Posted on March 12, 2012 by Dave Adalian

Tonight’s the Last Chance for a Five-Planet Night

Jupiter, Venus and Mercury, March 12, 2012

A trio of planets at 7:30 p.m. local time on March 12, 2012. Tonight is the last chance to see Mercury during this cycle.

Jupiter and Venus are going to be spectacular tonight.

For the last few weeks, Venus has been appearing as the Evening Star above the western horizon just after sunset. Jupiter, meanwhile, has been slowly making its way west all winter long. Tonight, the two brightest planets will be side by side after sundown.

Thanks to yesterday’s time change, they’ll be visible at about 7:30 p.m. local time. Look to the west; they’re hard to miss. Venus is the brighter of the two and sits to the right of Jupiter.

What is easy to miss is Mercury. As the closest planet to the Sun, it never gets very far out of the glare of dusk and dawn, but right now it is visible for a few minutes once the sky has grown dark enough. Mercury is just above the western horizon at about 7:30. It will be gone 15 minutes later. There will be one more chance tomorrow, but it’ll be close to impossible to find. By Wednesday there’ll be no chance of seeing it at all.

At the same time in the east Mars is rising in Leo. It’s unwavering red color will make it stand out among the lion’s bright stars. To Mars’ left is Denebola, the lion’s tail, and to its right is Rigel at the lion’s front paw. Mars is currently very close to Earth, having just come its closest for this pass last weekend.

The last of the five naked-eye planets, Saturn, rises at about 10 o’clock, though it will take longer until it’s easily visible. The ringed planet is in the constellation Virgo, in conjunction with the bright star Spica. Saturn will appear to the eye to have a steady golden hue, unlike brilliant blue Spica, which will shimmer and dance as the atmosphere warps its light.

Filed in Astronomy, constellations, Jupiter, Mars, Mercury, Saturn, Solar System, Venus, Winter | 2 Comments
Sirius on New Year's Eve 2011-12

Sirius on New Year's Eve 2011-12

Each New Year’s Eve, while merrymakers are making merry down on Earth to ring out the old year and welcome the new, overhead a remarkable cosmic coincidence signals the turn of the calendar at the stroke of midnight.

In the constellation Canis Major, or the Big Dog, is Sirius, the star that shines brightest as seen from Earth. While that distinction alone is makes Sirius a literal standout among the suns that fill our night sky, it has another quality worth mentioning.

To measure and map the locations of celestial objects, astronomers imagine a great arc in the sky connecting the celestial north pole to the south pole through the zenith. This is the meridian, a line dividing east from west and marking the point at which any object in our sky is at its highest.

Each Dec. 31 within a minute or two midnight, Sirius is on that line.

Before we get all double-rainbow, touched-by-the-great-spirit about this we should probably wonder how cosmic this coincidence really is. As the seasons go by every star has to eventually be on the meridian at midnight, once daylight saving time is taken into account, and New Year’s Eve just happens to be that night for Sirius. It’s men who decide when the calendar ends, so if this stellar coincidence is more than just happenstance, the origin is terrestrial, not divine.

Still, it’s kind of cool. To see it for yourself, just look due south at local midnight wherever in the world you happen to be. Then, take a look in the west where Jupiter will still be up. Between the two in the southwest are the bright and familiar stars of Orion, and to his right Taurus the Bull and the Seven Sisters. The red star rising in the east is Mars, which is gearing up for a spectacular show this spring.

As a side note, this column was inspired by astronomy TV host Jack Horkheimer, who made sure to point out the Sirius New Year’s Eve coincidence every year. Jack died in 2010, but his show goes on at http://www.jackstargazer.com/. Strangely, the folks who took over for Jack have continued the tradition but have forgotten that it was Jack who made it popular. As Jack used to say at the end of each week’s show, “Keep looking up!”

And Happy new year!

Posted on December 31, 2011 by Dave Adalian | Comment Now

Venus on Dec 19, 2011 at 5:30 p.m. local time.

Venus on Dec 19, 2011 at 5:30 p.m. local time.

Keep an eye on Venus this week as the Goddess of Love puts in a holiday appearance as the year comes to a close. Her stint as the evening star goes on all spring, but you don’t have to wait to see her. Right now, Venus is in the southwest as soon as the Sun sets, and is easy to find as the brightest object in that quarter of the sky.

Venus will be climbing higher as the days go buy, and meanwhile Jupiter is moving ever more westerly. Soon the pair will be in close conjunction at the beginning of March. Get a real sense of how the planets move and how our Solar System is laid out by keeping watch on their progress as time goes by.

Posted on December 19, 2011 by Dave Adalian | Comment Now
Posted on December 13, 2011 by Dave Adalian

Birthday of the Unconquered Sun

Around 5:30 a.m. UT on Dec. 22, the Sun will come to a standstill in the sky.

At least it would look that way if you happened to be in the right place when the time comes, but don’t expect earthquakes or tidal waves or a shift of the magnetic poles. You probably won’t even notice when it happens, as it does every year just before Christmas when our planet’s northern half tilts as far away from the Sun as it ever goes.

Reason for the Seasons

Our planet is quit bit off its center, or at least its axis of rotation is. If you take the Sun’s north pole as the standard for the rest of the Solar System, then Earth is a pretty laid-back place because its axis of rotation leans away from that standard by about 23.4 degrees.

The practical upshot of our planet’s relaxed attitude and poor posture are the annual changes in the weather we call the seasons. When the Northern Hemisphere is angled toward the Sun, more light strikes it and spring and summer result, while below the equator fall and winter pass. Half a year later and the situation and seasons are reversed.

A Pause for Change

Twice a year the Sun, with respect to the horizon, stops its apparent north-south progress and reverses. At the height of summer in late June, the Sun reaches as far north as it ever wanders then moves south again until the end of December, when it goes as far that direction as it can.

Because the Sun’s annual change in course is hardly perceptible at first it can seem for a few days it’s simply stopped moving, occupying the same place on the horizon at sunup and sundown. This illusion gives the event its name, solstice, combining the Latin words for “sun” (sol) and “to stand still” (sistere).

The solstices mark the start of summer each June and the start of winter, which this year will begin at 5:30 a.m. UT Dec. 22 or 9:30 p.m. PST on Dec. 21.

Deus Sol Invictus

For ancient cultures the winter solstice was a time of celebration. It marks a turning point, one that signals the start of harsh weather and deprivation, but at the same time gives promise spring lies not too far ahead.

In ancient Rome, the week before winter solstice was taken up by a festival called the Saturnalia, and eventually its finale on Dec. 25, the official Roman date of the winter solstice, came to be known as Dies Natalis Solis Invicti, the Birthday of the Unconquered Sun.

Filed in Astronomy, Earth, Seasons, Solar System, Winter | 1 Comment
Posted on November 15, 2011 by Dave Adalian

2011 Leonids: a Stay-at-Home Shower

A Leonid glows in the November sky of 2009. Image by Navicore.

If you were planning to drive out to a dark, clear site somewhere in the uninhabited countryside for the peak of the Leonid Meteor Shower on Thursday night, forget it.

The shower’s still going to happen, just as it does every November, but this year when the backwards question mark of Leo the Lion rises in the east, a quarter moon comes up with it, bringing a glow that will outshine any the dim shooting stars.

That doesn’t mean you shouldn’t turn out for the show. It means you get to enjoy the show from the comfort of your own yard.

Bits of Comet Dust

The Leonids are the product of Comet Temple-Tuttle. It visits the inner Solar System every 33 years like clockwork, shedding particles up to about nine millimeters in size. The particles are unusually dense, meaning they burn bright and long as they slam into Earth’s atmosphere at around 162,000 mph.

At that speed, those tiny but heavy particles generate as much force when they hit the atmosphere as a car moving 60 mph. That means they burn long and bright, sometimes leaving glowing trails of ions in the sky that can last for several minutes.

Slow Year for Meteors

Unfortunately, there won’t be that many of them this year, not like in 2001 when thousands of meteors an hour fell from the sky like a rain of fire. That only happens after Temple-Tuttle’s latest visit. This year, we can expect a rate closer to 20 an hour until the Moon rises, when the rate will drop to 10 or so. But, the ones that overcome the moonshine will be spectacular.

The Moon will rise around 11 o’clock, a few minutes before the backwards question mark that marks the head of Leo the Lion, making it easy to find. His hindquarters are the nearby triangle of stars to the north.

Viewing’s Good All Night Long

To enjoy the show dress warmly, even more than seems necessary since sitting still in the dark is chilling, and find a comfortable seat that points you away from Leo and the Moon since you don’t want to look at a light source that will ruin your night vision.

After midnight is the best time to view any shower, but because of the Moon’s interference that’s not as important this go, so as another bonus you can start your meteor hunt early and get to bed at a decent hour.

Or stay up all night and enjoy the show.

Filed in Astronomy, Autumn, meteors, skylights, Solar System | Comment Now
Posted on October 29, 2011 by Dave Adalian

Halloween Sky Is Filled with Bright Treats

image by *~Dawn~*

When the darkened streets on Halloween fill with ghosts, zombies, ghouls and witches darting doorstep-to-doorstep, overhead the sky will be filled with sugar-free treats not covered in colorful wrappers.

As the Sun sets around 6 o’clock and early pintsize revelers and parents set out for adventure, Venus is setting in the west. It will take a keen eye to find her low in the gloaming today, but as autumn goes on she grows brighter and stays up longer. Venus will shine all fall, winter and into spring as the Evening Star, not fading until summer comes again.

A Silver Sliver of Moon

While Venus quickly drops from sight on Halloween, a sliver of the Moon stays up longer. Just five days past new, the thin crescent sits in Sagittarius the Archer, where the misty corridor of the Milky Way begins it crawl across the sky. The Moon grows fatter each night until it rises full on Nov. 9.

When Venus is in full flower it’s the brightest planet in the night, but this Halloween the honor falls to Jupiter. Rising as the Sun sets, the largest planet hangs low in the east early on, rising as the candy bags fill. Jupiter is now in the dim stars of Aries the Ram, and with no other bright stars sharing the nearby sky it’s easy to pick out.

Bright Stars of All Hallows’ Eve

The first true stars to come out on Halloween night are the trio of bright suns of the Summer Triangle. More than a month into autumn, bright Vega, Deneb and Altair still hold their place overhead near the zenith. When darkness takes full hold, look north for the Polaris, but to find the Big Dipper search low along the northwest horizon where it rides this time of year.

Tracking back down from the Summer Triangle to Jupiter takes us through the Great Square of Pegasus, which will be about 10 degrees above Jupiter, twice the width of your fist held at arm’s length.

Let Jupiter Guide You

To the right of Jupiter is Fomalhaut, a single lonely star. Though it shines at magnitude 1.72, this brightest star in Piscis Austrinus, the Southern Fish, seems brighter than it should because it stands without companions.

On Jupiter’s other side, north but lower to the ground, are the dazzling Seven Sisters of Pleiades. Though they rise in the first hour after sunset, the Sisters won’t climb high enough for viewing for at least another hour after that. The later the night grows, the more beautiful they’ll become.

Filed in Astronomy, Autumn, constellations, moon, planets, Seasons, Solar System | Comment Now
Posted on October 10, 2011 by Dave Adalian

Use Your Pinkie to See the Moon Grow

Full Moon in Pink Clouds.

The October 2005 full moon rising over the Sierra Nevada by Dave Adalian.

It won’t jump out at you when you see the Moon this week, but October’s full moon is the smallest of the year.

September’s full moon is the Harvest Moon, when farmers of old stayed late in their fields bringing in the crop. The full moon following it is the Hunter’s Moon, when fields are clear and hunters stalk their prey by the light of the Moon. How much, or in this month’s case how little, light they get to aid them depends on how far the Moon is from Earth.

Watching the Wheels Go Around

The Moon’s orbit isn’t a perfect circle. It deviates by a percentage known as its eccentricity, in the Moon’s case a wobble large enough to create 12 percent difference between the apparent size of the full moon this month and the way it will look at its closest and therefore largest next spring.

On average, the Moon is about 385,000 kilometers from Earth. It deviates from that mean by about 6 percent in and out, putting it some 363,000 km away at its closest and at about 405,000 km when it’s furthest away as it will be this week.

How Far is Far?

At its closest point to Earth during perigee or at its farthest during apogee, the actual distances vary by several thousand kilometers. The October moon becomes full at 2:06 a.m. UT on Oct. 12, and its distance will be 406,355.801 km according to the US Naval Observatory.

That’s a change of nearly a thousand kilometers from the night before. Over the following 24 hours, the distance will decrease by just eight kilometers, but the 24 hours after that will see the Moon swing closer to Earth, closing the gap by some 600 km or about 0.2 percent.

Taking a Lunar Bearing

That difference isn’t nearly enough to detect with the naked eye, but measure the full moon anyway by holding your fist up at arm’s length with one pinky extended. You’ll find you could cover two side-by-side moons with your fingertip with some room left over. We’re all basically proportional, so this should work no matter how tall you are.

The full cycle of the Moon brings it closer to Earth from apogee for seven months and then out for another seven, so the next seven full moons will grow larger, and on May 6 the Moon will be at its closest again.

When you measure it then it will have grown by nearly an eighth in apparent size. The extra room will be gone and you’ll only be able to fit two full moons under the tip of your pinky. Try measuring all the full moons and see its face swell then shrink as the year passes.

Filed in Astronomy, Earth, moon | Comment Now
Meteor Trail

A Leonid meteor image captured by Navicore over Santa Cruz, CA. The annual Draconids meteor shower peaks Oct. 8.

The annual Draconids meteor shower, which runs Oct. 6-10, may have an unusually active peak this year, with astronomers predicting up to 1,000 meteors per hour during a window of 16:00 to 21:00 UTC on the night of Oct. 8. In the past, the Draconids shower has even produced meteor storms of up to 10,000 meteors an hour, though nothing like that is expected this year.

Unfortunately for observers outside of Europe and Asia, this year’s peak comes during daylight hours, and even if you’re in a favorable location for the peak, the Moon will be nearly full and up most of the night.

If you are in an area with dark, clear skies during the peak, by all means get out there and have a look, because despite the Moon’s interference, there’s still the possibility of seeing one of natures most beautiful displays.

For those of us who’ll be under blue skies, clouds or moonlight while the shower peaks, there is an alternative way to get in on the action, by listening to the radio signature of the meteors via online. A pair of webcasts will be live from now through the peak and you’ll be able to hear the otherworldly sounds of radio signals being bounced off the ion trails Draconid meteors make as they enter the atmosphere.

You can tune into the Draconids broadcast at these two websites:

Spaceweather Radio

Galileo Webcast

Both websites also have an explanation of how radio broadcasts can be used to detect incoming meteors just like a radar set-up.

Posted on October 7, 2011 by Dave Adalian | 1 Comment
Posted on October 3, 2011 by Dave Adalian

Find the False Dawn this Week Before It Drowns in Moonshine

When false dawn streaks the east with cold, gray line,
Pour in your cups the pure blood of the vine;
The truth, they say, tastes bitter in the mouth,
This is a token that the “Truth” is wine.
– Omar Khayyam, the Rubaiyat

Sometimes in the autumn, in the last cold hour before dawn, a light appears, extending in a wide triangle from the eastern horizon. It’s a weak light, dim by the standards of true dawn, but enough to fool the eye of someone standing a long and lonely watch through the night.

Zodiacal light seen from Mont Paranal.

Zodiacal light seen from Mont Paranal. Image by ESO. Click to enlarge.

Before the real sunrise sends up searching fingers of red-yellow over the horizon, this false dawn, which is only seen under the clearest, darkest of skies, fades from view, leaving those who see it wondering if it’s real.

It is. The phenomenon is one of those rare wonders that needs perfect conditions, the right season of the year and a large measure of chance to appear. Here’s what’s happening:

As the planets move along their orbits they leave bits of themselves in their wake. The ecliptic, the path in the sky the Sun and planets follow, is filled with leftovers that drifted behind. The constellations along this path are the familiar Zodiac, and so the floating debris is called the zodiacal cloud.

The pieces of debris in the zodiacal cloud are small, nothing much bigger than a about meter and mostly just motes of dust, but there is a huge number of them. Together, the motes in the zodiacal cloud reflect light just like the far-away nebulae that form after supernova explosions.

The zodiacal cloud is always glowing, but it is usually invisible to us because even the least amount of moonlight or other light pollution is enough to block it. The dust is spread evenly through the ecliptic, but because of forward scattering of light, only those particles that are near the Sun glow bright enough to be seen.

With all these factors at play it’s only at this time of year just after the equinox has passed, when the ecliptic stands almost straight up from the horizon and below it lurks the Sun, that everything’s right for sighting the zodiacal light, the famous false dawn of ancient song and story.

Normally, the zodiacal light would be available well into October, but this year the Moon will be full on Oct. 11, giving us just a handful of days this week with moonless mornings to fool ourselves with a false dawn.

Filed in Astronomy, constellations, Earth, moon, planets, skylights, Solar System, Zodiac, zodiacal light | Comment Now
Posted on September 26, 2011 by Dave Adalian

What’s in a name? Ask Uranus!

Uranus showing rings and clouds. Hubble Space Telescope, 2005.

We’re all mature individuals, so I know so no one will even crack a smile when I say that now is the perfect time to have a long, naked-eye look at Uranus.

Stop that!

It wasn’t Johann Elert Bode’s finest hour when he decided Uranus was the perfect name for the seventh planet from the Sun. In his defense, Bode was a German astronomer living in the late 18th and early 19th centuries, and Uranus probably doesn’t sound at all rude in his native tongue.

Uranus is a probably a better name than George, which is what the man who discovered it wanted to call it. Sir William Herschel was German but emigrated to England. When he first sighted Uranus on March 13, 1781, George III, also a native German, was on England’s throne. To honor him, Sir William named his new planet Georgium Sidus, the Georgian Planet.

Thankfully, it didn’t catch on. Neither did Uranus until the mid-1800s, and we’re stuck with it now.

No matter what you call it, this is the perfect time to get a look at the faintest of the naked-eye planets. Uranus is currently in opposition, meaning it rises at sunset and stays up all night long.

The bad news is Uranus is faint, shining at magnitude 5.7 on the edge of naked-eye visibility. To be honest, when a naked-eye object is this faint I cheat. A set of small binoculars will make the task of finding this dim gas giant much simpler.

To locate Uranus, find the Great Square of Pegasus and imagine a line passing through its two most eastern stars and continuing southeast. That line will pass just east of Uranus, which is currently in the Zodiacal constellation Pisces. (See chart below.) Near midnight is when Uranus will be highest in the sky and most visible.

There are no blue stars, so when you find one what you are really seeing is the methane-rich atmosphere of Uranus. The planet has a faint set of rings that went undetected until Voyager visited it in 1986, it’s got a rocky interior filled with ice, and it’s is the most tilted of the planets, leaning so far away from the Sun its south pole points at it.

As funny as it is to us, the name Uranus, which is usually pronounced YOUR-UH-NUS, makes it fit in with the other planets, all of which are named after Greek and Roman gods. Its 27 moons, however, are all named after characters in the plays of Shakespeare, making it the most literary of the planets.

Uranus Chart for Sept 2011

To locate Uranus, imagine a line through the eastern-most stars of the Great Square of Pegasus and continue it to the southeast. Uranus is found just east of that line. Binoculars will help, but it can be seen with the naked-eye.

Filed in Astronomy, constellations, planets, Solar System, Uranus, Zodiac | 1 Comment