Bob King, Author at Universe Today

February 20, 2015December 23, 2015 by Bob King

How to Photograph Tonight’s Spectacular Triple-Play Conjunction

Last night's one-day-old Moon photographed a half-hour after sunset. Details: handheld camera ISO 400, f/2.8, 1/15". Credit: Bob King

Tonight the thin, 2-day-old crescent Moon will join Venus and Mars in the western sky at dusk for one of the most striking conjunctions of the year. The otherworldly trio will fit neatly with a circle about 1.5° wide or just three times the diameter of the full moon. No question, this will catch a lot of eyes around the world. Why not take a picture and share it with your friends? Here are a few tips to do just that.

Moon, Mars and Venus around 6:45 p.m. (CST) on Feb. 20 in the western sky. Be sure to look for the darkly-lit part of the moon illuminated by sunlight reflecting off Earth called earthshine. It’s a beautiful sight in binoculars. Source: Stellarium — Moon, Mars and Venus around 6:45 p.m. (CST) on Feb. 20 in the western sky. Be sure to look for the darkly-lit part of the moon illuminated by sunlight reflecting off Earth called earthshine. Source: Stellarium, author

You won’t need much for an easy snapshot. In bright twilight, point your mobile phone toward the Moon and tap off a few shots, taking care not to touch the screen too hard lest you shake the phone and blur the image. The phone’s autoexposure and autofocus settings should be adequate to capture both the Moon and Venus. Mars is fainter and may only show if you can steady your phone against something to allow for a longer exposure without blurring. Assuming you use your phone in its default wide view, the Moon, Venus and Mars will form a tight, small group in a larger scene.

Last night, Feb. 19, Venus and Mars were 1 degree apart. Tonight they'll be even closer at just over 1/2° with the Moon a degree or so to their right. Credit: Bob King — Last night, Feb. 19, Venus and Mars were 1°apart. Tonight they’ll be even closer at just over 1/2° with the Moon about 1° to their right. Details: 65 minutes after sunset (mid-twilight), camera on tripod, 35mm lens at f/2.8, ISO 400 and 6 second exposure. Credit: Bob King

Phones provide the highest resolution in their wide setting. If you zoom in, the Moon will be bigger but resolution or sharpness will suffer. Someday phones will be as good as digital single lens reflex cameras (DSLRs) but until then, you’ll need one of these or their cousins, the point-and-shoot cameras, to get the best images of astronomical objects.

You’ll also need a tripod to keep the camera still and stable during the longer exposures you’ll need during the optimum time for photography which begins about 30 minutes after sunset. That’s when your photos will capture all three objects without overexposing the Moon and making it look washed-out. Ideally, you want to see the bright crescent contrasting with the dim glow of the earthshine.

Venus and Mars photographed in mid-twilight with a 100mm telephoto lens at f/2.8. To prevent trailing of the planets, I cut the exposure in half to 4 seconds and increased the camera's ISO to 800. Credit: Bob King — Venus and Mars photographed in mid-twilight with a 100mm telephoto lens at f/2.8. To prevent trailing of the planets, I cut the exposure in half to 4 seconds and increased the camera’s ISO to 800. Credit: Bob King

Lucky for us, the Moon’s sharp form makes an ideal target for the camera’s autofocus. Frame an attractive landscape or ask a friend to stand in the foreground. Set your lens to its widest open setting (usually f/2.8-3.5) and the ISO (your camera’s sensitivity to light) to 800. The higher the ISO, the shorter the exposure you can use to capture an image, but high ISOs introduce unwanted noise and graininess. 800’s a good compromise. If you can manually set your exposure, start at 4 seconds.

Compose your photo and then focus on the Moon and gently press the shutter button. Check the image on the back screen. Are you on target or is it too dark? If so, double the time. If too bright, half it. As the sky gets darker, you’ll need to gradually increase your exposure. That’s when the Moon will start to wash out and the beautiful deep blue sky turn black or the color of your local light pollution. Around here, that’s pinkish-orange. I’ve got lots of orange sky photos to prove it!

The key to good photos in twilight is balancing the different types of lighting - dusk, the sunlit crescent, the earth-lit portion and the planets. Shoot pictures at a variety of exposures between about 30-60 minutes after sunset when the western sky is still aglow but the Moon is bright and obvious. Credit: Bob King — Mercury and the Moon on Jan. 31, 2014. Besides finding a scene you like, the key to good photos in twilight is balancing the different types of lighting – dusk, the sunlit crescent, the earth-lit outline and the planets. Shoot pictures at a variety of exposures starting about 35 minutes after sunset when the western sky is still aglow but the Moon is bright and obvious. Credit: Bob King

All told, you can use a mobile phone to shoot from about 25-40 minutes after sunset and a DSLR from 25 minutes to 75 minutes after. If you’re shooting with a standard 24-35mm lens, keep your exposures under 20 seconds or the Moon and planets will start to streak or trail. The Rule of 500 is a great way to remember how long a time exposure you can make with any lens before celestial objects start trailing. So, 500/24mm = 20.8 seconds and 500/200mm (telephoto) = 2.5 seconds. That means if you plan to shoot the conjunction with a longer lens, you’ll need to up your ISO to 1600 or even 3200 in late twilight to get a tack-sharp, motionless photo.

I screwed this photo up of the Moon, Jupiter and Mars by overexposing the sunlit crescent. Credit: Bob King — I screwed this photo up of the Moon, Jupiter and Mars by overexposing the sunlit crescent. It’s all part of learning the ropes, a task made much easier nowadays by simply checking the view screen of your camera and trying a different exposure. Credit: Bob King

Telephoto images are a bit more challenging, but they increase the size of the pretty trio within the scene. When shooting telephoto images (even wide ones if you’re fussy), shoot them on self-timer. That’s the setting everyone used before the selfie took the world by storm. Most timers are pre-set to 10 seconds. You press it and the camera counts down 10 seconds before automatically tripping the shutter, allowing you time to put yourself in a group photo.

In astrophotography, using the self-timer assures you’re going to get a vibration-free photo. If it’s cold out and you’re shooting with a telephoto, vibration from your finger pressing the shutter button can jiggle the image.

Good luck tonight and clear skies! If you have any questions, please ask.

February 18, 2015December 23, 2015 by Bob King

When Light Just Isn’t Fast Enough

A pile of Skittles candy seen at rest. Credit: PiccoloNamek

Take a speed of light trip across the solar system starting at the Sun

We’ve heard it over and over. There’s nothing faster than the speed of light. Einstein set the speed limit at 186,000 miles per second (299,792 km/sec). No material object can theoretically travel faster. For all practical purposes, only light is lithe enough to travel at the speed of light.

Moving in such haste, a beam of light can zip around the Earth 8 times in just one second. A trip to the moon takes just 1.3 seconds. Fast for sure but unfortunately not fast enough. Hit play on the video and you’ll soon know what I mean. The view begins at the Sun and travels outward into the solar system at the speed of light.

Planet           Distance in AU            Travel time
....................................................................
Mercury              0.387        193.0 seconds   or    3.2 minutes
Venus                0.723        360.0 seconds   or    6.0 minutes
Earth                1.000        499.0 seconds   or    8.3 minutes
Mars                 1.523        759.9 seconds   or   12.6 minutes
Jupiter              5.203       2595.0 seconds   or   43.2 minutes
Saturn               9.538       4759.0 seconds   or   79.3 minutes
Uranus              19.819       9575.0 seconds   or  159.6 minutes
Neptune             30.058      14998.0 seconds   or    4.1 hours
Pluto               39.44       19680.0 seconds   or    5.5 hours
...................................................................

Distances and light times to the planets and Pluto (from Alphonse Swinehart)

You might first think that moving that fast will get us across the orbits of the eight planets in a hurry. I shouldn’t have been surprised, but I found myself already getting impatient by the time Mercury flew by … after 3.2 minutes. Earth was still 5 minutes away and Jupiter another 40! That’s why the video cuts off at Jupiter – no one would stick around for Pluto’s appearance 5 1/2 hours later.

As the video tediously but effectively demonstrates we live in a solar system where a few planets are separated by vast spaces. Not even light is fast enough to satisfy the human need for speed. But just to put things in perspective, the fastest current human-made objects is NASA’s Voyager I spacecraft, which recently reached interstellar space traveling at 38,000 mph (17 km/sec) or nearly 18,000 times slower than light speed.

Let’s explore further. Any material object, a Skittle for instance, moving that fast would become infinitely massive. Why? You’d need an infinite amount of energy to accelerate the Skittle to the exact speed of light. Since matter and energy are two faces of the same coin, all that energy creates an infinitely massive Skittle. Sweet revenge if there ever was.

You can however accelerate the pill-like candy to 99.9999% light speed with a finite if incredibly large amount of energy. Einstein’s cool with that. Here’s the weird thing. If you were travelling along at the speed of light it would look like a perfectly normal piece of candy, but if you were to look at it from the outside world, the sugary treat would be the entire universe. Both viewpoints are equally valid, and that’s the essence of relatively.

Wave-particle duality of light

To better imagine a day in the life of a photon, let’s go along for the ride. Photons are the particle form of light, which for a long time was only understood as waves of electromagnetic energy. In the weirdness of quantum world, light is both a particle and a wave. From our perspective, a photon rip by at 186,000 miles per second, but to the photon itself, the world stands still and time stops. Photons are everywhere at once. Omnipresent. No time passes for them.

In relativity theory, the movement of anything is defined entirely from an observer’s point of view. From the photon’s perspective, it’s at rest. From ours, it’s moving across time and space. We all have our own “coordinate frame”, so that wherever we are, we’re at rest. That’s relativity for you – all frames are equally valid.

Let say you’re in a plane. That sad bag of pretzels you were just handed is at rest because it’s in your coordinate frame. The person next to you is likewise at rest (and hopefully not snoring). Even the plane’s at rest. According to Einstein, it’s just as valid to picture the world outside the airplane window moving while the plane itself remains at rest. Next time you fly, close your eyes once the plane reaches altitude and a constant speed. You’ll hear the noise of engines, but there’s no way to know you’re actually moving.

Diagram showing how an object (sphere) contracts in the direction of motion as its speed increases. At far left, its velocity (V) is 0.3 times the speed of light. Credit: Askamathematician.com

Relativity also predicts that objects contract in the direction of their motion. Strange as it sounds, this has been verified by many experiments. The faster things travel, the more they contract.

The effect doesn’t become noticeable until an object approaches light speed, but the Apollo 10 service and crew modules reached a velocity of 0.0037% the speed of light. From the perspective of someone on the ground, the 11.03-meter-long module shrank by approximately 7.5 nanometers, an exceedingly tiny but measurable amount. (A sheet of paper is 100,000 nanometers thick). Likewise, distances contract, bottoming out at zero at light speed.

Length contraction occurs because a stationary observer sees a speedy spaceship traveler’s time tick by more slowly. Since light is measured in time units – light seconds, light years – in order for the two to agree on the speed of light (a constant across the universe) the traveler’s “ruler” has to be shorter. And it really is from your stationary perspective if you could somehow peer inside the ship. Traveling at 10% light speed, a 200-foot spaceship shrinks to 199 feet. At 86.5%, it’s 100 feet or half the size and at 99.99% only 3 feet!

We’ve traveled far today – sitting quietly in our frames of reference.

February 5, 2015December 23, 2015 by Bob King

An Even Closer View of Ceres Shows Multiple White Spots Now

One several images NASA's Dawn spacecraft took on approach to Ceres on Feb. 4, 2015 at a distance of about 90,000 miles (145,000 kilometers) from the dwarf planet. Image credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

NASA’s Dawn spacecraft has acquired its latest and closest-yet snapshot of the mysterious dwarf planet world Ceres. These latest images, taken on Feb. 4, from a distance of about 90,000 miles (145,000 km) clearly show craters – including a couple with central peaks – and a clearer though still ambiguous view of that wild white spot that has so many of us scratching our heads as to its nature.

Get ready to scratch some more. The mystery spot has plenty of company.

Take a look at some still images I grabbed from the video which NASA made available today. In several of the photos, the white spot clearly looks like a depression, possibly an impact site. In others, it appears more like a rise or mountaintop. But perhaps the most amazing thing is that there appear to be not one but many white dabs and splashes on Ceres’ 590-mile-wide globe. I’ve toned the images to bring out more details:

Here the spot appears more like a depression. Frost? Ice? Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

Here the white spot is at the asteroid's left limb. You can also see additional smaller spots that remind me of rayed lunar craters. Credit: — Here the white spot is at the asteroid’s left limb. You can also see lots of additional smaller spots that remind me of rayed lunar craters. Of course, they may be something else entirely. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

Look down along the lower limb to spot a crater with a cool central peak. Credit: — Look down along the lower limb to spot a crater with a cool central peak. Note also how many white spots are now visible on Ceres. The mystery spot is a little right of center in this view. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

Our mystery white spot is further right of center. Is it a rise or a hole? Credit: — Our mystery white spot is further right of center. Is it a rise or a hole?Are the streaks rays for fresh material from an impact the way the lunar crater Tycho appears from Earth? Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

Yet another view of the mystery spot. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

Now let’s take a look at an additional NASA animation of Ceres made using processed images. As the spot first rounds the limb it looks like a depression. But just before it disappears around the backside a pointed peak seems to appear. Intriguing, isn’t it?

February 5, 2015December 23, 2015 by Bob King

Rosetta to Snuggle Up to Comet 67P for Closest Encounter Yet

Rosetta will dance close to 67P on Valentine's Day coming to within 3.7 miles of the comet. Credit: Bob King

Who doesn’t like to snuggle up with their Valentine on Valentine’s Day? Rosetta will practically whisper sweet nothings into 67P’s ear on February 14 when it swings just 3.7 miles (6 km) above its surface, its closest encounter yet.

Rosetta had been orbiting the comet at a distance of some 16 miles (26 km) but beginning yesterday, mission controllers used the spacecraft’s thrusters to change its orbit in preparation for the close flyby. First, Rosetta will move out to a distance of roughly 87 miles (140 km) from the comet this Saturday before swooping in for the close encounter at 6:41 a.m. CST on Feb. 14. Closest approach happens over the comet’s larger lobe, above the Imhotep region.

The relative position of Rosetta with Comet 67P/Churyumov–Gerasimenko at the moment of closest approach this Valentine's Day when the spacecraft will pass just 3.7 miles (6 km) above the comet’s large lobe. Credit: ESA/C.Carreau — The relative position of Rosetta with Comet 67P/Churyumov–Gerasimenko at the moment of closest approach this Valentine’s Day when the spacecraft will pass just 3.7 miles (6 km) above the comet’s large lobe. Credit: ESA/C.Carreau with additions by the author

The close encounter will provide opportunities for Rosetta’s science instruments to photograph 67P’s surface at high resolution across a range of wavelengths as well as get a close sniff of what’s inside its innermost coma or developing atmosphere. Scientists will also be looking closely at the outflowing gas and dust to see how it evolves during transport from the comet’s interior to the coma and tail.

As Rosetta swoops by its view of the comet will continuously change. Instruments will collect data on how 67P’s dust grains reflect light across a variety of orbital perspectives – from shadowless lighting with the Sun at the orbiter’s back to slanted lighting angles – to learn more about its properties.

The Imhotep region of comet 67P features a large, relatively smooth region. Rosetta will make high resolutions of Imhotep during its close flyby. Credit: ESA/Rosetta/Navcam — The Imhotep region of comet 67P features a large, relatively smooth region and a smattering of large boulders. Rosetta will make high resolutions of Imhotep during its close flyby. Credit: ESA/Rosetta/Navcam

“After this close flyby, a new phase will begin, when Rosetta will execute sets of flybys past the comet at a range of distances, between about 15 km (9 miles) and 100 km (62 miles),” said Sylvain Lodiot, ESA’s spacecraft operations manager.

During some of the close flybys, Rosetta trajectory will be almost in step with the comet’s rotation, allowing the instruments to monitor a single point on the surface in great detail as it passes by.

Helpful animation of how ESA mission controllers are changing Rosetta’s orbit to ready the probe for the Valentine’s Day flyby.

Perihelion, when the comet arcs closest to the Sun at a distance of 115.6 million miles (186 million km), occurs on August 13. Activity should be reaching its peak around that time. Beginning one month before, the Rosetta team will identify and closely examine one of the comet’s jets in wickedly rich detail.

“We hope to target one of these regions for a fly-through, to really get a taste of the outflow of the comet,” said Matt Taylor, ESA’s Rosetta project scientist.

Yum, yum. Can’t wait for that restaurant review!

February 3, 2015December 23, 2015 by Bob King

Jupiter and the Full Snow Moon Come Together In a Beautiful Conjunction Tonight

A halo rings the bright moon and planet Jupiter (left of moon) Credit: Bob King

The Full Moon celebrates Jupiter’s coming opposition by accompanying the bright planet in a beautiful conjunction tonight.

Even last night Jupiter and the Moon were close enough to attract attention. Tonight they’ll be even more striking. Two reasons for that. The Moon is full this evening and will have crept within 4¹/₂° of the planet. They’ll rise together and roll together all night long.

The Full Snow Moon will share the sky with Jupiter in Cancer tonight not far from the Sickle or head of Leo the Lion. The map shows the scene around 8 o'clock local time. Source: Stellarium — The Full Snow Moon will share the sky with Jupiter in Cancer tonight not far from the Sickle or head of Leo the Lion. The map shows the scene around 8 o’clock local time. Source: Stellarium

February’s full moon is aptly named the Full Snow Moon as snowfall can be heavy this month. Just ask the folks in Chicago. The Cherokee Indians called it the “Bone Moon”, named for the tough times experienced by many Native Americans in mid-winter when food supplies ran low. With little left to eat people made use of everything including bones and bone marrow for soup.

Not only is the Full Moon directly opposite the Sun in the sky, rising around sunset and setting around sunrise, but in mid-winter they’re nearly on opposite ends of the celestial seesaw.

Jupiter, like tonight's Full Moon, will be directly opposite the Sun this Friday and in "full moon" phase. Credit: Bob King — Jupiter, like tonight’s Full Moon, will be directly opposite the Sun this Friday and in “full moon” phase. Because both planets are lined up on the same side of the Sun, Jupiter will also be at its closest to us for the year. Credit: Bob King

In early February the Sun is still near its lowest point in the sky (bottom of the seesaw) for the northern half of the globe. And while daylight is steadily increasing as the Sun moves northward, darkness still has the upper hand this month. Full Moons like tonight’s lie 180° opposite the Sun, placing the Moon near the top of the seesaw. Come early August, the Sun will occupy the Moon’s spot and the Full Moon will have slid down to the Sun’s current position. Yin and Yang folks.

Now here’s the interesting thing. Jupiter will also be in “full moon” phase when it reaches opposition this Friday Feb. 6. Take a look at the diagram. From our perspective on Earth, Jupiter and the Sun lie on opposite sides of our planet 180° apart. As the Sun sets Friday, Jupiter will rise in the east and remain visible all night until setting around sunrise exactly like a Full Moon.

So in a funny way, we have two Full Moons this week only one’s a planet.

Like me, a lot of you enjoy a good moonrise. That golden-orange globe, the crazy squished appearance at rising and the transition to the bright, white, beaming disk that throws enough light on a winter night to ski in the forest without a headlamp. All good reasons to be alive.

If Jupiter were moved to the Moon's distance it would span about 20 of sky or 40x the apparent diameter of the Full Moon. Credit: Roscosmos with additions by the author — If Jupiter were moved to the Moon’s distance it would span about 20 degrees or 40 times the apparent diameter of the Full Moon. Credit: Roscosmos with additions by the author

To find when the moon rises for your town, click over to this moonrise calculator. As you step outside tonight to get your required Moon and Jupiter-shine, consider the scene if we took neighboring Jupiter and placed it at the same distance as the Moon. A recent series of such scenes was released by the Russian Federal Space Agency (Roscosmos). I included one here and added the Moon for you to compare. Is Jupiter enormous or what?

February 2, 2015December 23, 2015 by Bob King

Rosetta Sees Fascinating Changes in Comet 67P

A new jet issues from a fissure in the rugged, dusty surface of Rosetta's comet. Credit: ESO/Rosetta/Navcam

It only makes sense. Sunlight heats a comet and causes ice to vaporize. This leads to changes in the appearance of surface features. For instance, the Sun’s heat can gnaw away at the ice on sunward-facing cliffs, hollowing them out and eventually causing them to collapse in icy rubble. Solar heating can also warm the ice that’s beneath the surface.

When it becomes a vapor, pressure can build up, cracking the ice above and releasing sprays of gas and dust as jets. New images compared to old suggest the comet’s surface is changing as it approaches the Sun.

Take a look at this photo taken on December 9 of a part of the neck of the comet called Hapi. I've labeled a boulder and three prominent cracks. Sunlight is coming from top and behind in this image. Compare to the photo below shot on Jan. 8. Credit: ESA/Rosetta/Navcam — Take a look at this photo taken on December 9 of a part of the neck of the comet called Hapi. I’ve labeled a boulder and three prominent cracks. Sunlight is coming from top and behind in this image. Compare to the photo below shot on Jan. 8. Credit: ESA/Rosetta/Navcam

Recent photos taken by the Rosetta spacecraft reveal possible changes on the surface of 67P/Churyumov-Gerasimenko that are fascinating to see and contemplate. In a recent entry of the Rosetta blog, the writer makes mention of horseshoe-shaped features in the smooth neck region of the comet called “Hapi”. An earlier image from Jan. 8 may show subtle changes in the region compared to a more recent image from Jan. 22. We’ll get to those in a minute, but there may be examples of more vivid changes.

Although the viewing angle and lighting geometry has changed some between this photo, taken Jan. 8, and the one above, it certainly appears that the three cracks have virtually disappeared in a month's time. The same boulder is flagged in both photos. Credit: ESA/Rosetta/Navcam — Although the viewing angle and lighting geometry has changed some between this photo, taken Jan. 8, and the one above, it certainly appears that the three cracks have virtually disappeared in a month’s time. The same boulder is flagged in both photos. Credit: ESA/Rosetta/Navcam

I did some digging around and found what appears to be variations in terrain between photos of the same Hapi region on Dec. 9 and Jan.8. Just as the other writer took care to mention, viewing angle and lighting are not identical in the images. That has to be taken into account when deciding whether a change in a feature is real or due to change in lighting or perspective.

Side by side comparison of the two image from Dec. 9, 2014 (left) and Jan. 8, 2015. Credit: ESA/Rosetta/Navcam

But take a look at those cracks in the December image that appear to be missing in January’s. The change, if real, is dramatic. If they did disappear, how? Are they buried in dust released by jets that later drifted back down to the surface?

Comparison of Jan. 22 and Jan. 9 photos of the "horseshoes" or depressions in 67P's Hapi region. Outside of differences in lighting, do you see any changes? Credit: ESA/Rosetta/Navcam — Comparison of Jan. 22 and Jan. 9 photos of the “horseshoes” or depressions in 67P’s Hapi region. Outside of differences in lighting, do you see any changes? Credit: ESA/Rosetta/Navcam

Now back to those horseshoe features. Again, the viewing angles are somewhat different, but I can’t see any notable changes in the scene. Perhaps you can. While comets are expected to change, it’s exciting when it seems to be happening right before your eyes.

Four-image mosaic shows the overall view of the comet on January 22 photographed 17.4 miles (28 km) from its center. The larger of the two lobes is at left; Hapi is the smooth region at the transition between the lobes. Credit: ESA/Rosetta/Navcam — Four-image mosaic shows the comet overall on January 22 from a distance of 17.4 miles (28 km) from its center. The larger of the two lobes is at left; Hapi is the smooth region at the transition between the lobes. Credit: ESA/Rosetta/Navcam

January 31, 2015December 23, 2015 by Bob King

Awesome New Radar Images of Asteroid 2004 BL86

Individual radar images of 2004 BL86 and its moon. The asteroid appears very lumpy, possibly from unresolved crater rims. The moon appears elongated but that may be an artifact and not its true shape. Credit: NASA

New video of 2004 BL₈₆ and its moon

Newly processed images of asteroid 2004 BL₈₆ made during its brush with Earth Monday night reveal fresh details of its lumpy surface and orbiting moon. We’ve learned from both optical and radar data that Alpha, the main body, spins once every 2.6 hours. Beta (the moon) spins more slowly.

The images were made by bouncing radio waves off the surface of the bodies using NASA’s 230-foot-wide (70-meter) Deep Space Network antenna at Goldstone, Calif. Radar “pinging” reveals information about the shape, velocity, rotation rate and surface features of close-approaching asteroids. But the resulting images can be confusing to interpret. Why? Because they’re not really photos as we know it.

For one, the moon appears to be revolving perpendicular to the main body which would be very unusual. Most moons orbit their primary approximately in the plane of its equator like Earth’s moon and Jupiter’s four Galilean moons. That’s almost certainly the case with Beta. Radar imagery is assembled from echoes or radio signals returned from the asteroid after bouncing off its surface. Unlike an optical image, we see the asteroid by reflected pulses of radio energy beamed from the antenna. To interpret them, we’ll need to put on our radar glasses.

Bright areas don’t necessarily appear bright to the eye because radar sees the world differently. Metallic asteroids appear much brighter than stony types; rougher surfaces also look brighter than smooth ones. In a sense these aren’t pictures at all but graphs of the radar pulse’s time delay, Doppler shift and intensity that have been converted into an image.

Another set of images of 2004 BL86 and its moon. Credit: NAIC Observatory / Arecibo Observatory — Another set of images of 2004 BL₈₆ and its moon. Credit: NAIC Observatory / Arecibo Observatory

In the images above, the left to right direction or x-axis in the photo plots the toward and away motion or Doppler shift of the asteroid. You’ll recall that light from an object approaching Earth gets bunched up into shorter wavelengths or blue-shifted compared to red-shifted light given off by an object moving away from Earth. A more rapidly rotating object will appear larger than one spinning slowly. The moon appears elongated probably because it’s rotating more slowly than the Alpha primary.

Meanwhile, the up and down direction or y-axis in the images shows the time delay in the reflected radar pulse on its return trip to the transmitter. Movement up and down indicates a change in 2004 BL86’s distance from the transmitter, and movement left to right indicates rotation. Brightness variations depend on the strength of the returned signal with more radar-reflective areas appearing brighter. The moon appears quite bright because – assuming it’s rotating more slowly – the total signal strength is concentrated in one small area compared to being spread out by the faster-spinning main body.

If that’s not enough to wrap your brain around, consider that any particular point in the image maps to multiple points on the real asteroid. That means no matter how oddly shaped 2004 BL₈₆ is in real life, it appears round or oval in radar images. Only multiple observations over time can help us learn the true shape of the asteroid.

You’ll often notice that radar images of asteroids appear to be lighted from directly above or below. The brighter edge indicates the radar pulse is returning from the leading edge of the object, the region closest to the dish. The further down you go in the image, the farther away that part of the asteroid is from the radar and the darker it appears.

Imagine for a moment an asteroid that’s either not rotating or rotating with one of its poles pointed exactly toward Earth. In radar images it would appear as a vertical line!

If you’re curious to learn more about the nature of radar images, here are two great resources:

* How Radio Telescopes Get “Images” of Asteroids by Emily Lakdawalla
* Goldstone Solar System Radar Observatory: Earth-Based Planetary Mission Support and Unique Science Results

January 29, 2015December 23, 2015 by Bob King

What Asteroid 2004 BL86 and Hawaii Have in Common

Toes of a pahoehoe flow advance across a road in Kalapana on the east rift zone of Kilauea Volcano, Hawaii and the binary asteroid 2004 BL86. Credit: U.S. Geological Survey (left) and NASA/JPL-Caltech

At first glance, you wouldn’t think Hawaii has any connection at all with asteroid 2004 BL₈₆, the one that missed Earth by 750,000 miles (1.2 million km) just 3 days ago. One’s a tropical paradise with nightly pig roasts, beaches and shave ice; the other an uninhabitable ball of bare rock untouched by floral print swimsuits.

But Planetary Science Institute researchers Vishnu Reddy and Driss Takir would beg to differ.

Using NASA’s Infrared Telescope Facility on Mauna Kea, Hawaii they discovered that the speedy “space mountain” has a composition similar to the very island from which they made their observations – basalt.

“Our observations show that this asteroid has a spectrum similar to V-type asteroids,” said Reddy. “V-type asteroids are basalt, similar in composition to lava flows we see in Hawaii.

Minerals on the surface of an object like the moon or an asteroid absorb particular wavelengths of light to create a series of "blank spaces" or absorption lines that are unique to a particular element or compound. Credit: NASA — Minerals on the surface of an object like the moon or an asteroid absorb wavelengths of light to create a series of “blank spaces” or absorption lines that are unique to a particular element or compound. Credit: NASA

The researchers used a spectrograph to study infrared sunlight reflected from 2004 BL₈₆ during the flyby. A spectrograph splits light into its component colors like the deli guy slicing up a nice salami. Among the colors are occasional empty spaces or what astronomers call absorption lines, where minerals such as olivine, pyroxene and plagioclase on the asteroid’s surface have removed or absorbed particular slices of sunlight.

You're looking straight down on the 310-mile-wide Rheasilvea crater / impact basin on the asteroid Vesta. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA — You’re looking straight down into the 310-mile-wide (500 km) Rheasilvea crater / impact basin on the asteroid Vesta. It’s though that many of the Vesta-like asteroids, including 2004 BL₈₆, originated from the impact. It Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

These are the same materials that not only compose earthly basalts – all that dark volcanic rock that underlies Hawaii’s reefs and resorts – but also Vesta, considered the source of V-type asteroids. It’s thought that the impact that hollowed out the vast Rheasilvia crater at Vesta’s south pole blasted chunks of mama asteroid into space to create a family of smaller siblings called vestoids.

This animation, created from individual radar images, clearly show the rough outline of 2004 BL86 and its newly-discovered moon. Credit: NASA/JPL-Caltech — This animation, created from individual radar images, shows the binary asteroid 2004 BL86 on January 26th. The moon’s orbital period is about 13.8 hours. Credit: NASA/JPL-Caltech

So it would appear that 2004 BL₈₆ could be a long-lost daughter born through impact and released into space to later be perturbed by Jupiter into an orbit that periodically brings it near Earth. Close enough to watch in wonder as it inches across the field of view of our telescopes like it did earlier this week.

The little moonlet may or may not be related to Vesta, but its presence makes 2004 BL₈₆ a binary asteroid, where each object revolves about their common center of gravity. While the asteroid is unlikely to become future vacation destination, there will always be Hawaii to satisfy our longings for basalt.

January 26, 2015December 23, 2015 by Bob King

News Flash: Asteroid Flying Past Earth Today Has Mini-Moon!

Wonderful news! Asteroid 2004 BL86, which passed closest to Earth today at a distance of 750,000 miles (1.2 million km), has a companion moon. Scientists working with NASA’s 230-foot-wide (70-meter) Deep Space Network antenna at Goldstone, California, have released the first radar images of the asteroid which show the tiny object in orbit about the main body.

While these are the first images of it, the “signature” of the satellite was seen in light curve data reported earlier by Joseph Pollock (Appalachian State University, North Carolina) and Petr Prave (Ondrejov Observatory, Czech Republic) according to Lance Benner who works with the radar team at Goldstone.

2004 BL86 measures about 1,100 feet (325 meters) across while its moon is approximately 230 feet (70 meters) across. The asteroid made its closest approach today (Jan. 26th) at 10:19 a.m. (CST), however it will peak in brightness this evening around 10 p.m. (4:00 UT) at magnitude +9.0. Unlike some flybys, 2004 BL86 will remain within a few tenths of a magnitude of peak brightness from 6 p.m. tonight (CST) through early tomorrow morning, so don’t miss the chance to see it in your telescope.

Don’t expect to see the diminutive moon visually – the entire system will only appear as a point of light, but I’m sure you’ll agree it’s cool just knowing it’s there.

The double asteroid (90) Antiope and S/2000 (90) 1. The two objects are separated by 171 km, and they perform their celestial dance in 16.5 hours. The adaptive optics observations could, however, never resolve the shape of the individual components as they are too small. Credit: ESO — The double asteroid (90) Antiope and its companion S/2000 (90) 1. The two objects are separated by 106 miles (171 km), and they perform their celestial dance in 16.5 hours. The adaptive optics observations couldn’t resolve the shape of the individual components as they are too small. Credit: ESO

Among near-Earth asteroids, about 16% that are about 655 feet (200 meters) or larger are either binary or triple systems. While that’s not what you’d call common, it’s not unusual either. To date, we know of 240 asteroids with a single moon, 10 triple systems and the sextuple system of Pluto (I realize that’s stretching a bit, since Pluto’s a dwarf planet) – 268 companions total. 52 of those are near-Earth asteroids.

With a resolution of 13 feet (4-meters) per pixel we can at least see the roughness of the the main body’s surface and perhaps imagine craters there. No details are visible on the moon though it does appear elongated. I’m surprised how round the main body is given its small size. An object that tiny doesn’t normally have the gravity required to crush itself into a sphere. Yet another fascinating detail needing our attention.

Of course the main asteroid will get your attention tonight. Please check out our earlier story on 2004 BL86 which includes more details as well as charts to help you track it as it flies across Cancer the Crab tonight. This is the best view we’re going to get of it for the next two centuries.

January 24, 2015December 23, 2015 by Bob King

Latest Research Reveals a Bizarre and Vibrant Rosetta’s Comet

Dust-covered, boulder-strewn landscape on the smaller of the two lobes of Comet 67P/Churyumov-Gerasimenko taken from a distance of 5 miles (8 km). Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

We’ve subsisted for months on morsels of information coming from ESA’s mission to Comet 67P/Churyumov-Gerasimenko. Now, a series of scientific papers in journal Science offers a much more complete, if preliminary, look at Rosetta’s comet. And what a wonderful and complex world it is.

Scientists have defined 19 regions on Comet 67P/Churyumov-Gerasimenko's nucleus grouped according to terrain. Each is named for an ancient Egytptian deity. Credits: ESA/Rosetta/MPS/OSIRIS Team/UPD/LAM/IAA/SSO /INTA/UPM/DASP/IDA — Scientists have defined 19 regions on Comet 67P/Churyumov-Gerasimenko’s nucleus according to terrain and named for Egyptian deities like Imhotep, Aten and Hathor. Credits: ESA/Rosetta/MPS/OSIRIS Team/UPD/LAM/IAA/SSO /INTA/UPM/DASP/IDA

Each of the papers describes a different aspect of the comet from the size and density of dust particles jetting from the nucleus, organic materials found on its surface and the diverse geology of its bizarre landscapes. Surprises include finding no firm evidence yet of ice on the comet’s nucleus. There’s no question water and other ices compose much of 67P’s 10 billion ton mass, but much of it’s buried under a thick layer of dust.

Despite its solid appearance, 67P is highly porous with a density similar to wood or cork and orbited by a cloud of approximately 100,000 “grains” of material larger than 2 inches (5 cm) across stranded there after the comet’s previous perihelion passage. Thousands of tiny comet-lets!
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