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.

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

 

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, 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.

The Transit of Venus from Winona, Minnesota

.....I was a bit jealous of a friend of mine who lives in Japan, and who would therefore have the Sun above the horizon for the entire time that Venus was transiting the Sun, only to find out that he barely got to see any of it, due to clouds.  We were much luckier in Minnesota.  The sky was clear for all of the transit, from the first kiss of Venus on the Sun until sunset, about three and a half hours later.

And there were ducklings.  Ducklings are cool.

.....My setup point was on the eastern side of Lake Winona, where we had an excellent view of the western horizon.  I didn't really advertise this fact with any real lead time, so this location let me attract interest from really quite a lot of people walking around the vicinity.  (I must specifically thank Tony Thelen, who had come to see the transit and did a lot to invite/collect/waylay passers-by to take a look.)

Trying to center the Sun

.....Solar observing adds complications, because if you do the wrong thing, you do nigh-instantaneous long-term damage to your eye.  There were two safe observing methods that I used for this event.  On the front of the telescope, I have a solar filter that blocks out the vast majority of the light, especially ultraviolet light.  Since I don't have a solar filter for my finderscope, and I seriously doubt that one exists, I try to get the Sun in view by making the shadow of the telescope as small as possible.  Even then, I usually need to take a few seconds "wandering around" in the sky.  

.....The Sun against the sky in not really a very large target, it only covers an area of the sky about one-half of one degree.  You could fit 360 Suns, side-to-side, across the sky from horizon to horizon.  Hold out at dime at arm's length, and you will easily cover the Sun.  In a telescope with a solar filter, the Sun appears as a bright yellow disk of light, and nothing else is even bright enough to show up.

And hanging out with the ducklings

.....I had done this part many, many times before, so all that was left was waiting for Venus to appear at the edge of the Sun.






.....Venus is closer to the Sun than the Earth; this is why Venus can be seen passing in front of the Sun.  It also means that we never see all of Venus against the sky.  When Venus is visible in the morning or evening sky, it is brighter than anything besides the Sun and the Moon, but seen through a telescope, Venus shows phases like the Moon.  Half of Venus is always lit, half of Venus always faces the Earth, but these can't be the same halves while Venus is visible, as shown below.

 

.....In fact, the only time we can see the full disk of Venus is when we cannot see Venus at all, when Venus transits the Sun.  What we see is the silhouette of Venus blocking the light of the Sun.  The dark marks on the Sun that are not the shadow of the planet Venus are sunspots, places where the Sun's magnetic field has been gnarled such that the magnetic field lines spring out from the surface, trapping gas at these kinks.  This gas isn't able to get replaced by new hot gas bubbling up from below, so it cools to a mere 7500 Fahrenheit, as opposed to the 10,000 Fahrenheit of the rest of the Sun's surface and appears dark against the much hotter surface.

.....When looking at something in a telescope, the image moves across the field of view due to the rotation of the Earth.  (Or, as it appears against the sky, celestial objects rising and setting.)  In this case, watching Venus move across the Sun is actually watching Venus moving in its orbit.  You can watch real change happening!  I think that this is one of the appeals in this type of astronomy.  The idea of the ancients that the heavens were eternal and changeless is still a pretty good day-to-day guide.  The Sun Moon, and planets make patterns, but something like this (that happened last in 1882, and then 2004, and the next one will be in 2117) lets us in to get a opportunity to mark one moment as separate and unique, to share with everyone else watching just at that moment.
 

.....Many ephemeral astronomical events are actually dependent on where you happen to be standing.  If you see a meteor, you share that with everyone else in a hundred miles or so, as that is small matter heating up in the Earth's atmosphere.  In a solar eclipse, such as the annular eclipse two weeks back (not well set up for most of the continental United States) the path of the eclipse is moving across the surface of the Earth, so where you are matters.  For this case, everything was happening 30 million miles away, so if you got to see it, you shared that moment with every other person on Earth watching at that time.

Speaking of these events ...

 .....The next solar eclipse will be on November 13th, but unless I have an audience in northernmost Queensland, you won't get to see totality. Northern Australia also gets an annular eclipse on May 9th.  North America gets a really good solar eclipse on August 21st, 2017, but I have plenty of time to write about that.  The next lunar eclipse for North America will be on April 15th, 2014. 

.....Happily, (with special thanks to my wife, and to Anthony Thelen, who are apparently much more accessible to people than I am when say "Hey, come look at the Sun!") a good time was had by all.

 

Photos by author (Sun, sunset), and Anne Marie Leckenby everything else.