Cosmos Website: Blog

The Night Sky in February 2012

By Harry J. Augensen

Professor of Physics & Astronomy, Widener University

Moon’s Phases
            Full "Snow" Moon on the 7^th                          New Moon on the 21^st

Stars and Constellations

 Clear, crisp February nights bring with them not only frigid temperatures but also a brilliant tapestry of winter stars.  The constellation Cassiopeia, which represents the throne of the Queen of ancient Ethiopia, can be seen high in the northwest, looking like the letter "M."  Even higher in the northwest above Cassiopeia is Perseus, whose brightest stars form a horn shape which opens toward the nearby Pleiades cluster.   Nearly overhead on February evenings is Auriga, the Charioteer, with the bright yellow star Capella as its "eye." Just south of Auriga is Taurus the Bull, with its bright orange star Aldebaran.  Aldebaran is classed as a red giant star, and it stands in the foreground of a more distant loose cluster of stars, the Hyades.  Further to the west of the Hyades is the more compact Pleiades star cluster, looking like a miniature dipper.  Following Taurus to the east is Gemini and its two brightest stars Pollux and Castor.  Orion the Hunter now stands high in the south, dominating the midwinter night sky.  Orion's two brightest stars, Betelgeuse and Rigel, are classed, respectively, as red and blue supergiants, and are among the most luminous stars known. 

 Just below and to the left of Orion is the brightest star in the night sky, Sirius, in the constellation Canis Major. 
The four brightest stars in Canis Major form a trapezoidal shape, consisting of Sirius (Alpha), Mirzam (Beta), Adhara (Epsilon), and Wezea (Delta), going clockwise from Sirius. Sirius is by far the brightest of the foursome, with the other three stars having apparent brightnesses roughly comparable with the second magnitude stars in the Big Dipper. But the impression of relative brightnesses was found to be completely misleading, once astronomers determined distances to these objects. Sirius, the Dog Star, is one of the Sun’s nearest neighbors, at only 8.6 light years distance.  This distance was first deduced by trigonometric parallax in 1838 by the German astronomer and mathematician Friedrich Bessel.  The other three are much farther away:  Adhara is 480 light years, Mirzam is 720 light years, and Wezea is 3800 light years distant from our solar system.  For any star to lie at these immense distances must imply that it is intrinsically very luminous, far more than our humble Sun.  In fact, Sirius possesses a total luminosity 26 times that of the Sun, but the luminosities are 5000, 7200, and 130,000 solar luminosities for Adhara, Mirzam, and Wezea, respectively.  Clearly, these are no ordinary stars.

Just a bit further to the east of Sirius is its neighbor Procyon in Canis Minor.  Like Sirius, Procyon is also nearby, at 11 light years away, and also like Sirius, Procyon is a binary star system containing a white dwarf.  After about 8 pm, you can spot some of the stars of spring mounting the sky in the east.  In particular, Regulus in the constellation Leo, lies low in the east-northeast.  Looking a little further northward, you may spot the Big Dipper, which is part of the constellation Ursa Major, or Big Bear, rising in the north-northeast.  The appearance of these groups is a sure celestial sign that spring will soon be here.   

  Naked-Eye Planets In the Evening and Morning Sky

Mercury reaches superior conjunction with the Sun on the 7^th, and is therefore too close to the Sun to be glimpsed for the first half of February.  Toward the end of the month, however, Mercury swings up into the evening sky,  setting  about an hour and a half after the Sun by month’s end.  At that time, look for what appears to be a yellow star low above the western horizon about 30 minutes to an hour after sunset.

 Venus is like a dazzling yellow gem hovering above the southwestern horizon at dusk.  Throughout February, Venus sets about three and a half hours after the Sun, allowing plenty of time to observe it well into the early evening.  See how soon you can spot Venus with the unaided eye moderately high in the southwest after sunset.

Jupiter continues to shine brightly high in the south-southwest during the evening hours, resembling a brilliant golden star in the otherwise dim constellation Aries.  Jupiter is second only to Venus among the planets in brightness, and it remains in good position for viewing until late evening.    As February opens, Jupiter is setting in the west around midnight, over three hours after Venus dips below the horizon.  By month's end, Jupiter is setting at about 10:30 pm EST, less than an hour after Venus.   With each passing night, Jupiter is sinking closer toward the horizon, while Venus is ascending.  The two planets will ultimately cross paths in a spectacular planetary conjunction next month.

Last February, Mars was in conjunction with the Sun and completely unobservable.  This February is another story entirely, with Mars approaching its opposition point with the Sun in early March.   As February opens, Mars resembles a very bright orange-red star in the constellation Leo.  Mars rises at about 8:30 pm at the beginning of February, and a little before 6 pm at the end of the month. By the end of February, Mars will be nearly the same brightness as Sirius, the brightest star in the night sky.  Amazingly, light takes only about 6 minutes to reach us from Mars, while it takes 8.7 years to reach us from Sirius!  Enjoy the color contrast between the two disparate bodies:  Mars glows distinctly orange-red while Sirius shines with a bluish white color.    

Rising in the east around 11:30 pm at the start of February, Saturn resembles a bright cream colored star located below Spica, Virgo’s brightest star.  By month’s end, Saturn is rising a little after 9:30 pm, around the same time that Venus is setting.  Even a modest telescope will reveal Saturn’s magnificent ring system.

Information on lunar phases and rise/set times of Sun and planets is obtained from the US Naval Observatory Data Services at http://www.usno.navy.mil/astronomy/. Additional information comes from Astronomical Calendar 2012 by Guy Ottewell (Raynham, MA: Universal Workshop, 2012)Times given apply for observers near to the latitude and longitude of Philadelphia, USA: 40 degrees North latitude, 75 degrees West longitude.

For more information on astronomy and weather, visit http://www.widener.edu/stargazing/, then click on Web Links & Resources. A set of free sky maps can be obtained at http://www.skymaps.com/

The Night Sky in January 2012

By Harry J. Augensen

Professor of Physics & Astronomy, Widener University

Moon’s Phases
            Full "Wolf" Moon on the 9^th                          New Moon on the 23^rd

Stars and Constellations

As January begins, only a handful of autumn stars are still viewable, including those belonging to Cetus, the Whale, and the four stars which comprise the Great Square of Pegasus, which are now descending in the west.  The rest of the evening is ruled by the brilliant stars of winter, which offer abundant rewards for braving the frigid conditions.  By 8 pm, the constellation Perseus stands nearly overhead, just to the east of the upside down "W" of Cassiopeia.  To the east of Perseus is Auriga, the Charioteer, whose eye is the bright yellow star Capella.  The name Capella is derived from the Latin, and means "little she-goat," a likely reference to the mythological goat that suckled the baby Zeus.  Capella is 42 light years away from our solar system and, although it appears as a single object to the eye, astronomers have deduced that it really consists of two stars, each of which is a giant over 10 times bigger in diameter than our Sun.

Just south of Auriga is Taurus the Bull, a zodiac constellation.  Taurus contains several attractions, including the bright orange star Aldebaran, the "V" shaped Hyades star cluster (which Aldebaran happens to lie in front of), and the compact star cluster the Pleiades, or the Seven Sisters.  Just below and to the left of Taurus is unquestionably the most brilliant of all the winter constellations:  Orion, the Hunter, which stands high in the south around the midnight hour during January. Orion is a veritable jewel box of relatively young stars, most of which lie hundreds or even thousands of light years from our solar system.  These include the four stars which outline his major perimeter (listed clockwise from the upper left):  Betelgeuse (pronounced beetle-juice), Bellatrix, Rigel, and Saiph. Betelgeuse is a red supergiant, while the other three are blue supergiants or giants.

Betelgeuse is highlighted in University of Illinois astronomer James Kaler's book, The Hundred Greatest Stars (New York: Copernicus Books, 2002).  The most recent distance measurement using the Hipparchos satellite puts Betelgeuse at roughly 650 light years from our solar system, with a rather large uncertainty of about 150 light years.  Betelgeuse is enormous, with a fuzzy diameter of around 800 solar diameters.  This makes it one of the largest stars known, its diameter having first been measured in 1920 by physicist A. Michelson.  Betelguese is also a very massive star, with about 15 times the mass of the Sun.  Betelgeuse is quite similar in size, temperature, and mass to another famous red supergiant, Antares in Scorpius, which lies in the opposite part of the sky.  Both stars are destined to eventually end their lives violently in brilliant supernova explosions.

Cutting across Orion’s middle is his belt, a very distinct line of three bluish-white stars, Alnitak, Alnilam, and Mintaka.  Alnitak and Alnilam lie over 1000 light years from our solar system and Mintaka is over 2000 light years distant. Extending downward from Orion’s belt is his sword, which contains the Orion Nebula, officially designated as Messier 42, a birthplace for thousands of new stars.  It lies at a distance of 1500 light years.   

Just east of Taurus is another zodiac group, Gemini, which contains the stars Pollux and Castor. Two faithful dogs, Canis Major, the Big Dog, and Canis Minor, the Little Dog , are found to Orion’s upper and lower left, respectively.  Canis Major contains the brightest appearing star in the sky, Sirius, which looks like a brilliant bluish-white beacon in the southeast during the evening hours of early winter. Canis Minor has his own bright star, Procyon, the "Pup."  Sirius and Procyon are among the Sun’s nearest neighbors in space, lying at distances of only 8 and 11 light years, respectively.

  Naked-Eye Planets In the Evening and Morning Sky

Venus is truly magnificent this January, resembling a blazing yellow star above the southwestern horizon at dusk.   On New Year’s Day, Venus sets about two and a half hours after the Sun, and by month's end that interval stretches to over three hours.  It gets dark enough to spot Venus with the unaided eye in the southwest about 20 minutes after sunset.   Those unfamiliar with the night sky may mistake Venus for an airplane landing light, or even a UFO!

As darkness falls in the evening, Jupiter can be spotted high in the south, resembling a brilliant golden star.   Though not as bright as Venus, Jupiter is still a beautiful sight, and it remains visible until long after Venus has set.  Jupiter sets in the west a little before 2 am EST on the 1st, and by midnight on the 31st.

Mars kept a pretty low profile during 2011, but the distance between Mars and Earth is now rapidly shrinking, resulting in Mars doubling in brightness during January.   As January opens, Mars resembles a bright orange star in the eastern part of the constellation Leo, near the border with Virgo.  Mars drifts eastward, and at midmonth it crosses into Virgo, but then by month's end it reverses course and begins to drift back toward Leo.  Mars rises a little past 10 pm on New Year’s Day, and at about 8:30 pm on the 31st. By the end of January, Mars will be brighter than any other visible star except Sirius, the brightest star in the night sky.  And by early March, when Mars reaches opposition with the Sun and is closest to Earth, Mars and Sirius will be nearly equal in brightness, though contrasting greatly in color:  a ruddy red Mars compared with a bluish white Sirius.

Saturn resembles a bright cream colored star located near Spica, the brightest star in Virgo. On New Year’s Eve Saturn rises around 2am, and by month’s end, Saturn is up around 12:30 am.   

Mercury reached its maximum morning elongation with the Sun in late December, and it remains in good position for viewing in the predawn sky during the first week of January.  On the first morning of 2012, Mercury rises about an hour and a half before the Sun.  Look for what appears to be a bright yellow star low above the eastern horizon about 30 minutes to an hour before sunrise.  By midmonth, Mercury is rising only an hour before sunrise, and thereafter it vanishes into the morning twilight, to reappear as an evening “star” in late February. 

Earth reaches perihelion, or closest approach to the Sun, on January 4th, when it will be about 3.5% closer to the Sun than it was in July.  However, it is the tilt of Earth’s axis, not its orbital eccentricity, which causes the seasons.

The peak of the Quadrantid Meteor Shower is predicted to occur in the early morning hours of January 4th.  The origin of this shower is debris left behind by object 2003 EH1, probably a comet fragment.  Look generally toward the east in the hours after midnight, after the bright waxing gibbous Moon has set and no longer interferes with seeing the fainter meteors.

Information on lunar phases and rise/set times of Sun and planets is obtained from the US Naval Observatory Data Services at http://www.usno.navy.mil/astronomy/. Additional information comes from Astronomical Calendar 2012 by Guy Ottewell (Raynham, MA: Universal Workshop, 2012)Times given apply for observers near to the latitude and longitude of Philadelphia, USA: 40 degrees North latitude, 75 degrees West longitude.

For more information on astronomy and weather, visit http://www.widener.edu/stargazing/, then click on Web Links & Resources. A set of free sky maps can be obtained at http://www.skymaps.com/

The Night Sky in December 2011

By Harry J. Augensen

Professor of Physics & Astronomy, Widener University

Moon’s Phases
            Full "Long Night" Moon on the 10^th                          New Moon on the 24^th 

Stars and Constellations

On December 22nd at 12:30 am EST, the Sun reaches its southernmost position in western Sagittarius, marking the official beginning of winter in the Northern Hemisphere and summer in the Southern Hemisphere.  At this time of year, the Northern Cross, known officially as the constellation Cygnus, stands upright on the northwestern horizon in early evening, with its bright star Deneb shining at the top of the cross.  Somewhat below Deneb lies the even brighter Vega,  still visible low in the western sky.  Fomalhaut, the white jewel of autumn, is now getting low in the southwest.  High in the southwest are the four stars comprising the Great Square of Pegasus.

Looking toward the north, the constellation Cassiopeia is now high up, looking like the letter "M."  Following Cassiopeia in the northeast is the constellation Perseus, which passes overhead during the late evening hours.  The most famous star in Perseus is Algol, known as the "Demon Star" in medieval Arabic culture, because it frequently seemed to "wink."  Modern astronomers have found that Algol actually consists of two stars which eclipse each other in their mutual orbit over a cycle of about 3 days, thus creating periodic changes in brightness (hence the winking).  Algol is listed in University of Illinois astronomer James Kaler’s book, The Hundred Greatest Stars (New York: Copernicus Books, 2002), which gives a distance to the stellar pair of 93 light years.  One of the stars is a blue-white in color, with a surface temperature of 12,000 K (twice as hot as our Sun), while the other is an orange subgiant star with a temperature of "only" 4000 K.  The stars are in a tight orbit, separated by only 7 percent of the distance between the Earth and Sun. 

By 9 pm, the brilliant star groups of winter move into fine position for viewing.  Capella, the yellow-white star in the constellation Auriga, the Charioteer, is ascending in the northeast.  High in the east, to the right of Auriga, is Taurus, the Bull, which contains the bright orange-red star Aldebaran.  Also part of Taurus is the compact Pleiades star cluster, or Seven Sisters.  Dominating the winter night sky is the constellation Orion, the Hunter, with its two very bright stars, reddish Betelgeuse and bluish-white Rigel. Most of Orion’s stars are hundreds of light years from our solar system.  Located in the east-northeast between Auriga and Orion is the constellation Gemini, which contains the twin stars Pollux and Castor.  After 9 pm, the brightest star in the night sky emerges in the southeast, below Rigel.  This is blue-white Sirius, the "dog star" of the constellation Canis Major.

  Naked-Eye Planets In the Evening and Morning Sky

Venus continues to slowly climb into better view with each passing week, glowing like a brilliant yellow star above the western horizon at dusk. On December 1^st,  Venus sets less than two  hours after sunset, and by  New Year’s Eve, Venus is setting about two and a half  hours after the Sun, and so should be easily visible in the west from about 30 minutes to nearly two hours after sunset.

Though not as bright as Venus, Jupiter is still an impressive sight.  And Jupiter graces the sky for a much longer time interval than Venus, from sunset until the early morning hours.  Once night falls, Jupiter radiates like a brilliant cream-colored star in a region of the sky just above Cetus and on the border between Aries and Pisces, two relatively faint zodiacal constellations.  Jupiter is already high up in the southeast as darkness falls; in mid-December it transits the meridian at around 8:30 pm, and sets in the west at 3:00 am EST.

Mars, which resembles a bright orange-red star in the constellation Leo, rises in the northeast at around 11 pm EST in mid-December.  Orange-red Mars contrasts with bluish-white Regulus, Leo’s brightest star, which lies to the west of Mars.  Mars brightens noticeably this month, roughly doubling in brightness between the 1^st and the 31^st.   Mars will continue to increase in brightness over the next several months, until it reaches opposition and maximum brightness in early March.   

Saturn lies in the early morning sky, rising around 3:30 am on the 1^st and by 2 am on New Year’s Eve.  Saturn resembles a bright star located near Spica, the brightest star in Virgo. Spica’s bluish white color contrasts well with the dull yellow color of Saturn. 

Mercury reaches inferior conjunction with the Sun on the 4th, when its orbit carries it between the Sun and Earth.  Within a week afterwards, the fast-moving Mercury vaults up into the morning sky, rising over 90 minutes before the Sun.  Mercury reaches its maximum elongation from the Sun on the 23^rd, when it rises around 5:30 am, or over 90 minutes before sunrise.   Look for what appears to be a bright yellow star low above the eastern horizon about 30 minutes to an hour before sunrise.

Information on lunar phases and rise/set times of Sun and planets is obtained from the US Naval Observatory Data Services at http://www.usno.navy.mil/astronomy/. Additional information comes from Astronomical Calendar 2011 by Guy Ottewell (Raynham, MA: Universal Workshop, 2011)Times given apply for observers near to the latitude and longitude of Philadelphia, USA: 40 degrees North latitude, 75 degrees West longitude.

For more information on astronomy and weather, visit http://www.widener.edu/stargazing/, then click on Web Links & Resources. A set of free sky maps can be obtained at http://www.skymaps.com/

The Night Sky in November 2011

By Harry J. Augensen

Professor of Physics & Astronomy, Widener University

Moon’s Phases
Full "Frost" Moon on the 10thNew Moon on the 25th 

Stars and Constellations

Once our clocks go back to Standard Time in early November, the sky becomes dark shortly after 5 pm and stargazing can commence. The star groups of summer are now just a memory, with one notable exception: the "summer" right triangle of Vega, Deneb, and Altair, which can still be seen high in the west. On the other hand, the stars of autumn reach their full spendor on November evenings. High in the northeast is the familiar "W" shape of the constellation Cassiopeia, followed by Perseus, which represents the hero of mythology who rode the winged horse Pegasus and rescued Andromeda from Cetus, the Sea Monster (the Whale in modern times). The constellations of Andromeda and Cetus are both relatively faint, but the Great Square of Pegasus, which sits high in the south by around 8 pm, is quite distinct. The Great Square is comprised of four stars, known as Alpheratz, Markab, Scheat, and Algenib, all of which are much more luminous than our Sun. But, because they are located at distances ranging from about 70 light years for Alpheratz to 500 light years for Algenib, they appear as mere points of light. Below the Great Square is the solitary bright whitish star Fomalhaut in Pisces Austrinus (the Southern Fish). The name Fomalhaut is translated as "mouth of the fish."

Cetus is the fourth largest constellation in the sky, but most of its stars are relatively faint (because they are so distant). Nevertheless, Cetus contains at least one star which is celebrated because it appears to vary greatly in brightness: Omicron Ceti, also known as Mira (meaning the Wonderful One). Mira is featured in University of Illinois astronomer James Kaler’s book, The Hundred Greatest Stars (New York: Copernicus Books, 2002). Mira was discovered by the German astronomer David Fabricius in 1596 (over a decade before the telescope was invented), and has become famous as the prototype for an entire class of stars which vary in light over long periods of time. Mira is an enormous red giant star, of around 350 times larger than our Sun; the latest distance estimates put Mira at around 420 light years from our solar system. Spectroscopic analyses show that it expands and contracts over a period of about 11 months, and it is this phenomenon that causes Mira to change in brightness. Modern astronomers know that Mira is going through a late and unstable phase in the evolution of a normal star (like our Sun) which results in extreme mass loss and in the eventual metamorphosis into a tiny white dwarf star. In fact, the Sun is expected to undergo this phase in roughly five billion years. Interestingly, Mira has a faint companion star known as Mira B which is itself a white dwarf.

Although winter officially begins in December, a few winter stars can be previewed on November nights. One of the brightest of the early winter stars to make its appearance on November evenings is yellow-white Capella (meaning "little she goat"), situated in the constellation of Auriga (the Charioteer). It is low in the northeast around 8 pm, but if you stay up late, Capella will pass nearly overhead around 1 am at midmonth. In the east you may spot the stars of Taurus, the Bull, which contains the bright reddish star Aldebaran. Aldebaran appears to be part of a "V" shaped cluster of stars known as the Hyades. Even more famous is the Pleiades cluster in Taurus, a beautiful, compact group of stars shaped like a miniature dipper.

  Naked-Eye Planets In the Evening and Morning Sky

In the early evening sky, Venus continues to slowly but steadily increase its separation from the Sun following conjunction back in August. At the beginning of November, Venus sets only about an hour after sunset, and may be difficult to locate low above the western horizon, especially if there are obstructions. By month's end, Venus is setting a little less than two hours after the Sun, and can best be spotted about half an hour to an hour after sunset; it resembles a brilliant yellow star low in the west.

As November opens, Mercury is setting only about 45 minutes after the Sun, and will be a challenge to locate hovering below the much brighter Venus and just barely above the western horizon. Things improve a bit toward mid-November, when Mercury reaches greatest evening elongation with the Sun (specifically on the 13th), when Mercury sets over an hour after sunset. Your best bet is to find Venus and scan just below it, ideally about 30 minutes after sunset. Mercury sinks rapidly toward the Sun during the closing weeks of November, and will vanish into evening twilight by month’s end.

Jupiter reached opposition with the Sun at the end of October, and it continues to shine magnificently nearly all night long throughout November. During the early evening hours, Jupiter resembles a brilliant cream-colored star located in the constellation Aries near the eastern border with Pisces and just above Cetus. At midmonth, Jupiter is already well up in the east as evening twilight ends; it transits the meridian at around 10:30 pm, and sets in the west at 4:30 am EST. Since Jupiter is visible most of the night, this is an excellent time to view it through a telescope, which will reveal distinct cloud bands in its atmosphere and also its four Galilean moons.

Mars rises in the northeast at around midnight EST at midmonth, and resembles a bright orange-red star. Mars now resides in the constellation Leo, and is somewhat brighter than nearby Regulus, Leo's brightest star. While not very impressive now, watch for Mars to increase substantially in brightness during the winter months.

Saturn was in conjunction with the Sun last month, but it is already up in the morning sky before dawn. As November begins, Saturn rises nearly one and a half hours before the Sun; by the 30th, this interval increases to three and a half hours. Look for Saturn about an hour before sunrise low in the east; it looks like a bright cream colored star located near Spica, a true star of bluish white color and of roughly the same brightness in the constellation Virgo.

The Leonid Meteor Shower is expected to reach its peak after midnight on November 17th. Look generally toward the east where the constellation Leo will be rising, although meteors can be seen in any part of the sky. Unfortunately, the last quarter moon will wash out many of the fainter meteors until the early morning hours, so try to view before the moon rises.

Information on lunar phases and rise/set times of Sun and planets is obtained from the US Naval Observatory Data Services at http://www.usno.navy.mil/astronomy/. Additional information comes from Astronomical Calendar 2011 by Guy Ottewell (Raynham, MA: Universal Workshop, 2011)Times given apply for observers near to the latitude and longitude of Philadelphia, USA: 40 degrees North latitude, 75 degrees West longitude.

For more information on astronomy and weather, visit http://www.widener.edu/stargazing/, then click on Web Links & Resources. A set of free sky maps can be obtained at http://www.skymaps.com/

The Night Sky in October 2011

By Harry J. Augensen

Professor of Physics & Astronomy, Widener University

Moon’s Phases
Full "Hunter's" Moon on the 11thNew Moon on the 26th 

Stars and Constellations

The month of October ushers in the autumn sky while bidding farewell to the stars of summer. You will also notice that the sky gets dark considerably earlier than it did in September. (Next month, after our clocks have been switched back one hour to Standard Time, the Sun sets before 5 pm.) The "summer" right triangle is just west of overhead by 8 pm EDT in mid-October. Despite the designation, this trio of bright stars Vega (in Lyra), Deneb (in Cygnus), and Altair (in Aquila) will remain visible in the early evening sky through the end of the year. Arcturus, the fourth-brightest star in the sky and normally associated with late spring, can still be spotted as it sets low in the west-northwest, its orange color a fitting tribute to the pumpkin harvest at this time of year. Antares in Scorpius may still be glimpsed very low in the southwest after sunset, but most of the rest of Scorpius is lost in the glare of evening twilight. Following Scorpius in the southwest is Sagittarius, the Archer, followed in turn by the faint constellation Capricornus, the Sea Goat.

The notion that Capricornus represents a "sea goat" goes back to the ancient Babylonians. In Greek mythology, however, Capricornus was associated with the god Pan, a creature having the torso of a man and the legs of a goat. As a zodiac constellation (like Scorpius and Sagittarius), the Sun passes within the borders of Capricornus from about January 18 to February 14, which is about a month after it passes through the astrological sign of the same name.

As evening unfolds, the stars of autumn take center stage. Following Capricornus in the southeast is Aquarius, the Water Bearer. Just below Aquarius and low in the southeast after 9 pm EDT in mid-October is the whitish star Fomalhaut, located in Pisces Austrinus, the Southern Fish. The Great Square of Pegasus, which is actually a rectangle consisting of four stars, is situated high in the south-southeast at about this same time, and is another sure sign of autumn. Wrapped around the southern and eastern sides of the Great Square is Pisces, the Fishes, the next zodiac constellation after Aquarius.

High in the northeast is the famous "W" shape of the constellation Cassiopeia, the Queen of ancient Ethiopia. The "W" opens up toward Polaris, the North Star. Polaris actually consists of three stars, the brightest of which is a supergiant star with a luminosity of 2500 suns. It is also classed as a pulsating variable star known as a Cepheid (after the prototype in the constellation Cepheus). Such stars expand and contract in size in cycles of several days. In the case of Polaris, its pulsation cycle takes 4 days. Polaris lies at a distance of 431 light years from our solar system.

Between Pegasus and Cassiopeia lies the constellation Andromeda, the chained maiden in Greek mythology. This faint constellation contains within its boundaries the famous Andromeda Galaxy, which lies over two million light years from our solar system. The Andromeda Galaxy is often thought of as a sister galaxy to our own Milky Way, and is the most distant object visible (barely) to the naked eye. The now obsolete Y-shaped group Gloria Frederici (Frederick’s Glory) lies in the region between Andromeda, Cassiopeia, and Lacerta. It was created by Johannes Bode around 1790 in memory of Frederick the Great of Prussia, who had died a few years earlier. Its stars have since been absorbed into Andromeda and Cassiopeia.

Naked-Eye Planets In the Evening and Morning Sky

As October opens, Venus is still closely aligned with the solar orb, setting only a half hour after the Sun. By the end of the month, Venus will be setting an hour after sunset and resembling a bright yellow star very low in the west. Trick-or-treaters may be able to spot it about 30 minutes after sunset on Halloween night, if they have a clear view of the western horizon. In the coming weeks, Venus will continue to climb higher above the western horizon, and by year's end it will have emerged completely from the twilight background to be a spectacular yellow-white beacon in the western sky during the early evening hours. Hopefully Venus will not be reported as a UFO too often!

Mercury, like Venus, is immersed in the evening twilight for much of October. By the end of October, Mercury sets only about 45 minutes after the Sun, and, since it is much fainter than Venus, will be a challenge to find low in the west.

Jupiter is at its regal best this October, when it dominates the night sky (except of course for the Moon) from early evening until dawn. Jupiter resembles a brilliant cream-colored star, and is so bright that it might be initially mistaken for an airplane landing light as it stands above the northeastern horizon during the early evening hours of October. A small telescope reveals cloud bands in its atmosphere, and four bright satellites in its vicinity. Jupiter is up by around 8 pm EDT (roughly an hour after sunset) at the beginning of the month, and just before sunset on Halloween. Jupiter reaches opposition with the Sun on the 28th, when it rises as the Sun sets and sets when the Sun rises, and therefore is viewable all night. Of the planets, only Venus is brighter, but until Venus climbs out from the glare of evening twilight in the opposite part of the sky over the next few months, Jupiter will assume the lead role on the stage of the celestial theater.

Rising in the northeast at around 1:30 am in mid-October, Mars looks like a bright orange-red star in the night sky, of about the same brightness as nearby Pollux in Gemini. Right now Mars pales in comparison with magnificent Jupiter, but Mars is slowly and steadily brightening with each passing month, destined to reach its peak next March when Earth passes Mars in its orbit about the Sun.

Saturn is lost in the twilight glare at the start of October. Shortly after reaching conjunction with the Sun on the 13th, however, Saturn vaults quickly into the morning sky, and by Halloween morning it rises nearly one and a half hours before the Sun does.

Information on lunar phases and rise/set times of Sun and planets is obtained from the US Naval Observatory Data Services at http://www.usno.navy.mil/astronomy/. Additional information comes from Astronomical Calendar 2011 by Guy Ottewell (Raynham, MA: Universal Workshop, 2011)Times given apply for observers near to the latitude and longitude of Philadelphia, USA: 40 degrees North latitude, 75 degrees West longitude.

For more information on astronomy and weather, visit http://www.widener.edu/stargazing/, then click on Web Links & Resources. A set of free sky maps can be obtained at http://www.skymaps.com/

The Night Sky in September 2011

By Harry J. Augensen

Professor of Physics & Astronomy, Widener University

Moon’s Phases
Full "Harvest" Moon on the 12thNew Moon on the 27th 

Stars and Constellations

Despite the formal arrival of autumn on September 23 at 5:05 am, the stars of summer are still well placed for viewing during the early evening hours. By about 9 pm, orange-colored Artcurus in the summer constellation of the Herdsman is low, but still visible, in the west. The Big Dipper, a part of the constellation Ursa Major, is low above the northwestern horizon, and so you will not be able to see it if trees or buildings obstruct your view of this part of the sky. The handle of the Dipper arcs to Arcturus. Orange-red Antares in the Scorpion is quite low in the southwest. You should also be able to discern the "teapot" asterism of Sagittarius, just east of Antares. The constellation Sagittarius contains the nucleus or core of our own Milky Way Galaxy, which may be seen, if you are away from city lights, as a hazy band stretching across the sky.

The summer triangle of Vega in Lyra, Deneb in Cygnus, and Altair in Aquila is nearly overhead in the early evening. About halfway between Vega and Altair is the moderately bright star Albireo, also known as beta Cygni. A telescope reveals that this star is actually two stars, one yellow and the other blue. The color of a star indicates its surface temperature: blue stars are the hottest (upwards of 20,000 degrees Fahrenheit), white stars are less so (15,000 degrees), yellow stars like the Sun are moderately cool (11,000 degrees), and red stars like Antares are the coolest (6000 degrees or less). All three stars of the summer triangle are whitish in color, indicating that they are all somewhat hotter than our Sun.

As the stars of summer gradually fade into the evening twilight, the first stars of autumn are rising in the eastern sky. Making its appearance in the southeast after about 10 pm EDT is the white star Fomalhaut, which lies in the constellation of Pisces Austrinus (the Southern Fish). Rising due east at about this time is the Great Square of Pegasus, four whitish stars in the form of a rectangle (not quite square) lying on its edge.

Low in the northeast is the constellation Cassiopeia, which, like Ursa Major, is a far northern, circumpolar constellation. It never sets as seen from the latitudes of the United States and much of Europe and Asia. According to legend, Cassiopeia was the queen of ancient Ethiopia, and Cepheus was her husband, the king. Cassiopeia is said to have been a very attractive, but also very vain queen, who spent much of her time sitting in front of a mirror. She once boasted that she was more beautiful than the sea nymphs, who promptly complained to Poseidon, the god of the sea. As punishment, Poseidon placed Cassiopeia, along with Cepheus, in the sky, condemned to circle around the polestar for all eternity. The constellation Cassiopeia, which has the distinct shape of a "W," actually represents her throne. Useful for orienting oneself,  the "W" opens up toward Polaris, the North Star.

Although it contains no first magnitude stars, the constellation Cassiopeia does contain a number of moderately bright stars, some of which are quite interesting. Alpha, the brightest of the group and marking the lower right corner of the "W," is an orange giant, roughly 50 times the diameter of our Sun and lying 220 light years away. Fully three of Cassiopeia’s other stars, Beta, Gamma, and Rho, are featured in University of Illinois astronomer James Kaler's book, The Hundred Greatest Stars (New York: Copernicus Books, 2002). Beta (also known by its proper name Caph), which marks the upper right point of the "W," is a yellow giant star with a surface temperature similar to that of our own Sun (hence the yellow color) but with a diameter of about four times that of the Sun. It lies 54 light years distant and varies in brightness. Gamma marks the center of the “W,” and is a much different type of star than Alpha or Beta. Gamma is a very hot, massive bluish-white star which is spinning at a rate of 150 times faster than our Sun, or once every four hours. This rapid spin has caused the star to be much more flattened than a typical sphere. Finally, Rho is the most impressive of all the stars of Cassiopeia; it lies at a distance of 8000 light years, much farther than the other stars in this group, but is more luminous than “ordinary” supergiants like Deneb and Rigel. Rho is estimated to have a diameter of 450 times that of the Sun, and a luminosity of over one-half million Suns. As a stellar heavyweight of about 40 solar masses, its days are numbered; it will almost certainly end its life as a spectacular supernova within the next few thousand years.

Cassiopeia is also noteworthy historically because a bright supernova was seen within its boundaries in November of 1572 by the Danish astronomer Tycho Brahe. It apparently shone as brightly as the planet Venus, and remained visible to the naked eye for two years before fading from view. Astronomers today estimate that the supernova progenitor was probably about 9000 light years away. The remnant of the explosion is today detectable at radio, optical, and x-ray wavelengths.

Naked-Eye Planets In the Evening and Morning Sky

As darkness falls in early September, Saturn can be spotted very low in the west, resembling a star of about the same brightness as the true star Spica, which lies some distance to its left. Saturn sets around 9 pm on the 1st, and by 7 pm (only a half-hour after sunset) on the 30th. Afterwards, Saturn vanishes into the glow of evening twilight, only to reappear in the predawn sky at the end of October. The reverse is happening for Venus. After having adorned the morning sky for the first part of 2011, Venus passed behind the Sun as viewed from Earth (superior conjunction) last month, and is now beginning to move into the evening sky. However, Venus is still too close to the Sun to be viewed all month, and will only gradually emerge from the solar glare toward the end of October.

Rising above the northeastern horizon around 10 pm EDT at the start of September, Jupiter begins its reign over the late evening sky. The sight of Jupiter is nothing short of magnificent – it glows like a luminous cream-colored star that is far brighter than any true star in the night sky. By month’s end, Jupiter is rising around 8 pm, which is just about when evening twilight ends.

Rising in the northeast at around 2 am in mid-September, Mars resembles an orange-red star in the constellation Gemini similar in both brightness and color to the nearby true star Aldebaran in Taurus. Currently, Mars is still only a modest light in the sky compared with the other naked-eye planets, with a brightness somewhere between that of nearby stars Pollux and Castor. However, as the distance between it and Earth decreases over the next several months, Mars will in fact be gradually brightening. Few would guess from looking at this unimpressive point of light right now that when it makes its closest approach to Earth in six months Mars will shine like a brilliant red gem in the night sky.

As September begins, Mercury rises about 90 minutes before the Sun, and is therefore ideally situated for viewing in the pre-dawn sky. Look for Mercury about 30-60 minutes before sunrise, resembling a bright yellow star hovering low above the eastern horizon. Over the next few weeks, Mercury sinks toward the Sun, reaching superior conjunction with it on the 28th, when it passes behind the Sun as seen from Earth.

Information on lunar phases and rise/set times of Sun and planets is obtained from the US Naval Observatory Data Services at http://www.usno.navy.mil/astronomy/. Additional information comes from Astronomical Calendar 2011 by Guy Ottewell (Raynham, MA: Universal Workshop, 2011)Times given apply for observers near to the latitude and longitude of Philadelphia, USA: 40 degrees North latitude, 75 degrees West longitude.

For more information on astronomy and weather, visit http://www.widener.edu/stargazing/, then click on Web Links & Resources. A set of free sky maps can be obtained at http://www.skymaps.com/