Archive for February, 2016

The Sky This Week, February 23 – March 1, 2016 !

The Sky This Week, 2016 February 23 – March 1

Why we “leap”.
Jupiter & satellites, 2016 FEB 21, 04:16 – 04:48 UT

The Moon moves into the morning sky this week, waning as she moves through the constellations of the late spring and early summer sky. Last Quarter occurs on March 1st at 7:11 pm Eastern Standard Time. Luna rises with Jupiter on the evening of the 23rd, then passes the bright star Spica in the wee hours of the 26th and 27th. She closes out the week near ruddy Mars before dawn on the 29th and March 1st.

This week is a special one that only comes along once every four years, almost. It is a leap year, when February has one extra day tacked on to give us a year of 366 days’ duration. The reason for this is that the Earth takes a bit more than 365 days to complete one orbit around the Sun, so to keep our civil and astronomical calendars in synch we have to periodically add a day. The concept of leap days goes back to the time of Ptolemy, but it was the Roman emperor Julius Caesar who first gave us our modern calendar with a leap year occurring every four years. This four-year cycle approximated four trips of the Earth around the Sun with an excess error of about 11 minutes per year, which was a good approximation for the time. The problem with this approximation was that the calendar “slipped” a day with respect to the seasons after 130 years. Nonetheless, the Julian Calendar remained in widespread use for the next 1600 years. By the mid-16th Century, however, the vernal equinox was falling on March 11, 10 days before its “traditional” date of March 21st. Since the date of Easter and all of the “moveable feasts” observed by Christians were tied to the equinox, this caused considerable confusion among clergy and lay people. In 1582 Pope Gregory XIII reformed the calendar after years of study by deleting 10 days between October 4th and 15th and changing the “rules” for leap years. Under the Gregorian reform leap years occurred in years evenly divisible by 4 except for years that ended in “00”. These years were ordinary years unless they were evenly divisible by 400. Under this system the year 2000 is a leap year, but 1900 and 2100 are not. This system results in a 400-year cycle of 97 leap years, reducing the error of the calendar year to an excess of around 26 seconds compared to the astronomical year. Under this system the calendar will shift one day every 3000 years, which should give future calendar reformers plenty of time to come up with a new and even better system. Despite its obvious advantages, the Gregorian Calendar was not widely accepted outside of Catholic countries. England and its colonies grudgingly accepted it in 1752, and countries that are dominated by the Orthodox Christian church still use the Julian Calendar to fix their important dates.

Our early evening sky is still dominated by the bright constellations of winter, but shortly after sunset you’ll see a very bright object ascending in the eastern sky. Jupiter is racing into the evening sky, rising about four minutes earlier on successive nights. The giant planet will reach opposition on March 7, so he is in the prime-time of his 2016 apparition. Old Jove presents the largest apparent disc size of all of the planets, which makes him the best target for the small telescope after the Moon. Despite his vast distance of over 650 million kilometers (400 million miles) the planet’s enormous girth allows us to see a stunning variety of features in his roiling atmosphere. A six-inch telescope will reveal many of these features, while smaller instruments should reveal his dark equatorial cloud bands and dancing Galilean moons.

Mars receives a visit from the waning Moon as the week closes. The red planet is moving eastward toward the stars in the “head of the constellation of Scorpius, which is led by the rose-tinted star Antares. Mars and Antares provide a fine color complement in the pre-dawn sky, and you’ll have a good chance for the next several weeks to compare the planet with the “rival of Mars”.

Saturn is also visible in the hours before sunrise, and after Jupiter is the next best planetary sight in the small telescope. The ringed planet is over twice as far from us as Jupiter, but even a small telescope will easily show his amazing rings. Compare all three planets on the next clear morning, and watch their movements over the next few months.


The Sky This Week, February 16 – 23, 2016 !

The Sky This Week, 2016 February 16 – 23

Swimming in a lunar “sea”.
Gibbous Moon, 2012 SEP 24, 01:51 UT
Imaged with an 80 mm (3.1-inch) f/6 refractor and Canon EOS Rebel T2i DSLR
Mare Imbrium is bisected by the terminator at the upper left.

The Moon waxes through her gibbous phases this week, with Full Moon occurring on the 22nd at 1:20 pm Eastern Standard Time. February’s Full Moon is popularly known as the Snow Moon or Hunger Moon, indicative of the harsh weather that often accommodates the year’s shortest month. Look for the Moon near the bright star Regulus on the evenings of the 21st and 22nd. On the 23rd she cozies up to bright Jupiter, with less than two degrees of space between them.

Luna’s gibbous phases reveal some of her most interesting terrain, and I often like to spend evenings at the telescope checking over the changes revealed on successive nights. The largest of the Moon’s so-called “seas” gradually become visible as the terminator line slowly increases the Moon’s phase. The highlight for the next few nights is the Mare Imbrium, the “Sea of Rains”, which forms the largest circular basin on the Moon’s surface. The Imbrium basin is the result of an impact by a very large asteroid some 3.9 billion years ago that gradually filled with lava erupted from the Moon’s interior. The distance across its prominent rim is some 1250 kilometers (800 miles) and is peppered with many solitary craters of varying sizes. Look for a number of isolated mountain peaks near the northern rim of mare Imbrium. Prominent also are the large dark-floored crater Plato and the large indentation in the Mare’s northeast rim. This feature, known as the Sinus Iridum or “Bay of Rainbows”, is not far from the site of the most recent soft-lander probe to the Moon, the Chinese Chang’e 3, which touched down and released a small rover on December 14, 2013.

The Moon washes out the darker sky this week, leaving the bright and colorful stars of the Great Winter Circle to capture your gaze. In some ways the bright sky helps one to identify the basic constellation patterns without the “chaff” of many fainter stars to add to an already confusing sight. The basic stars of Orion, for instance, show up very well against the brighter sky background. It’s relatively easy to find the Hunter’s “shoulders” and “knees” split by the diagonal trio of the “belt” stars. Other outlines become simpler to recognize as well. The constellation of Auriga, the Charioteer, lies directly overhead in the evening and forms a very nice pentagon shape. The southernmost star in the pentagon, Al Nath, is “shared” as the northern “horn” of Taurus, the Bull, whose face is delineated by the Hyades star cluster and the bright reddish star Aldebaran. Opposite Aldebaran, along the line that passes through Orion’s belt stars, is dazzling Sirius, the brightest star in the sky.

Bright Jupiter is preparing to make his grand entrance to the evening sky. The giant planet now rises just over an hour after sunset, and by the end of the week he rises very close to the nearly full Moon. Old Jove is now just a few weeks from opposition, when he appears in the sky all night long. This is the best time of the current apparition to observe Jupiter and his four bright Galilean moons as the planet’s apparent diameter grows to its largest size in the weeks surrounding opposition. If you have a telescope of four inches aperture or more look for the planet’s famous Great Red Spot on the late evenings of the 17th and 19th. On the 20th you can watch the shadow of Io drift across the planet’s vast, streaked face.

Mars stays close to the meridian as morning twilight begins to brighten the eastern sky. The red planet is drifting eastward toward the stars that form the “head” of Scorpius, the Scorpion, about 15 degrees west of the bright star Antares. This star’s name means “Rival of Mars”, so it’s a good time to compare the two and admire their ruddy tints.

You can compare the colors of Mars and Antares to the golden hue of Saturn, which lies just over eight degrees northeast of Antares. You’ll find the ringed planet in the southeastern sky as dawn begins to brighten the horizon. Point a small telescope at him and you’ll be rewarded with a wonderful view.

Venus can still be found low in the southeast before the Sun rises, but you’ll only be able to see her in the brightness of morning twilight. You’ll need a clear flat horizon to catch a good glimpse of her before the arrival of the Sun.

The Sky This Week, February 9 – 16, 2016 !

The Sky This Week, 2016 February 9 – 16

A secret in a sword.
Messier 42, the “Great Orion Nebula” and surroundings
Imaged from near Morattico, VA, 2014 January 1
80 mm (3.1-inch) f/6 refractor and Canon EOS Rebel T2i DSLR

The Moon returns to the evening sky this week, waxing through her crescent phases as she moves through the faint autumnal constellations. First Quarter occurs on the 15th at 2:46 am Eastern Standard Time. Luna treads a lonely path through the sky, passing no bright objects until the evening of the 15th, when she closes in on the bright star Aldebaran in the constellation of Taurus, the Bull. Residents in the Pacific Northwest will see Aldebaran slip behind the Moon’s dark limb shortly before moonset that night.

We are now at that time of the year when the days are becoming noticeably longer. The total length of daylight is now well over an hour more than it was at the winter solstice, and the rate at which daylight is being added amounts to nearly three minutes per day. Nevertheless, you still have plenty of darkness to enjoy the bright stars of the winter constellations. The Great Winter Circle, dominated by the prominent constellation of Orion, the Hunter, straddles the meridian at 8:30 pm. This area of the sky plays host to one of the most remarkable sights that you’ll find in all of Nature, the Great Orion Nebula. To find it, locate the three prominent “Belt Stars” that are Orion’s most striking feature. Hanging below the left-most star of the belt you’ll see a small line of three fainter stars known as “The Sword”. From a dark location the middle one of these will look a little fuzzy to the naked eye. Point a pair of binoculars at the sword and you’ll see that the middle star is surrounded by a soft amorphous glow. Viewing through telescopes of increasing aperture reveals the star in the center of this nebulosity to be a quadruple star system known as the Trapezium, surrounded by convoluted swirls of softly glowing gas. Bright streaks are silhouetted behind dark clumps of material, rendering the entire nebula as a great three-dimensional structure that defies verbal description as well as the artist’s ability to render it. In large telescopes the central region glows with a ghostly greenish tint. What you are looking at is the center of a vast cloud of interstellar gas and dust, the core of a huge cloud of material that is the site of rampant new star formation. The stars of the Trapezium are very energetic young stars that emit copious quantities of ultraviolet light, causing the surrounding gas to fluoresce with characteristic colors of hydrogen and doubly-ionized oxygen. If our eyes were sensitive to the spectral lines of these atoms the entire constellation would be shot through with the glow of these vast clouds of material that contain enough stuff to form over 10,000 stars as massive as our Sun. Most of Orion’s bright stars formed from this bright stellar nursery within the past few million years, and more will follow over the next few million. There are several other examples of these star-forming regions throughout the Milky Way Galaxy, but the Orion Nebula is one of the closest to us, about 1500 light-years distant, and is probably the largest in the Galaxy. Take advantage of its prominent placement to explore it on the next clear evening.

After studying the Orion Nebula for a while you can turn your attention eastward to focus on the rising planet Jupiter. Old Jove rises at around 8:00 pm and should be sufficiently high by 10:00 pm for a quick telescopic peek. If you’re up until midnight his placement becomes even better as he rises above the turbulence of the horizon. Point a small telescope at Jupiter on any night and you’ll see some sort of configuration of his four bright moons, but if you do so on the night of the 13th you’ll see a nice, symmetrical formation with two moons on either side of the planet. On the following night the planet’s famous Great Red Spot rotates onto the disc and is well-placed for viewing in a modest-aperture telescope.

Ruddy Mars is still a morning object, best observed before sunrise at around 6:00 am. At this time he’s on the meridian in the southern sky, glowing with his characteristic pinkish hue. He is beginning to brighten as we move closer to opposition in late May. His disc should start to show detail in telescopes of six-inches of aperture, and it will double in size by the time opposition occurs.

Saturn shines prominently near the bright star Antares in Scorpius. There’s a very nice color contrast between the two objects, and they are both bright enough to follow into morning twilight. A small telescope will provide a very rewarding view of Saturn, which will reach his opposition in early June.

Venus now rises after the onset of morning twilight, but you should still be able to find her low in the southeast well before the Sun breaks the horizon. Venus will linger in this position for the next few months before emerging into the evening sky later this summer.

The Sky This Week, February 2 – 9, 2016 !

The Sky This Week, 2016 February 2 – 9

Of shadows and dark skies
The “Horsehead Nebula” and surroundings in Orion
Imaged from near Morattico, VA, 2016 January 3
80 mm (3.1-inch) f/6 refractor and Canon EOS Rebel T2i DSLR

The Moon graces the pre-dawn sky as a waning crescent this week, passing through the rising stars of early summer in the southeast. New Moon occurs on the 8th at 9:39 am Eastern Daylight Time. Look for Luna about four degrees northwest of yellow-hued Saturn on the morning of the 3rd. On the morning of the 6th she forms a compact triangle with the dazzling planet Venus and the more subdued glow of elusive Mercury. This will be a rare opportunity to glimpse all five of the “naked-eye” planets as well as the Moon in the sky at the same time!

According to folklore, the lack of a shadow cast by an indigenous rodent in rural Pennsylvania this morning is an indicator of an early spring. As we mentioned last week this observance has ancient roots tied to the mid-point of the astronomical season of winter. The actual “cross-quarter day” as measured by the astronomical calendar falls on the 4th, just over six weeks from the vernal equinox. Meteorological spring begins on March 1st, so whether the groundhog sees his shadow or not the end of winter is inevitable. If nothing else, this quaint tradition only serves to remind us of how important the motions of the sky were in human culture. Watching the Sun, Moon, planets, and stars was an integral part of our ability to sense and manipulate the passage of time and to use that skill as a tool for planning our future activities. This trait distinguishes us from all other species on the planet and has led us to the most distant frontiers of exploration of the space around us.

Your view of that space around us is probably hampered by our ability to turn night into virtual day thanks to artificial night lighting. You can help to quantify how much of the night sky we’re losing by participating in the Globe at Night citizen-science program between now and the 10th. The program invites observers from around the world to observe and count the number of stars they can see in the prominent winter constellation of Orion, the Hunter. Orion is very well-placed for viewing between 8:00 and 10:00 pm EST, high in the southern sky. You can use the Globe at Night’s web app to make your reports or use one of the apps available for smart phones. There’s even an app for recent-model iPhones that use the device’s camera to measure the brightness of the sky and report it directly to the observation database. You are encouraged to make multiple observations, especially if you can observe from many different locations. The objective of this research is to raise global awareness about the spread of light pollution and its effects on the global ecology. Unlike many more complicated threats to the climate, this one is relatively easy to fix. Just turn off the lights!

As Orion crosses the meridian, the bright planet Jupiter crests the eastern horizon. By the end of the week the giant planet rises at around 8:00 pm. In just over one month he’ll reach opposition, so we’re now in the middle of “prime-time” observing of the distant world. He’s well up by midnight and presents a disc that’s easily resolved in small telescopes. Larger instruments will show a wealth of detail on his alternating bright and dark cloud formations, and a four inch telescope should be sufficient to show his famous Great Red Spot. This feature is particularly well-placed on the night of the 7th, when it lies on the planet’s centerline just before midnight.

Mars is still best placed for viewing before sunrise, crossing the meridian at around 6:00 am. The red planet is beginning to brighten as Earth approaches him on or faster, inner orbit around the Sun. Small telescopes will reveal a small bright pink-hued disk, while modest instruments of five or six inches should start to show some surface detail.

Saturn receives a visit from the Moon before dawn on the 3rd. The duo form a wide triangle with the ruddy star Antares in the constellation of Scorpius. Saturn’s rings are tipped generously toward our line of sight, so they can be seen with virtually any optical aid.

Venus and Mercury are separated by around five degrees all week, with Mercury reaching his greatest elongation from the Sun on the morning of the 7th. If you can find Venus in the brightening morning twilight, use binoculars to look for Mercury between Venus and the horizon. On the morning of the 6th the two planets are visited by a slender waning crescent Moon. You should be able to find all three objects in a tight triangle about 10 degrees above the southeast horizon.