Supermoon (! or ?)

.....I was going to call this post "Moon of Steel", but I was terrified at the last minute by thoughts what might come to someone Googling this column.  Sunday (June 23rd) is the full Moon, a somewhat shiny yet mundane event (although not in the literal sense of the word) that occurs every twenty-nine and a half days.  Sunday is also the Moon's perigee (closest approach to Earth), an event that occurs every twenty-seven and three-tenths days.  Again, not very notable.

.....What is a little more notable is that both of these are happening on the same day.  Since the Moon is at its closest point, the Moon will appear a little larger in the sky than it usually does, and therefore a little brighter.  How much of a difference will this make?

This ain't it.

....Not all that much.  The orbit of the Moon has an eccentricity of 0.0549.  The eccentricity describes the shape of a curve.  A circle has an eccentricity of 0, a parabola has an eccentricity of 1.0, and a ellipse has an eccentricity between these two values.  The Moon's orbit isn't too far from a cicle.

.....On this diagram, the Moon's orbit is sketched in red, while a perfect circle is sketched in blue.  While the difference is not gigantic, it is there, and it does affect the "Supermoon". (Should I capitalize that? Will Time/Warner/DC sue me?  I am not sure.)

.....This means that the Moon at its closest appears 11.8% larger than the Moon at its smallest.  Since the brightness depends on the cross-sectional area, the Moon at its closest appears to have a 25% larger area against the sky, compared to the Moon at its farthest, or 11% more than the Moon at its average distance from the Earth.  This doesn't have as big an effect as you might think, because 25% more light doesn't mean that it would appear 25% brighter.  Consider that when you wake up in the middle of the night and navigate your way through your place, you can see to do that.  When you walk outside at noon the next day, you can see then as well, without your eyes exploding.  In astronomical terms, this is less than one magnitude difference (in which 5 magnitudes separates a bright star from the faintest visible stars)

...Even in terms of size, the Supermoon will not stand out greatly.  In the image below (constructed by the author from an image by NASA), the Supermoon is compared by the minimum Moon).

 .....But we don't see the Moon compared with itself, we see the Moon against the background stars, and that does not stand out.

.....In fact, the Moon will be at its least impressive (in the Northern Hemisphere)  because this is so close to the Summer Solstice, it happens when the Sun is at the northernmost point in its path across the sky , which means that the Moon will be at the southernmost point in the ecliptic (the path that the Sun, and basically the Moon and planets as well) follow across the sky.  To take a sample latitude of, say, 44 degrees north latitude, the Sun will be almost 70 degrees above the horizon at its highest, and the Moon that night will only be at 26 degrees above the horizon.  The Sun will spend 13 hours above the horizon, while the Moon will only be up for nine hours.

.....This might be a good thing, for casual hanging-out-and-looking-at-the-Moon purposes.  The not well explained horizon illusion causes the Sun or Moon to appear larger (even when it isn't) if it is rising or setting.  If the Moon is close to the horizon all night, there is more of a chance for this.  If the Moon is low in sky, it is also easier to hang out and look at the Moon from a chair on your porch, hanging out with your friends.  (NOTE: obtain friends before trying this.)

..... There is one major effect caused by the Moon's elliptical orbit.  For absolutely no good reason (you could claim this as evidence for a God if you didn't mind a kinda weird and petty god), the angular size of the Moon in the sky is basically the same as the angular size of the Sun in the sky.  This means that when the Moon moves in front of the Sun, the entire Sun can be covered, resulting in a solar eclipse.  When the Moon is at its far point, the Moon does quite do it, and we are left with an annular eclipse.

Perseid Meteor Shower 2012

.....The most reliable meteor shower of the year is the Perseid meteor shower, usually peaking on the night between August 11th and August 12th.  In younger years, this was the one time during the year that I could get the whole family as interested in astronomy as I was, a situation that I found was pretty common.  I have a lot of good memories of this shower, both growing up in the southeast, and times that I've visited my wife's family.  Now that we live farther away from our families, and will see them less often, it is good to have this as a link to the past.

..... Every dark, moonless night not dominated by city lights, we can expect to see a few shooting stars per hour, flashing randomly across the sky. These typically come from one of three sources: Leftover bits of flotsam and jetsam that have been floating around the solar system for the last five and a half billion years (cool), little bits that have been boiled off of comets as they passed around the Sun (also cool), or nuts/bolts/heat shields/tool boxes that have come off of space craft and are crashing back down to Earth (less cool).  I lived in central Florida for several years, and when I realized that probably the bulk of the meteors I was seeing from there were bits and pieces left over from launches, I admit that some of the romance died.

.....Each time a comet passes through the inner solar system, if it still has much of its original ice, that ice will boil off, taking some dust pebbles with it, and the ice will reflect sunlight, resulting in the bright coma and tail. What happens to this once the comet goes back to the outer reaches of the solar system? Nothing. That comet rubble stays in orbit, resulting in the comet's orbit eventually becoming a dusty tube of gunk around the Sun. If the Earth should pass through this gunk, then when the particles hit the Earth's atmosphere they will light up from the heat of friction generated from going from a temperature of less than three hundred degrees below zero (Fahrenheit) to thousands of degrees. Since all of these meteors are coming from the same general area in space, they will appear to come from the same general area of the sky, meaning that the meteors will all seem to radiate out from the same point. (Called, reasonably enough, the "radiant".)

.....Each August, the Earth passes through the remnant trail of the comet Swift-Tuttle, generating the Perseid meteor shower because the radiant of the meteors (the dotted circle in the image below) is in the constellation of Perseus.  Meteor showers do not require a telescope or binoculars; just go outside and look (in this case to the northeast, especially after midnight).

.....A lot of this is part of the standard run up to a meteor shower.  Happily, this year the Moon will have a very small effect on the meteors this year.  The Moon will not rise over the horizon until after 1 AM, so it will have a very small effect.  This is good.  Looking at different sources, the number of meteors per hour for the Perseid Meteor shower is usually given as a number between 60 and 120.  (Wow!)  Now let's look at that as the sky gets brighter due to the Moon.  Even if we take the most generous version, that considers that we can see all the way down to our eyes limit.  With the bright Moon, we can't.  With an interfering Moon, even if we could see down to fifth magnitude (as opposed to sixth magnitude, our limit), we would go from 120 down to about 46.  The full Moon is much more limiting than this, however.  Even if we assume a third magnitude limit, we're down to about seven.  Per hour.  With any bad or humid air, this could limit us to second magnitude (maybe three meteors an hour, if we're lucky), or first (maybe three meteors every four hours).  This year, again, we don't have the Moon to worry about.

.....Looking for Perseids can still be done in the nights leading up to Saturday night, but the peak will be pretty concentrated on Saturday night/Sunday morning.  Here is a map of the northeastern part of the sky on Saturday at about midnight.

.....Do you have any family memories of the Perseid meteor shower?

Landing on Mars

.....Late tonight, (at 10:31 PM PDT / 12:31 AM CDT / 1:31 AM EDT) the NASA Mars Science Laboratory will reach Mars, and in a period of seven minutes will attempt to go from a speed of 13,000 mph to zero.  As far as this goes, I cannot do a better job describing the challenges involved than this video.  On top of this, all of this has to be completely planned out; there will be no chance to manage any of the entry from Earth; the time that the signals take to go from the Earth to where Mars is now is fourteen minutes.  If a problem showed up in the signals coming from the spacecraft, and someone on Earth tried to respond, it would be almost half an hour until that order got to the probe.

.....Because of the time it takes a probe to go from Earth to Mars (for this trip, 253 days), we cannot track the motion of this probe by drawing a straight line from the Earth to Mars, and simply assuming the probe traveled on this path.  We must trace out a curved path from where the Earth is at launch to where Mars will be when the probe reaches Mars' orbit.  In fact, when the probe was launched, Mars was rising after midnight, just getting into position for a decent observing season.  As the Mars Science Laboratory moved through the gulf between the planets, the Earth actually passed Mars on the inside (at the beginning of March), and then on for five more months until now.  As seen in the Earth sky, Mars, Saturn, and the star Spica form a triangle low in the west just as it is getting dark.  The base of the triangle will be parallel to the horizon.  Mars will be the base "star" on the right, and Saturn will be on top.  Go out and take a look, and consider for a moment just what we as a species are attempting.

.....You may also wish to read this piece (warning! naughty words!); I will have something to say on this line tomorrow.

Night 1: Mars and Saturn

002:Mars
003:Saturn
004 Titan
005:Rhea

.....So far, I have had two successful observing nights, taking me up to nineteen objects on my list.  I'll go through these objects by type of object, because that makes the most sense to me at this moment.

.....The first two things I looked at in the night sky were the planets Saturn and Mars, low in the west.  I started with Mars because Mars was closer to the western horizon (just above the trees for me), and close to being lost.

.....Mars is currently low in the west, and setting very shortly after dark.  Since I want to see what I can get over the course of one year, Mars had to be observed now.  The problem comes from Mars being as close to the Earth as it is.  Let me explain.  Mars is the next planet farther out from the Sun, and so it moves in its orbit a little more slowly than the Earth does.  Saturn is much farther out, and moves much more slowly.  That means that one year after Saturn's best appearance in the sky, when the Earth has made one orbit around the Sun, Saturn has moved a little bit farther along (1/30th of the way along its orbit), and so the Earth must move a little bit father to catch up.  In the case of Mars, Mars has an orbit that takes 1.88 Earth years to complete.  When the Earth has gone once around the Sun, Mars has made a little less than half of one orbit, so Mars would then be on the other side of the Sun.  It will take almost another full year for the Earth to catch up to Mars in its orbit.


.....I have a confession to make:  I have never really been a fan of observing Mars.  Part of this might be due to Mars' habit of being visible basically every other year.  Heck, in addition to this, the relative size of Mars in the sky can change notably, due to how the position of Mars changes with respect to the Earth, and its own exceptionally elliptical orbit.  (Notably as far as looking at it in a telescope goes.  Despite the emails that still go around every August, Mars will never appear as a big red moon in the sky.)  The image below shows the orbit of Mars (red) and the orbit of the Earth (blue), to demonstrate how widely the distance between the two can change.

  ..... The two orbits can come pretty close to each other; this happened in August of 2003.  Marked on the chart was the last closest approach of the Earth to Mars, when Earth passed Mars in its orbit back in March.  Even at this closest approach, this wasn't as good as the 2003 event.  In a telescope, the image of Mars would be about 2/3rds the size at an absolute closest approach.  Mars as it appears today is almost a third the apparent size that it had back in March.

Don't count on this good a view

.....On a good night, the facing ice cap of Mars may be visible, as well as some darker/lighter areas on the planet.  These darker/lighter areas have lead to problems in the past.  This is a best-case scenario, though.  The thin atmosphere of Mars can sustain dust storms that can last several weeks, and the thinness of the atmosphere means that these storms can cover all of Mars.  My view of Mars was as a distinctly red dot.  That's it.  (That is probably simply due to how low Mars was in the sky.)

.....Saturn showed a better view.  Saturn is one of the few things in the sky that actually looks as one would expect it look.  Most people, seeing beautiful photos of nebulae or galaxies are quite disappointed seeing them in the telescope.  Cameras can be left open building and building up light in a way the eye cannot.  Saturn, however, clearly shows its amazing and beautiful rings.  Also visible are some of its brightest moons.  On the sketch that I made, I went back after the fact to identify which moons I had seen.  There must have been some thin clouds that night, or perhaps it simply was not fully dark yet, because I was only able to see Saturn's two brightest moons, Titan and Rhea.  Titan has a visual magnitude of 8.50 (dimmer than what can be seen with the eye; I describe star brightnesses here), and Rhea has a brightness of 9.89.  

.....I have omitted the decimal point from the labels on my sketch for hopefully obvious reasons.  I can usually see down to about a visual magnitude of 12 or so in my telescope, on a good night, so Tethys (m = 10.39), Dione (m = 10.59), and even Enceladus (m= 11.89) should have been doable.  I'll try and add those to the list next year.  Saturn will be a morning star starting in January, moving slowly back into view in the evenings.

.....What are the other planets doing right now?  Until November, Venus will be a morning star.  I could get up before dawn in order to see that, but I think I'll focus on the sky as it is seen in the evening ... just because that is when most people have the combined time and inclination to look at the sky.  After November, Venus will pass behind the Sun for a few months, and appear as an evening star again in May of next year.  So, there is time to see Venus as part of my "Big Year" in a more comfortable fashion.

.....Mercury is an evening star now, but Mercury is also very hard to see.  The closest planet to the Sun is also (by necessity) always close to the Sun in sky, so one needs a very good eastern/western horizon to see it.  At 9:30 PM, Mercury is about 8 degrees above the horizon.  Hold your hand out at arms length.  The four fingers of one hand, viewed across, block about 8 degrees against the sky, so when Mercury can be see, it will be pretty close to the horizon.

.....Neptune will be well placed for viewing in September; Uranus will be a bit later, in October, and Jupiter will be placed for good evening viewing by November.  

Day 1: I Cheat, Still Lose

.....For the first object on my Big Year (at least pass one of it), I decided to pick the Sun, which is fair - it's in the sky!  I won't spend much time talking about how to find this particular object, as it is usually pretty easy to find.  In any observation of the Sun, as I did with my post on the Transit of Venus, it is pretty much required to say *DO NOT OBSERVE OBSERVE THE SUN WITH MATERIAL THAT IS SPECIFICALLY BUILT FOR LOOKING AT THE SUN!*  It is not possible to stress that enough!

.....So I used a filter that blocks out the vast majority of the light, and all of the UV light.  As before, I found the Sun by minimizing the shadow of the telescope, and then moving back and forth until the disk comes into sight, only to see ...

 .....Boring!  The sunspots that were visible in the images I took of the Transit of Venus have rotated out of our view, and they have not been replaced by new ones.  (The blurs that look like clouds moving across the Sun are on Earth, and perhaps just on the interface between the camera and the telescope.)

 .....See?  Sunspots then, but not now.  Even the image taken from NASA's Solar Dynamics Observatory show very little, just one of the last sunspots slipping off of the edge.

Source

.....Sunspots are caused because the Sun has a powerful magnetic field, and that the Sun is not solid.  Let us start by assuming that at some instant, the Sun has a magnetic field similar to the Earth.  There is a north magnetic pole, and a south magnetic field, and there are field lines that connect one to the other.  Magnetic fields are generated by moving charge, and the orbit of each electron around each hydrogen atom (hydrogen makes up the overwhelming majority of the Sun and other stars) is itself a moving charge, and so each atom has a magnetic field, and these tiny, tiny magnetic fields are forced to line up by the Sun's overarching magnetic field.  

.....The Sun rotates a little faster at the equator than it does at the poles, unlike the Earth (although it would be nice to have a little more variety to the south of Minnesota than just Iowa), and as the gas at the equator is moved forward, it actually carries that magnetic field forward, distorting the field lines.  The Sun keeps rotating, and the field lines start getting twisted more and more until the magnetic field lines are actually forced to branch off of the Sun's surface.  When the Sun's magnetic field gets too wrapped up in itself, it does clear itself out, and start over (with the poles reversed).

This NASA site also has an animation.

.....When this happens, the gas at the kinks, where the magnetic field leaves and rejoins the Sun's surface, gets locked in place.  This gas cannot be replaced by the hot gas below it, as is usual in stars, and that gas cools off to a paltry 7100 Fahrenheit, as opposed to the 10,000 Fahrenheit of the rest of the surface.

.....This does have an effect on the Earth.  When those loops leave the Sun's surface, some material does travel along that path, and when the loop breaks down, that material is ejected into space.  Since a moving charge creates a magnetic field, this mass of moving charged particles carries a magnetic field with it.  If this eruption hits the Earth, then it could give rise to spectacular displays of Northern/Southern Lights (the aurora), but it could also damage satellites or more.  In 1989, an ejection of this charged mass hit the Earth, and from space the Earth's power grid looks like one big ol' antenna.  This "antenna" caught the charge, and the overload knocked out power to the northeast US and southeast Canada.

.....There is also an effect of the Sun's sunspots on the Earth's climate, although this is imprecisely understood.  Times of low sunspot activity have corresponded to periods of lesser temperatures on Earth, with a multi-year lack of any sunspots at all corresponding to the "Little Ice Age".

Source, and more detail on its impact on climate.

.....Closer to the present, after 1998 (for several years, the hottest year on record), there was a period of several years with few to no sunspots; this would be expected to have a cooling effect on the Earth.  Indeed, for a few years after this (also impacted by the behavior of El Nino / La Nina systems), the temperature did decrease slightly, but solar activity picked back up, and we are back to setting records for "hottest year ever".  (So far, this spring was the hottest ever recorded in the US.)  There have been arguments that solar effects are what drives climate change, but close examination shows that solar variation correlates well to Earth's average temperature variation ... until about 1950.  Then something else (interpreted by pretty much everybody outside the fossil fuel industry as "human effects") dominates.

   

NASA

 

A Solstice Announcement

.....I recently saw the (in my opinion, greatly undervalued) film, The Big Year, and that gave me an idea.  I am going to use my astronomy blogs to attempt my own "Big Year".  In the movie, the main characters are birders, who attempt to see as many different birds as they can during the course of a calendar year.  I am going to attempt to see (and report on) as many different things as possible in the sky over the course of a year.

.....Instead of using a calendar year (waiting until January 1st, 2013), I am choosing to start on the summer solstice because this starting point is at least more directly tied to astronomy, and because a lot of objects in the spring sky are galaxies, and kind of challenging to view.  For each of these objects, I hope to write up a little bit about the object, how to find it, what it looks like, and a bit about what the thing actually is - what we know about it, and how the object is being seen in modern astronomy.  Bold hopes!

.....The decision starts with the question of how to choose which things to look for.  Any star atlas will show hundreds of deep sky objects (objects outside of the solar system): double stars, variable stars, star clusters, nebulae, and galaxies.  How to choose?  The star atlas Sky Atlas 2000 has a tremendous number of objects, many requiring telescopes much larger than mine. (All references to specific products should not be taken to represent any relationship between myself and the producers of those products and myself - although, hey, this space for rent - these are representative products that I own, and that I will use for this project.)  If I use one of the catalogs of deep sky objects, then I could miss a lot of interesting objects left out by the list (such as the Messier Catalog, based off of observations made in the late 1700's) or objects out of my telescope's range (like many of the objects in the New General Catalog - the NGC from the 1840's, which replaced the General Catalog of the 1820's). 

.....I chose to use the Sky & Telescope's Pocket Sky Atlas, in the hopes that the editorial judgements made constructing this will leave material suitable for my quest, although there are some other objects that I'll throw in as well.

.....Well, tonight it is raining where I am, but I hope to get this show on the road tomorrow!  In the meantime, Happy Solstice!  (If you celebrate it.  If you don't, watch out for any large wicker figures.)

The June Sky of 2012

.....I am going to start a project on midsummer's night, but I'll talk more about that then.  Before I get to that to point, I hope to go through the types of things that can be seen in sky, as well as the different ways in which you can observe the skies (eyes, binoculars, telescope).  I hope you will be surprised by how much it is possible to see!

.....For now, here is an image of the night sky for June of this year.  This is an attempt to replicate the apparent bowl of the night sky on a flat screen (or piece of paper, if you print it out).  If you have never used one of these, if you are facing, say, south, then the stars above the "S" on the map will be aligned above the southern horizon.  If you are facing east, then turn the screen so that the "E"is at the bottom (maybe it would be easier to print this out), and those stars will be above the eastern horizon.

.....The brighter the star, the larger the dot on the map.  Star brightnesses are described by "magnitudes", in which lower numbers are brighter.  A star of the first magnitude is bright, while a star of the sixth magnitude is typically the faintest star that can be seen by the unaided eye.  My map has stars down to the fifth magnitude, because including all of the stars down to the sixth magnitude, both because this would leave the map crowded, and because most people are located where city lights drown out many of the fainter stars.  As a comparison, here it what these stars would look like if only the first magnitude stars were visible:

.....The view of the sky could be confusing, so the sky has been divided up into constellations.  The "official" set of constellations come from the Romans ... well, they have Roman names, but the figures were largely taken from Greek mythology ... except for the ones taken from Babylonian and Indian mythology.  The constellations with names printed in blue have already been discussed in blog articles here: Ursa Major, Ursa Minor, Bootes and Corona Borealis, Serpens and Ophiuchus, Libra, Scorpius, Hercules, Cygnus, Lyra, Draco and Aquila.  I hope to add more as quickly as I can.