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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 for April 2011: Saturn is the show – almost the whole show!

April 2010 Astronomical events

Note: While many events are visible throughout the world, the exact time and location in the sky can be dependent upon your latitude and longitude. Since I’m in the mid-northern latitudes (41.5N, 71.1W), specifics, where place-dependent, are calculated for this location.

Saturn is the real planet story for April 2011. Though Venus does continue to put in an appearance just before dawn, Saturn reigns in the night sky as the only planet visible.

This is the brightest Saturn has been in three years – nearly as bright as Arcturus, the guidepost star that dominates our eastern sky and is about as close to magnitude zero as you can get. Saturn is at magnitude  0.4 and easily found as it rises in the late twilight  about 30 degrees  – three fists held at arm’s length – south of Arcturus. Our “look east” star chart shows it well for mid-month, about 45 minutes after sunset.

Arcturus and Saturn dominate the eastern horizon during evening twilight in April - and, of course, are visible the rest of the night. Click for larger image. (Preapred from Starry Nights Pro screen shot.)

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

Unfortunately, the feature that makes Saturn most interesting – its rings – does require a small telescope. Binoculars – especially more powerful ones – may hint at the rings by showing the planet with tiny “ears” on either side, the way Galileo saw it. But the smallest telescope will reveal a charming image  of the planet and the rings, which are tilted now more than they have been in recent years and so are easy to spot.

Saturn reaches opposition in early April – which means it’s opposite the Sun  and thus rises as the Sun appears to set at nightfall.

As it grows darker you may notice an arc of third magnitude stars just above Saturn and running roughly northeast to southwest. The star of these three that is just a few degrees west of Saturn is one of the most famous and beautiful double stars in our sky, “Porrima.” A medium-size telescope trained on this star on a still night will show it is really two stars very close to one another and about as identical in brightness and color as two stars can be! It’s a charming sight that would not have been seen just a few years ago unless you had a very large instrument.  The reason is that the two stars are in a 169-year orbit around one another and reached their closest juncture just  six years ago.  Now they are slowly getting farther apart and thus easier to see as a pair.  When closest they are separated by about four times the distance between the Sun and Earth. When farther apart that separation is about 81 times the distance between the Sun and Earth, so the orbit is very elliptical.  If you have a telescope, you may enjoy reading more about them in the double star blog I do with my friend John Nanson, found here.

Catch the start of the morning planet parade!

Venus rises in the east-southeast about an hour before the Sun and at magnitude  minus four it is easy to spot in the pre-dawn – though keep in mind, even at daybreak it is only about 10 degrees – one fist – above the horizon. On April first from my location on the East Coast it may be possible to find a very slim, crescent Moon roughly 12 degrees north of Venus and about the same altitude. Using binoculars will help.

And using binoculars will be essential if, near the end of the month, you want to catch the start of this spring parade of planets in the morning.  This will get better in May, but on April 30 if you have an unobstructed eastern horizon and look from about half an hour to 15 minutes before daybreak, you may catch some of these planets.

Morning planets, April 30, 2011, as viewed from mid-northern latitudes on the East Coast of the US. (Prepared from Starry Nights Pro screen shot.)

The Moon will be a thin, waning crescent, but high enough so it should not be too difficult to see. Venus will be obvious. Mercury and  Mars are both first magnitude objects and so will be very difficult to spot as they rise in strong twilight. Jupiter – much brighter at Magnitude  -2 – should be easier, but being close to the horizon means you’ll be looking through a lot of air, and if there is any haze or clouds they’ll easily wipe it out. Binoculars are a must, but as daybreak nears, give it up! You don’t want to chance seeing the Sun in binoculars and thus damaging your eyes.  If you don’t find the planets within 15 minutes of daybreak put down you binoculars and enjoy the waning twilight.

April meteors

I hesitate to even mention these, but there’s always a chance.  In the morning on April 22 and 23rd the Lyrid meteor shower should put in a weak appearance. The Lyrids excite folks largely because they have unpredictable outbursts that on rare occasions can be spectacular. This year will not be one of those occasions if the experts are correct, and this meteor shower, weak enough as it is, will be competing with a Moon just four or five days past full. So, if you’re feeling lucky – very lucky … 😉

The Moon

  • New Moon – April 3, 2011
  • First quarter – April 11, 2011
  • Full Moon – April 17, 2011
  • Last quarter – April 24, 2011

And then there are those man-made objects in space!

There are some special astronomical events  that we don’t list here because they’re very specific to where you live and when you observe. These are events involving man-made objects in space – the passages of the International Space Station, Iridium flares, and other bright satellite and space craft passages. There are two excellent ONLINE sources for such events. I urge you to check both, see how they differ, and then make your own decision as to what works best for you.

  • The first is provided by Spaceweather, and you’ll find it by going to their Web site and clicking on the “Satellite Flybys” link on the top.
  • The second is the Heavens Above site, and while this requires you to register, the process is painless and free and the result is a lot of information that is specific to your location. You need to know your latitude and longitude, but you can get those by using the link in the “configuration” section near the top of the Heavens Above page. This is a one-time process. Once registered and logged in, study the menu – there’s a wealth of information on satellites and many other things.

Northern Lights!

And while on the subject of special events, the Sun is growing more and more active these days and that means a greater and greater chance of a beautiful display of northern lights.  This leads me to check Spaceweather frequently , for they will alert you to these displays for which there is only a day or two advanced warning.  Besides, it’s a fascinating web site with lots of interesting photos, worth checking every day anyways.

Look North in April 2011! 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 discovering this system since 1650.

My “sliced bread” reference figures into this dispute 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. But don’t let the different dates bother you because the exact distance to these stars is in dispute.

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 my double star blog 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 (2010) Wikipedia reference to Mizar:

. . . in 2009, it was reported by astronomer Eric Mamajek and collaborators that Alcor actually is itself a binary, consisting of Alcor A and Alcor B, 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 mind!

Look East: April 2011 brings the World’s Fair Star and Saturn!

In 1933 it was believed Arcturus was 40 light years from us, so it was appropriare to use its light, which would have begun its journey when the 1893 World's Fair was in progress, to turn on the lights for the 1933 Fair. The 40-inch telescope at Yerkes Observatory captured the energy from Arcturus to do this. Click image for larger view.

Arcturus isn’t universally known as the “World’s Fair Star,”  but  it should be.  Its light bridged two World’s Fairs , making a physical 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 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.”  That should keep you from confusing it with the bright “star” to the south of it shortly after sunset on these April 2011 nights – the ringed planet Saturn. Saturn will be about the same altitude as Arcturus, but 30 degrees (about three fists held at arm’s length – to the south. Even binoculars won’t reveal the trademark rings, however – for that you need a small telescope. Here’s the chart.

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.

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 -.04 it’s very close to 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 Arcturus is actually 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.

But Arcturus (-.04) also wins this “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 only a tad more than 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 is next to impossible. 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 athorities, 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.

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.

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, Mars, Procyon, Sirius, Pollux, Castor, Betelegeuse, Orion’s Belt, Rigel, Capella, the Kite, Aldebaran, the Winter Hexagon, the Pleiades.

Building MESSENGER – the Model

NASA provides a neat little model you can make of the MESSENGER spacecraft by simply printing out the directions and doing a little cutting and folding. You can download it here. And if you have the energy and time, you can build a more sophisticated version by downloading this.

If all goes well, MESSENGER will become the first spacecraft ever to go in orbit about the planet Mercury. It will do so on March 17, 2011.  You can read all about MESSENGER – and how to see Mercury yourself  in March of 2011 –  by going to our March “Events” post.

Here are step-by-step photos of building the first – and simpler – of the two  MESSENGER models.  We’ve added a simple way to effectively display your work.

Tools:

  • scissors
  • paper glue (we used rubber cement)
  • model knife (optional)

Materials:

  • 4 sheets of paper – we used  24lb
  • a couple coffee storrers,  pipe cleaners, or something similar (most straws are too big around)
  • short length of  black thread
  • small piece of clear tape
  • paper clip

Building time is about 30-40 minutes.)

Step-by-Step

1. Assuming you have printed out the sheets, cut out the spacecraft body. (Click on any image to view a larger version.)

2. Cut out the three white circles (indicated by arrows) on the spacecraft body. I found a model knife was best for this. (You can actually do this as the first step – but in any event do it before folding.)

3. Fold along white lines to make the box-like body.

4. Put fast-drying glue on the edges of the folds.

5. Finish spacecraft body and set aside to dry.  Cut out the gold spacecraft sunshade.

6. Fold and  glue sunshade together with color side out.

7. Cut out the strip labeled “bridge,” fold lengthwise, and glue together, color side out.  Set aside to dry.

8. Cut out solar panels.

9. Fold, but do not glue together until you have noted the position the boom (coffee stirrer) will be inserted, This is marked by dotted lines on the dark side of the solar panels.

10. Put glue onthe inside being careful to leave the area marked by the dotted lines free of glue. (A tad tricky, since the lines are on  he other side.)

11.Fold the bridge along the dotted lines and glue one side of it to the spacecraft body in rectangle outlined on it.

12. Put glue on the taps of the bridge, then glue the sunshade to it. Set aside to dry.

13. We found that it was difficult to simply stick the boom into the slots left for them in the solar panels, but these slots were easy to open with any sharp object,. We used a toothpick to do the job.

14. We mounted one solar panel tot he boom,t hen slid the boom through the wholes in the spacecraft body.  We did not glue the solar panels as they seemed to fit tightly enough.

15. Here’s the almost finished spacecraft before  folding the sunshade to give it an arched shape and adding the thread and paper-clip hook to display it. Note the solar panels and gold side of the sunshade are pointed in the same direction – which would be towards the Sun with the instruments aimed at Mercury.

16. Ooops – alomost forgot the boom. Didn’t have a straw, or stirrer as recommended, so we used a pipe cleaner, cut down to size. We also folded the sunshade into a gentle arch that looks more like the pictures of the craft.  However, we found it awkward to display  the spacecraft properly by just sitting it down on something.  So we added a piece of black thread to the top, center edge of the sunshade with clear tape. On the other end I tied a paperclip , bent into a hook to make an easy hanger.  Here’s the thread taped to the sunshade.

17. And here’s the finished model, dangling under the lamp over the dining room table – a fitting. space age centerpiece for March, 2011! Hey – it’s a space craft. It’s not supposed to sit on the table. it’s supposed to be out there flying.

Looking at this  little modest model gives me pause . I try to develop a sense – in myself and in my visitors to Driftway Observatory – of the incredible emptiness of space by having one person hold a soccer ball representing our Sun while another visitor holds a 2mm glass bead representing our Earth.  On this scale Mercury would be less than 1mm in diameter – barely visible even when in your hand.  But I ask the person with the bead to hold it at what they think is the correct distance from the Sun. Usually they guess this to be a foot or two away – sometimes boldly they move several feet away. But no one guesses the correct answer, which is about 75 feet away. Now think of that. A 2mm bead – Earth – out at 75 feet from our soccer ball Sun!   Another 2mm bead – Venus – would be placed at about 54 feet out from the Sun.  And then a third, tiny Mercury – at roughly 29 feet.

And now try to imagine how tiny the real MESSENGER  spacecraft – roughly the size of a table – would have to be made to fit into this scale model! Then close your eyes picture the MESSENGER entering this vast, empty interplanetary ocean  and traveling for seven years in that emptiness, then arriving at just the right spot and just the right time, to be placed in orbit.  This vital little craft with its complex instruments going all that distance – almost 5 billion miles in total at speeds that sometimes exceeded 140,000 miles an hour.  (To put that in perspective, the fastest rifle bullet goes about 2,700 miles an hour and our Apollo astronauts traveled about 25,000 miles an hour during part of their lunar journey.

And all around Messenger is just about nothing except for a hostile emptiness and the incredible heat of our Sun as it moves in close.  Awesome! Just plain awesome. Three cheers for little MESSENGER – and three cheers for us – a species that dares to challenge the hsotile vastness of space, and send it’s robot silicon  and ceramic envoys on a mission of exploration for new knowledge.

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