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    My Journey through the Astronomical Year

    Think of this as a "companion text" to this, the main web site. Not required reading, butI hope you'll find it interesting and helpful.

Events April 2014: Mars, the Moon, and the Earth’s Shadow – Yes, a Total Lunar Eclipse !

 

anatomy-of-a-lunar-eclipse-graphic

Love those Lunar eclipses, but who was in charge of the scheduling for this one? Some insomniac like me, no doubt, for on the East Coast of the USA where I live this thing really doesn’t pick up steam until about 2 am April 15, then continues until near when the Moon sets just before dawn. The West coast residents get a somewhat more timely view.

Here’s the schedule for those in the Eastern Daylight Time zone on the morning of April 15:

1:57 am partial eclipse begins

3:06 am totality begins

3:45 am mid-eclipse

4:25 am totality ends

5:33 am partial ends

The Moon sets about the time the Sun rises, which varies according to location. (Eclipses happen at the same time all over the world – but of course what time that is for your location depends on your time zone – and for some, the Moon simply won’t be in your sky during the eclipse hours.  For a complete guide to where this eclipse can be seen and when for your location, see the NASA eclipse pages.

There’s an incredible NASA eclipse Javascript on this page that delivers all sorts of eclipse data and time for anywhere in the world – however, I did notice that the times were  standard – so you need to adjust for daylight savings if relevant.

What adds a special touch to this eclipse is that Mars will be pretty close to the Moon from the time the Moon rises near sunset. I always like watching the fainter stars come out as the Moon goes into total eclipse, then slowly vanish as it comes back. But with this eclipse, Mars will provide a special treat with it’s ruddy hue shining brighter than any of the nearby stars – though Arcturus and Spica will both rival it.  Here’s a chart for my location – the same relationships will apply anywhere, but those farther west will see the orientation of the chart shift since the Moon and stars will be higher in their sky at this point.

 

eclipsed_moon

Click image for larger version. (Prepared from Starry Nights Pro screen shot.)

 

The Scorpion should be beautiful on the southern horizon. For me the Moon is about 22 degrees above the southwest horizon at this point. If you have trouble finding it – eclipses vary on how dark they get, then simply look for Mars and Spica – if you get Spica in binoculars the Moon will be in the same field about 2 degrees east of it.

April Planet Parade

Click image for larger view. (Made from screen shot of Starry Nights Pro.)

No, you can’t see the Moon – it’s eclipsed! (Actually, it can be quite red and fairly easy to see – or it can be quite dark and difficult to see during totality. ) Click image for larger view. (Made from screen shot of Starry Nights Pro.)

Jupiter is high in the western sky all month, setting in the wee hours of the morning; by the end of the month it sets closer to midnight, but is still brighter than any star or any other planet in the evening sky.

However, Mars rivals Jupiter, taking over in the eastern sky in the early evening hours and remaining visible all night throughout April. It’s in retrograde motion this month, which means it appears to climb a bit higher in our sky as the month goes on, moving west against the background of stars. This is the best opportunity for two years for telescope users to get a good look at Mars.

Saturn gets high enough to view in the eastern sky about three hours after sunset at the start of the month, and two hours after sunset by the end of the month.

Venus is best seen low in the east about 45 minutes before sunrise, and on April 25th has a nice pairing with the crescent Moon. While Jupiter is brighter than any star, Venus is two magnitudes brighter than Jupiter, so it shows up well even though it is well into morning twilight before it is high enough to see easily. I like finding pretty spots to try to capture the crescent Moon, Venus, and foreground landscape  in twilight.  Here’s a shot I got at the Town Farm in Westport MA when there was a similar  arrangement of the Moon and Venus in March 2014.

venus_moon_farm

Click image for larger view.

 

A Meteor Sprinkle

The annual Lyrids meteor “shower” is not nearly as intense as the Perseids in August or the Geminids in December, but if the night is clear it could be fun. It is supposed to peak (roughly 20 meteors per hour) on April 23 when a  waning crescent Moon will rise after 3 am and start to interfere some.

I must admit that with a shower like this I take it casually. That is, I go out and observe other things, but I keep an eye out for meteors, and if I see one, I try to trace its path backwards to see if it points in the general direction of the constellation Lyra – if it does, I assume it’s part of the shower and not a random meteor. You might see a shower meteor a few days before or after the peak, and it might come at any time of night in any part of the sky, but if I were going to pick an hour to keep a sharp eye out for Lyrids, it would be between 2 am and 3 am on the morning of April 23.

The Lyrids are believed to be remnants of Comet Thatcher, which orbits the Sun about every 415 years.

 

 

Look North in April 2014! See Mizar – the best thing since – well, since sliced bread!

In April the Big Dipper is climbing high overhead in the northeast and starting to pour its contents into the Little Dipper – not a very good idea, but fun to contemplate. Meanwhile, the only double star pair where both stars have proper names – Mizar and Alcor – is high in the northeast and ready to challenge your eyesight and boggle your mind.

Mizar is the middle of the three stars that form the handle of the Big Dipper – the same three that we use as an arc to trace a path to Arcturus. (That reference is explained in this month’s “Look East” post.) Wait until an hour or more after sunset, then focus on that center star. Is it one star – or two? For my old eyes, it is one. And since my eyes are not that bad, I question those who say this is an “easy” test of eyesight. But lots of people do indeed see two stars there when they look carefully. Maybe you’re one of them. If you’re not sure, or can see just one, take a look with your binoculars. Now you certainly should see two.

The brighter of the two is Mizar, the fainter one Alcor. More on that in a minute. First, here’s our northern sky for this month.

Arrows indicate directions in the sky where north is always the direction towards the north celestial pole, and west is always the direction the stars appear to move. Click image for larger view. (Developed from Starry Nights Pro screen shot.)

Download a printer-friendly version of this chart here.

And here’s what you should see when you look with binoculars at the Big Dipper’s handle.

Zooming in on the center star in the Big Dipper’s handle using binoculars, you should see it is really two stars – Mizar and Alcor. Click image for larger view. (Developed from Starry Nights Pro screen shot.)

The words “double star” simply mean that a star that appears as one to our naked eyes, is seen as two when optical aid is used. But they may simply be two stars that are closely aligned, yet in reality very far apart and have no real connection to one another. “Binary star” is the term used for two stars that are gravitationally linked to one another. So here’s the double rub with Mizar:

  • When you are looking at Mizar and Alcor, you probably are looking at six stars, not two!
  • Scientists still dispute whether Mizar and Alcor are a true double, even though they have been observing this system with telescopes since 1650!

My “sliced bread” reference figures into the Mizar/Alcor picture in a roundabout way. I have trouble remembering things. So when I wanted to remember the approximate distance to Mizar – 80 light years – I asked myself what interesting thing was going on 80 years ago that can help me remember the distance to these stars? And the answer – given a little research – was that about 80 years ago America was introduced to sliced bread all packaged neatly. Actually, sliced bread was first introduced in 1928, according to Wikipedia, but it was in 1930 that the first national marketing campaign began for “Wonder Bread.” Wonderful. So about 80 years ago the light you see left Mizar and Alcor to begin its journey to your eye.  Don’t let the different dates bother you because an approximation is close enough.

And Mizar alone is a lot more interesting than sliced bread.

Even a small telescope reveals that Mizar itself is a beautiful double! That’s what was revealed when a telescope was turned on it in 1650. But no telescope can reveal to the eye that these two stars are in fact, each a double! The stars in each pair are so close to one another that only an instrument known as an interferometer can reveal them. So what we see as Mizar is in fact four stars. (Double stars are a special love of mine, and I wrote about observing Mizar  in the double star blog I share with John Nanson here.)

But what about Alcor? The Hipparchos satellite, the best modern source for star distances, found Mizar to be 78.1 light years away and Alcor to be 81.1. Those are great ball park figures and good enough for the sliced bread reference. But they may be wrong. The astronomer James Kaler wrote a few years ago in his book “The Hundred Greatest Stars” that these distances may be wrong – in fact, some evidence suggested then that Mizar was actually farther away than Alcor. Kaler concluded in his book that they are “probably paired.”

But now comes more evidence as reported in the current (2014) Wikipedia reference to Mizar:

. . .In 2009, it was independently reported by two groups of astronomers (Eric Mamajek et al., and Zimmerman et al.) that Alcor actually is itself a binary, consisting of Alcor A and Alcor B (a red dwarf star), and that this binary system is most likely gravitationally bound to Mizar, bringing the full count of stars in this complex system to six.

So what our naked eye reveals as one or two stars, may indeed be a complex system of six stars! Which in my mind says that slicing up Mizar and Alcor this way may be – well, may be the best thing since sliced bread and just the sort of thing that makes observing the stars such a treat for the eye and mind!

Look East in April 2014 – take a simple slide to the World’s Fair Star and bump into Mars as a bonus!

 

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The name”Arcturus” derives from Ancient Greek and means “Guardian of the Bear.” It is the brightest star in the constellation Boötes. Click image for a much larger version. (Prepared from Starry Nights Pro screen shot.)

 

Click here to download a printer-friendly version of the above chart.

Arcturus isn’t universally known as the “World’s Fair Star,”  but  it should be.  Its light bridged two World’s Fairs, making an astronomical link between the one in 1893  and a second in 1933 – both held in Chicago.  It’s intriguing that  the general public was excited enough about science – in the middle of the Great Depression – to make such a link attractive to the Fair’s promoters. Light from Arcturus  – believed at that time to be 40 light years away – was captured by the 40-inch refractor at Yerkes Observatory and its energy used to turn on the lights for the 1933 Fair.

This put the public spotlight not only on Arcturus, but it raised consciousness about the vast distance between us and that star, since the light being used had started its journey during the 1893 Fair and arrived just in time to start the next Fair. When you know light can circle the Earth more than seven times in a single second, you start to understand just what an incredible journey that was.

Of course Arcturus has many other distinctions. For one thing, it makes a perfect connection with the best known asterism in the sky, the Big Dipper.  To find it, all you have to remember is “follow the arc to Arcturus.

And in 2014 you get a bonus – keep following that arc and you’ll quickly come toa slightly brighter “star,” the planet Mars! More about that in our “events” post for April, but I did add Mars to this month’s “look east” chart. It forms a nice triangle with Arcturus and Spica, another bright star we’ll meet next month as it’s quite low this month.

Getting back to Arcturus – another way to remember where to find Arcturus is its name, derived from ancient Greek, which can be translated as “Bear Watcher.”  That’s because Arcturus looks like it’s keeping an eye on the “Great Bear,” Ursa Major, as both circle the northern pole.

You can also think of the magnitude system by which we rate the brightness of stars as starting near Arcturus. At magnitude minus .04 it’s about as close to zero as you can get – the minus sign indicating it is a tad brighter than zero.  Its absolute magnitude is also pretty close to zero since absolute magnitude is defined as how bright a star would be if it were about 33 light years from us, and by modern measurement Arcturus is now believed to be about 37.6 light years from us.  That makes its absolute magnitude -.29.

Arcturus has the distinction of being the brightest star in the northern celestial hemisphere, but this is splitting hairs in several ways. It means it’s the brightest star north of the celestial equator. Sirius, now over in the southwest, is obviously  brighter. But Sirius is south of the celestial equator. Both stars are located close enough to the celestial equator so they can be seen from most places on Earth.

It’s interesting to note, however, that Mars is outshining it this month- by quite a bit. In round numbers, Arcturus is zero, Mars is minus 1.2 and Sirius, setting in the est early on April evenings, is minus 1.5.

But Arcturus (-.04) also wins the “brightest star in the northern hemisphere” distinction by another hair. Remember that the lower the magnitude number, the brighter the star. Both Vega (.03) and Capella (.08) are north of the celestial equator, and the difference in brightness between Arcturus (-.04), Vega (.03), and Capella (.08) is roughly a tenth of a magnitude.  For practical purposes, they all look the same.  But in practical terms, making the comparison by naked eye is – well –  very impractical. Capella is currently fairly high in the northwest. But next month, when Vega is high enough in the east to see well,  Capella will be rather low in the northwest. At that time Arcturus should look brighter – but its actual brightness will be aided by the fact that it is high over head at that time, so you are seeing it while looking through a lot less air than you will be when looking at Vega or Capella. Besides, visually trying to compare stars that are this far apart in our sky is next to impossible since you have to look away from one to see the other. I simply think of all three as magnitude zero and leave the hair splitting to the scientists and their instruments.

Oops – we interrupt this program for a bulletin from 1907!

Yes, having just written how impractical the naked eye comparison is, I found this passage in “The Friendly Stars” by Martha Evans Martin, a book that was published more than a century ago:

Arcturus and Capella are so nearly equal in brightness that astronomers differ as to which outranks the other, even when they measure  their light with a supposedly accurate  instrument and a trained eye. To my own eye Arcturus outshines Capella, and on asking various inexperienced persons for off-hand opinions as to the relative brightness of the two stars, I have invariably had an answer in favor of Arcturus. The best authorities, however, make Capella a shade brighter.

Oh my! And now with 100 years of scientific progress, the verdict is that Martha Evans Martin and her causal observer friends were correct – and the “best authorities”  wrong. Arcturus is the brightest.  So much for my idea that you can’t tell the difference with the naked eye! Give it a try and see what you think. (You can find a chart for Capella and more details about that star  in this post.) Since we’re ranking stars, however, Arcturus is actually fourth on the list of brightest stars – two others that are ahead of it, Canopus and Rigel Kentaurus, are not seen by observers in mid-northern latitudes. Sirius, of course, is.

While Arcturus radiates a lot of energy, much of it is not in the form of visible light. It has what’s known as a “peculiar spectrum” and radiates much of its energy in the infrared portion of the spectrum.  This means that to our eyes it doesn’t look as bright as it really is.

Orange-ish Arcturus is 215 times as bright as our Sun and 25 times the Sun’s diameter. (Image courtesy of  Windows of the Universe.)

One more deception of sorts: This brightness is not because Arcturus is so big – well , yes it is, but not big in terms of the amount of stuff in it, but big in terms of surface area. If you’re measuring the amount of stuff that makes up Arcturus – its mass – it is about the same size as our Sun. But Arcturus has a much greater surface area, so think of it as a hugely bloated version of our Sun. (Keep that in mind when you look at the comparison sketch above.) It is a much older star and is now going through its red giant phase, something our Sun will probably do several billion years from now, burning the Earth to a cinder in the process.

Hmmm . . . to get an idea of how much impact that large surface area has, if you put our Sun out near Arcturus it would be barely visible to the naked eye – and then under truly dark –  not light polluted – skies.

Vital stats for Arcturus, also  known as Alpha Bootes:

•    Brilliance: Magnitude  -.04, brightest star in the celestial northern hemisphere; shines with the luminosity of 215 Suns.

•    Distance: 37 light years

•    Spectral Type: K1 Giant

•    Position: 14h:15m:38s, +19°:10′:5

Guideposts reminder

Each month you’re encouraged to learn the new “guidepost” stars and asterisms rising in the east about an hour after sunset. One reason for doing this is so you can then see how they move in the following months. So if you have been following – even if this is just your second month – look for the previous guidepost stars and asterisms that you have learned and that are still with us in April. Here’s the list from east to west.

  • Arcturus
  • Leo’s Rump  (triangle)
  • The Sickle
  • Regulus
  • the Beehive
  • Procyon
  • Sirius
  • Pollux
  • Castor
  • Betelegeuse
  • Orion’s Belt
  • Rigel
  • Capella
  • the Kite
  • Aldebaran
  • the Winter Hexagon
  • the Pleiades 
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