• Choose a month

  • Rapt in Awe

    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.

Look East in April 2012 – take a simple slide to the World’s Fair Star and continue on to Saturn!

In 1933 it was believed Arcturus was 40 light years from us, so it was appropriare to use it's light, which would have begun it's journey when the 1893 World's Fair was in progress, to turn ont he lights for the 1933 Fair. The 40-inch telescope as 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.”  What’s real cool this April is you can slide on down from the Dipper’s handle to Arcturus, then keep sliding along the same curve and you will hit another bright “star,” Saturn. At the beginning of the month you’ll have to wait until about two hour after sunset for this to be easy, but by mid month it should be obvious an hour or so after sunset assuming you have an unobstructed eastern horizon.  Saturn will be about one fist  – 10 degrees – above the horizon then.  And by the end of the month it will be higher still.

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.)

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 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.

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.

Look North in April 2012! 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 osberving this system 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. But 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 (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 eye and mind!

Close encounters of the Venus kind! March, April, May, June 2012 – Mark your calendar!

(Go here for a personal update on observing this even – with pictures.)

Venus is a visual treat any night – and for that matter day –  this spring, dazzling us in the western sky right after Sunset as it puts in it best performance of this year and has close encounters with the Moon, the Pleiades, and finally the Sun itself. This last is a once-in-a-lifetime-appearance – the other events are less rare, but, of course, the weather has to cooperate.  Nothing is needed for most of these experiences but your naked eye, though binoculars help and a small telescope makes it even more fun. The last event – the encounter with the Sun – does require a telescope and one with a special filter to make viewing safe.

Here’ s a quick visual guide to Venus events, followed by a guide on how to find Venus in broad daylight – no kidding – and what’s more, late March through April is the best time to try to see this brilliant planet at mid day! I’ll update this post for May. Please note, the charts are specific to my location which makes them generally best  for the East Coast of the US. You can see this show from anywhere in the world, but the exact positions of Venus and the Moon on any given evening will vary somewhat depending on your latitude and longitude.

March 25, 2012

About 10 degrees separate Jupiter from Venus and Venus from the Pleaides - but the Moon and Jupiter should fit in the same low power binocular field, as should the Moon and Venus on the next night. Prepared from Starry Nights Pro screen shot - click to enlarge.

March 26, 2012

About 10 degrees separate Jupiter, Venus, and the Pleaides - but the Moon and Venus should fit in the same low power binocular field, as didthe Moon and Jupiter on the previous night. Prepared from Starry Nights Pro screen shot - click to enlarge.

March 27, 2012

Jupiter, Venus, and the Moon form a nice line that marks the ecliptic - the plane of our solar system, and if you look to the East you'll see this path completed by Mars. Prepared from Starry Nights Pro screen shot - click to enlarge.

April 2, 3, and 4 – a once-in-eight-years encounter between Venus and the Pleaides!

You really need binoculars to see this because the glare of Venus will mask the most beautiful of star clusters, the Pleiades. The encounter will be best on April 3 - but nice the night before and after. Click to enlarge. Prepared from Starry Nights Pro screen shot.

Venus gets near the bright stars of the Pleiades every eight years. This year it will pass through the south side of the cluster, which means that on April 3 , using binoculars, you should be able to see Venus to the left of the four core bright stars in the cluster.  The mythological implications are staggering – I can see the headlines in Ancient Greece now –  Goddess of Love Meets Seven Sisters!  Here’s how Wikipedia sums up their sex lives:

Several of the most prominent male Olympian gods (including Zeus, Poseidon, and Ares) engaged in affairs with the seven heavenly sisters. These relationships resulted in the birth of their children.

  1. Maia, eldest of the seven Pleiades, was mother of Hermes by Zeus.
  2. Electra was mother of Dardanus and Iasion, by Zeus.
  3. Taygete was mother of Lacedaemon, also by Zeus.
  4. Alcyone was mother of HyrieusHyperenor and Aethusa by Poseidon.
  5. Celaeno was mother of Lycus and Eurypylus by Poseidon.
  6. Sterope (also Asterope) was mother of Oenomaus by Ares.
  7. Merope, youngest of the seven Pleiades, was wooed by Orion. In other mythic contexts she married Sisyphus and, becoming mortal, faded away. She bore to Sisyphus several sons.

April 22, 2012

The late April show may not have all the appeal of the one in late March, but it's still nice. You will probably need binoculars to pick out Jupiter, even though it is still quite bright. Prepared from Starry Nights Pro screenshot - click to enlarge.

April 24, 2012

On April 24, 2012 the Moon splits Aldebaran and Venus, though Aldebaran may be hard to see despite being a first magnitude star, so you may have to use binoculars. Prepared from Starry Nights Pro screenshot - click to enlarge.

April 25, 2012

On April 25, 2012 the Moon is still close enough to Venus to make an interesting combination. Prepared from Starry Nights Pro screenshot - click to enlarge.

May 22, 2012

On May 22, 2012 the situation looks much different.  Venus is now getting much closer to the Sun – remember it has a date with the Sun in early June – but it still gives us one more nice combination with the Moon. Again, unobstructed western horizon is important.  The other stars named in the chart are all bright “guidepost” stars but may be difficult to see in strong twilight – however, they will be the first to appear as twilight fades. Prepared from Starry Nights Pro screenshot – click to enlarge.

June 5, 2012 – Once-in-a-Lifetime Show – Venus transits the Sun

As I wrote in January

So circle June 5, 2012. What is a transit of Venus? It’s a time when we can see Venus as a black dot cross the disc of the Sun – a time when Venus is actually between us and the Sun – and it happens rarely.  There have been just seven such transits since the invention of the telescope! And – of course – be careful! You will need special equipment to observe such a transit. Never look at the sun either with your naked eye or any  binocular or telescope unless it is one especially equipped just for looking at the Sun.  Such equipment isn’t expensive, though, and if you already have a telescope, would be a good investment to consider for this event and to regularly see  sunspots. I’m sure there will be several public observation points set up for those who don’t have such a telescope.

More details will be provided in May.

Orrery View – why we see what we see – the dance of the Moon and planets

The dance between the  bright planets and the Moon is always fascinating, but made all the more so if you understand what is going on back stage – why we see what we see.  To do that, I suggest you study the following Orrery views taken from the Solar System live web site. Take care to note the line of sight between earth, a given planet, and the Sun.  Everything is in motion,of course, but the motions that count the most for the changes we see in our Western sky right now from night-tonight are these:

  • The  moon moves about 12 degrees – more than our extended fist – each evening because of its orbit around the Earth.
  • Venus moves relatively quickly, so it’s change of position is a combination of its own movements and the motions of the Earth as we both circle the Sun.
  • The changes in how we see Jupiter are primarily caused by our own motiona round the Sun. Jupiter is in motion, but it is slower and so far away that it takes weeks, if not months to notice its motion against the background of stars. However, as with the stars, it’s position change a little each night because of the motion of the Earth.

And on June 5, 2012 – the day that Venus will transit the Sun, here’s a close-up view of the line-up of Venus, Earth, and the Sun.

In April 2012 you can meet the Goddess of Love in broad daylight – no fooling!

Actually, you can do it right now. We’re talking Venus, here, and our sister planet is so bright even in March that you can see it with the naked eye in the middle of a clear day! All you have to do is know when and where to look – and please, please avoid the nearby Sun!

What’s more, April is the best time to look for it this year because this is the month when it is at its brightest and also near it’s greatest distance from the Sun. That great distance makes it easier to see – and safer.

Here’s how. On a clear day look for Venus in the path the Sun took across the sky, but about forty -five degrees behind it. (Use your fist to get a rough idea, remembering one fist, held at arms length, is about 10-degrees.) Use binoculars and once you spot it and know exactly where to look, use your naked eye. And play it safe by leaving the Sun blocked from sight by a nearby building, tree, or other obstacle.

OK -let me expand on those instructions and give you some specifics and hints of how best to do this.

First – the day should be clear – really clear with the bluer the sky the better. Not all “clear” days are equal. Astronomers are looking for “transparency” as well, which means you don’t want a milky, white sky.

 Second – You should know that Venus follow the same general path as the Sun does across the sky – sometimes behind it (as now), and sometimes ahead of it. Usually Venus is too close to the Sun to easily – and safely – pick out. But this April – and for that matter the end of March – it well be separated from the Sun by about 45 degrees – the most it will be all year.

 Third, pick your viewing location carefully.  Everyone should know not to look at the Sun, but I don’t want your enthusiasm for seeing Venus in daylight to lead to an accidental viewing of the Sun – and besides, this will make the seeing easier. STAND ON THE EAST SIDE OF A BUILDING AFTER THE SUN HAS PASSED SO EVEN IF YOU ACCIDENTALLY LOOK TOWARDS THE SUN, YOU WON’T SEE IT!

Fourth, pick your time – generally from noon until sunset, but I think the best time will be when Venus is highest in the sky – near what is called it’s “transit.”  That gives you a good place to look – due south and roughly at the same altitude as the Sun was at around noon.  In April, 2012, Venus transits about three hours after the Sun. In other words, if you know when the Sun is at its highest point – locally, for me, that’s close to 1 pm on April 1 – then Venus will be coming along to the same point about three hours later – about 4 pm.

Fifth – begin your search with binoculars – any binoculars will do, but generally one with low power and thus a reasonably wide field of view.  And one caution. You will systematically scan the correct area of sky – but do your scanning slowly. I was out testing this the other day and found it was very , very easy to see Venus in binoculars – yet I missed it over and over again because I was scanning too fast!

Could I see it with the naked eye  in March? No. Not on the three days I looked and saw it in binoculars.  Maybe the days just weren’t clear enough – there was a lot of moisture in the air. And maybe my old eyes are just not keen enough for this sort of thing.  But I did see Venus this way several years ago and it’s one of those sights that when you first find it, you can’t believe you were missing it.

The best hint I’ve read for this – and this is true with binoculars as well as your eyes – first focus your binoculars on the  most distant object you can see – hopefully something a good half mile or more away away. That way they’ll be roughly in focus to pick up Venus.  (You can even do this the night before by focusing them on a star.)  And when you’re searching with the naked eye? Do the same thing. Focus your eyes on some distant object, THEN look up for Venus. (Our eyes tend to default to a near – or nearer – focus point if we’re not careful. )

It’s always cool to see a bright planet – but it is so much cooler to see a bright planet in broad daylight – even with binoculars Venus will be a sparkling white diamond against a beautiful blue sky.

%d bloggers like this: