April 24th, 2015 / Author: astrobob
As of 3:15 p.m. CDT, ice is the clear vote-getter for the composition of Ceres’ white spots. Credit: NASA
Since so many of us are wondering what the heck those white spots are on the dwarf planet Ceres, NASA’s decided to hold a contest. Click the image and you’ll be taken to a page where you can vote on one of six choices – volcano, geyser, rock, ice, salt deposit or other.
Until Dawn moves in for a closer look in the months ahead, it’s anyone’s guess what the spots might be. Ice is currently leading with 37% of the vote. After you’re finished, you’ll see the latest numbers. Your vote won’t change the final outcome of course, but you might just win an “I-told-you-so” for your effort.
April 24th, 2015 / Author: astrobob
Jim Schaff (left) describes features on the Sun to visitors at last year’s Astronomy Day event. Credit: Bob King
Take off those tin foil hats and step out into the sunshine. Tomorrow, amateur astronomers around the planet will celebrate International Astronomy Day, an annual public feast of astronomy. Schools, clubs and planetariums will feature workshops, sky programs and public viewing sessions to increase awareness and appreciation for this improbable and awesome universe into which we were born.
Angie Gregory of the Arrowhead Astronomical Society describes the rotation of the Sun at her 2014 Astronomy Day presentation. Credit: Bob King
To find out if a group near you is sponsoring an event, check the List of Events on the Astronomical League’s Astronomy Day page. You can also look under the Astronomy Clubs menu to browse the websites of clubs in any of 50 states.
Here in Duluth, Minn. we’re getting an early start on festivities with a 7 p.m. talk by UMD physics professor Marc Seigar on the 25th anniversary of the Hubble Space Telescope. The show will be held at the Marshall Alworth planetarium on the UMD campus and costs $3 for adults and $2 for kids six and up. Children under five get in free.
Astronomy Day features lots of hand-on exhibits and people happy to answer your questions about the sky or telescope equipment. Credit: Bob King
Tomorrow’s the big day with non-stop planetarium shows, workshops, safe solar observing, special lectures and lots of hands-off stuff for the kids — all free of charge. You can even look at real moon rocks collected by the Apollo astronauts and study pond life under a microscope. With Europa, Ganymede, Mars and Enceladus potential havens for microscopic life, why not get better acquainted with Earth’s tiniest inhabitants?
The whole shebang runs from 10 a.m. to 4 p.m. at the planetarium. Click HERE for directions.
“Astronomy is big, it’s exciting and it changes the way you look at the world,” said Shane Loeffler, who’s helping to organize the event.
One of our favorite exhibits – Touch the Planets – will be back again this year. The textures might surprise you. Credit: Bob King
The school will also premiere a new full-dome planetarium show called “Sunstruck” with showings at 2:00 p.m. and again at 3:00 p.m. The 20 minute show takes viewers on a journey to discover the wonders of our sun and its potential effects on our technology and future.
Shane Loeffler, planetarium assistant, holds a disk containing samples of Apollo moon rocks. Credit: Bob King
Sure sounds like a lot of fun. Hope to see you there if you’re in the area.
April 23rd, 2015 / Author: astrobob
This image shows the sparkling centerpiece of Hubble’s 25th anniversary tribute this week. Westerlund 2 is a giant cluster of about 3,000 stars located 20,000 light-years away near the Gum 29 nebula in the constellation Carina. Credit: NASA, ESA, the Hubble Heritage Team (STScI/AURA), A. Nota (ESA/STScI), and the Westerlund 2 Science Team
I think it’s fair to say that the Hubble Space Telescope has produced more beautiful images of the cosmos than any other telescope … ever. Part of the reason is its longevity. Another is Hubble’s unique ability to take incredibly long time exposures far above the blurring influence of Earth’s atmosphere. As an orbiting telescope, its images show pinpoint stars and spectacular detail that have only recently being replicated by ground-based telescopes using special optical techniques.
Hubble deployed by the Space Shuttle Discovery in 1990. Credit: NASA
It wasn’t always that way. Hubble was launched into low-Earth orbit in the spring of 1990, but within weeks the first images returned revealed a serious flaw — the 94-inch primary mirror had been ground precisely but to the wrong shape. This serious error meant that images returned suffered from a defect known as spherical aberration.
Basically, Hubble couldn’t focus star images sharply across its entire field of view. The defect was traced back to an instrument used to measure how precise the mirror had been ground. A lens within the device was ever so slightly out of position, resulting in the mirror being ground with the wrong figure.
The spiral galaxy M100 before and after the corrective optics package was installed. Credit: NASA
A corrective optics package was developed to reverse the aberration and installed by a team of space shuttle astronauts in December 1993. Since January 1994, Hubble’s been snapping one crisp image after another.
The telescope bears the name of Edwin Hubble, the 20th century astronomer who discovered the true enormity of the universe and the fact that it’s not static but in continual expansion. This week the Hubble Space Telescope (HST) celebrates its 25th anniversary. But in a selfless role reversal, instead of sending an anniversary card to Hubble, Hubble sent us a sumptuous image of the star cluster Westerlund 2.
These pillars are composed of dense gas and dust near Westerlund 2 are a few light-years tall and point to the central cluster. They are thought to be incubators for new stars. Credit: NASA, ESA, the Hubble Heritage Team (STScI/AURA), A. Nota (ESA/STScI), and the Westerlund 2 Science Team
This amazing cluster is only 2 million years old and contains some of the brightest, most massive stars known. Powerful ultraviolet light and stellar winds streaming from the cluster’s giants tear into the clouds, sculpting them into fantastic shapes. When the stellar winds hit dense walls of gas, they create shocks, which generate a new wave of star birth along the wall of the cavity. The red dots scattered throughout the landscape are a rich population of forming stars that are still wrapped in their gas and dust cocoons.
The red dots scattered throughout the cosmic landscape captured in this Hubble image are a rich population of forming stars that are still wrapped in their gas and dust cocoons. Credit: NASA, ESA, the Hubble Heritage Team (STScI/AURA), A. Nota (ESA/STScI), and the Westerlund 2 Science Team
Your eyes and mine can’t see these stars, but Hubble has the ability to peer into the thermal infrared and spot them by the heat they give off. They’re still just proto-stars, but they’ll continue to collapse and compress until one day they’re hot enough to ignite hydrogen in their cores and become true stars like the Sun.
While its legacy of photographs is what most of us associate with the Hubble, it’s also a superb research instrument that’s enlarged our understanding of the universe in so many ways. Here are five of its most ground-breaking discoveries:
Hubble Ultra-Deep field photos shows thousands of galaxies. Credit: NASA/ESA
The Hubble Deep Field and Ultra-Deep Field photos each show several thousand galaxies in two tiny specks of sky. Some of them are up to 10 billion years old and much smaller and irregularly shaped than the galaxies we see in the current era. Astronomers suspect that through mergers, these rough-hewn “building blocks” helped create the more familiar spiral and elliptical galaxies of the present.
800-light-year-wide spiral-shaped disk of dust fueling a massive black hole in the center of galaxy NGC 4261. Measuring the speed of the gas whirling around the black hole, we know it’s 1.2 billion times more massive than the Sun. Credit: NASA/ESA
Supermassive black holes are everywhere!
Hubble sharp optics and ability to see in the infrared (thermal energy beyond the red end of the spectrum) led to the discovery in 1994 of the first supermassive black hole in the center of the galaxy M87 in Virgo. Based on the motion of the material whirling about the center, the object is estimated to be about 3 billion times more massive than the Sun and concentrated into a space smaller than our solar system. By 1997 we knew that the Milky Way and 27 nearby galaxies held supermassive black holes in their cores. Now we know they’re common, showing up in nearly every large galaxy observed.
Timeline of the history of the universe from the Big Bang to the current day. Credit: Rhys Taylor, Cardiff University
Measuring the age of the cosmos
Edwin Hubble discovered the expansion of the universe in the 1920s. Since that time, astronomers have been trying to determine exactly how fast it’s expanding, a value called the Hubble Constant. In 1999, astronomers using the superior sharpness of the Hubble telescope, determined its value by measuring the distance to 18 galaxies as far away as 65 million light years. Once the expansion rate was nailed down, astronomers could “roll the tape backwards” and estimate the age of the universe. Drum roll please. It turns out this big place has been around for between 12-14 billion years. That’s now been refined to 13.7 billion years, the amount of time that’s elapsed since the birth of the universe at the Big Bang.
The universe slows down then speeds up
Through study of a the remote supernova 1997ff, astronomers discovered that gravity (from matter) slowed down the expansion of the universe after the Big Bang. Later, in 1998, two other supernova studies using data from Hubble, revealed that after slowing down for a long time, the expansion rate of the universe is now on the increase. What would cause it balloon up even faster? That’s the million dollar question. It’s called ‘dark energy’ and we’re still trying to figure out what THAT is.
Proto-planetary disk of dust and gas surrounding newborn stars in the Orion Nebula photographed by Hubble. Credit: NASA/ESA
Baby planets like pancakes
Through studies of nebulae like the famous and familiar Orion Nebula, Hubble discovered that pancake-shaped dust disks around young stars are common. And that implies planets are probably common. Scientists believe that our solar system formed from just such a disk 4.5 billion years ago with the Sun at center and the planets coalescing from the material remaining around it. In 2001, astronomers using the Hubble made the first direct detection of the atmosphere of a planet orbiting a star other than the Sun. The star, HD 209458, is located 150 light years from Earth in Pegasus.
So you see, the Hubble has a little something for everybody.
April 22nd, 2015 / Author: astrobob
Norway pines catch the last rays of sunlight on a ridge north of Duluth, Minn. Credit: Bob King
Happy Earth Day skywatchers! Just because we’re always gazing up doesn’t mean we don’t appreciate a horizontal look around every once in a while. Everything about this planet sustains our fascination with the sky.
Sutures in a deer skull found near a hiking trail. Credit: Bob King
Sunlight, water and the atmosphere keep us alive, while the ground itself provides a handy platform for us to stare out into space with eye and telescope. Surfaces aren’t to be taken lightly. Not all planets have ground or even clear skies. Venus is under a permanent overcast while only Mars and Mercury have surfaces from which to look up. Having something to stand on is handy, but having air to breathe really makes life golden on the blue marble.
Flakes of frost condensed on the icy surface of a creek in Duluth. Credit: Bob King
In honor of Earth Day I thought I’d share a few photos I’ve taken while looking down instead of up. The images are pretty random, grabbed from a folder that’s been sitting around on my hard drive, but they’re examples of what I like to do in my free time.
Drops of sap oozing down a white spruce tree develop a crazed and crinkled surface as they dry. Credit: Bob King
I love this planet as much as you do and wish at times I could spend the rest of my life just wandering around the globe exploring every nook and cranny with my camera. Earth’s coated with life. Every rock breeds some form of tiny microbe. It’s hard to imagine a place where not a single living cell resides. Yet every night we look up, we see these places. The barren moon, airless asteroids, frozen planets, hellishly hot planets.
A chestnut-sided warbler sings from a branch on a spring morning. Credit: Bob King
I realize that’s an assumption but not a single definitive sign of life has yet to turn up in the thousands of meteorites in our collections. Nor have any of the planets or moons in our solar system been forthcoming.
I’ve great hope we’ll find some form of microscopic life on Europa, Enceladus, Ganymede or Mars in the next couple decades. For now, I’m content to slop around the bogs and sniff my way through the fragrant forests of planet Earth.
April 21st, 2015 / Author: astrobob
The Sun photographed in extreme ultraviolet light by NASA’s Solar Dynamics Observatory this morning still shows the coronal hole that will influence Earth’s space weather tonight. Credit: NASA
We’re in for some sky excitement the next couple nights. Tonight there’s a fair chance for northern lights as blustery solar winds
arrive from another coronal hole at the Sun.
Forecasters are calling for a G1 or minor geomagnetic storm that’s expected to kick in this
afternoon and last into the early morning hours Wednesday. With the moon only a crescent, we’ll have dark skies for aurora watching. Look for that telltale twilight-like glow in the northern sky at nightfall as a tip-off that a display is in progress.
NASA used an all-sky camera to photograph multiple Lyrids during the 2014 shower. Credit: NASA
Then, starting Wednesday and continuing through Thursday morning the annual Lyrid meteor will salt and pepper the sky with meteors. We’ve waited more than three months since the January Quadrantids for a meteor shower to return, so I’m looking forward to this one.
The Lyrids fly from the general direction of the bright star Vega which comes up in the northeastern sky around 11 p.m. local time this week. The Big Dipper can help you find it. Source: Stellarium
Like the first flowers, the Lyrids return every April with a peak rate of 10-25 meteors per hour. They originate or radiate from a point in the sky about an outstretched fist southwest of bright Vega in the constellation Lyra the Harp.
Even though the radiant actually lies in neighboring Hercules, the shower’s always been associated with Lyra (Lyrids) both because of Vega’s dominance and the original, loosey goosey borders of the constellations. Before 1930, the borders of the 88 constellations were vague and the Lyrids were close enough to Lyra to assume its name. Had the shower turned up after the International Astronomical Union precisely defined borders, we’d be calling them the Herculids!
Lyra and Hercules border one another with the actual radiant located in Hercules. Source: Stellarium
Although not a big-time shower like the August Perseids, this should be a good year for the Lyrids. You can start watching around 11 o’clock local time Wednesday night (April 22) when Vega climbs above the treeline in the northeastern sky. Rates will increase through the night and peak around 4 a.m.-5 a.m. when the radiant is highest in the sky just before dawn.
The sky facing east-southeast around 3 a.m. local time Thursday April 23. A perfect time to catch the Lyrids! Created with Stellarium
Dress warmly, pack a hot beverage and get comfy in a reclining chair. Or a hot tub. In which case, don’t dress warmly. Those are my mantras for any meteor shower. Even though Lyrids will radiate from a particular direction, they can show up anywhere in the sky. Early in the evening, you’re best to face east. Prefer the early morning? Face southeast.
We see a meteor shower when Earth passes through a comet debris stream. Every April, we pass through material shed by Comet Thatcher. Illustration: Bob King
Like many meteor showers, the Lyrids are the flotsam and jetsam of comets. You’ve been reading about all the dust released by Rosetta’s comet as it’s warmed by the Sun. Comets that cross Earth’s path put that dust to good use. As we speed into the debris sputtered from their nuclei, the particles strike our atmosphere and incinerate in a blaze of light to make a meteor.
C/1861 G1 (Thatcher), which takes roughly 415 years to make one orbit around the Sun, is responsible for the Lyrids. Every so often we pass through a thick filament of dust deposited by Thatcher and get treated to an outburst of Lyrids with numbers reaching more than 100 per hour. That’s expected to happen in 2040 and 2041, so stick around.
April 20th, 2015 / Author: astrobob
Dawn took this new photo of Ceres on April 14 from a vantage point 14,000 miles (22,000 km) above Ceres’ north pole. I rotated the image to place the crater and spots at top. Click to see the animation. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
NASA’s Dawn spacecraft just got a little closer to “Spot 5″, the name given to the pair of brilliant white spots located inside a 57-mile-wide crater on the dwarf planet Ceres.
This animated sequence of images from NASA’s Dawn spacecraft shows northern terrain on the sunlit side of dwarf planet Ceres. The bright spots – named Spot 5 by Dawn’s science team – rotate up from the right side. Credit: NASA/JPL-Caltech
Today we have pictures that are a little sharper and clearer than the last set from March, but still not close enough to do more than tantalize. They show a single spot in the crater’s center and two smaller, slightly fainter spots.
There’s also another extended bright area that pops into view at the start of the sequence (top middle) that soon fades as it rotates toward the terminator or day-night line on Ceres. The new images also show even more craters than earlier ones.
So you can see how the light changes on the white spots as Ceres revolves, these are individual cuts made from the video starting at top left – when they were in deep shade – to lower right. Credit: NASA/JPL with montage by Tom Ruen
Starting April 23, Dawn will begin its first “science orbit”, taking observations from 8,400 miles (13,500 km) above the surface or nearly twice as close. Throughout the remainder of the spring, summer and fall, NASA mission controllers will continue to lower the probe’s orbit until it’s just 233 miles (275 km) by late November. Stay tuned!
April 20th, 2015 / Author: astrobob
Looking at Comet 67P/Churyumov–Gerasimenko at exactly the right moment, Rosetta captured the moment a jet bursts into action. The first image was captured at 1:13 CDT on March 12, the second two minutes later. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
In a rare catch, the Rosetta spacecraft photographed a new jet coming to life on Comet 67P/C-G. Giving the comet the appearance of a rocket at takeoff, the jet appeared unexpectedly from a shadowed underside off the comet’s nucleus known as Imhotep.
Scientists have seen plenty of activity at the comet for the past few months as ices like water and carbon dioxide that compose the nucleus vaporize in the Sun’s heat and leave as jets or mini-geysers. All that material feeds the glowing head of the comet called the coma. Once in the coma, the physical pressure of the Sun’s rays pushes the dust away to form a tail which glows by reflected sunlight. At the same time, the released gas responds to solar UV light and glows blue, forming a second tail.
“This was a chance discovery,” says OSIRIS principal investigator Holger Sierks from the Max Planck Institute for Solar System Research (MPS) in Germany. “No one has ever witnessed the wake-up of a dust jet before. It is impossible to plan such an image.”
Not only that, but it’s interesting that the jet shot out from a shadowed area. Usually jets happen on the sunny, day-side of the nucleus, where solar energy is strongest.
“In these images we see Imhotep on the brink of dawn,” OSIRIS scientist Jean-Baptiste Vincent from the MPS explains. “It is possible that the first rays of sunlight hit some cliffs or outcrops that remained hidden to Rosetta due to the orbital position at the time.”
It’s possible that heat from adjacent warmer regions traveled beneath the surface and set off a wave of vaporization, cracking the surface and explosively releasing pent-up gas. In other words, a form of cometary flatulence.
By tracking brightness variations along the length of the new feature, scientists have measured the speed of the ejected mix at 17 miles an hour (8 meters/sec) or about the speed of a fast ride on a bicycle.
Comet 67P/C-G was just recovered from the ground this past week after being too close to the Sun to observe. This photo was taken on April 19, 2015, and you can clearly see a small, bright coma and faint tail. Credit: Jean François Soulier, Jean Gabriel Bosch, CAO, San Pedro de Atacama
Most of Comet 67P/C-G’s dust outbursts last for a full rotation of 6 hours, with some still active up on the return spin. Other jets are bigger, more explosive but shorter-lived events that can spew enough material to make a comet suddenly brighten by several magnitudes. One such big pop happened on 67P on April 30, 2014, when its coma brightened and expanded over 1,100 miles (1,800 km). Once the material dissipated, 67P faded back to its original brightness.
Although I joked earlier about the rocket-like appearance of the new jet, material being shot away from the comet acts as a gentle form of thrust that over time can accelerate or decelerate its motion. This in turn can lead to changes in the time the comet reaches perihelion as well as uncertainties in exactly when it’s expected to return next.
April 18th, 2015 / Author: astrobob
An oval patch of glowing green aurora pulses in Cassiopeia last night (April 17). Credit: Bob King
It’s been a fantastic 4 nights of northern lights. For now, Earth’s magnetic environment has returned to quiet conditions. Similar to the run of auroras that began on St. Patrick’s Day, this one finished with the same peculiar, sausage-shaped patches.
Last night I noticed a single elongated glow about two fists across in the northern sky in late twilight that slowly pulsed in brightness, often disappearing for 10-15 seconds and then reappearing in the same spot. Like breath on a mirror.
Another view of the diffuse aurora seen last night across the northern sky. Credit: Bob King
During the night, the patch slinked slowly westward into Cassiopeia and then disappeared altogether around 11 o’clock. At midnight it reappeared in the northeastern sky below the Northern Cross. The strange apparition added quiet intrigue to the evening’s boisterous calls from the frogs.
Use bright Venus to help point you in the right direction. This map shows the sky facing west-northwest around 40 minutes after sunset. Mercury is 7° to the lower right of the moon. Created with Stellarium
Tomorrow night (April 19), look to the northwest about 40 minutes after sunset for a rare alignment of a day-old moon and two planets. One of them, Mars, has been around since last spring. Back then it was much closer to Earth and brilliant. Since then the two planets have separated with Mars now far away and rather faint. You wouldn’t ordinary seek it out so low in a bright sky, but the youthful crescent moon will certainly lure you there.
Mercury’s approximate path and altitude during its dusk appearance this spring. Notice how its phase changes from the current gibbous to half to crescent. Source: Stellarium, Bob King
The moon will be just a bit more than one day old and appear as a razor-thin sliver about 5-7° high (three to four fingers held at arm’s length). It should be easily visible from anywhere with a wide open view to the west-northwest. Because of its relative faintness, Mars will probably require binoculars to see. Focus on the moon first and then slide to the right to find the star-like planet.
As an inner planet, Mercury goes through phases just like Venus and the Moon. We see it vary from crescent to “full moon” as its angle to the Sun changes during its revolution of the Sun. Credit: ESO
Mercury shines at magnitude -0.5, even brighter than Vega or Arcturus, but it’s only a few degrees high, so you might need binoculars to see it, too. Once again, the moon comes to the rescue. Look either with your eyes or binos 7° (four fingers) to its lower right.
Mercury quickly moves up from the horizon in the next two weeks for its best evening appearance of the year for northern hemisphere skywatchers. As it comes into better view, the planet will slowly fade and change phase just like the moon. You can see the phases through a small telescope magnifying about 75x. Be sure to look for Mercury early when it’s highest or the blurring effect of the atmosphere will turn it into a ball of quivering mush.
Saturn pops up in the head of the Scorpion in late April around 11-11:30 p.m. This photo was taken early this morning just after midnight. Credit: Bob King
With Mercury joining the scene, we now have five — count ’em — five planets visible in the evening sky. Throw in the Earth and that makes six out of a total of eight! Mercury and Mars hang low in the west; Venus can’t be missed, shining like a lighthouse high in the west at dusk; Jupiter dominates the southern sky in Cancer and if you stay up till 11:30, you’ll see Saturn rise in Scorpius low in the southeastern sky.
Such riches for planetary enthusiasts. Go out and meet your solar system at the next opportunity.
April 17th, 2015 / Author: astrobob
Meet some of the more personable COSIMA dust grains. To get an idea of their size, the plate is 100 millimeters (~1/2 inch) across. Credits: ESA/Rosetta/MPS for COSIMA Team MPS/CSNSM/UNIBW/TUORLA/IWF/IAS/ESA/BUW/MPE/LPC2E/LCM/FMI/UTU/LISA/UOFC/vH&S
Here’s a family portrait only a scientist could love. 12,000 grains of Comet 67P/C-G were collected between last August and mid-March of this year on nine target plates measuring a little less than 1/2-inch square (1 cm). This photo shows one of these targets with grains collected up to December 12.
Imagine my thrill seeing that one of the motes was named “Bob”. Rosetta employed its COSIMA instrument to capture the grains wafting from the comet onto the sticky target surfaces. After taking close-up photos of the particles, COSIMA then analyzed the composition of selected grains using a secondary ion mass spectrometer, a device that shoots a beam of ions (atoms that have lost or gained an electron) at a grain and collects the ions that are bounced back for analysis. By identifying the sputtered ions, scientists can determine the individual elements that compose the grain.
Montage of photos of Comet 67P/Churyumov-Gerasimenko taken by Rosetta. Obvious in all the images are the active plumes of gas and dust grains leaving the comet, some of which have been captured by COSIMA. Credit: ESA/Rosetta/Navcam
Last October, COSIMA found magnesium and sodium this way in a dust grain named Boris. 95% of known minerals observed in comets resemble olivine and pyroxenes, common in meteorites and in the upper mantle of the Earth. Sodium has also been seen in comet comas and tails, and originates in dust grains, but its mineral source remains uncertain.
A false color/color enhanced view showing the smooth Hapi region connecting the head and body of Comet 67P/C-G. Photos taken through separate color filters have been combined to enhance slight color differences in the comet’s nucleus. The bluish tint in the smooth area might indicate the presence of ice at or just below the dusty surface. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
Many of the particle names are given for COSIMA team members, along with other Rosetta mission team colleagues. But by the time they had reached 2,000 particles, names were getting in short supply, so Sihane Merouane, who’s responsible for cataloguing the grains, decided they’d only name dust particles larger than 40 microns (about 1/3 the width of a human hair) with some exceptions made for special, smaller particles.
There’s nothing like a name to make even the most obscure objects approachable. Touché team!
April 16th, 2015 / Author: astrobob
Orion the Hunter and his three belt stars (left) are reflected in a lake north of Duluth last night. Venus, along with the Hyades and Pleiades star clusters, shine at right. Credit: Bob King
Last night while watching the northern lights, we saw the Great Hunter head for the hills. Orion has been the center of attention since December, as recognizable in the southern sky as the Big Dipper is in the north. Now he’s trotting off toward the western horizon, replaced by Jupiter, Leo and the constellations of spring.
Like a furniture clearance commercial that airs during the nightly news, ALL WINTER CONSTELLATIONS MUST GO! With new inventory coming in, the sky’s gotta make room.
Like it or not, Orion will toddle out of the picture soon. The rising and setting of the stars is a reflection of our planet’s rotation; the Earth spins toward the east, pushing up new stars from the eastern horizon and leaving those in the west behind. We see this grand parade every clear night.
View of Earth’s orbit around the sun seen from above the northern hemisphere. As our planet moves to the left during its yearly swing around the Sun, the background constellations appear to drift to the right or westward. Credit: Bob King
But there’s a more subtle shift happening at the same time. As Earth travels in its orbit around the sun, we peer out into different sectors of the sky at night as the weeks and months pass. Like a runner facing a different set of fan-packed bleachers while circling the track in a 1000-meter race, Earth faces Orion in winter, Leo in spring, Scorpius in summer and Pegasus in the fall.
They constellations appear to drift westward very gradually at the rate of about 1° per day. That’s small enough we don’t notice night to night. But the degrees add up. In two weeks, a constellation will drift about 14° to the west — more than the length of your fist held at arm’s length against the sky.
To see this for yourself, find a bright star like Betelgeuse in Orion or Arcturus in Bootes (located below the Big Dipper’s Handle) and note its position in relation to a nearby landmark like a church steeple, mountaintop or Pizza Hut at a particular time. Wait a few nights and then return to the exact same spot at the same time, and you’ll see that the star has slid westward.
Just the way the rising and setting of the stars is an illusion caused by Earth’s rotation, the seasonal drift of the stars and constellation is a sleight of hand caused by Earth’s revolution around the Sun. Now you know why the stars can sit still — it’s YOU who’s doing the moving.
Earth zips around the Sun at a speed of 18.5 miles per second (30 km/sec), covering 26,640 miles each day. In the time it takes for you to notice your reference star has moved – we’ll say 3 nights – you and the home planet have traveled nearly 80,000 miles!
Falcon 9 lifts off April 14 carrying the 9,300-pound Dragon spacecraft, which was loaded with about 4,300 pounds of supplies and payloads for the International Space Station (ISS). Credit: SpaceX
Being outside at night can be a wonderful thing because you inevitably see something unexpected. Two nights ago, I was out with my astro class and we saw the weirdest pair of satellites in the northeastern sky – a bright one and a faint companion just a few degrees apart. Both moved quickly and faded out in less than a minute.
I later discovered we saw the Dragon cargo ship en route to deliver supplies to the International Space Station and the upper stage of the Falcon 9 rocket that lofted the ship into orbit.
You can see either or both in the next few nights by going to Heavens Above and selecting your city and then clicking on the Dragon CRS-6 link just below the ISS link under the Satellites heading. Passes are only a minute or two long and occur in evening twilight. The brighter object will be the rocket stage.
The Falcon rocket’s second stage engine burns for about 7 minutes to deliver the Dragon ship to its initial orbit. Credit: SpaceX
Bring binoculars and you might still be able to see the solar panel covers that were ejected from the Dragon as separate fainter objects nearby. Dragon will arrive at the space station around 6 a.m. CDT tomorrow (April 17), when astronauts will use the robotic arm to secure it. I expect that tonight, Dragon will follow the ISS by only a couple minutes.
Last night’s aurora glowed until the wee hours. I hope you were able to see at least some of the show. Tonight, forecasters predict another chance for more northern lights though they’re expected to be a little “quieter” than yesterday.