Observing Archives

August 10, 2015December 23, 2015 by David Dickinson

The 2015 Perseids: Weather Prospects, Prognostications and More

The venerable ‘old faithful of meteor showers’ is on tap for this week, as the August Perseids gear up for their yearly performance. Observers are already reporting enhanced rates from this past weekend, and the next few mornings are crucial for catching this sure-fire meteor shower.

First, here’s a quick rundown on prospects for 2015. The peak of the shower as per theoretical modeling conducted by Jérémie Vaubaillon projects a broad early maximum starting around Wednesday, August 12th at 18:39 UT/2:39 PM EDT. This favors northeastern Asia in the early morning hours, as the 1862 dust trail laid down by Comet 109P Swift-Tuttle — the source of the Perseids — passes 80,000 km (20% of the Earth-Moon distance, or about twice the distance to geostationary orbit) from the Earth. This is worth noting, as the last time we encountered this same stream was 2004, when the Perseids treated observers to enhanced rates up towards 200 per hour. Typically, the Perseids exhibit a Zenithal Hourly Rate (ZHR) of 80-100 per hour on most years.

This translates into a local peak for observers worldwide on the mornings of August 12th and 13th. Comet 109P Swift-Tuttle orbits the Sun once every 120 years, and last reached perihelion in 1992, enhancing the rates of the Perseids throughout the 1990s.

Don’t live in northeast Asia? Don’t despair, as meteor showers such as the Perseids can exhibit broad multiple peaks which may arrive early or late. Mornings pre-dawn are the best time to spy meteors, as the Earth has turned forward into the meteor stream past local midnight, and rushes headlong into the oncoming stream of meteor debris. It’s a metaphor that us Floridians know all too well: the front windshield of the car gets all the bugs!

The flight of the Perseid radiant through August. Image credit: Dave Dickinson/Stellarium

Weather prospects — particularly cloud cover, or hopefully, the lack of it — is a factor on every observer’s mind leading up to a successful meteor hunting expedition. Fortunately here in the United States southeast, August mornings are typically clear, until daytime heating gives way to afternoon thunder storms. About 48 hours out, we’re seeing favorable cloud cover prospects for everyone in the CONUS except perhaps the U.S. northeast.

Weather and cloud cover prospects for the mornings of August 12th and August 13th. Image credit: NOAA

The Moon is also under 48 hours from New on Wednesday, allowing for dark skies. This is the closest New Moon to the peak of the Perseids we’ve had since 2007, and it won’t be this close again until 2018.

Fun fact: the August Perseids, October Orionids, November Leonids AND the December Geminids are roughly spaced on the calendar in such a way that if the Moon phase is favorable for one shower on a particular year, it’ll nearly always be favorable (and vice versa) on the others as well.

Sky watchers have observed the annual Perseid meteors since antiquity, and the shower is often referred to as ‘The Tears of Saint Lawrence.’ The Romans martyred Saint Lawrence on a hot grid iron on August 10^th, 258 AD. The radiant crosses from the constellation Perseus in early August, and sits right on the border of Cassiopeia and Camelopardalis on August 12^th at right ascension 3 hours 10’ and declination +50N 50.’ Technically, the shower should have the tongue-twisting moniker of the ‘Camelopardalids’ or perhaps the ‘Cassiopeiaids!’

The last few years have seen respectable activity from the Perseids:

2014- ZHR = 68 (Full Moon year)

2013- ZHR = 110

2012- ZHR = 120

2011- ZHR = 60 (Full Moon year)

2010- ZHR = 90

You can see the light-polluting impact of the nearly Full Moon on the previous years listed above. Light pollution has a drastic effect on the number of Perseids you’ll see. Keep in mind, a ZHR is an ideal rate, assuming the radiant is directly overhead and skies are perfectly dark. Most observers will see significantly less. We like to watch at an angle about 45 degrees from the radiant, to catch meteors in sidelong profile.

Imaging the Perseids is as simple as setting up a DSLR on a tripod as taking long exposures of the sky with a wide angle lens. Be sure to take several test shots to get the combination of f-stop/ISO/and exposure just right for current sky conditions. This year, we’ll be testing a new intervalometer to take automated exposures while we count meteors.

Clouded out? NASA TV will be tracking the Perseids live on Wednesday, August 12^th starting at 10PM EDT/02:00 UT:

Remember, you don’t need sophisticated gear to watch the Perseids… just a working set of ‘Mark-1 eyeballs.’ You can even ‘hear’ meteor pings on an FM radio on occasion similar to lightning static if you simply tune to an unused spot on the dial. Sometimes, you’ll even hear a distant radio station come into focus as it’s reflected off of an ionized meteor trail:

And if you’re counting meteors, don’t forget to report ‘em to the International Meteor Organization and tweet ‘em out under hashtag #Meteorwatch.

Good luck and good meteor hunting!

August 10, 2015December 23, 2015 by Bob King

See Venus at Her Most Ravishing

Venus dwindles to a captivating crescent nearly 1 arc minute across as seen on August 8, 2015. An infrared filter was used to increase contrast between the planet and otherwise bright sky. Credit: SEN / Damian Peach

Venus is HUGE right now but oh-so-skinny as it approaches inferior conjunction on August 15. Like crescents? You’ll never see a thinner and more elegant one, but first you’ll have to find it. Here’s how.

There’s only one drawback to enjoying Venus at its radically thinnest — it’s very close to the Sun and visible only during the daytime. A look at the diagram above reveals that as Venus and Earth draw closer, the planet also aligns with the Sun. At conjunction on August 15, it will pass 7.9° south of our star, appearing as an impossibly thin crescent in the solar glare. The sight is unique, a curved strand of incandescent wire burning in the blue.

Venus at inferior conjunction on January 10, 2014 shows both the sunlit crescent and cusp extensions from sunlight penetrating the atmosphere from behind. Credit: Tudorica Alexandru — Venus at inferior conjunction on January 10, 2014 shows both the sunlit crescent and cusp extensions caused by sunlight penetrating the atmosphere from behind. During this previous inferior conjunction, Venus passed north of the Sun, so we see the bottom of the crescent illuminated. Credit: Tudorica Alexandru

If you’re patient and the air is steady, you might even glimpse the cusps of the illuminated crescent extending beyond their normal length to partially or even completely encircle Venus’s disk. These thread-like extensions become visible when the planet lies almost directly between us and the Sun. Sunlight scatters off the Venus’s dense atmosphere, causing it to glow faintly along the limb. One of the most remarkable sights in the sky, the sight is testament to the thickness of the planet’s airy envelope.

Going, going, gone! Or almost. Venus photographed in its beautiful crescent phase on two occasions this past week. — Going, going, gone! Venus photographed in its beautiful crescent phase on two occasions last week. When the planet reaches inferior conjunction this Saturday (August 15), the crescent will expand to nearly 1 arc minute across. No planet comes closer to Earth than Venus — just 27 million miles this week. Credit: Giorgio Rizzarelli

Today, only 1.7% of the planet is illuminated by the Sun, which shines some 11° to the northwest. The Venusian crescent spans 57 arc seconds from tip to tip, very close to 1 arc minute or 1/30 the width of the Full Moon. Come conjunction day August 15, those numbers will be 0.9% and 58 arc seconds. The angular resolution of the human eye is 1 minute, implying that the planet’s shape might be within grasp of someone with excellent eyesight under a clear, clean, cloudless sky. However — and this is a big however — a bright sky and nearby Sun make this practically impossible.

No worries though. Even 7x binoculars will nail it; the trick is finding Venus in the first place. For binocular users, hiding the Sun COMPLETELY behind a building, chimney, power pole or tree is essential. The goddess lurks dangerously close to our blindingly-bright star, so you must take every precaution to protect your eyes. Never allow direct sunlight into your glass. Never look directly at the Sun – even for a second – with your eyes or UV and infrared light will sear your retinas. You can use the map provided, which shows several locations of the planet at 1 p.m. CDT when it’s highest in the sky, to help you spot it.

The Sun's position is shown for 1 p.m. local daylight time, while Venus is shown for three dates - today, conjunction date and Aug. 21. As Venus moves from left to right under or south of the Sun, its phase swings from evening crescent (left) to morning crescent from our perspective on Earth. Source: Stellarium with additions by the author — The Sun’s position is shown for 1 p.m. local daylight time facing due south, while Venus and its corresponding phase is depicted before, at and after conjunction. As Venus moves from left to right south of the Sun, its phase changes from evening crescent (left) to morning crescent from our perspective on Earth. Source: Stellarium with additions by the author

If you’d like to see Venus on a different day or time, download a free sky-charting program like Stellarium or Cartes du Ciel. With Stellarium, open the Sky and Viewing Options menu (F4) and click the Light Pollution Level option down to “1” to show Venus in a daytime sky. Pick a viewing time, note Venus’s orientation with respect to the Sun (which you’ve hidden of course!) and look at that spot in the sky with binoculars. I’ll admit, it’s a challenging observation requiring haze-free skies, but be persistent.

By coincidence, the Moon and Venus will be about the same distance from the Sun and appear as exceedingly thin crescents on the afternoon (CDT) of August 13. Source: Stellarium — By coincidence, the Moon and Venus will be about the same distance from the Sun and appear as very similar thin crescents around 1 p.m. CDT on August 13. Venus should still be visible using the methods described below, but the Moon will be impossible to see. Source: Stellarium

A safer and more sure-fire way to track the planet down involves using those setting circles on your telescope mount most of us never bother with. First, find the celestial coordinates (right ascension and declination) of the Sun and Venus for the time you’d like to view. For example, let’s say we want to find Venus on August 10 at 2 p.m. Using your free software, you click on the Sun and Venus’s positions for that time of day to get their coordinates, in this case:

Venus – Right ascension 9h 42 minutes, declination +6°.
Sun – RA 9h 22 minutes, dec. +15° 30 minutes

Now subtract the two to get Venus’ offset from the Sun = 20 minutes east, 9.5° south.

Dust off those setting circles (declination shown here) and use them to point you to Venus this week. Credit: Bob King — Dust off those setting circles (declination shown here, marked off in degrees) and use them to point you to Venus this week. Credit: Bob King

Next, polar align your telescope using a compass and then cover the objective end with a safe mylar or glass solar filter. Center and sharply focus the Sun in the telescope. Now, loosen the RA lock and carefully offset the right ascension 20 minutes east using your setting circle, then re-lock. Do the same with declination, pointing the telescope 9.5° south of the Sun. If you’re polar alignment is reasonably good, when you remove the solar filter and look through the eyepiece, you should see Venus staring back at you from a blue sky. If you see nothing at first, nudge it a little this way and that to bring the planet into view.

Sometimes it takes me a couple tries, but I eventually stumble arrive on target. Obviously, you can also use this technique to spot Mercury and Jupiter in the daytime, too. By the way, don’t worry what the RA and Dec. read on your setting circles when you begin your hunt; only the offset’s important.

When inferior conjunction occurs at the same time Venus crosses the plane of Earth's orbit, we see a rare transit like this one on June 5, 2012. Credit: Bob King — When inferior conjunction occurs at the same time Venus crosses the plane of Earth’s orbit, we see a rare transit (upper right) like this one on June 5, 2012. Credit: Bob King

This year’s conjunction is one of the best for finding Venus in daylight because it’s relatively far from the Sun. With an orbital inclination of 3.2°, Venus’s position can range up to 8° north and south of the Earth’s orbital plane or ecliptic. Rarely does the planet cross the ecliptic at the same time as inferior conjunction. When it does, we experience a transit of Venus. Transits always come in pairs; the last set occurred in 2004 and 2012; the next will happen over 100 years from now in 2117 and 2125.

I hope you’re able to make the most of this opportunity while still respecting your tender retinas. Good luck!

August 7, 2015December 23, 2015 by Bob King

Kick Back, Look Up, We’re In For a GREAT Perseid Meteor Shower

Multi-photo composite showing Perseid meteors shooting from their radiant point in the constellation Perseus. Earth crosses the orbit of comet 109P/Swift-Tuttle every year in mid-August. Debris left behind by the comet burns up as meteors when it strikes our upper atmosphere at 130,000 mph. Credit: NASA

Every year in mid-August, Earth plows headlong into the debris left behind by Comet 109P/Swift-Tuttle. Slamming into our atmosphere at 130,000 mph, the crumbles flash to light as the Perseid meteor shower. One of the world’s most beloved cosmic spectacles, this year’s show promises to be a real crowd pleaser.

The author tries his best to enjoys this year's moon-drenched Perseids from the "astro recliner". Credit: Bob King — The author takes in last year’s moon-drenched Perseids from a recliner. Credit: Bob King

Not only will the Moon be absent, but the shower maximum happens around 3 a.m. CDT (8 UT) August 13 — early morning hours across North America when the Perseid radiant is highest. How many meteors will you see? Somewhere in the neighborhood of 50-100 meteors per hour. As always, the darker and less light polluted your observing site, the more zips and zaps you’ll see.

Find a place where there’s as few stray lights as possible, the better to allow your eyes to dark-adapt. Comfort is also key. Meteor showers are best enjoyed in a reclining position with as little neck craning as possible. Lie back on a folding lawn chair with your favorite pillow and bring a blanket to stay warm. August nights can bring chill and dew; a light coat and hat will make your that much more comfortable especially if you’re out for an hour or more.

The Perseids appear to radiate from spot below the W of Cassiopeia in the constellation Perseus, hence the name "Perseids". Source: Stellarium — The Perseids appear to radiate from spot below the W of Cassiopeia in the constellation Perseus, hence the shower’s name. This map shows the sky facing northeast around 12:30 a.m. local time August 13. Source: Stellarium

I’m always asked what’s the best direction to face. Shower meteors will show up in every corner of the sky, but can all be traced backwards to a point in Perseus called the radiant. That’s the direction from which they all appear to stream out of like bats flying out of a cave.

Another way to picture the radiant it is to imagine driving through a snowstorm at night. As you accelerate, you’ll notice that the flakes appear to radiate from a point directly in front of you, while the snow off to the sides streams away in long trails. If you’re driving at a moderate rate of speed, the snow flies past on nearly parallel paths that appear to focus in the distance the same way parallel railroad tracks converge.

At some personal peril, I grabbed a photo of snow in the headlights while driving home in a recent storm. Meteors in a meteor shower appear to radiate from a point in the distance in identical fashion. Photo: Bob King — Meteors in a meteor shower appear to radiate from a point in the distance in identical fashion to driving a car in a snowstorm. The motion of the car (Earth) creates the illusion of meteors radiating from a point in the sky ahead of the observer. Credit: Bob King

Now replace your car with the moving Earth and comet debris for snow and you’ve got a radiant and a meteor shower. With two caveats. We’re traveling at 18 1/2 miles per second and our “windshield”, the atmosphere, is more porous. Snow bounces off a car windshield, but when a bit of cosmic debris strikes the atmosphere, it vaporizes in a flash. We often think friction causes the glow of meteors, but they’re heated more by ram pressure.

A bright fireball breaking to pieces near Yellow Springs, Ohio. Meteors are really tubes of ionized air energized by the passage of comet bits. Credit: John Chumack

The incoming bit of ice or rock rapidly compresses and heats the air in front of it, which causes the particle to vaporize around 3,000°F (1,650°C). The meteor or bright streak we see is really a hollow “tube” of glowing or ionized air molecules created by the tiny rock as its energy of motion is transferred to the surrounding air molecules. Just as quickly, the molecules return to their rest state and release that energy as a spear of light we call a meteor.

Imagine. All it takes is something the size of a grain of sand to make us look up and yell “Wow!”

Speaking of size, most meteor shower particles range in size from a small pebble to beach sand and generally weigh less than 1-2 grams or about what a paperclip weighs. Larger chunks light up as fireballs that shine as bright as Venus or better. Because of their swiftness, Perseids are generally white and often leave chalk-like trails called trains in their wakes.

Comet 109P/Swift-Tuttle captured during its last pass by Earth on Nov. 1, 1992. A filament of dust deposited by the comet in 1862 may cause a temporary spike in activity on Aug. 12 around 18:39 UT. Credit: Gerald Rhemann — Comet 109P/Swift-Tuttle seen during its last pass by Earth on Nov. 1, 1992. A filament of dust deposited by the comet in 1862 may cause a temporary spike in activity around 18:39 UT on August 12. Credit: Gerald Rhemann

This year’s shower is special in another way. According to Sky and Telescope magazine, meteor stream modeler Jeremie Vaubaillon predicts a bump in the number of Perseids around 1:39 p.m. (18:39 UT) as Earth encounters a debris trail shed by the Comet Swift-Tuttle back in 1862. The time favors observers in Asia where the sky will be dark. It should be interesting to see if the prediction holds.

How To Watch

Already the shower’s active. Go out any night through about the 15th and you’ll see at least at least a handful of Perseids an hour. At nightfall on the peak night of August 12-13, you may see only 20-30 meteors an hour because the radiant is still low in the sky. But these early hours give us the opportunity to catch an earthgrazer — a long, very slow-moving meteor that skims the atmosphere at a shallow angle, crossing half the sky or more before finally fading out.

I’ve only seen one good earthgrazer in my earthly tenure, but I’ll never forget the sight. Ambling from low in the northeastern sky all the way past the southern meridian, it remained visible long enough to catch it in my telescope AND set up a camera and capture at least part of its trail!

A Perseid meteor streaks across the northeastern sky two Augusts ago. This year's shower will peak on the night of August 12-13 with up to 100 meteors per hour visible from a dark sky. Credit: Bob King — A Perseid meteor streaks across the northeastern sky two Augusts ago. Give the shower an hour’s worth of your time – you won’t be disappointed. Credit: Bob King

The later you stay up, the higher the radiant rises and the more meteors you’ll see. Peak activity of 50-100 meteors per hour will occur between about 2-4 a.m. No need to stare at the radiant to see meteors. You can look directly up at the darkest part of the sky or face east or southeast and look halfway up if you like. You’re going to see meteors everywhere. Some will arrive as singles, others in short burst of 2, 3, 4 or more. I like to face southeast with the radiant off to one side. That way I can see a mix of short-trailed meteors from near the radiant and longer, graceful streaks further away just like the snow photo shows.

If there’s a lull in activity, don’t think it’s over. Meteor showers have strange rhythms of their own. Five minutes of nothing can be followed by multiple hits or even a fireball. Get into the feel of the shower as you sense spaceship Earth speeding through the comet’s dusty orbit. Embrace the chill of the August night under the starry vacuum.

August 6, 2015December 23, 2015 by David Dickinson

Stealing Sedna

An artist's conception of Sedna. this assumes that Sedna has a tiny as yet undiscovered moon. Image credit; NASA/JPl-Caltech

Turns out, our seemly placid star had a criminal youth of cosmic proportions.

A recent study out from Leiden Observatory and Cornell University may shed light on the curious case of one of the solar system’s more exotic objects: 90377 Sedna.

Distant Sedna (circled) moving against the starry background). Image credit: NASA/Hubble

A team led by astronomer Mike Brown discovered 90377 Sedna in late 2003. Provisionally named 2003 VB12, the object later received the name Sedna from the International Astronomical Union, after the Inuit goddess of the sea.

From the start, Sedna was an odd-ball. Its 11,400 year orbit takes it from a perihelion of 76 astronomical units (for context, Neptune is an average of 30 AUs from the Sun) to an amazing 936 AUs from the Sun. (A thousand AUs is 1.6% of a light year, and 0.4% of the way to Proxima Centauri, the closest star to our solar system). Currently at a distance of 86 AU and headed towards perihelion in 2076, we’re lucky we caught Sedna as it ‘neared’ (we use the term ‘near’ loosely in this case!) the Sun.

But this strange path makes you wonder what else is out there, and how Sedna wound up in such an eccentric orbit.

Zooming out; the inner solar system (upper left), the outer solar system (upper right), the orbit of Sedna (lower right) and the inner edge of the Oort cloud (lower left). Image credit: NASA

The study, entitled How Sedna and family were captured in a close encounter with a solar sibling looks at the possibility that Sedna may have been snatched from another star early on in our Sun’s career (of interstellar crime, perhaps?) The team used supercomputer simulations modeling 10,000 encounters to discover which types of near stellar passages might result in an ice dwarf world in a Sedna-like orbit.

“We constrained the parent star of Sedna to have between one and two times the mass of the Sun and its closest approach to be 200-400 AUs,” Dr. Lucie Jilkova of Leiden Observatory told Universe Today. “Such a close encounter probably happened while the Sun was still a member of its birth star cluster — a family of about 1,000 stars, so called solar siblings, born at the same time relatively close together — which was about 4 billion years ago.”

The best fit for what we see today in the outer solar system in the case of Sedna, is a close (340 AU) passage from the Sun — that’s over 11 times Neptune’s distance — of a 1.8 solar mass star inclined at an angle of 17-34 degrees to the ecliptic. Sedna’s current orbital inclination is 12 degrees.

Rise of the Sednitos

The paper assigns the term ‘Sednitos’ (also sometimes referred to as ‘Sednoids’) for these Edgeworth-Kuiper Belt intruders with similar characteristics to Sedna. In 2012, 2012 VP113, dubbed the ‘twin of Sedna,’ was discovered by astronomers at the Cerro Tololo Inter-American Observatory in a similar looping orbit. The ‘VP’ designation earned the as yet unnamed remote world the brief nickname ‘Biden’ after U.S. Vice President Joe Biden… hey, it was an election year.

There’s good reason to believe something(s?) out there shepherding these Senitos into a similar orbit with a comparable argument of perihelion. Researchers have suggested the existence of one or several planetary mass objects loitering out in the 200-250 AU range of the outer solar system… note that this is

a separate scientific-based discussion versus any would-be Nibiru related non-sense, don’t even get

us started…

If researchers in the study are correct, Sedna may have lots of company, with perhaps 930 planetesimals predicted in the ‘Sednito region’ of the solar system from 50 to 1,000 AUs and 430 more additional planetesimals littering the inner Oort cloud from the same early event.

“We focused on a particular example of a stellar encounter with characteristics from the ranges mentioned,” Dr. Jilkova said. “For this example, we estimated that there would be about 430 bodies similar to Sedna in the outer solar system (beyond 75 AU).”

Fun fact: One possible controversial candidate for the birth cluster of Sol and our solar system is the open cluster M67 in Cancer. It’s an intriguing notion to try and track down the star we stole Sedna from 4 billion years ago using spectral analysis, though researchers in the study point out that the other more massive star is probably an aging white dwarf by now.

Astronomy from the surface of Sedna is mind-bending to contemplate. Currently 86 AU from the Sun and headed towards perihelion in 2076, Sol would appear only 20” across from the surface of Sedna, but would still shine at magnitude -17 to -18 near perihelion, about 40 to 100 times brighter than a Full Moon. Fast forward about 5,500 years towards aphelion, however, and the Sun would dim to a paltry magnitude -12, a full magnitude (2.5 times) dimmer than the Full Moon.

The view from Sedna looking towards the inner solar system in 2015. Image credit: Starry Night Education Software. — The view from Sedna looking towards the inner solar system in 2015. Note the five degree red field of view marker. Image credit: Starry Night Education Software.

Shining at magnitude +21 in the constellation Taurus, astronomers know little else about Sedna. Based on brightness estimates, Sedna measures about 1,000 km in diameter. It does appear to be the reddest object in the solar system, and may turn out to be the ‘red twin of Pluto’ as recently revealed by NASA’s New Horizons spacecraft, complete with a surface rich in tholins.

And a new generation of observatories may uncover a treasure trove of Sednitos. The European Space Agency’s Gaia astrometry mission should uncover lots of new asteroids, comets, exoplanets and distant Kuiper Belt objects as a spin-off to its primary mission. Then there’s the Large Synoptic Survey Telescope, set to see first light in 2019.

“The key piece of the puzzle is to actually observe more Sedna-like objects.” Dr Jilkova said. “Currently, we know only of two such bodies. More discoveries are expected in the following years and they will shed light on the origin of Sedna and its family and the ‘criminal record’ of the Sun.”

It’s a fascinating story of interstellar whodunit for sure, as our Sun’s early days of wanton juvenile delinquency unravel before the eyes of modern day astronomical detectives.

August 4, 2015December 23, 2015 by David Dickinson

The Dog Days and Sothic Cycles of August

The month of August is upon us once again, bringing with it humid days and sultry nights for North American observers.

You’ll often hear the first few weeks of August referred to as the Dog Days of Summer. Certainly, the oppressive midday heat may make you feel like lounging around in the shade like our canine companions. But did you know there is an astronomical tie-in for the Dog Days as well?

We’ve written extensively about the Dog Days of Summer previously, and how the 1460 year long Sothic Cycle of the ancient Egyptians became attributed to the Greek adoption of Sothis, and later in medieval times to the ‘Dog Star’ Sirius. Like the Blue Moon, say something wrong enough, long enough, and it successfully sticks and enters into meme-bank of popular culture.

Sirius (to the lower right) along with The Moon, Venus and Mercury and a forest fire taken on July 22, 2014. (Note- this was shot from the Coral Towers Observatory in the southern hemisphere). Image credit and copyright: Joseph Brimacombe

A water monopoly empire, the Egyptians livelihood rested on knowing when the annual flooding of the Nile was about to occur. To this end, they relied on the first seasonal spotting of Sirius at dawn. Sirius is the brightest star in the sky, and you can just pick out the flicker of Sirius in early August low to the southeast if you know exactly where to look for it.

Sundown over Cairo during the annual flooding of the Nile river. Image Credit: Travels through the Crimea, Turkey and Egypt 1825-28 (Public Domain). — Sundown over Cairo during the annual flooding of the Nile river. Image Credit: *Travels through the Crimea, Turkey and Egypt 1825-28* (Public Domain).

Sirius lies at a declination of just under 17 degrees south of the celestial equator. It’s interesting to note that in modern times, the annual flooding of the Nile (prior to the completion of the Aswan Dam in 1970) is commemorated as occurring right around August 15th. Why the discrepancy? Part of it is due to the 26,000 year wobbling of the Earth’s axis known as the Precession of the Equinoxes; also, the Sothic calendar had no intercalculary or embolismic (think leap days) to keep a Sothic year in sync with the sidereal year. The Sothic cycle from one average first sighting of Sirius to another is 365.25 days, and just 9 minutes and 8 seconds short of a sidereal year.

But that does add up over time. German historian Eduard Meyer first described the Sothic Cycle in 1904, and tablets mention its use as a calendar back to 2781 BC. And just over 3 Sothic periods later (note that 1460= 365.25 x 4, which is the number of Julian years equal to 1461 Sothic years, as the two cycles ‘sync up’), and the flooding of the Nile now no longer quite coincides with the first sighting of Sirius.

Such a simultaneous sighting with the sunrise is known in astronomy as a heliacal rising. Remember that atmospheric extinction plays a role sighting Sirius in the swampy air mass of the atmosphere low to the horizon, taking its usual brilliant luster of magnitude -1.46 down to a more than a full magnitude and diminishing its intensity over 2.5 times.

This year, we transposed the seasonal predicted ‘first sightings’ of Sirius versus latitude onto a map of North America:

Another factor that has skewed the date of first ‘Sirius-sign’ is the apparent motion of the star itself. At 8.6 light years distant, Sirius appears to move 1.3 arc seconds per year. That’s not much, but over the span of one Sothic cycle, that amounts up to 31.6’, just larger than the average diameter of a Full Moon.

Sirius has been the star of legends and lore as well, not the least of which is the curious case of the Dogon people of Mali and their supposed privileged knowledge of its white dwarf companion star. Alvan Graham Clark and his father discovered Sirius B in 1862 as they tested out their shiny new 18.5-inch refractor. And speaking of Sirius B, keep a telescopic eye on the Dog Star, as the best chances to spy Sirius B peeking out from the glare of its primary are coming right up around 2020.

Sirius image Credit — The dazzling visage of Sirius. Image credit: Dave Dickinson

Repeating the visual feat of spying Sirius B low in the dawn can give you an appreciation as to the astronomical skill of ancient cultures. They not only realized the first sighting of Sirius in the dawn skies coincided with the annual Nile flooding, but they identified the discrepancy between the Sothic and sidereal year, to boot. Not bad, using nothing but naked eye observations. Such ability must have almost seemed magical to the ancients, as if the stars had laid out a celestial edge for the Egyptians to exploit.

You can also exploit one method of teasing out Sirius from the dawn sky a bit early that wasn’t available to those Egyptian astronomer priests: using a pair of binoculars to sweep the skies. Can you nab Sirius with a telescope and track it up into the daytime skies? Sirius is just bright enough to see in the daytime against a clear blue sky with good transparency if you know exactly where to look for it.

Let the Dog Days of 2015 begin!

August 3, 2015December 23, 2015 by Bob King

The Resplendent Inflexibility of the Rainbow

A colorful piece of rainbow begs the question - why Roy G. Biv? Credit: Bob King

Children often ask simple questions that make you wonder if you really understand your subject. An young acquaintance of mine named Collin wondered why the colors of the rainbow were always in the same order — red, orange, yellow, green, blue, indigo, violet. Why don’t they get mixed up?

The familiar sequence is captured in the famous Roy G. Biv acronym, which describes the sequence of rainbow colors beginning with red, which has the longest wavelength, and ending in violet, the shortest. Wavelength — the distance between two successive wave crests — and frequency, the number of waves of light that pass a given point every second, determine the color of light.

The familiar colors of the rainbow spectrum with wavelengths shown in nanometers. Credit: NASA

The cone cells in our retinas respond to wavelengths of light between 650 nanometers (red) to 400 (violet). A nanometer is equal to one-billionth of a meter. Considering that a human hair is 80,000-100,000 nanometers wide, visible light waves are tiny things indeed.

So why Roy G. Biv and not Rob G. Ivy? When light passes through a vacuum it does so in a straight line without deviation at its top speed of 186,000 miles a second (300,000 km/sec). At this speed, the fastest known in the universe as described in Einstein’s Special Theory of Relativity, light traveling from the computer screen to your eyes takes only about 1/1,000,000,000 of second. Damn fast.

But when we look beyond the screen to the big, wide universe, light seems to slow to a crawl, taking all of 4.4 hours just to reach Pluto and 25,000 years to fly by the black hole at the center of the Milky Way galaxy. Isn’t there something faster? Einstein would answer with an emphatic “No!”

A laser beam (left) shining through a glass of water demonstrates how many times light changes speed — from 186,222 miles per second (mps) in air to 124,275 mps through the glass. It speeds up again to 140,430 mps in water, slows down when passing through the other side of the glass and then speeds up again when leaving the glass for the air. Credit: Bob King

One of light’s most interesting properties is that it changes speed depending on the medium through which it travels. While a beam’s velocity through the air is nearly the same as in a vacuum, “thicker” mediums slow it down considerably. One of the most familiar is water. When light crosses from air into water, say a raindrop, its speed drops to 140,430 miles a second (226,000 km/sec). Glass retards light rays to 124,275 miles/second, while the carbon atoms that make up diamond crunch its speed down to just 77,670 miles/second.

Why light slows down is a bit complicated but so interesting, let’s take a moment to describe the process. Light entering water immediately gets absorbed by atoms of oxygen and hydrogen, causing their electrons to vibrate momentarily before it’s re-emitting as light. Free again, the beam now travels on until it slams into more atoms, gets their electrons vibrating and gets reemitted again. And again. And again.

A ray of light refracted by a plastic block. Notice that the light bends twice - once when it enters (moving from air to plastic) and again when it exits (plastic to air). — A ray of light refracted by a plastic block. Notice that the light bends twice – once when it enters (moving from air to plastic) and again when it exits (plastic to air). The beam slows down on entering and then speeds up again when it exits.

Like an assembly line, the cycle of absorption and reemission continues until the ray exits the drop. Even though every photon (or wave – your choice) of light travels at the vacuum speed of light in the voids between atoms, the minute time delays during the absorption and reemission process add up to cause the net speed of the light beam to slow down. When it finally leaves the drop, it resumes its normal speed through the airy air.

Light rays get bent or refracted when they move from one medium to another. We've all seen the "broken pencil" effect when light travels from air into water. — Light rays get bent or refracted when they move from one medium to another. We’ve all seen the “broken pencil” effect when light travels from air into water.

Let’s return now to rainbows. When light passes from one medium to another and its speed drops, it also gets bent or refracted. Plop a pencil in a glass half filled with water and and you’ll see what I mean.

Up to this point, we’ve been talking about white light only, but as we all learned in elementary science, Sir Isaac Newton conducted experiments with prisms in the late 1600s and discovered that white light is comprised of all the colors of the rainbow. It’s no surprise that each of those colors travels at a slightly different speed through a water droplet. Red light interacts only weakly with the electrons of the atoms and is refracted and slowed the least. Shorter wavelength violet light interacts more strongly with the electrons and suffers a greater degree of refraction and slowdown.

Isaac Newton used a prism to separate light into its familiar array of colors. Like a prism, a raindrop refracts incoming sunlight, spreading it into an arc of rainbow colors with a radius of 42. Left: NASA image, right, public domain with annotations by the author — Isaac Newton used a prism to separate light into its familiar array of colors. Like a prism, a raindrop refracts incoming sunlight, spreading it into an arc of rainbow colors with a radius of 42. The colors spread out when light enter the drop and then spread out more when they leave and speed up. Left: NASA image, right, public domain with annotations by the author

Rainbows form when billions of water droplets act like miniature prisms and refract sunlight. Violet (the most refracted) shows up at the bottom or inner edge of the arc. Orange and yellow are refracted a bit less than violet and take up the middle of the rainbow. Red light, least affected by refraction, appears along the arc’s outer edge.

Rainbows are often double. The secondary bow results from light reflecting a second time inside the raindrop. When it emerges, the colors are reversed (red on the bottom instead of top), but the order of colors is preserved. Credit: Bob King

Because their speeds through water (and other media) are a set property of light, and since speed determines how much each is bent as they cross from air to water, they always fall in line as Roy G. Biv. Or the reverse order if the light beam reflects twice inside the raindrop before exiting, but the relation of color to color is always preserved. Nature doesn’t and can’t randomly mix up the scheme. As Scotty from Star Trek would say: “You can’t change the laws of physics!”

So to answer Collin’s original question, the colors of light always stay in the same order because each travels at a different speed when refracted at an angle through a raindrop or prism.

Light of different colors have both different wavelengths (distance between successive wave crests) and frequencies. In this diagram, red light has a longer wavelength and more "stretched out" waves compared to purple light of higher frequency. Credit: NASA — Light of different colors have both different wavelengths (distance between successive wave crests) and frequencies. In this diagram, red light has a longer wavelength and more “stretched out” waves compared to purple light of higher frequency. Credit: NASA

Not only does light change its speed when it enters a new medium, its wavelength changes, but its frequency remains the same. While wavelength may be a useful way to describe the colors of light in a single medium (air, for instance), it doesn’t work when light transitions from one medium to another. For that we rely on its frequency or how many waves of colored light pass a set point per second.

Higher frequency violet light crams in 790 trillion waves per second (cycles per second) vs. 390 trillion for red. Interestingly, the higher the frequency, the more energy a particular flavor of light carries, one reason why UV will give you a sunburn and red light won’t.

When a ray of sunlight enters a raindrop, the distance between each successive crest of the light wave decreases, shortening the beam’s wavelength. That might make you think that that its color must get “bluer” as it passes through a raindrop. It doesn’t because the frequency remains the same.

We measure frequency by dividing the number of wave crests passing a point per unit time. The extra time light takes to travel through the drop neatly cancels the shortening of wavelength caused by the ray’s drop in speed, preserving the beam’s frequency and thus color. Click HERE for a further explanation.

Why prisms/raindrops bend and separate light

Before we wrap up, there remains an unanswered question tickling in the back of our minds. Why does light bend in the first place when it shines through water or glass? Why not just go straight through? Well, light does pass straight through if it’s perpendicular to the medium. Only if it arrives at an angle from the side will it get bent. It’s similar to watching an incoming ocean wave bend around a cliff. For a nice visual explanation, I recommend the excellent, short video above.

Oh, and Collin, thanks for that question buddy!

July 27, 2015December 23, 2015 by David Dickinson

Blues for the Second Full Moon of July

An artificially created 'Blue Moon,' using the white balance settings on the camera. Image credit and copyright: John Chumack

Brace yourselves for Blue Moon madness. The month of July 2015 hosts two Full Moons: One on July 2^nd and another coming right up this week on Friday, July 31^st at 10:43 Universal Time (UT)/6:43 AM EDT.

In modern day vernacular, the occurrence of two Full Moons in one calendar month has become known as a ‘Blue Moon.’ This is a result of the synodic period (the amount of time it takes for the Moon to return to a like phase, in this case Full back to Full) of 29.5 Earth days being less than every calendar month except February.

In the ‘two Full Moons in one month’ sense, the last time a Blue Moon occurred was on August 31st, 2012, and the next is January 31^st, 2018. The next time a Blue Moon occurs in the month of July is 2034, and the last July Blue Moon was 2004.

We say “once in a blue Moon,” as if it’s a rarity, but as you can see, they’re fairly frequent, occurring nearly once every 2-3 years or so.

Now, we’ll let you in on a secret. Like its modern internet meme cousin the ‘Super-Moon,’ astronomers don’t sit in mountain top observatories discussing the vagaries of the Blue Moon. In fact, astronomers rarely like to observe during the weeks surrounding the light-polluting Full Moon, and often compile data from the comfort of their university offices rather than visit mountaintop observatories these days…

The modern Blue Moon is now more of a cultural phenomenon. We’ve written previously about how an error brought us to the current ‘two Full Moons in one month definition.’ A more convoluted old timey definition was introduced in ye ole Maine Farmer’s Almanac circa 1930s as “the third Full Moon in an astronomical season with four.”

Legend has it that the Maine Farmer’s Almanac denoted this pesky extra seasonal Full Moon with ‘blue’ instead of black ink… to our knowledge, no examples exist to support this intriguing tale. Anyone have any old almanacs in the attic holding such a revelation out there?

The ghostly glow of the gibbous moon in Jean-Francois Millet's The Sheepfold. Image Credit: Public Domain — The ghostly glow of the gibbous moon in Jean-Francois Millet’s The Sheepfold. Image Credit: Public Domain

We’ve also laid out the occurrences for both types of Blue Moons for the remainder of the decade, as well as its New Moon cousin and internet meme to be, the Black Moon.

Untitled — The rising waxing gibbous Moon on the night of September 23rd, 1950. Image credit: Stellarium

Of course, the Moon most likely won’t appear to be physically blue, no matter what friends/family/co-workers/anonymous persons on Twitter say. The Moon can actually appear blue, as it did on September 23^rd, 1950 for much of the eastern United States and Canada through the haze of several forest fires in western Canada. The Moon was actually at waxing gibbous phase on the evening of this phenomenon, and as far as we can tell, no photographic documentation of this event exists. Spaceweather, has, however gathered a gallery of blue moon eyewitness reports over the years, including a few images. This occurs when moonlight is filtered through suspended oil drops about a micrometer in diameter which scattered yellow and red light, leaving a Moon with a ghostly indigo glow.

So there’s definitely another challenge to catch and photograph a truly ‘Blue Moon’ under such rare atmospheric circumstances… and remember, the Moon doesn’t have to be near Full to do it!

Watch that Moon, as we’ve got a few red letter dates coming up through the remainder of 2015. First up: the Supermoon season cometh in August, as we have a series of three Full Moons falling less than 24 hours from perigee on August 29^th, September 28^th, and October 27^th. Our money is on that middle one as having the potential to generate the most online lunacy, as it’s also the last total lunar eclipse of the current tetrad of four total lunar eclipses for 2014 and 2015, a ‘super-blood moon eclipse’ anyone? Though the dead won’t rise from the grave to mark such an occasion, you can be sure that many a sky aficionado will stumble zombie-like into the office the next day after pulling an all-nighter for the last good North American total lunar eclipse until 2018.

And it’s worth noting the path of the Moon, as it reaches its shallow mid-point in the last half of 2015. The Moon’s orbit is tilted about five degrees relative to the ecliptic, meaning that it can ride anywhere from 18 degrees—as it does this year—to 28 degrees from the celestial equator. This cycle takes about 19 years to complete, and a wide-ranging ‘long nights Moon’ last occurred in 2006, and will next occur in 2025.

A 'mock Blue Moon...' — A ‘mock Blue Moon…’ induced by use of a military flashlight filter. Image credit: Dave Dickinson

So don’t fear the Blue Moon, but be sure to take a stroll under its light this coming Friday… and perhaps enjoy a frosty Blue Moon beer on the eve of the sultry month of August.

July 23, 2015December 23, 2015 by David Dickinson

Astronomers Spot a Intriguing ‘5-Star’ Multiple System

An interesting multiple star discovery turned up in the ongoing hunt for exoplanetary systems.

The discovery was announced by Marcus Lohr of Open University early this month at the National Astronomy Meeting that was held at Venue Cymru in Llandudno, Wales.

The discovery involves as many as five stars in a single stellar system, orbiting in a complex configuration.

The name of the system, 1SWASP J093010.78+533859.5, is a phone number-style designation related to the SuperWASP exoplanet hunting transit survey involved with the discovery. The lengthy numerical designation denotes the system’s position in the sky in right ascension and declination in the constellation Ursa Major.

And what a bizarre system it is. The physical parameters of the group are simply amazing, though not as unique as some media outlets have led readers to believe. What is amazing is the fact that both pairs of binaries in the quadruple group are also eclipsing along our line of sight. Only five other quadruple eclipsing binary systems of this nature are known, to include BV/BW Draconis and V994 Herculis.

The very fact that the orbits of both pairs of stars are in similar inclinations will provide key insights for researchers as to just how this system formed.

The first pair in the system are contact binaries of 0.9 and 0.3 solar masses respectively in a tight embrace revolving about each other in just under six hours. Contact binaries consist of distorted stars whose photospheres are actually touching. A famous example is the eclipsing contact binary Beta Lyrae.

An animation of the orbits of the contact binary pair Beta Lyrae captured using the CHARA interferometer. Image credit: Ming Zhao et al. ApJ 684, L95

A closer analysis of the discovery revealed another pair of detached stars of 0.8 and 0.7 solar masses orbiting each other about 21 billion kilometres (140 AUs distant) from the first pair. You could plop the orbit of Pluto down between the two binary pairs, with room to spare.

But wait, there’s more. Astronomers use a technique known as spectroscopy to tease out the individual light spectra signatures of close binaries too distant to resolve individually. This method revealed the presence of a fifth star in orbit 2 billion kilometers (13.4 AUs, about 65% the average distance from Uranus to the Sun) around the detached pair.

“This is a truly exotic star system,” Lohr said in a Royal Society press release. “In principle, there’s no reason it couldn’t have planets in orbit around each of the pairs of stars.”

Indeed, ‘night’ would be a rare concept on any planet in a tight orbit around either binary pair. In order for darkness to occur, all five stellar components would have to appear near mutual conjunction, something that would only happen once every orbit for the hypothetical world.

Such a planet is a staple of science fiction, including Tatooine of Star Wars fame (which orbits a relatively boring binary pair), and the multiple star system of the Firefly series. Perhaps the best contender for a fictional quadruple star system is the 12 colonies of the re-imagined Battlestar Galactica series, which exist in a similar double-pair configuration.

How rare is this discovery, really? Multiple systems are more common than solitary stars such as our Sun by a ratio of about 2:1. In fact, it’s been suggested by rare Earth proponents that life arose here on Earth in part because we have a stable orbit around a relatively placid lone star. The solar system’s nearest stellar neighbor Alpha Centauri is a triple star system. The bright star Castor in the constellation of Gemini the Twins is a famous multiple heavyweight with six components in a similar configuration as this month’s discovery. Another familiar quadruple system to backyard observers is the ‘double-double’ Epsilon Lyrae, in which all four components can be split. Mizar and Alcor in the handle of the Big Dipper asterism is another triple-pair, six-star system. Another multiple, Gamma Velorum, may also possess as many as six stars. Nu Scorpii and AR Cassiopeiae are suspected septuple systems, each perhaps containing up to seven stars.

Fun fact: Gamma Velorum is also informally known as ‘Regor,’ a backwards anagram play on Apollo 1 astronaut ‘Roger’ Chaffee’s name. The crew secretly inserted their names into the Apollo star maps during training!

What is the record number of stars in one system? Hierarchy 3 systems such as Castor are contenders. A.A. Tokivinin’s Multiple Star Catalogue lists five components in a hierarchy 4 system in Ophiuchus named Gliese 644AB, with the potential for more.

How many stars are possible in one star system? Certainly, a hierarchy 4 type system could support up the eight stars, though to our knowledge, no example of such a multiple star system has yet been confirmed. Still, it’s a big universe out there, and the cosmos has lots of stars to play with.

A wide-field view of the constellation Ursa Major, with Theta Ursae Majoris selected (inset). image credit; Stellarium — A wide-field view of the constellation Ursa Major, with Theta Ursae Majoris selected (inset). Image credit; Stellarium

And you can see 1SWASP J093010.78+533859.5 for yourself. At 250 light years distant, the +9^th magnitude binary is about 1.5 degrees north-northwest of the star Theta Ursa Majoris, and is an tough but not impossible split with a separation of 1.88” between the two primary pairs.

Finder chart for 1SWAP J093010.78+533859.5 with a five degree Telrad foV. Image credit: Stellarium

Congrats to the team on this amazing discovery… to paraphrase Haldane, the Universe is proving to be stranger than we can imagine!

July 21, 2015December 23, 2015 by David Dickinson

Moonspotting-A Guide to Observing the Moons of the Solar System

Like splitting double stars, hunting for the faint lesser known moons of the solar system offers a supreme challenge for the visual observer.

Sure, you’ve seen the Jovian moons do their dance, and Titan is old friend for many a star party patron as they check out the rings of Saturn… but have you ever spotted Triton or Amalthea?

Welcome to the challenging world of moon-spotting. Discovering these moons for yourself can be an unforgettable thrill.

One of the key challenges in spotting many of the fainter moons is the fact that they lie so close inside the glare of their respective host planet. For example, +11^th magnitude Phobos wouldn’t be all that tough on its own, were it not for the fact that it always lies close to dazzling Mars. 10 magnitudes equals a 10,000-fold change in brightness, and the fact that most of these moons are swapped out is what makes them so tough to see. This is also why many of them weren’t discovered until later on.

But don’t despair. One thing you can use that’s relatively easy to construct is an occulting bar eyepiece. This will allow you to hide the dazzle of the planet behind the bar while scanning the suspect area to the side for the faint moon. Large aperture, steady skies, and well collimated optics are a must as well, and don’t be afraid to crank up the magnification in your quest. We mentioned using such a technique previously as a method to tease out the white dwarf star Sirius b in the years to come.

What follows is a comprehensive list of the well known ‘easy ones,’ along with some challenges.

We included a handy drill down of magnitudes, orbital periods and maximum separations for the moons of each planet right around opposition. For the more difficult moons, we also noted the circumstances of their discovery, just to give the reader some idea what it takes to see these fleeting worlds. Remember though, many of those old scopes used speculum metal mirrors which were vastly inferior to commercial optics available today. You may have a large Dobsonian scope available that rivals these scopes of yore!

Mars- The two tiny moons of Mars are a challenge, as it’s only possible to nab them visually near opposition, which occurs about once every 26 months. Mars next reaches opposition on May 22^nd, 2016.

Phobos:

Magnitude: +11.3

Orbital period: 7 hours 39 minutes

Maximum separation: 16”

Deimos:

Magnitude: +12.3

Orbital period: 1 day 6 hours and 20 minutes

Maximum separation: 54”

The moons of Mars were discovered by American astronomer Asaph Hall during the favorable 1877 opposition of Mars using the 26-inch refracting telescope at the U.S. Naval Observatory.

Jupiter- Though the largest planet in our solar system also has the largest number of moons at 67, only the four bright Galilean moons are easily observable, although owners of large light buckets might just be able to tease out another two. Jupiter next reaches opposition March 8^th, 2016.

Ganymede:

Magnitude: +4.6

Orbital period: 7.2 days

Maximum separation: 5’

Callisto

Magnitude: +5.7

Orbital period: 16.7 days

Maximum separation: 9’

Magnitude: +5.0

Orbital period: 1.8 days

Maximum separation: 1’ 50”

Europa

Magnitude: +5.3

Orbital period: 3.6 days

Maximum separation: 3’

Amalthea

Magnitude: +14.3

Orbital period: 11 hours 57 minutes

Maximum separation: 33”

Himalia

Magnitude: +15

Orbital period: 250.2 days

Maximum separation: 52’

Note that Amalthea was the first of Jupiter’s moons discovered after the four Galilean moons. Amalthea was first spotted in 1892 by E. E. Barnard using the 36” refractor at the Lick Observatory. Himalia was also discovered at Lick by Charles Dillon Perrine in 1904.

Titan and Rhea imaged via Iphone and a Celestron NexStar 8SE telescope. Image credit: Andrew Symes (@failedprotostar)

Saturn- With a total number of moons at 62, six moons of Saturn are easily observable with a backyard telescope, though keen-eyed observers might just be able to tease out another two:

(Note: the listed separation from the moons of Saturn is from the limb of the disk, not the rings).

Titan

Magnitude: +8.5

Orbital period: 16 days

Maximum separation: 3’

Rhea

Magnitude: +10.0

Orbital period: 4.5 days

Maximum separation: 1’ 12”

Iapetus

Magnitude: (variable) +10.2 to +11.9

Orbital period: 79 days

Maximum separation: 9’

Enceladus

Magnitude: +12

Orbital period: 1.4 days

Maximum separation: 27″

Dione

Magnitude: +10.4

Orbital period: 2.7 days

Maximum separation: 46”

Tethys

Magnitude: +10.2

Orbital period: 1.9 days

Maximum separation: 35”

Mimas

Magnitude: +12.9

Orbital period: 0.9 days

Maximum separation: 18”

Hyperion

Magnitude: +14.1

Orbital period: 21.3 days

Maximum separation: 3’ 30”

Phoebe

Magnitude: +16.6

Orbital period: 541 days

Maximum separation: 27’

Hyperion was discovered by William Bond using the Harvard observatory’s 15” refractor in 1848, and Phoebe was the first moon discovered photographically by William Pickering in 1899.

Uranus- All of the moons of the ice giants are tough. Though Uranus has a total of 27 moons, only five of them might be spied using a backyard scope. Uranus next reaches opposition on October 12^th, 2015.

Titania

Magnitude: +13.9

Orbital period:

Maximum separation: 28”

Oberon

Magnitude: +14.1

Orbital period: 8.7 days

Maximum separation: 40”

Umbriel

Magnitude: +15

Orbital period: 4.1 days

Maximum separation: 15”

Ariel

Magnitude: +14.3

Orbital period: 2.5 days

Maximum separation: 13”

Miranda

Magnitude: +16.5

Orbital period: 1.4 days

Maximum separation: 9”

The first two moons of Uranus, Titania and Oberon, were discovered by William Herschel in 1787 using his 49.5” telescope, the largest of its day.

Neptune- With a total number of moons numbering 14, two are within reach of the skilled amateur observer. Opposition for Neptune is coming right up on September 1^st, 2015.

Triton

Magnitude: +13.5

Orbital period: 5.9 days

Maximum separation: 15”

Nereid

Magnitude: +18.7

Orbital period: 0.3 days

Maximum separation: 6’40”

Triton was discovered by William Lassell using a 24” reflector in 1846, just 17 days after the discovery of Neptune itself. Nereid wasn’t found until 1949 by Gerard Kuiper.

Pluto-Yes… it is possible to spy Charon from Earth… as amateur astronomers proved in 2008.

Charon

Magnitude: +16

Orbital period: 6.4 days

Maximum separation: 0.8”

In order to cross off some of the more difficult targets on the list, you’ll need to know exactly when these moons are at their greatest elongation. Sky and Telescope has some great apps in the case of Jupiter and Saturn… the PDS Rings node can also generate corkscrew charts of lesser known moons, and Starry Night has ‘em as well. In addition, we tend to publish cork screw charts for moons right around respective oppositions, and our ephemeris for Charon elongations though July 2015 is still active.

Good luck in crossing off some of these faint moons from your astronomical life list!

July 20, 2015December 23, 2015 by Jason Major

This is Our Planet From a Million Miles Away

Earth imaged on July 6, 2015 by NOAA's DSCOVR satellite from L1. Credit: NOAA/NASA/GSFC

This picture of our home planet truly is EPIC – literally! The full-globe image was acquired with NASA’s Earth Polychromatic Imaging Camera (aka EPIC; see what they did there) on board NOAA’s DSCOVR spacecraft, positioned nearly a million miles (1.5 million km) away at L1.

L1 is one of five Lagrange points that exist in space where the gravitational pull between Earth and the Sun are sort of canceled out, allowing spacecraft to be “parked” there. (Learn more about Lagrange points here.) Launched aboard a SpaceX Falcon 9 on Feb. 11, 2015, the Deep Space Climate Observatory (DSCOVR) arrived at L1 on June 8 and, after a series of instrument checks, captured the image of Earth’s western hemisphere above on July 6.

The EPIC instrument has the capability to capture images in ten narrowband channels from infrared to ultraviolet; the true-color picture above was made from images acquired in red, green, and blue visible-light wavelengths.

More than just a pretty picture of our blue marble, this image will be used by the EPIC team to help calibrate the instrument to remove some of the blue atmospheric haze from subsequent images. Once the camera is fully set to begin operations daily images of our planet will be made available on a dedicated web site starting in September.

DSCOVR's location at L1 (NOAA/NASA) — DSCOVR’s location at L1 (NOAA/NASA)

Designed to provide early warnings of potentially-disruptive geomagnetic storms resulting from solar outbursts, DSCOVR also carries Earth-observing instruments that will monitor ozone and aerosols in the atmosphere and measure the amount of energy received, reflected, and emitted by Earth – the planet’s “energy budget.”

But also, from its permanent location a million miles away, DSCOVR will be able to get some truly beautiful – er, EPIC – images of our world.

DSCOVR is a joint mission between NOAA, NASA, and the U.S. Air Force. Learn more about DSCOVR here.

Source: NASA

UPDATE: President Obama liked this image so much, he decided to Tweet about it with a message of planetary conservation!

The POTUS' Tweet about the DSCOVR image on July 20, 2015. — The POTUS’ Tweet about the DSCOVR image on July 20, 2015.

UPDATE 7/29/15: Here’s another view from DSCOVR on July 6, showing Europe, Africa, and the Middle East: