The Night Sky This Month (January 2012)

The Planets Mercury Innermost Mercury shines at magnitude –0.4 and can be spotted 10° above the southeastern horizon a half-hour before sunrise. Your best chance to see the planet is in early January, as Mercury sinks toward the horizon with each passing morning and will disappear by the middle of the month. Through a telescope, Mercury shows a 6"-diameter disk that is 80-percent illuminated.

Mercury is an unusual planet physically, with a blasted hot surface of 900° F basalt, a very eccentric orbit of 88 days, and a rotational period of only two-third of the year. It has a globe that is denser than that of any other planet apart from the Earth. There seems to be an iron-rich core about 2250 miles in diameter (larger than the whole of the Moon), containing about 80-percent of the total mass; by weight Mercury is 70-percent iron and only 30-percent rocky material.

The planet's surface is heavily cratered - the formations range from small pits up to colossal structures larger than anything comparable on the Moon. It is believed that many of these craters were created four billion years ago, around the time our solar system was formed. Back then, the solar system was full of debris varying in size from tiny pebbles to massive boulders several miles across.

Finder map (early January) - 30 minutes before sunrise, looking southeast.

Venus

Venus' thick atmosphere was photographed above in ultraviolet light by the Hubble Space Telescope. NASA/JPL [larger image]

Venus is often considered the Evening Star or the Morning Star, depending on which time of day it is up and dominating the twilight. For example, until late May 2012, Venus will appear as a brilliant yellow star in the evening sky, right after sunset. Located 25° above the southwestern horizon half an hour after sundown, it remains on view until after 8 P.M. local time. At the beginning of January, Venus spans 13" across and shows a disk 82-percent lit. By late in the month, the disk has grown to 15.2" and the phase has shrunk to 74-percent illumination. The planet shines at a stunning -4 magnitude, about ten times brighter than the brightest star Sirius, and by far the brightest celestial object after the Sun and Moon. Venus is so bright due to a combination of factors. Venus is covered with an opaque layer of highly reflective clouds of sulfuric acid. These clouds reflect 70-percent of the sunlight that hits them. For comparison, the Earth reflects 36-percent and Mars and the Moon around 15-percent of the

sunlight striking them. Venus is also rather large, being only a bit smaller than the Earth - its radius is 95-percent as large as Earth's. The final piece of Venus' brightness puzzle is its close distance to Earth. Right now, the planet is 1.1 astronomical units (102 million miles) from Earth.

Finder map (early January) - 30 minutes after sunset, looking southwest.
Finder map (mid-January) - 30 minutes after sunset, looking southwest.
Finder map (late January) - 30 minutes after sunset, looking southwest.

Mars

On the left, a map of Mars from 1894, originally prepared by Eugene Antoniadi and redrawn by Lowell Hess. On the right, a picture of similar orientation, captured by the Hubble Space Telescope. Comparison of the two images shows that large features were impressively recorded, but that an extensive system of canals just does not exist. HST/NASA [larger image]

Mars pokes above the eastern horizon around 10 P.M. local time and is well up in the south before dawn. The planet is on its way to opposition next March, when it will be at its closest approach to Earth and will reach a width of 14". Right now, the disk is less than 10"-wide, too small to show features in most instruments. Over the past century, our fascination with Mars has been

stimulated largely by the prospect that life may exist there. These speculations resulted from ground-based telescopic observations apparently showing oases and canals stretching across the dusty plains of Mars, but often glimpsed at the limit of telescopic visibility.

In 1877, when Mars was exceptionally close to the Earth, the Italian astronomer Giovanni Schiaparelli reported that a maze of dark, narrow straight lines traverses the planet's surface. He called them "canali", the Italian word for "channels", assuming that they were natural features.

Some years later, in 1892, the French astronomer Camille Flammarion subsequently wrote that the canals are apparently artificial, redistributing scarce water across the planet's surface. Flammarion was also convinced that the Martian inhabitants might be more advanced than us, describing them in popular books.

At about the same time, a descendant of a wealthy Boston family, named Percival Lowell, convinced much of the American public that there was intelligent life on Mars. He even built an observatory in Flagstaff, Arizona, with the specific intention of observing and explaining the Martian canals.

Most astronomers, however, could not see the canals, concluding that they were an optical illusion if they existed at all. As it turned out, the canals have no objective reality, beyond the tendency of the human mind to seek order in chaos.

Finder map (early January) - midnight, looking east.
Finder map (mid-January) - midnight, looking east.
Finder map (late January) - midnight, looking southeast.

Jupiter

Jupiter reached opposition to the Sun in late October, 2011, when it was closest to Earth and at its largest and brightest. Although Jupiter is now slowly receding from our home planet, it remains visible well after midnight and looks stunning through a telescope. The gas giant shines at magnitude -2.6 and lies in a star-barren region near the border between Aries and Cetus.

Jupiter has 64 known moons, and four of them - the Galilean satellites - are very large. Ganymede and Callisto are bigger than the planet Mercury, with diameters of 3,270 and 2,995 miles, respectively. Io has a diameter of 2,260 miles, just larger than our Moon. Europa is the smallest Galilean, with a diameter of 1,940 miles. The other Jovian satellites are comparatively small, ranging from the irregular Amalthea (155 x 91 x 80 miles) to the minuscule Leda, only 9 miles across.

The four Galilean moons can easily be seen with binoculars or small telescopes. On most nights, the satellites are lined up around Jupiter, in a line passing through the equator of the planet and extending out several Jupiter-diameters from it. They all orbit at different distances from their parent planet, and so, move round with different orbital periods. Hence, the moons are constantly changing their configurations.

Finder map (early January) - one hour after sunset, looking southeast.
Finder map (mid-January) - one hour after sunset, looking south.
Finder map (late January) - one hour after sunset, looking south.

Saturn

This illustration shows a close-up of Saturn's ring system. NASA/M. Weiss [larger image]

Throughout January, Saturn is 40° high in the south as dawn begins, and gets a little higher every morning. The ringed planet resides among the background stars of Virgo the Maiden and remains within 5° of the blue- white star Spica all month. Through a telescope, Saturn sports an angular size of 17", while the rings span 38". Saturn is the most striking member of our planetary family. With an equatorial diameter of about 75,000 miles, it is the second largest planet circling the Sun. Appearing as a bright yellowish object in our night sky, Saturn presents a maximum

apparent diameter of 20" and reaches magnitude -0.2 at opposition, when it lies closest to the Earth. This is about ten times fainter than Jupiter.

The planet's most attractive feature is, of course, the magnificent ring system. The rings consist of countless particles of water ice, ranging in size from small grains to irregularly shaped pieces generally a few feet across. It is interesting to note that if all of the material of the rings of Saturn were formed into a single moon, the moon would be about the mass of Janus (one of the smallest of Saturn's moons) and only 1/20,000 the mass of the Earth's Moon.

Finder map (early January) - one hour before sunrise, looking south.
Finder map (mid-January) - one hour before sunrise, looking south.
Finder map (late January) - one hour before sunrise, looking south.

Uranus

Uranus lies in the same binocular field of view as Lambda Piscium, the star that forms the southeast corner of the "Circlet" in Pisces, and is itself an easy binocular target. The planet glows at magnitude +5.9 and looks just like a star of that brightness. A telescope easily reveals its 3.4"-diameter disk, which has a distinct blue-green color.

The famous German-English amateur astronomer William Herschel discovered Uranus in 1781, and once astronomers realized it was an unknown world, the size of the solar system doubled. Uranus was the first new planet to be found since antiquity, but at the outset it was not at all clear that a new world had been spotted.

Herschel's telescope provided the world's best view of the new object, but even Herschel thought he had discovered a comet. His journal record for his first sighting on Tuesday, March 13, 1781, documents his suspicion: "In the quartile near Zeta Tauri the lowest of the two is a curious either Nebulous Star or perhaps a Comet". Four nights later, Herschel observed it again. Despite its lack of a tail, he concluded - because it had moved - that he had a comet on his hands.

Independent observatories soon verified the existence and motion of Herschel's new "comet", but attempts to determine its orbit and predict its position failed. It was obvious that this object was much more distant than anyone had thought, and calculations soon showed it to be a planet, moving far beyond the orbit of Saturn. After some discussion it was named Uranus, after the Greek god of the sky.

Finder map - field width 15°, stars to magnitude +8.

Neptune

Neptune, the solar system's outermost gas giant, is a dynamic planet with several large, dark spots reminiscent of Jupiter's hurricane-like storms. NASA/JPL [larger image]

Seek out Neptune in western Aquarius, 1.5° north of the 4th-magnitude star Iota Aquarii. The distant world lies 2.8 billion miles from Earth and glows dimly at magnitude +7.9. A 4-inch diameter telescope is probably the minimum required to see the planet and resolve its disk, only 2.4" across. Neptune is a cold, dark world. With a mean solar distance of 2,798 million miles (30.11 astronomical units), light levels at Neptune are more than 800 times dimmer than they are on Earth. Noon on Neptune would appear no brighter than what a human would experience at dusk on Earth. Even the Sun would take on an appearance more like a star than the bright disk seen from our home planet. Because Neptune is so distant, so far, only one spacecraft, Voyager 2, has visited the planet - a flyby in 1989. The spacecraft observed Neptune almost continuously between June and October of that year. It measured the planet's radius and interior rotation rate, confirmed that Neptune has rings, and discovered six new moons. Voyager 2 also

recorded pulses of radio emission, zonal cloud bands, and large scale storm systems with up to 1,500 miles per hour winds - the strongest measured on any planet.

Finder map - field width 15°, stars to magnitude +8.5.

Pluto

The dwarf planet is barely emerging from the glow of dawn, so it will be obscured for many observers. It will not be high enough above the horizon for telescopic viewing until about mid-February.

The Deep Sky

Star clusters are among the most beautiful objects in the night sky. Several are easily visible with the naked eye, notably the Pleiades and the Hyades in Taurus and the Beehive Cluster in Cancer; many are within the range of binoculars or small telescopes. Star clusters come in two varieties: globular clusters and open clusters (sometimes also called galactic clusters). Globular star clusters were born during the early days of the Milky Way and are as old as our galaxy itself. They are huge compact spherical balls of ten thousand to a million stars and are found in the galactic halo, well above and below the thin disk of the Galaxy. Open clusters, in contrast, lie in and near the arms of our

M35, pictured above on the upper left, can be found in the constellation Gemini, near the feet of the twins. NGC 2158, a more compact open cluster, is visible above on the lower right. CFHT/J.C. Cuillandre [larger image]

Milky Way Galaxy and may contain anything from a few dozen to a few hundred stars.

A beautiful open star cluster, easily visible in binoculars and on the fringe of naked- eye visibility, lies almost directly in the galactic anticenter direction (i.e. directly outward from us in the opposite direction from the center of the Galaxy), about one hundred light years above the galactic central plane.

M35 can be found in the constellation Gemini, near the feet of the twins, close to the border with Taurus. It contains over one hundred member stars scattered across an area as large as the full Moon. Binoculars show the cluster as a mottled patch enveloped in mist, but small telescopes clearly show individual stars, of 8th magnitude and fainter.

The brightest stars of the cluster average about 400 times the luminosity of our Sun and their spectral types range from B3 to G0; M35 also contains several yellow and orange giant stars of late G and early K type. Careful observers will note that the stars are arranged in disconnected chains, somewhat reminiscent of the lights on a Christmas tree.

Finder map - field width 15°, stars to magnitude +7.5.

Asteroids

The most geologically diverse asteroid, Vesta shows light and dark features much like our Moon. This image of the asteroid was taken by the Dawn spacecraft in 2011. NASA/JPL/UCLA [larger image]

For years, astronomers had little interest in asteroids - in fact, they considered them a nuisance. Those of them trying to count stars found that asteroids made their work harder, and those trying to photograph stars found their photographic plates filled with irritating little streaks. It was not until fairly recently that astronomers decided that asteroids are in fact very interesting indeed. To date, eight main-belt asteroids have been photographed close up (from largest to smallest): 4 Vesta, 21 Lutetia, 253 Mathilde, 243 Ida, 433 Eros, 951 Gaspra, 2867 Steins, and 25143 Itokawa. The Dawn spacecraft imaged Vesta, and the Rosetta probe passed within 1,965 miles of Lutetia in July 2010. The Galileo spacecraft studied Ida and Gaspra on its way to Jupiter, while the NEAR Shoemaker spacecraft visited Mathilde and Eros.

All these robotic space missions showed that asteroids have a wide range of shapes mimicked well by potatoes. Some are binaries or contact doubles, but the bigger ones like 4 Vesta are nearly round. As these huge boulders rotate, their brightnesses change and enable astronomers to figure out how long it takes them to turn. In Vesta's case, the day passes quickly, in just 5.34 hours.

The best time to observe Vesta is in the early evening, when Aquarius the Water Bearer - the constellation through which the asteroid tracks - is highest above the southwestern horizon. Delta Aquarii serves as a good guidepost for following the slow nightly motion of 8th-magnitude Vesta, but it may take a few nights of telescopic observing before you notice the asteroid's movement.

Finder map - field width 20°, stars to magnitude +8.5.

Comets

Comet Garradd will be visible in binoculars and small telescopes all through January. Catalin Paduraru/AstroSnake.com [larger image]

If you own a small telescope or a good binocular, you have a chance to see comet C/2009 P1 Garradd as it streaks through our solar system, most likely never to return. Comet Garradd can be found among the background stars of the constellation Hercules, a few degrees east of the globular cluster M13, and according to recent reports, it should glow at 7th magnitude. This "dirty ice ball" appears as a bright, round fuzz ball roughly 10' across, with little hint of a tail. The key to finding C/2009 P1 Garradd is to start about one hour before sunrise from a site that has an unobstructed view of the eastern horizon. Do not let the magnitude fool you into thinking this will be an easy target from the city. Urban sky glow will easily make the comet disappear. Comet C/2009 P1 Garradd, like all other comets, is a chunk of ice and dust only a few miles across. The ice is mostly frozen water and carbon dioxide, and

the dust is simple silicates. When far from the Sun, the ice is frozen and the comet is too small and too faint to be seen. But as the comet approaches the Sun, it warms. Sunlight thaws the ice, which evaporates (it does not melt), carrying with it the dust that was embedded in it.

The gas molecules absorb solar radiation, and then reradiate it at another wavelength while the dust acts to scatter the sunlight. The effect of this is the creation of a coma - a spherical envelope of gas and dust (perhaps 60,000 miles across) surrounding the nucleus - and a long tail consisting of gases and more dust particles.

Finder map - field width 30°, stars to magnitude +7.

Comet P/2006 T1 Levy was discovered in 2006 and takes slightly longer than five years to orbit the Sun on a track that brings it from Earth's neighborhood out to Jupiter's. The comet is expected to reach about 7th-magnitude sometime around mid-January and moves quickly across the evening sky. It starts the month in Pegasus and traverses both Pisces and Cetus before winding up in Eridanus.

In order to view comets, the first thing to consider is using good binoculars or a decent telescope. Although any kind of telescope can be used for comet observing, a short focal length instrument will deliver the best views. These kinds of telescope will give you a much larger field of view with a given eyepiece, hence increasing the contrast between faint comets and the background sky.

Most comets will require excellent-quality clear skies (no haze whatsoever) and a dark observing location. Furthermore, observers will need to allow time for their eyes to become dark-adapted, undergoing a physiological change to night vision that takes about 20 minutes and allows optimal detection of faint objects. Extraneous artificial lights can, of course, ruin this dark adaption in moments.

Finder map - field width 80°, stars to magnitude +5.5.

Meteors

The Quadrantids, a major annual meteor shower, are visible from December 28 through January 12. The peak of activity is much sharper than that of most showers, lasting only a few hours; this year the peak should arrive around 7:00 UT (2:00 A.M. EST) on Wednesday morning, January 4th. At best over one hundred Quadrantids an hour can be seen, although the meteors of this shower are not as bright as other great displays such as the Perseids and Geminids. The Quadrantids radiate from the northern part of the constellation Bootes, near the handle of the Big Dipper. This area of sky was once occupied by the now-defunct constellation Quadrans Muralis, the Mural Quadrant, from which the shower takes its name. Unfortunately, this area is not well placed for observation until after

Meteors are tiny specks of space dust that burn up during their fatal encounter with the Earth's upper atmosphere. Pierre Martin [larger image]

midnight, so Quadrantid watchers must be prepared to brave the small hours until dawn to see the shower at its best.

The January Quadrantids have been known since about 1835, with a more or less continuous observational record since the 1860s. Their parent body is uncertain, although it may be the faint short period (5.24 years) comet 96P/Machholz 1. Quadrantid meteors are medium-paced at 25 miles per second. The fainter meteors are often described as bluish, whereas the bright Quadrantids sometimes show a pronounced yellow-green color.

Map - Quadrantids radiant position.

The Coma Berenicid meteors come from a radiant very easy to locate, near the large naked eye star cluster designated Melotte 111. In early January, the radiant rises about 11 P.M. local time and is nearly overhead at predawn. This weak shower has no definite peak and lasts approximately from December 12 to January 23.

Noted first in 1959, the Coma Berenicids are associated with comet 1913 I, discovered in the early morning hours of December 30, 1912, by B. Lowe, an amateur astronomer in South Australia. They are some of the fastest meteors known, entering the Earth's atmosphere at about 40 miles per second. Although activity is low (with an average fall rate of three meteors per hour), this shower still warrants study.

The best way to enjoy a meteor shower is to dress warmly, set down a blanket or lawn chair, get comfortable, and watch the stars. Remember that on any night of the year, meteors appear faster, brighter, and more numerous after midnight - when the leading edge of the Earth's atmosphere spins into the debris trail.

Light pollution and a bright Moon will significantly reduce the number of visible meteors. If you live in an urban area, it may be worth driving at least one hour outside the metropolitan area to find better skies. Pick a spot that is shielded from lights and allow your eyes to adjust to darkness for a few minutes.

Map - Coma Berenicids radiant position.

Some meteors do not belong to any known shower. These are the sporadic meteors, caused by random bits of comet debris spread throughout the inner solar system. They appear randomly across the sky all year long.

In this month's night sky careful observers can expect around fourteen sporadics per hour during the morning hours and two during the dark evening.

Observing Aids

Northern Hemisphere's Sky - This map portrays the sky as seen near 40° north latitude at 8 P.M. local time in early January and 7 P.M. in late January.

Southern Hemisphere's Sky - This map is plotted for 35° south latitude. It shows the sky at 10 P.M. local time in early January and 9 P.M. in late January.

Visibility of the Planets - The table provides general information about the visibility of the planets during the current month.

Phases of the Moon - This Moon Phase Calendar shows the Moon's phase for every day in January.

Jupiter's Moons - The diagram shows the positions of Galilean satellites on each day in January at midnight.

Sky Events

January 1 - First Quarter Moon at 1:15 A.M. EST.

January 2 - The Moon is at apogee, the point in its orbit when it is farthest from Earth.

January 4 - The Quadrantid meteor shower is at peak activity. The Earth is at perihelion, its annual closest approach to the Sun.

January 5 - The Moon is 3.1° south of the Pleiades star cluster at 4:17 A.M. EST.

January 9 - Full Moon at 2:30 A.M. EST.

January 16 - The Moon is 2° south of Spica (Alpha Virginis) at 2:21 A.M. EST. Last Quarter Moon at 4:08 A.M. EST. January 17 - The Moon is at perigee, the point in its orbit when it is nearest to Earth. January 23 - New Moon at 2:39 A.M. EST. January 30 - The Moon is at apogee, the point in its orbit when it is farthest from Earth. First Quarter Moon at 11:10 P.M. EST.

The information provided on this page is accurate for the world's mid-northern latitudes. Finder maps for the five naked eye planets are plotted for 40° north latitude, but can also be used from other latitudes close to 40° north. Except the two all-sky maps, all other maps can be used no matter the latitude. Local time (local daylight time during summer) represents the time of the reader.

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