Crescent moon visits a ‘wintering’ Venus / Mercury-moon conjunction for y’all

The slender crescent moon brushes Venus Tuesday morning at dawn low in the northeastern sky. The Pleiades star cluster, better known as the Seven Sisters, floats just above the pair. This map shows the sky facing northeast around 4 a.m. June 24. Stellarium

Wonder where the moon’s been hiding lately? Unless you’re up around 3 a.m. it’s been scarce this past week. All that time our favorite cratered world has been slimming down in the morning sky.

Now it’s a waning crescent fingernail, what many consider the moon’s most eye-catching phase.

Tuesday morning June 24 at dawn the thin crescent will join Venus in the constellation Taurus just below the pretty Pleiades star cluster. About 1 1/2 degrees or three moon diameters will separate Venus and the moon. To see this beautiful conjunction, look low in the northeastern sky at the start of dawn.

For the best view of the Seven Sisters, I recommend binoculars. Whenever I’ve had a reason to be up before sunrise in early summer I make a point of looking at the cluster. Taurus, neighboring Auriga and the Pleiades all belong to the winter sky, but we get a preview of that inevitable season as early as the first mornings of summer. There’s something delicious about seeing the first stars of winter as the robins sing in the dewy woods.

An extremely thin moon will pass very close to Mercury on Thursday morning June 26 as seen from the southern U.S. This view shows the sky facing northeast right around sunrise for New Orleans, LA. The moon will only be about 5 degrees high at the time. Use binoculars to find it. Seeing Mercury will require a small telescope. Stellarium

Live in the far southern U.S.? You’ve got one more lunar visitation. This one will be challenging. On Thursday morning, the moon, just 21 hours before new, will glide a fraction of a degree south of the planet Mercury in a bright sky only minutes before sunrise. The moon will hover very low (5 degrees) in the northeast in a bright sky. Whatever you do, bring binoculars. You might need them to find the moon at all.

Like the moon, Mercury’s an extremely thin crescent and very faint, shining at just magnitude 3.5. Skywatchers might spot it in binoculars, but I’m not betting on it. With very clear skies, there’s a chance of seeing the planet directly above the northern cusp of the moon with a small telescope. Should you succeed, you’ll be rewarded with the rare sight of two delicate crescents one atop the other. Find a location with a wide open view to the northeast and start looking about 15 minutes before sunrise.

The moon will cover up or occult the planet for observers in northern South America, but again, this will happen in a bright sky and prove tricky to see.

Just a reminder. Although no auroras showed last night at mid-latitudes, there’s still a chance for a minor storm tonight. I’ll send out a notice if that happens.

 

Full Frosty Moon bumps into Pleiades and Hyades tonight

Tonight’s Full Frosty Moon will rise around sunset in the northeastern sky. November’s full moon is also known as the Full Beaver Moon. Credit: Bob King

Every full moon’s an occasion to get outside for a moonlit stroll. No binoculars or telescope needed. It’s surprising how much you can see by moonlight once your eyes get accustomed to its dark luster. Full moonlight, especially when the moon rides high in the sky as it does this month, makes me think of what daytime might look like on a planet orbiting a dim red dwarf star. Think how the sense of vision would have evolved in creatures on such a planet. To make the most of weak illumination, owl-like eyes could come in handy.

November’s full moon goes by two names – Full Beaver Moon and Full Frosty Moon. The first refers to the time to set beaver traps before the small waterways and swamps froze; the second to what covers the lawn after a clear night this month. Should you be fortunate enough to have clear skies this evening, you can watch the moon rise in the northeastern sky in the constellation Taurus. As always, the full moon rises around sunset directly opposite the sun. Click HERE to find the moonrise time for your city.

The full moon sits smack in the middle between the Pleiades and Hyades clusters tonight. Can you see them through the glare? Created with Stellarium

We all know how glaringly bright the moon is when you stare at it. Most stars in its vicinity are swamped by glare and invisible, but tonight, if you reach your hand up and block the brilliant disk, you might be able to make out two nearby star clusters, the Pleiades (Seven Sisters) and Hyades. First magnitude Aldebaran in the Hyades should be easy to see. While the bright orangish star looks like it belongs to the V-shaped group, it’s really in the foreground 65 light years away, 88 light years closer than the Hyades.

The Pleiades might be easier to spot, but if you’re having trouble with either, binoculars will make finding them a breeze. Well off to the moon’s upper left you’ll see the bright, twinkling star Capella in the pentagon-shaped constellation Auriga the Charioteer. Starting with Capella, can you trace the constellation’s outline?

Oblique view of the 8-mile-wide (13 km) crater Dugan J photographed by LRO. Dugan J is a simple, bowl-shaped crater. Debris from the rim has fallen downslope to fill the crater bottom. See closeup photo below. Credit: NASA/GSFC/Arizona State University

NASA’s Lunar Reconnaissance Orbiter page (LRO) is where I go when I need to visit the moon up close. I’ve included a couple recent postings so you can relish the details. Orbiting at just 31 miles (50 km) high, LRO can distinguish features as small as two feet (0.5 meter) across. When mission control took closeups of the Apollo landing sites, the spacecraft was lowered even further to 13 miles (21 km). Need more “lunar cowbell”? Check out the zoomable gallery.

Zooming into Dugan J on the LRO site almost feels like you’re standing on the rim looking in! Credit: NASA/GSFC/Arizona State University

Passing time with the Pleiades, the late night skywatcher’s fuzzy friend

The Pleiades (middle right) and neighboring stars are reflected in Boulder Lake near Duluth, Minn. recently. Credit: Bob King

“Many a night I saw the Pleiads, rising thro’ the mellow shade,
Glitter like a swarm of fire-flies tangled in a silver braid.”

- from Locksley Hall by Lord Alfred Tennyson, Victorian poet

The Pleiades star cluster catches the eye of the late night skywatcher as we transition into September. Is there a surer sign of winter’s slow approach than the return of this little dipper of stars to the eastern sky? I saw the bunch last night struggling to clear the treetops around 11 p.m. By midnight it stood apart – a beautiful sight with both the naked eye and binoculars.

The bright stars in the Pleiades are named for the daughters of Atlas and Pleione in Greek mythology. Credit: John Lanoue

I love watching the Pleiades (PLEE-uh-deez). There’s nothing quite like it in the heavens. Most stars are single and separate from each other, but the Pleiades packs more than a handful into a single compact shape that stands apart from nearly everything else in the sky.
You’ve probably noticed that the cluster looks a little fuzzy. That’s due in part to seeing so many stars – some visible and many below the naked eye limit – so close together they blend and blur the same way billions of faint stars in the Milky Way do to create a hazy, speckled band across the sky. That’s not all. The Pleiades stars are caught up in a dim cloud of stellar dust or nebulosity that further softens their appearance.

A telephoto view of the Pleiades shows many more stars – much like the view in a pair of binoculars. Credit: Bob King

Each bright “Pleiad”, as they’re called, is named after a daughter of the Greek god Atlas, whose job it was to hold up the sky, and Pleione, a protectress of sailing. Say hi to Maia, Electra, Alcyone, Taygete, Asterope, Celaeno and Merope. Oh, and don’t forget the parents – they’re included too.

The Pleiades is one of brightest and closest star clusters in the sky. It contains some 3,000 stars and lies about 400 light years from Earth. From side to side the group spans 13 light years or about halfway from Earth to the bright star Vega. Like a school of fish, all the Pleiads move together as a gravitationally-bound swarm through space. Within the cluster, you’ll also find double and multiple stars including Alcyone (al-SY-oh-nee), a fine quadruple splittable in just about any telescope.

The brilliant blue-white stars in the Seven Sister Cluster reveal a cloud of interstellar dust through which the cluster is moving. The brightest patch of nebulosity surrounds the star Merope and is visible in a small telescope from a dark sky. Click to enlarge. Credit: NASA/ESA/AURA/Caltech, Palomar Observatory

Time exposure photos reveal hazy clouds of stardust swaddling the cluster. This was originally thought to be gas and dust left over from the Pleiades’ formation. Recent studies now show that the group just happens to be passing through a random cloud of interstellar dust. Starlight reflecting off minute dust grains light up the cloud a chilly blue-white, the same color as the hottest, most brilliant Pleiads.
So how many Pleiades can you see?  Atlas, Alcyone, Merope, Electra and Maia are easy. Pleione and Taygeta are tougher, and only the very keen-eyed can spot Asterope and Celaeno. When the group rides high in the south just before dawn in a dark sky you might spot additional outliers using averted vision (looking to the side and around an object instead of staring straight at it). I’ve heard reports of some observers seeing 15 to 20!

The view facing northeast around 11:30 p.m. in early September. Capella is a brilliant star in the constellation Auriga.

Take a look at this stellar treat the next night you’re out late. Enjoy the fact that you don’t have to freeze while doing so. Come November, when the Seven Sisters appear in the east as soon as it’s dark, you’ll need a warm coat and hat when you venture out for a look.

Delicious Comet Lemmon-cluster pairing; moon greets 7 Sisters at dawn

Comet C/2012 F6 Lemmon cruises by the open cluster NGC 7789 in Cassiopeia last night July 2, 2013. Click to supersize. Credit: Damian Peach

It’s a beautiful thing when two completely different celestial objects pair up. Seen side by side, we can appreciate the unique qualities of each by contrast with the other. Two fine examples stand out this week.

Comet Lemmon, which has been chugging across the sky for months, pulled up alongside the rich star cluster NGC 7789 this week. The cluster is sandbox of pinpoint stars tucked off to one side of the W of Cassiopeia. I’ve been watching the scene the past two nights through the telescope. Last night both comet and cluster shared the same field of view.

Compared to the pointillistic stellar swarm, the comet looked ghostly and ethereal. And to think that one of these belongs to our solar system and the other resides on the far edge of the galaxy at a whopping 7,600 light years from Earth … well, it simply jazzes the brain cells. What can I say?

Then there’s composition to consider. Comets and the sun are made of virtually the same materials – hydrogen (frozen H2O in a comet’s case) and a dusting of carbon, nitrogen, oxygen, silicon and on and on. Yet comets are cold, relatively uncompressed dust. Not the sun. Put enough dust in one place and gravity will eventually crush it into a sphere hot enough to start its innards burning. A star is born. Interstellar dust left by earlier stellar generations is their common bond.

Watch the moon come up below the Pleiades star cluster tomorrow morning. The crescent will be only three days from new moon. This map shows the sky facing northeast at early dawn. Stellarium

Tomorrow morning we’ll see another auspicious duo. The waning lunar crescent rises at dawn below the Seven Sisters star cluster. Also known as the Pleiades (PLEE-uh-deez), the dipper-shaped group is more closely associated with the winter sky than the summer. In July it re-emerges during morning twilight, stalks the wee hours in August and looks down on earthlings from overhead on December evenings.

You can watch both moon and sisters with the naked eye, but binoculars will enhance the view. Next to the cluster, will the tweezers moon look closer to home than ever before? Take a look and see what you think.

Waning moon stalks Jupiter as Halloween approaches

The waning gibbous moon heads toward Jupiter in the next few nights. The two will be closest – only 2 degrees apart – the day after Halloween. The map shows the sky facing east around 9:30 p.m. local time. Created with Stellarium

Jupiter doesn’t know it, but the stealthy moon is on track to make a close approach to the planet this Thursday night. Tonight you’ll find the waning gibbous moon in edging into the constellation Taurus about one outstretched fist to the right of the Seven Sisters or Pleiades. Since it’s only one day past full, you’ll probably need binoculars to see the cluster. On Thursday, Jupiter and the slimming moon combine forces to shine with a mesmerizing radiance in the northeast around 9:30 p.m. and later.

Jupiter’s innermost bright moon Io moves into the planet’s shadow starting at 11:10 p.m. CDT this evening. Even a small telescope will show the eclipse. Create with Meridian software

If you have a telescope, you’ll see Jupiter’s moon Io to disappear as it’s eclipsed by Jove’s giant shadow. Eclipse occurs at 11:10 p.m. (CDT) tonight Oct. 30. Start watching a few minutes before that time. By 11:15 the moon will be gone.

Jupiter Wednesday night Oct. 31 at 9:30 p.m. (CDT) with Io’s shadow transit already in progress. South is up in both Jupiter panels. Created with Meridian software

Halloween night offers up yet another telescopic treat. As soon as Jupiter’s up in the east, you can follow the progress of Io’s inky shadow as it tracks across the clouds of the planet’s southern hemisphere. The event is called a shadow transit.

It begins at 8:18 and wraps up at 10:28 p.m. If you return at around 11:15 p.m. you’re in for another surprise – Io itself will exit the west side of the planet and appear like a bright pearl pinned to Jupiter’s limb.

Jupiter on Oct. 14 with the shadow of Io visible as a dark dot inside the planet’s limb. The two prominent stripes are the north and south equatorial cloud belts. Click image to see the video of Jupiter rotating. Credit: Damian Peach

Amateur astronomer and astrophotographer Damian Peach, who takes some of the finest, most detailed pictures of the planets and moon, recently compiled a sequence of photos of Jupiter made between Oct. 10 and 13 into a very cool animation. Click the link to watch an entire 9.8 hour rotation of the planet condensed into less than a minute. Peach hails from the UK and uses an 11.8 inch (30cm) Meade Schmidt-Cassegrain for his photography.

What’s lovelier than the Pleiades in September?

The Pleiades star cluster rises between the trees in the northeastern sky on a recent night. The attractive group comes up around 10 p.m. local time and is high in the east around midnight. Photo: Bob King

What’s lovelier on a September night than watching the Pleiades rise in the east? Whether you’re alone or in a group, when the “seven sisters” appear, everyone stops what they’re doing for a minute to admire this most beautiful star cluster. When I’m at a star party, someone inevitably calls out their first appearance like a courier announcing Caesar’s return to Rome. Yes, they’re that big of a deal.

The Pleiades represent the seven daughters of Atlas and Pleione, which are also members of the dipper-shaped cluster. Asterope and Calaeno usually require binoculars to see. Credit: John Lanoue

The name Pleiades (PLEE-uh-deez)  comes from ancient Greek myth. Also called the Seven Sisters Cluster, the stars represent the seven daughters of the titan Atlas and sea-nymph Pleione. The origin of the name is uncertain but may be related to the word plein ( ‘to sail’), since the stars’ conjunction with the sun in spring and rising at sunset in fall marked the beginning and end of the sailing season in ancient Greece. Other possible origins include peleiades (‘flock of doves’) which is consistent with the story of Zeus turning the sisters into doves as they were pursued by Orion.

An interpretation of the Pleiades from a 10th century Anglo-Saxon manuscript called a codex (Codex Vossianus 79).

Being a compact group of bright stars quite unlike any other in the sky, the Pleiades have figured prominently in the sky lore of many cultures. Most people I know refer to the cluster as a “little dipper” or miniature version of the Big Dipper. My eye sees a shopping cart or baby stroller. Here’s just a small sampling of how others have interpreted their appearance:

* Japan – a strainer or dabs of paint on the sky
*  Celtic mythology – associated with a fall festival of the dead since the cluster rose in the east as the sun disappeared in the west in that season
* Maya Indians – a rattlesnake’s tail
* Mono people (Native Americans) of California – Six wives who loved onions more than their husbands and who now live happily in the sky.
*  Babylonians – Mul Mul or “star of stars”
* Maori of New Zealand – “Matariki” or little eyes
* Czech Republic – “Kuratka” or many small, young chickens

It’s their sheer compactness that delights the eye. They’re gathered so close together they seem enveloped in a fuzzy cocoon that further adds to their appeal. Poet Alfred Lord Tennyson said it best in his poem Locksley Hall:

“Many a night from yonder ivied casement, ere I went to rest,
Did I look on great Orion sloping slowly to the West.

Many a night I saw the Pleiads, rising thro’ the mellow shade,
Glitter like a swarm of fire-flies tangled in a silver braid.”

The Pleiades cluster contains about 1000 stars. Its core – what we see with the naked eye – is about 8 light years across or twice the distance to Alpha Centauri. Most of its stars are young, hot and blue. The cloudiness around the stars is starlight reflecting off a dust cloud through which the cluster is currently passing. Credit: NASA

My old friend Roy would recite those famous lines on winter nights observing together from my old suburban Chicago neighborhood. I have many memories of good times with the Pleiades and many associations, too. They’re always a reminder of the coming winter when they sail high across the southern sky. In mid-September the sisters make  their first appearance in the east around 10 o’clock.; by mid-October they’re up at 8.

The Pleiades are exactly what they appear to be – a real, physically connected cluster of stars. They coalesced from a cloud of dust and gas about 100 million years ago smack in the middle between the appearance of the first flowering plants and disappearance of the dinosaurs. Located about 440 light years from the Earth, the light you see tonight left the cluster in the late 1500s, some 30 years before Galileo first pointed his telescope at them. His sketch shows many more stars that you can see with the naked eye alone.

Sketches of the Pleiades by Galileo. Notice the line of stars stretching to the left of the “dipper”.

At a casual glance, you’ll probably see just five or six stars, but if you peer closely, the seventh, Pleione, will materialize. The real fun starts when you avert your vision and look around rather than directly at the cluster. A smattering of faint stars will suddenly pop into view boosting your total to 8, 10, 14??

Give it a try, then beam in on them with binoculars. Whoa! Instead of seven, you’ll see many dozens, including a most attractive stream of stars  shown so well in Galileo’s drawing.

I wish you smooth sailing with the daughters of the night.

Venus and her sisters; Tell time at night with the Big Dipper sky clock

Venus and the Seven Sisters star cluster last night - what a sight! Details: 200mm at f/5.6, ISO 800 and 20-second guided exposure. Photo: Bob King

It was great to stand in the front yard last night under a clear sky and see Venus and the Pleiades. A casual glance showed a sprinkling of little stars around the brilliant planet. Binoculars gave the best view of the “8 sisters” with Venus the dominant by far. I tried to see how many Pleiads I could count with the naked eye. The five brightest were easy enough but the sixth – Taygeta – was tricky. Pleione was beyond me. It was also fun to recall that 8 years ago to the day I stood in the yard and watched Venus in almost the same position inside the cluster. Apparently I was on time for my next appointment.

A wider view of Venus and the Pleiades along with Jupiter (at bottom). 35mm at f/5.6, ISO 800 and 20 seconds. Photo: Bob King

Tonight Venus glides up and to the left of the star cluster, so if it was cloudy by you last night, you have another shot at seeing them together.

After a good swig of the western sky show, I checked out a new paperless way to tell time using the Big Dipper and North Star. In yesterday’s blog we looked at a simple star clock you can make with paper and scissors. Today we’ll pretend we’re out at night with neither watch nor guide.

The map below shows the North Star as the center of a clock face with the two Pointer Stars in the Bowl of the Big Dipper as the hour hand.  Our example shows the sky at 9 p.m. local time.

To start, face north and look high in the northeastern sky to find the Big Dipper. Draw a line through the two Pointer Stars until you arrive at the first easy-to-see star. That’s the North Star or Polaris. It’s about 5 “Pointer lengths” away. The line connecting the North Star and Pointer Stars now becomes the hour hand on our celestial clock.

To find the time using the Big Dipper and North Star we imagine the northern sky as the face of a clock. Key hours are marked. Illustrations created with Chris Marriott's SkyMap

1. Estimate the time the Pointer hour hand indicates to the nearest quarter hour (15 minutes). In our example, it’s 1 o’clock.

2. This next step is key. We now adjust the clock for the time of year. On March 7, the Pointer Stars stand directly above the North Star at midnight standard time. All you have to do is figure to the nearest quarter month how much time has elapsed since March 7. Since tonight’s April 4th, that rounds off to one (1) month. If it was April 15 instead, the number would be 1 1/4 or 1.25.

3. Add the two figures from above and then multiply by 2 as in: 1 (from 1 o’clock) and 1 (one month) = 2. Then 2 x 2 = 4. Now subtract that sum from 24, so 24-4 = 20. The result will be the time in 24-hour or military style. 20 hours military is the 20th hour of the day or 8 p.m. Add an hour for daylight-saving time and we arrive at 9 p.m. By gosh, that’s correct! Note: If your final number is greater than 24, subtract from 48 instead.

Facing north about 5:15 this morning, the Pointers were now off the left of the North Star in the 9 o'clock position. I figured the time as: 9+1=10. Multiply by 2 = 20. Subtract 24 - 20 = 4 and added one hour for DST to arrive at 5 or 5 a.m. Close enough.

It’s important to remember to add that hour for daylight time when it’s in use and to face north. With practice – and checking against a watch for accuracy – you’ll soon become a master of time at night. Be aware that where you are within your time zone will affect your time estimate. If you try this a few times, you’ll soon be able to factor that in and fine tune your time. I tried this simple method both last night and this morning before dawn and was frankly surprised how well it worked. If you’ve got some time on your hands, let us know how you fare.

Venusian delights; Orion preps for leave of absence

The moon drops by Mars and Regulus in Leo Monday and Tuesday nights. Maps created with Stellarium

Watch tonight as the gibbous moon nears Regulus and Mars in Leo high in the southeast. The trio will form a line about 10 degrees long or a fist held at arm’s length against the sky. In the western sky, don’t forget Venus and the Pleiades or Seven Sisters star cluster. The brilliant planet enters into the cluster’s domain this evening. A pair of binoculars will give a wonderful view. Tomorrow night Venus will join the sisters for a sleepover.

Binocular view of Venus and the Pleiades tonight. Try to catch the two if weather allows. It won't happen again for 8 years.

When you’re out at nightfall this week, give a look toward Orion, now tipping over in the western sky by 9-10 p.m. In another few weeks, the hunter will disappear from view when he’s swallowed up by evening twilight.

You’ll notice that Orion’s Belt is now nearly horizontal. The left end points to twinkling Sirius, the brilliant white star in the south-southwest; the right end toward the orange star Aldebaran and the V-shaped Hyades star cluster and beyond to the Pleiades.

Orion tips to the west by 9 o'clock in the evening during early April. Use his Belt to navigate a nearly straight line to Sirius, the Hyades and Pleiades. Photo: Bob King

This laying-down” of Orion is a sure sign of winter’s passing. Time to bury the sword and embrace the season’s rain, warmth, ticks, flowers, mud and greenery.

Venus and Pleiades on a beautiful collision course

Night by night Venus and the Pleiades approach each other until the planet's smack inside the cluster next Wednesday evening April 3. Positions shown for around 9 p.m. CDT. Created with Stellarium

If you enjoyed the dazzle of Jupiter and Venus at dusk recently, get ready for Act II, when Venus passes through the most famous star cluster of all, the Pleiades. Also known as the Seven Sisters cluster, the Pleiades is that little bunch of stars in the shape of a miniature dipper. It’s located in the zodiac constellation Taurus the Bull and sparkles in the western sky at nightfall.

The stars in the Pleiades are named after the seven daughters of Atlas. Dad and mom (Pleione) are also included. Most people can see six with ease. Pleione is more difficult; Celaeno and Asterope are generally not visible. Credit: John Lanoue

Although not as showy as Jupiter and Venus together, rarely does a bright planet passes directly through the sky’s brightest star cluster. The Pleiades represent the seven daughters of Atlas, the Greek god who carried the heavens on his shoulders. Located 425 light years from Earth, the cluster is rich in hot, blue-white stars. Astronomers estimate its age at 100 million years.

Venus inches closer to the sisters night by night until joining them on April 3. That evening the planet will blaze just to the left of cluster’s brightest star Alcyone (al-SYE-oh-nee). Don’t expect Venus to quietly blend in. At magnitude -4.4, it shines more than a thousand times brighter than 3rd magnitude Alcyone.

Brilliant Venus in the Seven Sisters cluster back on April 3, 2004. Photo: Bob King

Over millions of years, the regular and repeating gravitational attraction between Venus and Earth have caused their orbits to reach what astronomers call “near-resonance”. The two planets are now in a comfortable relationship such that for every 8 orbits Earth makes around the sun, Venus completes 13. Seen from Earth, Venus returns to nearly the exact same part of the sky every 8 years.

No matter when you look up at Venus, you’ll see it there again in 8 years. And if you guessed that the last Venus-Pleiades visit occurred in April 2004, you’re right!

I’m curious how many cluster stars will be visible with the naked eye with Venus tucked inside on April 3. The best views will be with binoculars and small, low power telescopes. If you’ve never looked at the Pleiades before with optical aid, you’ll love the view. So many more stars are visible, and with the brightest planet in their midst, get ready for a spectacle.

Auroras way up north plus the moon visits a famous star cluster

Andy Keen, who lives in Northern Lapland in Finland, had a great view of the northern lights last night. "The colours were fabulous - green, red, pink, turquoise, neon blue - the full works," he said. Details: 14mm lens at f/2.8, ISO 800 and 4-second exposure. Click image to see more photos and a video on Keen's website.

Bright auroras have dressed up the Arctic sky the past two nights after the sun’s wind of charged particles – electrons and protons – pried an opening in Earth’s magnetic field and spiraled down into the upper atmosphere. There’s still a possibility for aurora tonight primarily for those living in the far north. Take a look if clear skies are in your forecast. We’ve had clouds in my town and a now a blizzard on its way, so my eyes will be blinkered for a while.

The moon will be near the Seven Sisters star cluster tonight (Feb. 28) and the Hyades cluster tomorrow night. Created with Stellarium

Tonight the quarter moon is tucked under everyone’s favorite naked eye star cluster called the Pleiades (PLEE-uh-deez) or Seven Sisters. The cluster is shaped like a tiny dipper, and when the moon’s not quite so close to it, most of us see six or seven stars with ease. Binoculars show dozens more. The Pleiades, located about 400 light years from Earth, is a relatively young group of stars compared to our sun; their birth from a massive cloud of dust and gas happened during the age of the dinosaurs a mere 100 million years ago. It’s also the brightest star cluster in the sky.

The Hyades form a distinctive V-shape that represents the face of Taurus the Bull. The bright star at left, called Aldebaran, is a foreground star and not a member of the cluster. It's often referred to as the bull's eye. Photo: Bob King

One outstretched fist to the left or east of the Seven Sisters is a larger, looser star cluster called the Hyades (HY-uh-deez). It’s the closest star cluster to our solar system at a distance of 151 light years. That’s one of the reasons it appears larger and more spread out than the neighboring Pleiades. The Hyades occupy a volume of space some 30 light years across and are moving through space together like a school of fish.

Despite its closeness, the Hyades are fainter than the Pleiades because its stars are more than six times older with ages around 625 million years.

Clusters are born with stars of all different masses. Mass or the amount of stuff a star has determines its temperature, color and how fast it devours the nuclear fuel in its core. The biggest, brightest ones burn up their fuel fastest, either ending their lives as supernovas or evolving into dim white dwarfs. Because of the Hyades rather advanced age, its brightest stars have either blown up or faded away, leaving the smaller, fainter but more frugal fuel users – basically stars with masses similar to or less than the sun – dominating the herd.

Astronomers uses the "eyes" of the Earth on a particular date and then again six months later to measure a nearby star’s parallax or shift against the more distant background stars. Illustration: Bob King

The Hyades are probably the most famous star cluster in the world of astronomy, even eclipsing the Pleiades in importance. Why? Because they were a key steppingstone into deep space as astronomers looked for ways to determine distances to remote stars.

Astronomers use parallax, the apparent shift of nearby stars against the distant background stars when seen from two widely-separated points of view, to measure the distance to the closer stars. You can see a parallax shift when you hold a finger at the end of your nose while opening and closing your right and left eyes in a blinking pattern. Your finger will appear to shift back and forth against the distant background. Measure the distance between your eyes and the angle your finger makes, and you can find the distance to your finger with simple trigonometry.

In this illustration, you can see how a star shifts against the background ones when photographed through a high powered, professional telescope on opposite sides of Earth’s orbit. Illustration: Bob King

To measure the distance to  a star using parallax, astronomers need a super-wide set of eyes, because even the closest ones are so incredibly far away, they show only minute shifts.

That’s where Earth’s orbit comes in (see above). We measure the star’s position against the background stars on one side of our orbit and then again six months later when we’re on the other side. Since we know the baseline length – 180 million miles – and can measure the parallax shift, we can easily calculate the star’s distance. It works beautifully -  at least out to about 300 light years. After that, the shifts are too small to measure directly.

That’s where the Hyades come in. The cluster contain lots of stars of many different types, and since it’s so close, we can use parallax to measure its distance. Next we find a cluster with similar stars but too far away to show a shift and measure the brightnesses of those stars. Since we’ve determined that its stars are the same types as those in the Hyades but say, 100 times fainter, we know they must be 10 times farther away or approximately 1,500 light years from Earth. Bingo! We’ve taken another step deeper into the cosmos.

(Just an FYI – The intensity of light falls off as the square of the distance. It’s known as the inverse square law. 100 times fainter = 10 times farther. 10,000 times fainter = 100 times farther.)

Using the Hyades stars this way, astronomers have hopscotched into the depths of the galaxy. A most clever way to “expand” our universe, don’t you think? To learn more about parallax, please click HERE, and don’t forget to send the Hyades a “thank you” this week.