The Perseid Meteor Shower of 2018

.....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.  A meteor shower is an event (more common and often less impressive than one might expect) in which there is an increase in the number of meteors over this random baseline of meteors, and those meteors appear to come from one preferential area of the sky.

.....The most reliable meteor shower of the year is the Perseid meteor shower, usually peaking on the night between August 11th and August 12th, but this year peaking on the evening of August 12th into early on the 13th.  The reason for this unusual variation (read: any variation at all) has to do with the nature of what causes this meteor shower. 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). For regular meteor showers, we need a regular source,, and that takes us to comets.

Images of Comet Swift-Tuttle taken by the astronomer (born in Tennessee!) E. E. Barnard in 1892

.....These are photographs of the comet (Comet Swift-Tuttle) that gives rise to the Perseid meteor shower.  The reason why comets appear with impressive comas (the area around the head of the comet) and tails is due to ice and particles boiled off the comet as the comet enters the inner solar system.  Sunlight reflects off of the highly reflective (i.e., shiny) ice, and makes the comet far more prominent than it would otherwise be.  The ice is broken down by sunlight, but as the ice boils off, small rocky particles are drawn off with it.  These particles don't just disappear - they can't.   They stay in the same orbit that the particles had when they were part of the comet, spread out by the small relative momentum they got (relative to the comet) as the particles came off of the central cometary body, smeared out a bit more over time as gravitational effects of distant planets.  Over a long enough time frame, this can fill the orbit of the comet with dust and pebbles.

.....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. We will get a special effect due to all of these particles following the same path, a particular effect will come from this.  Consider the Earth passing through a cloud of these particles:

.....It might appear from this sketch that since the meteoroids could hit the Earth anywhere on the leading half, that the meteors could come from anywhere in the sky, but what is important to remember is that the "sky", the stars that form the backdrop that we are looking against, are all very, very far away.




.....If one were to run those paths in the picture backwards, all of the paths would track back to a single point, far enough in the distance.  As seen against the stars, that point would be a specific point in the sky.  These 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).  In the case of the Perseids, most books state the an observer can see from 60-120 meteors per hour, but that comes with a couple of limitations.

.....That number assumes that you are observing the meteor shower with the radiant directly overhead from a very dark site.  With the radiant low in the northeast, even early in the morning one should expect to see perhaps 40 meteors an hour.  This year, the New Moon is on the 11th, so at least the Moon will have no effect.  If you are watching from an urban or suburban location, the fainter meteors will be lost against background light, so the number could be much less, even if the number of meteors is equal to what is expected.

.....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, which didn't happen very often.  Those memories are really helpful, of those times at our house and on vacation; of cool August nights in the UP of Michigan with my wife's parents; of nights with our friends at our own house. I have a lot of good memories of this shower.

.....Technically, the peak will be from Sunday afternoon through Sunday evening, but not only are those not good times to see meteors (against a clear blue sky), but I've always found it much easier to get rest on a Sunday than a working Monday, in any event.  Looking for Perseids can still be done in the nights leading up to the peak, although the number drops off pretty quickly after the peak has passed.


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

Finally, Another Lunar Eclipse!

.....After several years, there will again be a Total Lunar Eclipse (yes, I capitalized everything) early Tuesday morning . The east coast is not well set, but the Upper Midwest, the Southwest, and the West Coast have some potential. Give it a shot!  What have you really got to lose?

.....(Sleep.  The answer is sleep, but in the grabd scheme of things, this is our best lunar eclipse for a few years.)

.....To see this, all you need is a good view of the skies (from the Americas). If you have a telescope, or even binoculars, that will make things even better, but it isn't necessary.

.....The first stage is when the Moon enters the Earth's penumbra, the shadow where part of the Sun, but not all of it, is blocked. This will be pretty much undetectable. The Moon enters the penumbra at: 11:18 PM (CDT/ UT -6, which is 12:18 AM Tuesday in the Eastern Time Zone, and 10:18 PM in Mountain Daylight Time, and so on.)  The Moon will entirely be within the umbra by about 12:19 AM CDT, but again, this will still be hard to detect.

.....The Moon starts to enter the umbra, the central shadow at 12:21 AM (again, CDT, the best time zone) , and totality, with the Moon entirely in the umbra from 1:28 AM to 2:52 AM. 

.....On Earth, a total eclipse of the Sun is completely dark, but in a lunar eclipse, the light being blocked by the Earth behaves differently than light being blocked by the Moon.  The Moon has no atmosphere, so the shadow of the Moon is sharp, but the light must pass through the Earth's atmosphere.  Look at the sky -- the reason that the sky is blue is because the shorter the wavelength of light (the bluer the light is), the more than the light gets scattered.  The blue light is scattered first, and the setting Sun appears red because red light is scattered last.  This red light is spread into the shadow, and the totally eclipsed Moon will appear a deep red, sometimes getting so faint that theFull Moon is hard to find in the sky.

.....The Moon leaves the umbra at 4:00 AM CDT, so the party is then pretty much over.

.....This lunar eclipse happens after the Spring Solstice (believe it or not, those of us looking at snow tonight), so the Sun is getting higher in the sky.  The Full Moon (exactly on the opposite side of the sky) will be in Virgo, a bit lower in the sky.The Full Moon will be very close to the planet Mars and the bright star Spica.  Spica can be identified by starting at the Big Dipper, as follows:

.........If you follow the curve of the Big Dipper's handle, the curve will arc towards the bright star Arcturus, in Bootes (coming soon), and if you go past Arcturus, you will speed on to Spica, in Virgo.  Mars is the bright red object that will be a bit higher in the sky than Spica.  From the Upper Midwestern United States, the Moon will be about a third of the way up the sky at maximum eclipse, high enough, where it should be easily seen.

.....If you do get a chance to see it, please let me know!

A Dolphin Happening

.....The headline refers to the appearance of a newly visibly star in the tiny constellation of Delphinus the Dolphin - it has nothing to do with the Miami Dolphins' new logo.

Seriously, what the heck?

.....On August 14th, Japanese astronomer Koichi Itagaki took an image of this part of the sky, and saw the image of a star that had not been visible the previous night. Over the following nights, the star brightened to a magnitude of about 4.5 (a faint but definitely visible star if you have a decent sky, sketchy in a suburban sky, and a vain hope for city skies).  While it has dimmed a bit, and while the brightening moon is watching out all but the brightest stars, no matter why you are watching this from, the nova is easily findable in binoculars.

.....Delphinus is a small constellation, and it does not have any bright stars, but it is still relatively easy to find.  Here is a view of the summer triangle, below.

.....Delphinus is outside the triangle proper, close to Altair in Aquila.  While it does not have any really bright stars, the five primary stars are so close together in the sky that the constellation is relatively easy to find.  Find the Summer Triangle, start from Altair (the southern point on the triangle, look to the east and slightly north, and you should be able to find the Dolphin fairly quickly.  Even if you are looking tonight, when the Moon is bright and near the constellation, Delphinus is compact enough that I hope you can find the constellation in binoculars, with most (if not all) of the figure visible at the same time.  Now let us zoom in on Delphinus

.....Allow me to toss in a word about constellations versus asterisms.  A constellation is as "official" as it gets.  The official set of 88 constellations were designated by the International Astronomical Union in 1930, along with official boundaries.  the boundaries are useful in marking which things happen in which constellation.  For example, this is Nova Delphinus 2013 - even though the nova is well away from the traditional lines tracing out the figure, the nova is still inside the borders of Delphinus.  An asterism is any pattern that is not a constellation, but is still helpful or popular enough to use. The most famous asterism is the Big DIpper; This is but a part a of the constellation of Ursa Major, but the biggest and brightest part.  Many people who could not trace out the rest of Ursa Major can find the Big Dipper easily enough.

.....The asterism that I am adding to help find the nova looks to my mind something like the constellation of Hercules, so I am naming this asterism "Argolese".  No, not out of any part of mythology.  I'm going to the series of weak Italian strongman movies repackaged for America as the "Sons of Hercules" series.  (If you are going to watch it, watch it through here.)

.....To give directions, I'm going to need to refer get more specific than just "Delphinus", or even "Argolese".  I'm going to have to give directions using the stars themselves, so I'm going to need names.  Here is a map showing the names assigned to these stars:

.....The Greek letters, as I have explained before, are one way to identify stars without giving individual "names" to each one.  You might also notice that the names of the two stars that do have names have strangely appearing names.  Most stars with individual names have Arabic names, with some Greek and Latin.  What is up with "Sualocin" and "Rotanev"?  These come from Niccolo Cacciatore, an Italian astronomer making a star catalog who Latinized his own name (into Nicolaus Venator) and slipped it into the catalog.  (But not as "Nicolaus" and "Venator", no, that would just be silly ...)

.....Draw an imaginary line from d Delphinii through Sualocin and track that outward.  "Argolese" should appear above the line, and the nova will (at least of tonight) be notably brighter than any of the stars around it.

.....So what is this thing, assuming that it is a classical nova?

.....Consider a pair of stars orbiting a common center of mass.  One of stars, the more massive one, goes through its evolution more quickly, reaching and passing the point at which all of its outer mass is cast off (a good deal of that mass being cast off ends up on the companion), and the cooling core is left as a white dwarf.  Now observe the orbit decay, and the two stars spinning closer to each other, so close that the companion star is squeezed, matter starting to dump towards the white dwarf.  But the stars are moving so quickly that the stream of matter misses the white dwarf, and is caught up in a disk around the white dwarf.

.....This disk will keep building over time, until the pressure builds to the point where the hydrogen would begin to fuse into helium, releasing energy in the way that a active star does.  When matter surrounding the core of a star in the form of, say, a star, undergoes fusion, the outer envelope of the star holds it together through pressure.  Since the disk is only the cross-section of a star, the fusion consumes and destroys the disk, releasing a tremendous amount of energy for few weeks, and then, in most cases simply starts all over again with a new, forming disk.  And this is what you'd be looking at in Delphinus right now. 

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.