Skywatch February 2001

Feb 1-4     Feb 5-11   Feb 12 -18   Feb 19 - 25   Feb 26 -28

This is the Skywatch Line for Thursday, February 1st. Written by Peter Jennes.

Tonight, the Moon is just past first quarter and will be high in the south at sunset. Almost everyone knows that the Earth revolves around the Sun but few realize that they can use the first and last quarter Moon to illustrate the Earth's motion. If you could look down on the Earth from high above either pole at new Moon, you would see that the Moon was between the Earth and the Sun. Then at full Moon you would see the Earth between the Moon and the Sun.

In contrast, at first and last quarter, the Earth, Moon, and Sun form a right angle with the Moon lying directly on the Earth s orbital path. The first quarter Moon lags behind the Earth and when you look at tonight s first quarter Moon you are looking at the point in space that the Earth occupied two and one-half hours ago. At last quarter the opposite is true and the Moon is ahead of the Earth. Therefore, when you look at the last quarter Moon this coming Valentines Day, you are looking at the point in space where the Earth will be in two and one-half hours.

By tomorrow night, the Moon will be passing below Saturn and as the night goes on, you will be able to watch the Moon s orbital progress as its motion carries it below Jupiter. By February 7th, the Moon s orbital motion brings the Moon as close to the Earth as it will get for all of 2001 and less than one day later, the Moon is full. Whenever the Moon is new or full, ocean tides are higher. The same is true whenever the Moon is closest to the Earth. The close occurrence of full moon and lunar perigee can result in extremely high tides especially during intense storms.

By February 11th, moonrise does not occur until after 9:30. With the onset of moonless evening twilight, the next two weeks are prime time for viewing evening zodiacal light. Zodiacal light is a faint cone of light extending up from the horizon above the sunset point in the late winter and above the sunrise point in late summer. Sunlight reflecting off dust particles left in the plane of the solar system causes this eerie glow that only lasts for about an hour or two after sunset.

This is the Skywatch Line for Friday, February 2nd to Sunday February 4th. Written by David Lynch.

If you go out to gaze at the stars tonight you will see the constellation Ursa Major, the Great Bear, high overhead in the northern sky. Ursa Major is perhaps the most recognizable constellation in the sky in the northern hemisphere. That is because Ursa Major contains the Big Dipper. The Big Dipper is a pattern of stars within the larger constellation. Star patterns like this are called Asterisms". Ursa Major is a circumpolar constellation. It lies relatively close in the sky to Polaris, the "north star" or the "pole star". As the Earth's rotation appears to cause the stars to arc across the sky, Polaris seems to remain virtually stationary, as it occupies a spot in the sky almost directly above the Earth's northern geographic pole. Two of the stars in the dipper, Dubhe (Doo-bee) and Merak (Mare-ak), point toward Polaris. They are the two brightest stars in Ursa Major. A straight line drawn between the two stars leads the eye directly to the pole star. Duhbe is an Arabic word derived from a phrase meaning "back of the great bear". Merak translates as "loin of the bear", also in Arabic. Five of the seven dipper stars are actually a star cluster. They are associated with one another in space and move together in the same direction, Dubhe is, however, not a proper member of the group. Over time, say the next 100,000 years or so, Dubhe's contrary motion will seriously distort the pattern of the dipper. The cluster in the dipper is made up of five of the most visible stars plus a number of fainter stars visible only through a telescope (about 17 stars in all). At a distance of about 75 light years from Earth, the dipper is the closest star cluster to us. There are a number of objects other than individual stars within Ursa Major that provide interesting targets for the backyard astronomer. There are several Messier objects, originally cataloged by the 18th century French astronomer Charles Messier, including M81 and M82. These are two galaxies much like our own Milky Way. M81 is, in fact, considered by astronomers to be one of the most beautiful (and symmetrical) examples of a spiral galaxy that we know of. M82 is an unusual galaxy with respect to it's shape. It appears to be elongated, almost "spindle shape". It does not have the well defined spiral arms and accompanying dust lanes of M81. M97, the Owl Nebula, is another interesting deep sky object in Ursa Major. These objects can be located using a star chart like those found in the Edmund Mag 6 atlas, Norton's Star Atlas, or as published in monthly astronomy magazines such as Astronomy and Sky and Telescope. Enjoy your observing!

This is the Skywatch Line for Monday, February 5th. Written by Joseph Slomka.

The Sun sets tonight at 5:12, with twilight ending at 6:50 PM. The nearly Full Moon is already up and sets shortly before sunrise. Dawn breaks at 5:27 AM and ends with sunrise 7:05.

As the Sun sets, three bright planets attract attention of even casual sky watchers. Venus blazes in the southwest; it is the brightest object in the sky. In moderate >powers, Venus looks like a brilliant crescent, about forty percent illuminated. Venus is best seen while the sky is still bright, since its light literally dazzles the observer. Mercury is found to Venus' lower right, just above the tree line.

One must work quickly, Mercury is ending its three week visit to our skies and soon becomes lost in the twilight. In moderately powered telescopes and binoculars, Mercury also appears as a crescent.

While Venus is attracting attention, Jupiter and Saturn are also up. They occupy the high constellation Taurus. Binoculars easily show Jupiter to be a planet with tiny moons about it. At 7:30PM, the moons Io and Ganymede appear 18 seconds apart. This is a good test of your binocular's optics. Can you see one on top of the other?

Two very interesting variable stars are visible tonight. This means they become periodically dimmer. The most famous is Algol in Perseus, the "Demon Star." This star is on the bottom of the shorter leg in the constellation. Algol is an "eclipsing variable", which means that a dimmer star gets in front and fades Algol from second to third magnitude. This is a very easy event to observe; it happens every two days and twenty hours. Most astronomical magazines have tables which alert the observer to the day and time. Much different is Mira in Cetus. Mira is a "pulsating >variable", which means that changes are due to little understood processes within the star. When people first understood the variable nature of this star, they named it "Mira", Latin for "wonderful". It is more difficult to observe Mira's changes since they occur every 331 days.

This is the Skywatch Line for Tuesday, February 6th. Written by Bob Mulford.

 Throughout this month, Venus will be a brilliant evening star, visible in the south long before darkness falls. An observer will see Venus become even brighter during February. Greatest brilliancy of Venus occurs on Thursday, February 22.

Venus is the next planet in toward the Sun from the Earth. Because its closer to the Sun than the Earth, it completes one revolution around the Sun faster than the Earth does. This means that Venus periodically passes between the Sun and the Earth. As Venus overtakes the Earth, it gets closer and appears larger and brighter. In a telescope it changes from half illuminated on February first to a crescent shape by the end of the month. During February the crescent shape of Venus will become larger and brighter, but the crescent also gets thinner. Eventually, Venus will begin to fade. Each night during early March, Venus will set a little sooner after Sunset. By late March, Venus will pass between the Earth and the Sun and will not be seen. This is because we are viewing the dark night side of Venus.

By early April Venus will have passed the Earth and will now be visible in the morning sky. Venus rises a little sooner and gets a little brighter each day during April. By early May, Venus will be a brilliant morning star rising several hours before the Sun.

Sunset on Tuesday, February 6th is at 5:20 PM, and evening twilight ends by about 6:20. This Moon is almost full and will be visible all night long. Morning twilight begins about 6AM and Sunrise occurs at 7:08 AM on Wednesday.

This is the Skywatch Line for Wednesday, February 7th. Written by Ray Bogucki.

In each of the Moon's monthly orbits around the Earth, its elliptical path brings it, at one point, to its closest approach to Earth for that orbit. This point is called perigee, and the distance at perigee varies somewhat from orbit to orbit. Tonight, at about 5 p.m. the Moon stands at perigee and, at only 223 thousand miles, its closest approach to Earth for this year. Coincidentally, the Moon will reach its full phase just a few hours later, making this the largest full Moon of the year 2001. Because high coastal tides occur each month at the time of new Moon and full Moon, the close approach of the Moon tonight will generate unusually high tides for the next couple of days. On Friday, the distant gas giant planet Uranus, will pass behind the Sun, just as Mercury, the innermost and speediest planet, prepares to pass between Earth and the Sun going the opposite direction a few hours later. Venus, the second planet from the Sun shines brilliantly in the west at dusk, presenting a beautiful crescent in a small telescope. Venus is rapidly overtaking Earth and its disk size will increase dramatically from 30 arc-seconds at the beginning of this month to 43 arc-seconds, which is larger than Jupiter, at the end of the month. Although its apparent size is increasing rapidly, its brightness will remain about the same throughout the month because as the planet grows in size, its crescent shape becomes proportionately thinner. Also, if you're observing Venus with a telescope, watch carefully for any faint illumination in parts of the dark or night side of Venus' disk. While the faint illumination on the dark side of the crescent Moon has been recognized for centuries as "earthshine", or sunlight reflected from Earth back to the Moon, Venus has no nearby body to perform this function. The occasional reports by astronomers of this mysterious "ashen light" from Venus remains unexplained.

This is the Skywatch Line for Thursday, February 8th. Written by Peter Jennes.

Shortly after sunset, February's Full Snow Moon clears the eastern horizon. Rising above the horizon with the Moon is the entire length of Leo the Lion. Four degrees to the right of the Moon lies Regulus, the brightest star in Leo. Denebola, the second brightest star in Leo, will be 20 degrees or two hand widths to the left of the Moon. Although Denebola is the second brightest star in Leo, it is only second magnitude and may be difficult to spot without binoculars.

Denebola is a main-sequence star like our own Sun. However unlike our Sun, Denebola is a blue-white star and thousands of degrees hotter than our Sun. Because it is so much hotter, Denebola is nearly 20 times brighter than the Sun but Denebola's distance of 40 light-years dims the brilliance of the star. The name "Denebola" comes from the ancient Arabic name Al Dhanab al Asad, the lion's tail and as you may guess, Denebola marks Leo's tail. Looking at Denebola, you may notice that it occupies the tip of a wide, right triangle of stars. The modern rendition of Leo makes this triangle into Leo's tail, however this was not always true. Leo evolved from an Arabian constellation known as Asad. Thousands of years ago, when Asad the Lion was created, the Sun passed through it during the summer solstice. Because of that, Asad became the symbol of absolute power. On many early star charts, Asad's tail curved up over his back into a group of stars resembling the tuft of hair on a lion's tail. In 1602, Tycho Brahe amputated Asad's tail and created the constellation Coma Berenices from this misty cluster of stars. The rest of this starry lion lies to the west, above the Moon, in an easily recognized star pattern we now call the Sickle.

Because we have lost much of our agricultural heritage, this asterism is most often described as a backward question mark. Regulus, the brightest star in Leo, forms the dot at the bottom of the question mark. If you follow Leo's Sickle to its upper end, you will arrive at a wide pair of stars. Arabic astronomers grouped these two stars together and formed Al Ashfar, the Lion's Eyebrows.

This is the Skywatch Line for Friday, February 9th to Sunday February 10th. Written by David Lynch

 Skywatch line for Friday, February 9 through Sunday, February 11, 2001

If you go outside on a clear night this weekend at about 8:30 p.m. and look straight up you'll see a bright yellow star. Its name is Capella and it is part of the constellation of Auriga, the Charioteer. Auriga describes a roughly pentagonal shape and is not one of those constellations that is easily associated with its name. Capella is the fourth brightest star visible to observers at this latitude after Sirius, Arcturus and Vega. Overall it is the 6th brightest star in the sky and is the furthest north of any of the first magnitude stars. Although to the naked eye Capella looks like an individual star it is actually a binary system. There are two yellow stars revolving around each other that are both approximately the same temperature as the Sun. However, they are many times larger and brighter than the Sun. Both stars are thought to be approaching the red giant phase of stellar development. The pair of stars making up Capella are relatively nearby, being only about 45 million light years away. The name Capella means "she goat". Just to the southwest of Capella is a grouping of three smaller stars. These are known as "the kids". The northernmost of the kids is Epsilon Aurigae. This star has the rather peculiar habit of becoming noticeably dimmer every 25 years for a period of about 700 days. It is thought that this may be due to a larger, invisible companion star rotating around Epsilon Aurigae. If this is in fact the case this object would have to be the largest known star, being thousands of time larger than the Sun, about the size of the orbit of Saturn! This mysterious companion might also be a vast cloud of proto-stellar material or a new solar system being borne. Perhaps we should consider ourselves lucky to be orbiting a more ordinary, boring star like our Sun. The strip of sky that runs upward from the southwestern horizon through Canis Major, Monoceros, Orion, Gemini, Taurus, and finally Auriga overhead is the home of the winter Milky Way. Many of the brightest stars in the winter sky are found in this region. While observing this area of the sky through a telescope reveals magnificent sights like the Orion Nebula, viewing the star clouds of the Milky Way through an ordinary pair of binoculars can be equally rewarding. Enjoy your observing!

This is the Skywatch Line for Monday, February 12th. Written by Joseph Slomka.

The Sun sets at 5:21, with twilight ending at 7 PM. Dawn breaks at 5:18 AM, with the Sun rising at 6:56 . As the sky darkens, three planets are visible. Venus, in the southwest, is the most obvious. Venus is rapidly approaching conjunction between Earth and Sun. As a result, it becomes increasingly brighter and also a thinner crescent. Tonight, Venus is about a third illuminated. Venus sets about 9:12 PM. Jupiter and Saturn are already risen by sunset, and high overhead by twilight's end. Both planets occupy the constellation Taurus, with Jupiter being the brightest. Above Jupiter lies the Pleiades, a mini dipper of stars. This grouping is sometimes called "The Seven Sisters," but binoculars easily show far more stars. Jupiter is also a great binocular object. An observer can easily see the ball of the planet, with tiny moons about it. At 10:42 PM, binoculars show three moons in a line; a telescope is needed to show the moon Europa crossing the planet's face. Saturn is not a good binocular object; one can barely make out the oval shape of its ring system Tonight, NASA tries an unusual experiment. For the past year, the NEAR space probe has been circling the asteroid 433 Eros. This rocky world lies between Mars and Jupiter, the "Asteroid Belt." Astronomers have catalogued about 4000 asteroids. The asteroid belt's origin is obscure; some astronomers think it is the remnant of a disintegrated prehistoric planet, others that it represents leftovers of solar system formation. A few asteroids are visible in small telescopes and mentioned in astronomy magazines. Although Eros is about the size of Manhattan, it orbits the Sun just like Earth. NEAR is the first to study, close-up, one of these minor planets. Now, that its mission is almost over, NASA scientists will try to land the probe on Eros, hoping to get closer pictures and clues to its origin. Some asteroids have orbits that could cross the Earth's; NEAR was renamed Shoemaker in honor of the late Gene Shoemaker, who uncovered that danger.

This is the Skywatch Line for Tuesday, February 13th. Written by Bob Mulford.

The early evening sky this month is dominated by several bright planets. The brightest is Venus, visible in the southwest just after sunset. As darkness falls, look directly overhead. The brightest point of light is the planet Jupiter, which becomes visible long before it is dark enough to see any other stars. As twilight ends, another planet becomes visible. This is the ringed planet Saturn. This month Saturn is seen a little to the right of brilliant Jupiter. Saturn is not quite as bright as the star Capella, positioned to the left of Jupiter during March evenings.

Capella is the brightest star in the constellation Auriga, the Chariot Driver. It is surprising that this constellation is not very well known, since Capella is the sixth brightest star in the sky. Capella is 45 light years away and it's true magnitude is 160 times brighter than our Sun. In other words, Capella appears 160 times as bright as our Sun would if it were at the same distance as Capella.

Capella is actually a binary, or double star, composed of two stars orbiting each other at a distance of 70 million miles. This is too close for the two stars to be seen individually in any telescope. In 1899, astronomers at Lick observatory discovered that Capella was really a double star by studying Capella's spectrum.

Capella's name means "Goat Star". Why is there a "Goat Star" in a constellation representing a chariot? Long ago, when noblemen still used chariots, the chariot driver also had the job of caring for the livestock which belonged to the estate. For this reason, the constellation Auriga is often depicted with the chariot driver holding a goat in his arms.

This is the Skywatch Line for Wednesday, February 14th. Written by Ray Bogucki.

Two major astronomical news stories this week involve man-made objects. Last Wednesday, the space shuttle "Atlantis" was launched to deliver the U.S. research lab module to the International Space Station. Two days later, the shuttle docked to the ISS. As if to celebrate the event, the ISS made a perfect pass over this area at 5:52 on Saturday evening, shining a bit brighter than Saturn. Much farther out in the Solar System, the space probe, NEAR, the acronym for the Near Earth Asteroid Rendezvous mission, touched down to a soft landing on the surface of the asteroid 433 Eros. NEAR was launched by NASA 5 years ago, and after a 4-year odyssey, it slipped into orbit around Eros exactly one year ago today. During the past year it has been controlled to orbit from 200 miles to only 3 miles above the surface. It has sent back 160,000 pictures covering every square foot of the asteroid, which looks like a giant pock-marked potato, the size of Manhattan. The tens or hundreds of thousands of other asteroids, also known as minor planets, mostly orbit the Sun between the orbits of Jupiter and Mars. A few have been perturbed by the gravitational fields of nearby planets into orbits that come close to, or even cross, the orbit of Earth. In 1994, a small asteroid sped past Earth at a distance of only 60,000 miles, one-quarter of the distance to the Moon. This was a very near miss! Over the period of a year, the chance of Earth colliding with an asteroid is vanishingly small, but over a very long time period, it becomes a certainty. Only one asteroid, Vesta, is large enough and close enough to be seen occasionally with the unaided eye as a faint star. However, endless collisions among the asteroids in the asteroid belt generate clouds of fine particles which populate the inner solar system before falling into the Sun and these particles can be seen as a ghostly glow called zodiacal light along the ecliptic in a fully dark sky. For the next week, while the Moon is absent, look, after 7 p.m., for sunlight reflected from these particles, rising as a triangle of faint, white light from the western horizon toward Venus.

This is the Skywatch Line for Thursday, February 15th. Written by Peter Jennes.

Venus is now one week away from greatest brilliancy and only 33% illuminated. By next Thursday, Venus will be magnitude -4.6 and will appear as a slender, 22% illuminated crescent. As Venus gets low in the west tonight, telescope users will be able to observe a transit of both Jupiter's moon Io and it's shadow across the face of the planet. Around 7:30, Io begins to cross Jupiter's disk and about one hour later; Io's shadow also starts to cross the planet. Although it is easier to observe the shadow transit, you may be able to see Io during its two-hour transit if the night is clear.

Jupiter can also be used as a starting point for tracing the Seven of these stars are nearly equal in brightness, while the eighth is the brightest in the sky. Around 8 PM, look for this enormous G of bright stars due south and high overhead. Begin by looking for the V of stars forming the head of Taurus the Bull. The brightest star in Taurus' V is Aldebaran. This first magnitude star marks the beginning of the G's upper curve and it is just to the left of Jupiter.

Once you've found Aldebaran, look up and to the left to the next bright star. This is Capella in the somewhat circular shaped constellation of Auriga. Capella is about twice as bright as Aldebaran and marks the upper bend of the G. Down to the left from Capella you will find Castor and Pollux side by side in Gemini. These twin stars are almost as bright as Aldebaran and they form the left side of the G.

From the Twins, look due south for a star equal in brightness to Capella, this is Procyon in Canis Minor. Now move down and to the right for Sirius in Canis Major. Sirius is unmistakable in that it is the brightest star in the sky. After Sirius, continue moving up and to the right until you come to Rigel, the bright star at the lower right corner of Orion s hourglass shape. >From Rigel, a straight line to Betelgeuse through the middle star of Orion's belt completes the G.

This is the Skywatch Line for Friday, February 16th to Sunday February 18th. Written by David Lynch

Orion is easily the brightest constellation in the winter sky. You'll find it high in the southern sky in the early evening hours. The three bright stars that make up Orion's belt make it almost impossible to miss. Orion traverses the sky accompanied by three companions. Canis Major, the big dog, follows Orion just to his left. It too is easy to spot because it contains the brightest star in the sky, Sirius. Orion's other two companions are far less conspicuous. Canis Minor, or the little dog, is found above and to the left of its bigger canine cousin. There are only a couple of notable stars in Canis Minor. The brighter of the two is Procyon, which means "before the dog" in Arabic. The name no doubt comes from the fact that Procyon peeks up over the horizon before Sirius, also known as the "dog star". In ancient Egypt the appearance of Sirius presaged the flooding of the Nile River. Procyon, like nearby Sirius, has a companion star which is a white dwarf, and therefore much more difficult to see. The other relatively bright star in Canis Minor is Gomeisa (go-MY-za). Gomeisa means "bleary eyed". Perhaps that was named by an ancient astronomer who was lacking sleep! The band of the Milky Way passes between Sirius and Procyon. However, when looking in this direction you are looking away from the brighter, more dense, central part of our galaxy, so it's not as bright as the summer Milky Way. Stretching between Canis Major and Canis Minor is the rather unremarkable constellation Monoceros, the Unicorn. Although Monoceros contains both the Rosette Nebula and the Cone nebula, both are difficult targets for the amateur with a small telescope. Orion's other companion is Lepus, the Hare. Lepus scampers along underneath Orion and so is closer to the horizon and thus more difficult to see. So take a look at Orion and his entourage this weekend. Enjoy your observing!

This is the Skywatch Line for Monday, February 19th.

This is the Skywatch Line for Tuesday, February 20th. Written by Bob Mulford.

The brilliant star you see in the Southwest just after sunset is the planet Venus. Venus is visible long before the sky gets completely dark. Another bright planet is also visible at dusk this winter. Jupiter is >visible high in the south during twilight, long before you can see any other stars. After twilight becomes night, you can see a small group of bright stars arranged in a beautiful cluster a little above Jupiter. This is the galactic star cluster known as the Pleiades. Below and to the left of Jupiter is the larger star cluster known as the Hyades. The stars of the Hyades are arranged in a much larger and more open pattern than the Pleiades. In fact, most people do not even recognize the Hyades as a cluster until the group is pointed out to them.

Both of these clusters are visible to the naked eye and are very attractive in binoculars. However, they are only visible in the evening during the winter months, and by late spring they will be gone from our sky. Every day they set four minutes earlier, due to the earth turning slightly as it moves in its orbit about the Sun. Soon, they will pass behind the Sun as seen from our vantage point on the Earth. The glare of the Sun will block them from our view for several months.

The Pleiades are about twice the size of the full Moon, and the Hyades are several times larger than this. These clusters of stars are relatively near to us, and this is why they appear so large. There are many other star clusters like the Pleiades in the sky, but most are too far away to be seen without a telescope.

The area of sky near the constellations Auriga and Gemini contains several other clusters which can be found in binoculars. Seasonal star maps, such as the ones found in Sky and Telescope magazine each month, label these clusters as M35, M36, M37, and M38. In binoculars these clusters appear as hazy clouds of light about the size of the Moon. In even a small telescope these clusters are resolved into groups of dozens of brilliant, pinpoint stars.

This is the Skywatch Line for Wednesday, February 21st. Written by John Schroer of the Schenectady Planetarium.

During the early evening a brilliant light dominates the southwestern sky over the Capital District. Dubbed the "evening star" by stargazers, this apparition has confused and befuddled anyone not familiar with the nighttime skies. This bright object is the Planet Venus. Throughout human history, Venus has dazzled humanity with its brilliance, and inspired many, including science fiction writers.

During the "Golden Age of Science Fiction" in the 1930's and 40's, Venus was a frequent setting for space adventure stories. After all, cloud-covered Venus is nearly the same size as Earth and it's only a little closer to the Sun than our planet is. Readers and writers alike fancied Venus as an enticing safari planet -- a steaming worldwide jungle filled with unknown and exotic creatures.

Here is a sample from a 1939 short story from Isaac Asimov. "From low-hanging clouds fell eternal misty rain; squat rubbery vegetation stretched away in all directions. Now and then a Hop-scotch Bird fluttered wildly above them. Karl turned to gaze at the tiny dome of Aphrodopolis, the largest city on Venus!"

Nowadays we know better, thanks to a parade of U.S. and Soviet spacecraft that visited Venus dozens of times between 1961 and 1997. Venus is indeed warm, but more so than early sci-fi authors suspected. The surface temperature is 860 F (460 C) -- hot enough to melt lead! The air is thick and steamy, too. The atmospheric pressure is about 90 times that of Earth. And the steam .... it's sulfuric acid, a corrosive mist that floats cloud-like through Venus's 96% carbon dioxide atmosphere. Carbon dioxide is a greenhouse gas that traps infrared radiation beneath Venus's thick cloud cover. A runaway greenhouse effect is what makes Venus even hotter than Mercury! The clouds also hide a forbidding terrain, strewn with craters and volcanic calderas. There are no rivers, lakes, or oceans on Venus -- like Mars, Venus is bone dry.

This is the Skywatch Line for Thursday, February 22nd. Written by Peter Jennes.

Earlier today, Venus went through the perihelion point of its orbit. This means that Venus passed its closest to the Sun for the year. By co-incidence, Venus also reaches greatest brilliancy tonight. For Venus, greatest brilliancy occurs just before the inner planet, racing along on its faster orbit, catches up with, and passes Earth. As Venus catches up with the Earth, two things happen. First, the planet s phase changes from gibbous to crescent. Secondly, like an approaching train, as Venus gets closer, it appears to get larger. So although the illuminated portion of Venus gets narrower as it shrinks to a crescent, the apparent size of the planet gets larger from pole to pole. The net result is that Venus gets brighter as it gets narrower.

Tonight, Venus shines at a brilliant magnitude 4.6 and will be the brightest object in the sky until it sets just after 9 PM. Through any telescope or steadily held binoculars, you will be able to see the crescent shape. Looking at the crescent, all you are seeing is the tops of clouds. It is these clouds and the nearness of the planet that make Venus so brilliant. Clouds reflect an enormous amount of light compared to the rocky surfaces of the Moon and Mercury. In real numbers, the clouds of Venus reflect almost 75% of the light that falls on them compared to less than 10% for the surface of the Moon.

As brilliant as the clouds of Venus are, they also just as deadly. Composed of mostly carbon dioxide, the density of the Venus atmosphere is staggering. On the surface of Venus, the atmospheric pressure is 90 times greater than atmospheric pressure on Earth. In order to experience pressures this intense, you would have to dive down over 3200 feet in the ocean. Beside these crushing pressures, the concentration of carbon dioxide has set up the conditions for a runaway greenhouse environment. Because carbon dioxide is very efficient at trapping heat, the surface of Venus is the hottest planet in the Solar System. Surface temperatures of nearly 900 degrees have been measured on Venus surface; hot enough to melt lead. If crushing pressures and incinerating temperatures weren't t enough, clouds of sulfuric acid deliver caustic rains to the surface. Considering this, Venus is probably better visited with a telescope than in person.

This is the Skywatch Line for Friday, February 23rd to Sunday February 25th. Written by David Lynch

If you look just slightly southeast of the zenith, the point directly overhead, at about 9:00 in the evening you will see the constellation of Cancer, the crab. Cancer is certainly not one of the more noticeable of the 88 constellations (it contains no star brighter than 4th magnitude), however, there are definitely some interesting things about Cancer. Cancer is one of the twelve constellations of the zodiac. The zodiac is the group of constellations that cluster around the ecliptic, which is path that the Sun traces across the sky during the course of a year.

The ecliptic passes right through Cancer. If you were to view Cancer from a dark site, remote from city lights, you might notice how one of the "stars" in the central part of the constellation looks rather fuzzy. This object is not a single star, but a star cluster, called Praesepe (pree-SEE-pee), which means "manger". You may be more familiar with its more common name, the Beehive. Galileo was the first person to view the Beehive through a telescope in 1610. He was able to count about 40 stars through his tiny instrument. Today a backyard astronomer should be able to discern many more. As the Beehive is more than 1 degree across it isn't usually possible to see it in one view through a telescope. If you have a pair of binoculars you can get a more complete view of this cluster, so try looking at it through both if you can. This open or galactic star cluster is also found in Charles Messier's 18th century catalogue of deep sky objects as M44. M67, another star cluster, is located near the claw of Cancer's crab.

Clusters of this type are large structures, sometimes hundreds of light years across. Many stars found in galactic or open clusters are very young. Sometimes they are still surrounded by nebulosity, which is an indication that the materials from which they formed are still in the neighborhood. The Beehive is the closest open cluster to us, at a mere 525 light years. M67 is about three times that distance from us. Consider the possibility that our own Sun was once a member of a cluster, but its motion has carried it far from its place of origin in the intervening billions of years. So take a look at Cancer and the Beehive. Even a simple pair of binoculars will do, especially if you can view it from a dark site. Enjoy your observing!

This is the Skywatch Line for Monday, February 26th. Written by Joseph Slomka.

 This is the Skywatch Line for Monday, February 26. The Sun sets tonight at 5:38; twilight ends at 7:15 PM. Dawn breaks at 5:01 tomorrow, and ends with sunrise 6:35.

Tonight's sky is filled with interesting pairings. As the sky darkens look to the southwest. Venus is the most brilliant object in the sky. If observed with binoculars or small telescope, it is a small crescent. Due to its inside orbital track, it actually grows thinner, but bigger and brighter, as it approaches our Earth. Venus has already reached greatest brilliancy, but it will continue to dominate our evening for another month. The three day old Moon lies eleven degrees to Venus' left. The Moon is also a thin crescent, about the same as Venus. In fact tonight, both set together. This pairing makes for great binocular viewing.

The second group is also visible during twilight and the night. This is Jupiter, Saturn and the Pleiades. They can be found overhead. Jupiter is the brighter of the pair. It is easily seen in binoculars, as are its four moons. Once night falls, the four moons can easily be seen. Saturn can also be seen in binoculars, but it only appears as an elongated object; a telescope is required to see the rings clearly. Both planets are in close proximity to the Pleiades, a star group of great beauty when observed in binoculars.

The final paring takes place in pre-dawn skies. The planet Mars has entered the constellation Scorpius and lies above the scorpion's heart. That star is named Antares, one of the most famous stars. It is the brightest star of the constellation, but it is also one of the reddest visible stars. Naked eye observers can easily determine its color. Mars is also known as the "The Red Planet," since its color is also easily seen by eye alone. From ancient times, Mars and Antares have been compared. The ancients naturally thought that these heavenly bodies would be rivals, since they are so similar. In fact, Antares means "Rival of Ares," which is the Greek name for Mars, the God of War.

This is the Skywatch Line for Tuesday, February 27th. Written by Bob Mulford.

The brilliant evening star in the southeast is the planet Venus. Venus is easily visible during evening twilight, befors any of the stars are visible. Venus is only visible in the early evening and sets shortly before 9 PM.

As evening twilight ends, look for the stars of Orion the Hunter, high in the south. Southeast of Orion you can see the constellation Canis Major, the Large Dog. Canis Major includes the star Sirius, which is the brightest of all the fixed stars in the sky. Sirius is nine times brighter than the usual first magnitude star, although it is not nearly as bright as the planet Venus. Sirius is twice the size of our Sun, but there are other stars that are giants and are much bigger than this. The main reason for its brilliance is that it is closer to the Sun than most stars. Sirius is the second closest of the naked eye stars to the Earth. The combination of a moderately large star that is unusually close by is what makes Sirius outshine any other star in the night sky.

The name Sirius means "Dog Star". It is also referred to as the "Scorching One", because the summer months occur when Sirius rises with the Sun. Sirius was known as the "Nile star" to the ancient Egyptians; its annual appearance just before dawn at the beginning of summer heralded the coming rise of the Nile River, upon which Egyptian agriculture depended. To the Romans, however, the star was much more sinister. The ancient Romans were very impressed with the brilliance of Sirius, and they believed that, when Sirius was in the same part of the sky as the Sun, the heat from Sirius combined with the Sun to cause the hot weather in the Summer. Today we know that all the stars are much too far away to heat the Earth. Never-the-less, we still speak of the "dog days of Summer", an expression which comes from the fact that the August Sun is near the location of Sirius, the Dog Star, in the sky.

Sunset tonight occurs at 5:47 PM, and evening twilight ends a little before seven. Sunrise on Wednesday is at 6:37 AM.

This is the Skywatch Line for Wednesday, February 28th. Written by John Shroer.

Tonight's sky features three planets, the bright constellations of winter, and a constellation with the promise of Spring.

Located in the southwestern sky near the growing crescent Moon is the third brightest object in the night sky. Named the "Evening Star", Venus will out shine all other celestial objects present in the current sky.

Located nearly overhead in the evening sky you will find Jupiter and Saturn, the other two planets now visible. Jupiter is the brightest of the pair, located in the constellation of Taurus the Bull. Jupiter will have a clear white light, while Saturn will appear half as bright with a distinctive yellow hue.

Both Jupiter and Saturn are near the star cluster called the Hyades. This "V" shaped group of stars forms the face of Taurus, and features the bright golden colored star Aldebaran, the eye of the Bull. Tonight, Aldebaran, Jupiter, Saturn, and the Moon form a curving line in the sky.

Look to the eastern sky for the constellation Leo the Lion. Leo features a backward question mark that forms the head and mane of the king of beasts. Leo was known as the Herald of Spring, for this constellation rises in the eastern sky near the end of Winter.

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