NASA Goddard Space Flight Center.

For more information about the transit, you can visit NASA’s official transit webpage, thesuntoday.org, or transitofvenus.org.

Also, to help you get super pumped about the transit, here are some fun tidbits.

Here’s a link to my friend and fellow grad student, Mark Zastrow from Boston University’s Department of Astronomy, detailing the amazing and harrowing tale of 18th century French astronomer Guillaume Le Gentil‘s trek to observe the pair of Venus transits in the 1760s: The Worst Observing Run Ever

And to prove that Venus is actually going to cross the disk of the Sun, here’s a video from NASA’s SOlar and Heliospheric Observatory (SOHO) satellite. The video is of a series of coronagraph images. Coronagraphs image the corona, or atmosphere of the Sun, and associated flares and coronal mass ejections by blocking out the extremely bright disk of the sun. You’ll notice the big empty blue spot in the middle of the picture, that’s the blocked out part and that white ring indicates the actual outline of the Sun’s circumference. The Sun’s really bright, so you need to block out a lot more than just the disk. You’ll see some big blobs of particles and plasma coming off the Sun, that’s normal solar activity. And finally you’ll see that bright image approaching the Sun from the left, that’s Venus, reflecting the incredibly bright light from the Sun.

Hope you like all that. Enjoy the transit! And if you have any cool transit-viewing pics or experiences, feel free to share them in the comments!

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Magnetic reconnection: a prominent mystery, part 1…

So you might remember a few weeks ago, in my post “A lifetime goal accomplished: astroian, the NASA intern…“, I told you that I was working with the Magnetospheric Multiscale (MMS) team here at NASA Goddard Space Flight Center. I also gave you a brief introduction to what MMS was and how it worked. Now I’d like to explain the main phenomenon which MMS is planning to investigate: magnetic reconnection.

You might be saying, woah, that sounds too sciencey for me. Never fear, it’s not as intimidating as it sounds. First off let’s learn more about magnetic fields. So what is a magnetic field? Well it’s exactly what it sounds like, it’s a field– or region of influence– occupied by a magnetic force. So you know that refrigerator magnet that you bought on your last trip to Florida? You know, the one with the empty beach chair and the Sun wearing the sunglasses, yeah that’s the one. Well that magnet (and any other magnet you know of) has its own magnetic field. And when you bring that magnetic field close to something metal (like your refrigerator), you can feel the magnetic force acting on the magnet, pulling it towards the metal. You remember that whole “opposites attract” thing from grade school, right? Good. Now you know about magnetic fields.

So what causes a magnetic field? Oho, now you’re asking the big questions! There are several ways that magnetic fields can be generated. The first, and most basic is part of the foundation of the physics field known as electricity and magnetism— or electromagnetism. Electromagnetism basically deals with the properties and effects of charges, both electric and magnetic, both in free space and in materials, and is governed primarily by a basic set of four equations known as Maxwell’s Equations (shown in all their scary mathematical glory below- just breathe, it’s going to be fine).

Maxwell’s Equations governing electricity and magnetism. The amazing power of these equations is hard to comprehend, but just about everything in electromagnetism is governed by these equations, adjusted slightly based on the conditions. Credit: www.antenna-theory.com

The group of equations is named after 19th-century Scottish physicist James Clerk Maxwell, who didn’t really come up with the equations (as you can tell by the names of those other guys: Carl Gauss, Michael Faraday, and André-Marie Ampère), but grouped them all together, made some tweaks, and realized that they were all inter-related and could explain electromagnetism in their entirety. Eventually Einstein’s theory of special relativity would cause a commotion, but with some adjustments to the equations, they still work! It was really a stupendous realization by Maxwell. Anyways, back to magnetic fields, so looking at Maxwell’s equations, the last equation (Ampère Law) is the one that really governs how magnetic fields are generated. So let’s try to understand what Ampère’s Law is saying. On the right hand side we have two terms, the second one is has that δE/δt, that means the change in E (the electric field– which is given off my a charge) over t (time). The electric field (E) changes whenever you have a moving charge, or current. So think about where you’ve heard the word current before regarding electricity– in wires, exactly. So wires have moving charges, usually negatively-charged electrons, that cause a current and as Faraday’s Law shows us on the left-hand side, generates a magnetic field (H). So every wire that has current running through it generates a magnetic field. Now most of the time that magnetic field is pretty weak and most of the time builders try their best to insulate those wires so that you don’t have rogue magnetic fields leaking all over your house (not like it would really cause you any harm if you did).

So a moving electric charge causes a magnetic field, and conversely Faraday’s Law tells us that a changing magnetic field causes an electric field. You can see that intrinsically then, magnetism and electricity are interrelated. Inside our planet and most others in the solar system, we have molten metal rock, which is spinning around the planet’s rotational axis, in what we call a dynamo. This can cause what we call a current loop, and thanks to Mr. Ampère, we know that a current loop can cause a dipole magnetic field. And that’s almost exactly what we see when we measure Earth’s magnetic field (see picture below).

A depiction of what Earth’s dipole magnetic field would look like if it wasn’t affected by the Sun. In reality, the solar wind– the stream of energized particles coming from the Sun– warps the simple dipole shape. It is also odd that the “south pole” of the bar magnet is located in the northern geographic hemisphere. Credit: Hyperphysics, Georgia State University

And boy is that magnetic field a good thing for Earth, because without it we would be exposed to all of the might of the Sun’s magnetic field and all of the harmful radiation associated with it (See: Mars). Earth’s magnetic field is the same as would be generated by a simple bar magnet, with a north and south pole. Now, electric fields lines are defined by convention to illustrate how a positive charge would move in that field, so from positive to negative charge, and the “poles” of a magnet are always defined so that the “North” pole is the positive side and the “South” pole is the negative side, meaning that the field lines start in the north and travel south. Did you follow that? Good, now I’m going to confuse you. Research of Earth’s magnetic field has revealed that Earth’s magnetic “North” pole, aka the positive end of the bar magnet and beginning of its field lines, is actually at the Earth’s southern pole (in Antarctica) and its “South” pole, aka the negative end of the bar magnet and the end of its field lines, is in the Northern hemisphere (currently in Northern Canada but moving towards Russia). But of course, scientists now know that this north-south magnetic field alignment actually flips roughly every 200,000 years. We’re actually overdue for this phenomenon to happen again.

Here’s Earth’s magnetic field as it looks in reality. The region around Earth influenced by the planet’s magnetic field is called the magnetosphere. You’ll notice that the left side of the field (which is closest to the Sun) is compressed by the solar wind, while the right side is extended into what we call the magnetotail. Credit: NASA

Above is what Earth’s magnetic field actually looks like. The region influenced by the Earth’s magnetic field is known as the magnetosphere, hence the Magnetospheric Multiscale (MMS) mission. Okay so now we have all our necessary background information about magnetic fields, but we still don’t know about magnetic reconnection! Well I think that will have to wait for another post…

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Looking to launch and preparing for transit…

As many of you probably heard, SpaceX’s launch of its Falcon 9 and Dragon capsule to the International Space Station (ISS) that was slated for early Saturday morning was aborted at literally the last second before launch. The abort was triggered by readings of excess pressure in one of the rocket’s engines. The problem was ultimately traced back to a faulty valve on one of the rocket engines which was replaced on Sunday. Now with everything supposedly right as rain, SpaceX looks forward to launching at the opening of the next possible launch window, which opens at 3:44am on Tuesday. As you may remember, back in December 2010, SpaceX became the first ever private company to launch into space; now it looks into sweetening the deal as it’s slated to become the first private company to dock with the ISS. This is a VERY good thing for the American space program. Despite flurries of protest and new ideas from Congress to limit the competition in space commercialization, SpaceX is doing exactly what President Obama hoped companies would do when he announced the space commercialization initiative back in 2008– beating the rest of the competition to the punch. Not that Obama is specifically backing or rooting for SpaceX, but this is exactly what the President wanted, competition fostering and driving innovation and accelerated success. I’ll have to wholeheartedly disagree with Congressmen who argue that competition breeds lackluster performance and unsafe equipment. Let’s face it, when going into space, there’s an inherent level of risk. Even NASA, the be-all, end-all of space-faring lost two (Columbia and Challenger) out of its five Space Shuttles, so it happens. But let’s examine this: Orbital Sciences, another company vying for NASA launch contracts, has already launched two NASA-funded missions (nearly $700 million) into the Pacific Ocean. Now, using the Congressional argument, we would have been locked into using Orbital Sciences and SpaceX would not have gotten federal subsidies or contracts to help get it to where it is today. Now to be honest, Orbital Sciences and SpaceX are trying to work on two different goals at the moment: Orbital Sciences is set on launching new satellites into space and SpaceX is focused on transporting crews and cargo, but you can see my point. If anything, competition forces greater concern over safety and ensuring success and greatly reduces the probability of project delays and going over budget. And if you don’t think that’s true, just look at how careful SpaceX was this weekend. As President Hoover once said, “Competition is not only the basis of protection to the consumer, but is the incentive to progress.”

Ultraviolet image of Venus’ clouds as seen by the Pioneer Venus Orbiter on February  5, 1979. Credit: spacedaily.com

Switching gears a bit, you may or may not have heard, but a once-in-a-lifetime astronomical event is happening on the evening of  Tuesday, June 5, 2012: Venus will be transiting the Sun. What does that mean? Well what that means is that we (Earthlings) will be able to see Venus on the disk of the Sun. You may say to yourself: why is this so special, doesn’t Venus go around the Sun every year? Well yes, you’re right, Venus orbits the Sun once every 225 Earth days, but Venus’ orbit doesn’t exactly lie in the same plane as the rest of the planets– it’s off by what might seem a slight 3°. But since distances are so large in space– Earth is a whopping 93,000,000,000,000 miles from the Sun– that small angle means that Venus only crosses the line of sight between the Earth and the Sun twice (in events separated by eight years) every century. The last transit of Venus was back in 2004 (imaged below) and it won’t happen again until 2117. Now if you’d like to find out more about the transit, you can visit transitofvenus.org, they’ve got pretty much everything you need to know, including what the transit is, where and how you can see it, a short video summary of the event and why it’s important, and even a recipe for a nice cosmic cocktail to enjoy responsibly while you view the transit! You can also check out thesuntoday.org or NASA’s official page, which have lots of stuff including information about NASA’s planned live feed of the transit from the Keck telescopes in Hawaii and maps of transit events in your area!

The entire June 2004 transit of Venus is captured in a composite photograph composed of 11 separate images taken at 30 minute intervals. Photographs by Fred Espenak, MrEclipse.com

Jeremiah Horrocks, an English astronomer, predicted the first ever observed transit of Venus back in 1639– contradicting the great Johannes Kepler, who said that Venus would miss transiting the Sun– and then observed it using a telescope. In fact, the transit of Venus is very important historically– it’s one of the ways we calculated the size of our solar system. You see, when you have two observers watching the transit from two locations on Earth, each sees a distinct path (red and blue below) of Venus across the Sun.  The slight difference in time that Venus takes, moving from edge to edge, can mathematically unlock the distance from Earth to the Sun, and thus the size of our solar system. In fact, after realizing this, the great English astronomer Edmond Halley (of comet fame) greatly encouraged countries to send expeditions around the globe to time future transits of Venus across the sun. Explorers and scientists faced great peril and set out all over the world for the transits of the 17th (1761 and 1769) and 18th (1874 and 1882) centuries.

Two observers from different locations on Earth will see Venus trace different paths across the Sun. The difference in time of the transits between the two paths can be used to calculate the distance from the Earth to the Sun and thusly the size of the solar system. Credit: transitofvenus.org

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