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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 – June 2013 – Venus chases Mercury, Saturn is due south, and the Summer Solstice arrives

This is a delightful time to find the ever elusive Mercury because through the first two weeks of June it puts on its best show of the year for those in the Northern Hemisphere and it’s relatively easy to find because brilliant Venus points the way.

Look west about 30 minutes after Sunset on June 1, 2013 and you can find three planets ina row. Venus should be obvious to the naked eye. Find it and put it int he bottom of your low-power binocular field and you should see Mercury near the top of the field of view. Move Venus to the top and you should pick up Jupiter near the bottom of the field of view. Jupiter is brighter than Mercury, but may not appear to be because it will belower and more impacted by looking through the atmosphere and the twilight which will be brightest near the horizon.

Look west about 30 minutes after sunset on June 1, 2013 and you can find three planets in a row. Venus should be obvious to the naked eye. Find it and put it in the bottom of your low-power binocular field and you should see Mercury near the top of the field of view. Move Venus to the top and you should pick up Jupiter near the bottom of the field of view. Jupiter is brighter than Mercury, but may not appear to be because it will be lower and more impacted by looking through the atmosphere and the twilight which will be brightest near the horizon. Jupiter will soon drop out of sight but for the next two weeks Venus and Mercury will make easy targets.

Special June 2013 dates for viewing Mercury, Venus, Jupiter and the Moon:

  • 1 – Mercury at its brightest and Jupiter still in view.
  • 9 – A very thin crescent Moon little more than one day old will be roughly 10 degrees – one fist – beneath the pair of planets – Venus and Mercury.
  • 10 – A much easier to see – and quite pleasing – will be a 2-day lunar crescent  beside the pair (just south)  and almost fitting in the same binocular field of view.
  • 11 – The 3-day crescent Moon will have climbed well past the pair, but still make a nice show.
  • 18 – Mercury has reached its peak and started back down and on this date drawing within a couple degrees of Venus – just south. The two will be quite high – about 11 degrees half an hour after sunset, but Mercury will have faded to magnitude 1.1 making it a challenge to pick out in the twilight.

Also this month:

But let’s start with Mercury because the speedy little planet is always a challenge to see. Why? First, because it is very fast. Earth chugs along at a “mere”  66,000 miles an hour in its annual journey around our star, the  Sun. (Doesn’t feel like we’re going that fast, does it?) But Mercury, being closer to the Sun, moves much faster –  it covers a much smaller orbit at a blazing 107,000 miles an hour. So that means when it is well placed for observing it doesn’t stay that way long and it’s easy for the weather and the rest of life to get in the way of seeing it.

What’s more, because it is so near the Sun we only see it as it pulls out to one side or the other  of the Sun and it does that for relatively brief intervals.

And even these quick glimpses vary considerably because it’s orbit is much more lopsided than most. At one point it can be as much as 43.6 million miles from the Sun – and at another it may be as little as 28.6 million miles. (In comparison, Earth can vary from roughly 94.5 million miles from the Sun to 91.4 million miles.)

How far it is from the Sun impacts how easy it is for us to see. If close to the Sun it either rises or sets in strong twilight – and since it seldom gets much brighter than magnitude -1, it can be  quite difficult to pick out in the twilight. And even when it gets pretty far away from the Sun, it’s so small that it never becomes as bright as Venus – in fact, in June it will be easily outshone by Jupiter and Venus.  This June, Mercury will reach a maximum brightness of -0.4 and that on the first day – it grows a bit dimmer each night thereafter, though this will be hard to judge because it also puts more distance between it and the Sun, so that means we see it against a darker background each night.

Cool, huh? I mean it moves a little bit more into darker sky each night – but at the same time it dims a little each night – doesn’t want to make things too easy for us!  😉

But sometimes several factors combine to give us an especially good look at Mercury and this June is such a case – with the added bonus that the much brighter Venus will be near it and thus point the way to finding Mercury.  The basic routine is simple. You want to start looking about 30 minutes after sunset and when you spot Venus, turn your binoculars on it – about any binoculars will do – and for much of the month Mercury will fit  in the same field of view looking like a significantly dimmer star.  As it gets darker you should be able to pick it out with your naked eye – though if you wait too long it will be too close to  the Western horizon – so timing really counts.

As the month progresses Mercury will be a bit higher each night 30 minutes after sunset and Venus will appear to chase it – but Jupiter will drop out of view in just a few days.

Your first challenge, of course,is to merely find the planets in your evening sky and that require an unobstructed western horizon, good clear skies, and appropriate timing – and binoculars sure help, but aren’t absolutely necessary.

But what are you really seeing?

Or maybe the better question is: Why do you see the planets this way?

For the answer we turn to an Orrery – and there’s one online that can be found here. I used it – and modified the view with labels and arrows – to produce the two images that follow.  Essentially this is a view from overhead showing the counter-clockwise motion of the planets around the Sun.  It is only very roughly proportional and your challenge is to look at the Orrery view, then mentally place yourself on the Earth and imagine what your view at sunset would look like. Remember – now you’re getting down in the plane of the solar system and looking outward and what you see is a two-dimensional view that  cancels out the huge distances between the planets.

This June 1 view holds true for Mercury and Venus formost of the month. Jupiter quickly gets too close to the Sun. What we see at sunset are theplanets to the left of the arrow pointing west. As the Earth rotates, the arrow sweeps to the left and theplanets vanish from our view - although Saturn, seen int he southeast at the start of the evening, appears to climn higher in our sky as we turn towards it.  But, of course, nothing stands still. The Planets also revolve around the Sun, so from night to night Venus and Mercury will close the distance between themselves and Earth. The result in 30 days is shown in the next image.

This June 1 view holds true for Mercury and Venus for much of the month. Jupiter quickly gets too close to the Sun. What we see at sunset are the planets to the left of the arrow pointing west from the Earth. As the Earth rotates, the arrow sweeps to the left and the planets set – although Saturn, seen in the southeast at the start of the evening, appears to climb higher in our sky as we turn towards it. But, of course, nothing stands still. The planets also revolve around the Sun, so from night to night Venus and Mercury will close the distance between themselves and Earth. The result in 30 days is shown in the next image.

By the end of the month our view tot he west at Sunset shows us only Venus. Jupiter has long vanished fromt he scene and infact, may just becoming visible inthe pre-dawn sky with Mars.  Venus remain in view,  and Staurn is the dominant planet for much of the Summer night in 2013.

By the end of the month our view to the west at Sunset shows us only Venus. Jupiter has long vanished from the scene and in fact, may just be coming visible in the pre-dawn sky with Mars. Venus remains in view, and Saturn is the dominant planet for much of the Summer night in 2013.

As I watch this wonderful dance of the planets from night to night – and the changes are especially obvious with the swiftly moving inner planets of Mercury and Venus –  I try to get a picture in my minds eye of what’s really happening. Do this enough and when you look at a planet or the Moon in the sky, you can easily sense exactly where they are  in their orbits around the Sun – and where you are in respect to them. I find this a very satisfying piece of mental gymnastics – that we little creatures on our tiny little spaceship Earth, whirling and hurtling about the Sun at incredible speeds, have been able to figure this out. Don’t get me wrong – I take no c edit for that – just one of those special moments when I feel proud to be one of the billions of homo sapiens  here and feel maybe we have earned that name – sapiens indeed! 😉

One last piece of dynamics at work. As mentioned, Mercury is at its brightest at the start of the month.  By the 14 it has dropped about one whole magnitude to 0.76, by the 21st it’s magnitude 1.5, and by the 28th magnitude 2.6. So it will be getting harder and harder to see as it drops more and more into the twilight zone and as it loses brightness. Why does it get dimmer? Look at the Orrery charts – it is moving to a position between us and the Sun and just like the Moon, as it gets between us and the Sun it goes through phases. By the 28th it is a thin crescent and so is reflecting very little light our direction. (These phases can be seen with a small telescope, but you will not detect them with binoculars.)

Mercury and Venus week by week

The following chart shows you the changing positions of Venus and Mercury during June 2013. All are for 30 minutes after sunset for mid-northern latitudes, and all are prepared from Starry Nights Pro screen shots with labels added. Venus never gets much higher than 10 degrees above the horizon – not only throughout June, but essentially for the rest of the year it will be a pretty constant western star – slipping southward somewhat and eventually, in late fall, rising some , before going off stage in January 2014. Mercury’s appearance int he West is strictly for June and as you can see, by the end of the month it’s heading quickly for the horizon and is quite faint.

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Saturn – a southern star!

Wait until about an hour after sunset during June 2013, then look due south.  Almost four fists above the horizon (from mid-northern latitudes)  and about one fist apart are two bright “stars.” The slightly brighter one on the left (east) is Saturn. The other – which should appear bluer – is the first magnitude guidepost star  Spica. Down to the  lower left is another star of about the same brightness, Antares. Compare these three – they are roughly the same brightness, but Antares is tinted red, Saturn yellow, and Spica blue.  They  make a good introduction to noting star colors – which to my eye are more tints, but certainly detectable.

saturn_1

Who can resist the Solstice magic?

We’re fascinated with extremes and since the Sun is responsible for maintaining all life on Earth it’s rather natural to want to track its movements in our sky and mark its extremes. There’s no better time to do so than when it reaches it’s most northern point – the Summer solstice. And if you want to be really accurate that happens at 1:04 am EDT on the morning of June 21. So the time to greet the astronomical start of Summer is to mark the sunrise on June 21.

That said, this is more for those who are fond of records. Truth is you will be hard pressed to tell the difference of where exactly where the sun rises or sets a couple days before that date, or a couple days afterwards. The changes are just too small for us.  So you have to take the word of those who track such things with sophisticated math and instruments – 1:04 am June 21 is the time and date when the Sun reaches its most northerly point.  And the shortest night of the year is June 20-21.

All of this, of course, is for northern hemisphere observers. Our friends Down Under are marking the start of winter.

And speaking of special events . . .

On the night of June 22-23 we have a full Moon – the largest full Moon of the year.

Why is this larger than other full Moons? Because it is closer to us at this particular full Moon. How much larger is it? Significantly – but not so much that you really can tell the difference. To do that you need to see a larger full moon next to a small full Moon – and you can do that by going to this web site which gives a wonderfully detailed explanation.

Meanwhile, just sit back and enjoy it – and don’t confuse this with the Moon illusion phenomena – that is simply our eyes and brain playing tricks on us to make the Moon (or the Sun) look much larger when it is near the horizon, than when it is high in the sky.

Look East! Slide down to Saturn and Spica in May 2012!

It’s a tad easier to find Saturn and Spica if you found Arcturus in April, but if not you’ll simply get a “two-for-one-special” for your effort this month. As always, start about 45 minutes to an hour after sunset. In May 2012 there should be four bright “stars” in the East, but one is a planet. In order from north-to-south they are Vega, Arcturus, Saturn, and Spica. As the sky gets darker the bright stars of the Big Dipper, high in the northeast, will guide you.

All you really want is the three stars of the Dipper’s handle. It forms a wonderful arc, and if you follow the curve of that arc, it will always take you to Arcturus. Continue the same curve for about the same distance, and you will come to the beautiful – but fainter – blue-white gem, SpicaSaturn is very close to Spica, though yellowish, compared to the rich lue of the star. And Vega is way at the other end – just coming up in the northeast. It is very close to the same brightness as Arcturus. All of which, I’m sure, is much easier to grasp if you simply look at this month’s “look east” chart.

Notice that the distance between the last star in the handle of the Big Dipper and Arcturus is almost exactly the same as the distance between Arcturus and Spica - a good way to make sure you're looking at the right star! Also note the movement of Saturn from 2011 to 2013. Click image for larger version. (Developed from Starry Nights Pro screen shot.)

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

We dealt with Arcturus last month. Saturn will be in our sky most of the night and as always is a treat for the small telescope user. From a naked eye perspective,  it’s fun to remember that the name “planet” means “wanderer” in Greek, but all “wanderers” are not created equal. Mars, Venus, and Mercury move  so quickly in our night sky that you can easily mark their changes over a period of a few days -certainly a week.  Saturn is much more sluggish.

Look at the chart and you’ll see how little Saturn changes position over the course of an entire year – it moves roughly 12 degrees.  To see this,f ind Saturn. Hold your fist at arms length so Saturn is just below it. Just above your fist is where Saturn was last year. Put Staurn on top of your fist and just below your fist is where it will be next year. So how long will it take Saturn to get around the sky to roughly the same position? Well, 360/12 = about 30 years!  Now if you think a moment, the Moon takes about 30 days to get around our sky – and that means the Moon moves each day about 12  degrees –  the same distance covered by Saturn each year.  All of which should tell you that it would be reasonable to assume Saturn is much farther away from us than the Moon – which, of course, it is.

None of this is rocket science or in any way  profound, but I find it interesting to contemplate as I look up and see Saturn. I measure that distance it will travel in the next year and in my mind’s eye I perch above the Solar System and I see a long thin pie slice reaching from me to Saturn’s distance orbit and this helps me keep things in perspective – gives me a better intuitive feel for the neighborhood in which we live.  OK – for the record Saturn is moving at about 22,000 miles an hour, Mars about 54,000 miles an hour in a much shorter orbit, and we’re whipping right along close to 67,000 miles an hour – and we don’t even feel the wind in our face! Oh – and Saturn’s actual orbital period is 29.458 years.

On to this month’s new guidepost stars!

Vega and Spica are each fascinating stars, but let’s start with Vega. Shining brightly not far above the northeastern horizon as the evening begins, Vega comes about as close to defining the word “star” as you can get. In “The Hundred Greatest Stars” James Kaler calls it “the ultimate standard star” because its magnitude is about as close to zero as you can get (.03) and its color is about as close to white as you can get. (If you’re one of those who assumed all stars are white, you’re forgiven. Individuals vary in their ability to see different colors in stars and for everyone the color differences are subtle – in fact I think of them as tints rather than colors. )

It’s hard not to be attracted to Vega when you read Leslie Peltier’s wonderful autobiography, “Starlight Nights.” Vega was central to his astronomical observing throughout his career because he began with it when he first started reading the book from which I got the idea for this web site, “The Friendly Stars” by Martha Evans Martin. Peltier wrote:

According to the descriptive text Vega, at that very hour in the month of May, would be rising in the northeastern sky. I took the open book outside, walked around to the east side of the house, glanced once more at the diagram by the light that came through the east window of the kitchen, looked up towards the northeast and there, just above the plum tree blooming by the well, was Vega. And there she had been all the springtimes of my life, circling around the pole with her five attendant stars, fairly begging for attention, and I had never seen her.

Now I knew a star! It had been incredibly simple, and all the stars to follow were equally easy.

Vega went on to be the first target of the 2-inch telescope he bought with the $18 he made by raising and picking strawberries. (This was around 1915.) And Vega became the first target for every new telescope he owned until his death in 1980. If you still don’t know a star, go out and introduce yourself to Vega early on a May evening. Even without a plum tree to look over, you can’t miss her! And once you’ve done that you’re well on your way to making the night sky your own.  (And yes, Vega is the star from which the message comes in Cal Sagan’s book/movie “Contact.”)

Vital stats for Vega, also known as Alpha Lyrae:

• Brilliance: Magnitude .03 ; a standard among stars; total radiation is that of 54 Suns.
• Distance: 25 light years
• Spectral Type: A0 Dwarf
• Position: 18h:36m:56s, +38°:47′:01″

Spica, a really bright star – honest!

Spica is truly a very bright star, but the numbers you may read for its brightness can have you pulling your hair. That’s because there are at least four common ways to express the brightness of Spica and other stars, and writers don’t always tell you which way they’re using. So let’s look at these four ways and see what they mean for Spica.

The first is the most obvious. How bright does it look to you and me from our vantage point on Earth using our eyes alone? We then assign it a brightness using the magnitude system with the lower the number, the brighter star. (For full discussion of this system, see “How bright is that star?”)

By this measure Spica is 16th on the list of brightest stars and is about as close as you can come to being exactly magnitude 1. (Officially 1.04)Thopugh I should add here that the number really marks the midpoint of a magnitude designation – that is, any star that is in the range of magnitude .5 to magnitude 1.5 is called “magnitude 1” and so on for the other numbers ont he scale.

But that scale talks about what we see. It doesn’t account for distance. Obviously if you have two 60-watt light bulbs and one is shining 6 feet away from you and the other 1,000 feet away, they are not going to look the same brightness. But if we put them both at the same distance – say 100 feet – they would look the same. So it is with stars. To compare them we pretend they all were at the same distance – in this case 10 parsecs, which is about 32.6 light years. Put our Sun at that distance and it would be magnitude 4.83. (That’s about as faint as the fainest stars we see in the Little Dipper.) We call that its absolute magnitude.

The absolute magnitude for Spica is -3.55 – not quite as bright as dazzling Venus.

Wow! That’s pretty bright compared to our Sun! Yes it is. Sun 4.83; Spica -3.55. Don’t miss the “minus” sign in front of Spica’s number! That means there’s more than eight magnitudes difference between the Sun and Spica. And that relates to the next figure you are likely to see quoted. Something that is called its luminosity. Luminosity compares the brightness of a star to the brightness of our Sun. Unfortunately, the term is often misused – or poorly defined. Thus in the Wikipedia article I just read on Spica it said that “Spica has a luminosity about 2,300 times that of the Sun.” Yes, but what does that mean? It means that if we were to put the two side by side, Spica would appear to our eyes to be 2,300 times as bright as our Sun.

That is bright! But there’s more, much more. Spica is also a very hot star – in fact one of the brightest hot stars that we see with our naked eyes. But we miss most of that brightness because most of it is being radiated in forms of energy that our eyes don’t detect. In the case of Spica, that is largely ultraviolet energy. The Wikipedia article actually listed Spica’s luminosity twice, and the second time it gave it as “13,400/1,700.”

Oh boy – now we have Spica not 2,300 times as bright as the Sun, but more than 13,000 times as bright. Now that IS bright – but is it right? Yes! So why the difference? Again, the first “luminosity” given – 2,300 times that of the Sun – is measuring only what we can see with our eyes. The second is measuring total amount of electromagnetic radiation a star radiates and is properly called the “bolometric luminosity.” And why two numbers for that last figure? 13,400/1,700? Because while Spica looks like one star to us, it is really two stars that are very close together and one is much brighter than the other. So what we see as one star is really putting out energy in the neighborhood of 15,100 times as much as our Sun.

This can get confusing, so I suggest you remember three things about Spica.

1. It defines first magnitude, having a brightness as it appears to us of 0.98 – closer than any other star to magnitude 1.

2. It is really far brighter (magnitude -3.55), but appears dim because it is far away – about 250 light years by the most recent measurements.

3. It is very hot – appearing blue to our eyes – and because it is very hot it is actually radiating a lot more energy in wavelengths we don’t see, so it is far, far brighter than our Sun.

Spica is the brightest star in the constellation Virgo, one of those constellations where you can not really connect the dots and form a picture of a virgin unless you have an over abundance of imagination. Besides, the remaining stars are relatively faint. That’s why we focus on the bright stars and sometimes those simple patterns known as “asterisms” and use them as our guides.

Vital stats for Spica, also known as Alpha Virgo:

• Brilliance: Magnitude .98 ; as close to magnitude 1 as any star gets; a close double whose combined radiation is the equal of 15,100 Suns.
• Distance: 250 light years
• Spectral Types: B1,B4 Dwarfs
• Position: 13h:25m:12s, -11°:09′:41″

Guideposts reminder

Each month you’re encouraged to learn the new “guidepost” stars 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. If you have been reading these posts for several months, you may want to relate Spica to two earlier guidepost stars with which it forms a right triangle, Arcturus and Regulus. Here’s what that triangle looks like.

Click image for larger view. (Created, with modifications, from Starry Nights Pro screen shot.)

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

Once you have identified the Right Triangle, note carefully the positions of Spica and Regulus. They pretty much mark the “ecliptic.” This is the path followed by the Sun. Also, within about 9 degrees north or south of it, you will find the planets and the Moon. That’s well illustrated in 2012 by the presence of both Saturn and Mars, very near the ecliptic, as noted on our chart.

Arcturus and Regulus are not the only guidepost stars and asterisms in the May sky. Again, if you have been reading these posts for several months, be sure to find the stars and asterisms you found in earlier months. Early on a May evening these will include, from east to west, the following: Arcturus, Spica, Saturn, Leo’s Rump (triangle), The Sickle,  Mars, Regulus, the Beehive, Procyon, Sirius, Pollux, Castor, and in the northwest near the horizon, Capella, and the Kite. Venus will be a bright evening “star” in the west, and if you look early in the month you may catch a glimpse of Sirius and Betelgeuse before they set.

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