Archive for November, 2017

The Sky This Week, November 21 – 28, 2017 !

The Sky This Week, 2017 November 21 – 28

Enjoy the waxing Moon and the Horn of Plenty.
Crescent Moon, imaged on 2017 FEB 3
with the U.S. Naval Observatory’s 30.5-cm (12-inch) f/15
Alvan Clark/George Saegmüller refractor
and Canon EOS Rebel T2i DSLR.

The Moon waxes in the evening sky this week, gradually obscuring the faint autumnal constellations.  First Quarter occurs on the 26th at 12:03 pm Eastern Standard Time.  The timing is perfect for enjoying views of Luna’s surface over the holiday weekend.  After all, there’s only so much football that we can watch, and looking at the Moon is a great distraction from the struggles on the gridiron.  Luna treads a lonely path this week, with no bright objects to visit as she courses through the faint stars of Capricornus, Aquarius, and Pisces.

While most of the autumn constellations will get washed out by the light of the waxing Moon, there are a few which are bright enough to shine through the brightening sky.  The most prominent of these is a large square-shaped asterism that crosses the meridian between 8:00 and 9:00 pm.  Known as the “Great Square”, this star pattern consists of second-magnitude stars that make up a part of the mythical flying horse called Pegasus.  You’ll be hard-pressed to envision a horse from this group, especially since in classical representations half of him is missing and he’s upside down, but he is related in mythology to several other patterns that grace this part of the sky.  Go to the upper-left star in the square and look for two diverging chains of stars.  These represent the chains that bound the beautiful Andromeda to a rock for sacrifice as a result of the vanity of her mother Cassiopeia.  The latter figure is a W-shaped group that’s high in the northeast.  You’re supposed to imagine a queen on a throne admiring herself in a mirror in the five second-magnitude stars in this group!  The brighter chain of Andromeda’s stars point to the rising Perseus, who is the hero that eventually rescues the chained maiden.  All of these constellations play roles in one of the great legends of ancient times, and they still tell the same tale every clear fall night.

If you’re out near midnight after the big feast the eastern sky begins to light up with winter’s bright stars.  After the relatively sparse star patterns of autumn they are a welcome sight to accompany the lengthening nights.  By midnight the parade of first-magnitude stars known as the Great Winter Circle has cleared the eastern horizon, anchored by the striking figure of Orion, the Hunter.  The highest of the stars in the circle is now approaching the meridian in the form of a bright yellow-tinted luminary known as Capella.  The sixth-brightest star in all of the sky, Capella represents the she-goat Amalthea who suckled the infant Zeus.  The strong toddler accidentally broke off one of the goat’s horns, which then was transformed into the Cornucopia, the “Horn of Plenty” that provided its owner with whatever he or she desired.  This star and its associated legend have come to symbolize the bounty that we now celebrate as Thanksgiving.

It’s time to bid a fond farewell to Saturn for 2017.  The ringed planet now sets at the end of evening twilight, so any chance you have of spotting him in the southwest will be thwarted by the Sun’s afterglow.  We’ll now have to wait for Venus to emerge in the evening sky next spring.

After Saturn sets we have to wait until 3:30 am for Mars to rise to see the next naked-eye planet.  The red planet spends the week closing ranks with the bright star Spica in Virgo.  By the end of the week the two objects are about three degrees apart.  They provide a very nice color contrast as morning twilight begins to brighten the sky.

Jupiter rises at around 5:00 am and should be easily visible in morning twilight.  He will be the next target for Mars to set his sights on, and the two planets will steadily converge toward the end of the year.


The Sky This Week, November 14 – 21, 2017 !

The Sky This Week, 2017 November 14 – 21

The Seven Sisters on the rise
Messier 45, the Pleiades Star Cluster
imaged 2016 December 31 from Mollusk, VA by Geoff Chester
with an Explore Scientific AR102 4-inch f/6.5 refractor
and Canon EOS Rebel T2i DSLR.

The Moon spends most of the week in the glow of morning and evening twilight. New Moon occurs on the 18th at 6:42 am Eastern Standard Time. Luna may be found as a waning crescent in the company of the planets Mars, Jupiter, and Venus in the pre-dawn hours of the 15th, 16th, and 17th. She returns to the evening sky by the evening of the 20th, when you’ll find her low in the southwest as evening twilight fades.

The sky in the middle of November is one of transition between the setting stars of summer and the rising stars of winter. On the whole there aren’t that many bright stars above the horizon during the mid-evening hours. The solitary first-magnitude star among the autumnal constellations crosses the meridian at around 7:30 pm, low in the southern reaches of the sky. This solitary star is Fomalhaut, the brightest and only prominent star in the obscure constellation of Pisces Austrinus, the Southern Fish. It is one of the closer stars to the Sun at a distance of about 23 light years, but somehow its isolated place in the sky makes it seem much more remote. Fomalhaut transits the meridian just before the westernmost stars in the Great Square of Pegasus, the “signature” constellation of the seasonal sky.

High in the east during the later evening hours is a small knot of stars that have probably garnered more attention in skylore that the rest of the constellations combined. Urban skywatchers can see the group as a small fuzzy grouping on clear nights, and as you move farther from the middle of the city the group begins to come into better focus under darker skies. Viewers in the suburbs should be able to see around half a dozen stars in a pattern that resembles a small measuring spoon, while those graces with dark country skies can easily seven or more stars. The group goes by as many names as there are colloquial legends of the sky, and we call the group The Pleiades or The Seven Sisters. In Greek mythology they were the daughters of Atlas and half-sisters of the nearby Hyades, which surround the bright star Aldebaran. Since very ancient times the risings and settings of the Pleiades have dictated agricultural activities, and in the Mediterranean region they were seen as harbingers of stormy weather that comes with the arrival of winter. The vast pre-Columbian city of Teotihaucan, which was 1000 years old when the Aztecs ruled Mexico, has all of its major streets and its largest temple, the so-called “Pyramid of the Sun”, laid out in alignment with the setting of the Seven Sisters. The stars have even found their way into the mythology of J.R.R. Tolkien’s Middle Earth, where Hobbits, Elves, and Men knew them as Remmirath, “the Netted Stars”. The group is a true star cluster, one of the closest to the Earth, about 440 light-years away. Keen-eyed observers under very dark skies may be able to see up to a dozen of its components, while binoculars will reveal several dozen. Astronomers have counted about a thousand total cluster members. The brightest members are energetic young blue stars that have luminosities that are thousands of times that of the Sun.

Try to catch a last glimpse of Saturn in twilight on the evening of the 20th. On that night the slender waxing crescent Moon will be located about two degrees north of the ringed plane. Both objects will be low in the southeastern sky, and you’ll probably need binoculars to see Saturn in the relatively bright sky.

Mars may be found about five degrees above the waning crescent Moon before dawn on the 15th. He’s also fairly close to the bright star Spica, but you should be able to distinguish him by his ruddy tint, which contrasts nicely with the ice-blue of the star.

Venus starts the week close to Jupiter, and as the week passes the dazzling planet leaves Old Jove in her wake. Look for the pair in bright twilight, low in the east about half an hour before sunrise.

The Sky This Week, November 7 – 14, 2017 !

The Sky This Week, 2017 November 7 – 14

Gems in the autumn sky
Messier 31, the Andromeda Galaxy
imaged 2017 October 20 from Great Meadow, VA by Geoff Chester
with an Explore Scientific AR102 4-inch f/6.5 refractor
and Canon EOS Rebel T2i DSLR.

The Moon wanes in the late evening and morning skies this week, passing through the rising constellations of winter and spring.  Last Quarter occurs on the 10th at 3:36 pm Eastern Standard Time.  Look for Luna near the bright star Regulus in the constellation Leo on the morning of the 11th.  By the end of the week the Moon will be near ruddy Mars.  She’ll be just over three degrees east of the red planet before sunrise on the 15th.

The change back to Standard Time now pushes the onset of night an hour earlier.  You can still see the stars of the Summer Triangle in the hours after sunset, and from a dark location the summer Milky Way is still prominent as evening twilight ends.  The densest part of the home galaxy is now setting on the southwest, but the prominent star clouds and dark rifts still split the three stars Vega, Deneb, and Altair.  Its brightness slowly wanes as you look toward the northeast, but the number of bright stars begins to concentrate with the rising constellations of Cassiopeia and Perseus.  These two constellations are wonderful places to explore with binoculars or a small telescope, with dozens of star clusters scattered among their brighter stars.  One of my favorite objects in this area lies in the middle of the Milky Way between the two constellations.  The “Double Cluster” can be seen with the naked eye from a dark location, and its stellar nature is revealed with only slight optical aid.  My favorite views come with my 3- and 4-inch refractors using a low-power eyepiece.  These clusters each contain some of the most intrinsically bright stars in the sky, with luminosities over 100,000 times that of our Sun.  Looking south at around 8:00 pm, you’ll find a relatively sparse sky that’s dominated by a large square of second-magnitude stars that marks the constellation of Pegasus.  The upper left star of this square is Apheratz, shared by Pegasus and Andromeda.  Under dark skies you’ll notice two diverging “chains” of stars pointing toward Perseus.  Go to the second star in the brighter chain, then hop up two fainter stars to spot a small, fuzzy “cloud” that looks like a detached piece of the Milky Way.  Binoculars will reveal an elongated streak of light that refuses to resolve into stars in all but the largest telescopes.  This is the famous Andromeda Galaxy, Messier 31, the largest member of our Local Group of island universes.  At a distance of 2.5 million light years, this is the most distant object you can see with your unaided eye.  It’s estimated that this galaxy contains some 400 billion stars.  The Milky Way and M31 are approaching each other at a speed of about 110 kilometers (68 miles) per second.  It will collide with us in about 4 billion years!

Saturn still lingers in the southwestern sky, visible for a short time after the end of evening twilight before setting at around 7:00 pm.  His low altitude means that detailed views of his rings will be quite distorted by turbulence in our atmosphere.

You’ll find Mars rising in the hours before dawn.  The red planet begins the week just under two degrees south of the second-magnitude close double star Porrima in Virgo.  He continues to trek eastward toward the bright star Spica and is joined by the waning crescent Moon as the week ends.

Venus is now only visible in the brightening morning twilight, rising about an hour before the Sun.  You should be able to spot her if you have a low eastern horizon.  If you’re lucky and have a clear sky on the morning of the 12th look for Jupiter just a quarter of a degree from Venus in the brightening sky.  They will be in bright twilight but should be easy to spot in binoculars half an hour before sunrise.

The Sky This Week, October 31 – November 7, 2017 !

The Sky This Week, 2017 October 31 – November 7

Fall back after the Hunter’s Moon.
The Hunter’s Moon, 2016 October 16
imaged from Alexandria, VA by Geoff Chester
with an Explore Scientific AR102 4-inch f/6.5 refractor
and Canon EOS Rebel T2i DSLR.

The Moon brightens the sky for Halloween’s ghosts and goblins, then waxes to Full Moon on November 4th at 1:23 am Eastern Daylight Time. This Full Moon is popularly known as the Hunter’s Moon thanks to nearly the same orbital geometry as last month’s Harvest Moon. The times of successive moonrises around the time of Full Moon differ by about 35 to 40 minutes, adding a little extra light to the twilight hours. In bygone times this allowed hunters to have a little more time to chase game over the stubble of the harvested fields. In Native American skylore this was also known as the Beaver Moon, since this was the time of year when these industrious rodents were busily preparing for the coming of winter. During the week Luna moves through the faint autumnal constellations, ending the week in the middle of the rising stars of winter. On the evening of the 5th, watch the bright star Aldebaran slip behind the Moon at 7:59 pm Eastern Standard Time, shortly after moonrise. The star will reappear from behind Luna’s slender dark limb at 8:53 pm.

Remember to set your clocks back one hour as you turn in for the night on the evening of the 4th. Technically you should perform this annual ritual at 2:00 am on the morning of the 5th, according to U.S. Code. The subject of Daylight Time and clock-changing has long been a bone of contention ever since it was first legislated in 1918. It was initially adopted as a means to promote the tending of “victory gardens” during World War I, a concept which satisfied factory workers who wanted a little extra food on the table. Within year, though, the law was repealed and Daylight Time became a matter for states and local municipalities to decide. During World War II Daylight Time was observed continuously from February 9, 1942 until September 30, 1945, when once again it became a matter of local choice. It wasn’t until 1966 that a Federal statute was once again passed by Congress as the Uniform Standard Time Act. Under these rules Daylight Time began on the last Sunday in April and lasted until the first Sunday in October. Our current system, with Daylight Time in force from the third Sunday in March to the first Sunday in November, is the result of the Energy Policy Act of 2005. Since these rules are specified in the law of the land they are enforced by a civilian agency, so if you don’t like the current system please call the Office of General Counsel at the Department of Transportation. The Time Service Department here at the Naval Observatory is responsible for producing a uniform time scale, Coordinated Universal Time (UTC); we don’t tell people what to do with it! That said, at least we’ll get back the hour that we lost way back in March.

You will still find Saturn lingering in the southwestern sky as evening twilight begins to darken the sky. The ringed planet’s current tenure in the evening sky is rapidly coming to a close. He sets an hour after the end of evening twilight, and by the end of November you’ll be hard-pressed to spot him at all in the twilight glow.

The next bright planet to grace the sky is Mars, but you’ll have to either be a night owl or a very early riser to catch him. He rises shortly before 5:00 am EDT among the stars of Virgo and spends the week drifting between the third-magnitude star Zaniah and second-magnitude Porrima. His ruddy disc is currently a miniscule 4 arcseconds across, but he will become a great telescopic target when he reaches opposition in late July next year.

Brilliant Venus is now rising at the beginning of morning twilight. She hangs low above the eastern horizon as the sky brightens, so you’ll need to have a good eastern exposure to see her. By the end of the year she will be lost in the solar glare and won’t emerge in the evening sky until early 2018.