The Dudley Observatory

Skywatch February 2008
(newest at top)

This is Dudley Observatory's Skywatch Line for Friday, February 29, through Sunday, March 2, written by Alan French.

The Moon was at last quarter late Thursday night, so the Moon will not rise until well after midnight over the weekend and most of the night will be dark and moonless. Early in the evening, just after the last remnants of twilight have vanished, the constellations of winter are toward the south. This would be a good weekend to learn your way around these distinctive star patterns, or reacquaint yourself with old friends.

The easiest way to learn the brighter stars and constellations is with a planisphere. A planisphere has a wheel that shows all the stars possibly visible in our skies, with outlines of the constellations. This wheel fits inside a sleeve, and a window shows what stars are visible at any particular time on any night of the year. The wheel just has to be turned so that the date on its outside matches the time on the window.

Planispheres are often available at bookstores, or perhaps you have one sitting, forgotten, in a drawer somewhere. (Just make sure it applies to 43 degrees north latitude.) If you don't have one, a quick and easy project is to make your own. You can download the two printed pieces you need from the web, print them, and follow the simple instructions included. For the planisphere “kit,” visit www.lhs.berkeley.edu/starclock/skywheel.htm <http://www.lhs.berkeley.edu/starclock/skywheel.htm> and print out the parts and instructions for Uncle Al's Skywheel. If your family is going to join you learning the stars, I suggest a planisphere for each person.

One problem using a planisphere is maintaining your night vision. As you may have noticed, it takes your eye 15 to 20 minutes to get used to the dark, and more stars are visible once you are dark adapted. If you use a regular flashlight to look at your planisphere, you will lose your night vision, and have to start getting used to the dark all over again. The solution is to use a dim red flashlight. It should be just bright enough to read the planisphere when you are dark adapted. You can cover a flashlight with red plastic, tissue paper, thin paper, or nail polish to make your own astronomer's flashlight.

To use your plansisphere, set it so the time and date correspond to when you are out under the stars. Note there are compass directions – north, west, south, and east - written around the outside of the planisphere. If you are looking south, hold “south” at the bottom. If you decide to explore the northern sky, hold “north” at the bottom.

Early risers on Monday will have a chance to see the International Space Station and a pretty paring of the Moon and Jupiter.

The ISS will be moving out of the Earth's shadow, low in the southwest, and will first appear near Spica, the brightest star in the constellation Virgo, at 5:26:22 AM. It will be highest at 5:28:39 when it will be 64 degrees above the southeast horizon, and will vanish below the east northeastern horizon at 5:31:31. The path of the ISS passes below Hercules and Lyra, and then moves down through the lower part of Cynus, the Swan.

After watching the ISS look toward the southeast. You'll see a pretty crescent Moon with bright Jupiter about ten degrees above and somewhat to the right of it.

The weather cooperated with observers for the total lunar eclipse last Wednesday. The sky was clear and transparent. Just before the Full Moon began to enter the Earth's shadow, its brightness had lightened the sky so that only the brightest stars were visible, and the fresh snow cover on the ground, reflecting the moonlight, made it seem almost as bright as day. As the Moon began to enter the Earth's shadow, the sky slowly darkened until, at full eclipse, faint stars and even the Milky Way became visible, while neighbors standing around the telescope became spectral shadows. Then, just as the Moon's limb began to emerge from Earth's shadow and brighten as it reentered the sunlight, clouds moved in to obscure the view. Nevertheless, observing the first half of the eclipse was a splendid success.

Now that the Moon is nearing last quarter, and not rising until midnight, the early evening is very dark for observing the bright constellations in the south. The familiar form of Orion, described in our February 13 Skywatch line, is especially inviting. The stars in Orion appear bright, not because they are close, but because they are so large and luminous. For example, the three belt stars, all about magnitude 2, range in distance from 800 to l,000 light years away. Rigel, the blue-white star in Orion's foot, lies 820 light years away and shines at a dazzling zero magnitude. Betelgeuse, the brilliant ruby-tinged star in Orion's shoulder, is 520 light years away and is so large that if placed at the center of our Solar System, it would occupy the space almost out to the orbit of Jupiter. The orbits of Mars, Earth, Venus and Mercury would all be inside the star.

Probably the most stunning sight lies in Orion's sword, the three fainter stars that hang down in a line below the three brighter belt stars. Careful observation by eye suggests that the middle star in the sword is rather fuzzy. The view opens up in binoculars or a small telescope to reveal that the three stars are actually groupings of stars, with the central star appearing as a cloud that appears to be swirling around in some interstellar wind. This object, known as the Great Orion Nebula and designated as M42, is indeed a gargantuan cloud of gas and dust which is in the process of gravitationally collapsing to form brand new stars -- a stellar nursery. At the core of the cloud is a tight cluster of newly formed stars known as the "trapezium". These stars are very hot and emit powerful ultraviolet radiation which causes the surrounding gases to glow with a faint green light. The radiation has also blown a hole in the cloud so that large telescopes, such as the Hubble, can peer deep into the cloud and see new stars in the process of being born -- a remarkable sight!

This is the Skywatch Line for Monday and Tuesday, February 25th and 26th.
by Joe Slomka

The Sun sets at 5:37 PM, with night falling at 7:13. Dawn breaks at 5:20 AM; sunrise takes place at 6:37.

As twilight deepens, three bright objects dominate. The bright star Sirius blazes low in the southeast. Mars appears above Sirius. Now that it is well past closest approach, Mars is much smaller in our binoculars and telescopes. Only the largest telescopes clearly discern surface features.

Saturn appears low in the East. Saturn reached opposition yesterday. This means that the Ringed Planet rises about sunset and sets about sunrise. This is prime time for observation. Besides its rings, Saturn has about sixty moons, most seen only in large professional telescopes. However, amateur observers can see five. Astronomical almanacs, magazines and websites provide diagrams showing their position on any night.

Saturn is the highlight of any star party. First time viewers simply cannot believe that such a beautiful object exists. Although known from antiquity, Galileo first observed Saturn telescopically and could not understand what the rings were. Dutch astronomer Christian Huygens spoke of Saturn’s “Ring,” a solid ring. French astronomer Cassini discovered the first of several lanes. We now know that the rings consist of icebergs that orbit the planet, and are kept in place by swarms of “shepherd moons." Since Saturn is about a third smaller than Jupiter and almost twice as far, it would be much dimmer if not for the rings. In fact, when the rings appear edge-on, Saturn is noticeably dimmer. Jupiter, Uranus and Neptune also have rings, which are visible only to space probes.

The Moon rises before Midnight. Tuesday's dawn finds it between Virgo and Libra; Wednesday finds it at the bottom of Libra. It appears approximately seventy percent illuminated.

Also at Dawn, Jupiter rises above the handle of teacup-shaped Sagittarius. Venus and Mercury rise almost simultaneously. These bright planets are about a degree apart, low in the East. Mercury is the topmost and appears small and about half illuminated. Venus is much brighter and almost "full." This is the first of five Venus-Mercury conjunctions taking place this year.

Clear Skies
Joe Slomka

This is Dudley Observatory's Skywatch Line for Friday, February 22, through Sunday, February 24, written by Alan French.

The Moon was Full this past Wednesday, and area residents were treated to a total lunar eclipse under clear skies. The next total lunar eclipse visible from here will occur during the early morning hours on December 21, 2010.

The weekend sky will be dominated by a waning gibbous Moon. The Moon will rise at 7:23 PM Friday night, 8:38 Saturday night, and not until 9:43 Sunday night. Serious skywatchers will enjoy an hour of dark skies Friday, a little over two hours on Saturday, and more than three hours between the end of evening twilight and moonrise on Sunday night.

Two planets grace the evening sky. Mars, which will be very high in the southern sky at 7:30 PM, and Saturn, which is low toward the east. Although its brightness has been fading as Earth pulls ahead of and away from Mars, its reddish hue should make identification easy. Look toward the south and then look upward until you are almost looking overhead. Mars now appears only about 9.5 arc-seconds in diameter – smaller than the 10 arc seconds required for serious telescopic observation and the detection of fine details.

Saturn is always a telescopic treat, and virtually any telescope magnifying thirty times or more can show the planet's lovely rings. Through a four to eight inch telescope the planet is a lovely sight. Although you can look at Saturn anytime after dark, the best views will be just after midnight when Saturn is highest and you are looking through the least possible thickness of image distorting atmosphere.

As Saturn makes its 29 year journey around the Sun our view of Saturn's rings slowly changes. They go from “wide open,” when tilted to their maximum of about 27 degrees, to edge one where they disappear from view in many telescopes. Right now they are tipped only about eight degrees. Next year we will have a chance to see them – or not see them – when they are edge on.

If you are up 45 minutes before sunrise and have an excellent view to the east southeast you'll be able to watch rapidly sinking Venus pass Mercury over the next several days. Look toward the southeast at 6:00 AM. Bright Jupiter will be almost 18 degrees above the southeastern horizon. To the lower left of Jupiter, twenty five degrees away, you should see brilliant Venus (keep in mind that a fist held at arm's length spans ten degrees across the knuckles). On Saturday morning Mercury will be 2.7 degrees to the left of Venus and slightly higher in the sky. By Sunday morning Venus will have moved lower in the sky, and Mercury will be closer and to the upper left of Venus. Monday morning will find the pair only 1.2 degrees apart. By the middle of next week Venus will be almost directly below Mercury.

As the Earth sails serenely along its orbital path around the Sun, the Sun casts a dark umbral shadow of Earth that extends for almost a million miles into space. For the billions of people who inhabit the Earth, passing through this shadow is no challenge at all. Once each day, the rotation of the Earth carries our western horizon relentlessly upward until it overtakes and finally obscures the Sun in an event that we call sunset. As soon as the last bit of the Sun drops below the horizon, we enter the Earth's shadow. Interestingly, the sky does not become dark instantly because our atmosphere of gas, moisture, dust particles, etc., extends several hundred miles above us and continues to reflect sunlight down to us for a short, slowly darkening period known as twilight. Within a couple of hours, twilight ends and we enter the fully dark, umbral shadow of the Earth for a period which we call the night.

We are currently in one of the two eclipse periods which occur each year when the alignment is close enough for the Full Moon to pass straight through the Earth's shadow. It will do just that tonight, Wednesday. After rising in the east at sunset, the Moon will first enter the Earth's faint penumbral shadow at 7:36 p.m. This is not usually noticeable. An hour later, at 8:43, the Moon will encounter the edge of Earth's much darker umbral shadow. As the Moon slowly proceeds into the shadow, notice that the edge of the Earth's shadow is round. 2,500 years ago, Greek astronomers noted this, and declared that the Earth must be a sphere because it casts a round shadow from any direction. At 10:00 p.m., the Moon will be fully engulfed by the Earth's shadow, but it will not be completely dark. A pale, coppery-red light seems to illuminate it. In 1618, Johannes Kepler, in his treatise "Epitome", explained that an observer on the Moon would see the large disk of the Earth covering the Sun, but the Earth's atmosphere would act as a lens to refract the red rays of the Sun onto the Moon's surface. The Earth would appear as a black disk with a bright reddish ring of light around it.

In binoculars, the Moon, at full eclipse, loses its usual "bright disk" appearance and is revealed, in a startling 3-dimensional aspect, as an obvious sphere. By 10:50 the Moon will begin to emerge into the brighter penumbral shadow and resume its familiar bright Full Moon aspect. Now we only need to figure out how to keep the clouds away.

This is the Skywatch Line for Monday and Tuesday, February 18th and 19th.
by Joe Slomka

The Sun sets at 5:30 PM, with night falling at 7:05. Dawn breaks at 5:12 AM and ends with sunrise at 6:47.

Three bright objects greet us as the Sun sets. Monday night finds the Moon moderately high in the southeast; Tuesday the almost "full" Moon appears to the left of the star Sirius, the second brilliant object in the twilight. The Moon lies less than a degree from the Beehive star cluster. In fact, the Moon occults, or eclipses, some Beehive stars between 3 AM and 4:30 AM Tuesday morning. The Moon's brilliance may wash out some of the dimmer stars, but binoculars or telescope should permit viewing the event.

Mars completes the trio, high in the southeast. Mars is much dimmer than either the Moon or Sirius. Mars still hovers about four and a half degrees away from the Crab Nebula, a telescopic supernova remnant. It also provides a marker for several nearby star clusters. Mars sets at 3:37 AM.

By nightfall, Saturn remains less than six degrees from Regulus, the brightest star in Leo, and closing in. The Ringed Planet also recedes from the trio of galaxies that it accompanied beneath Leo's belly.

First light sees the Moon low in the West, and Saturn high in the southwest. Jupiter rises an hour after Mars sets, and is well up by Dawn. Early risers can use binoculars to see the four Galilean moons.

Venus rises during Dawn and is shortly followed by Mercury. This elusive planet shines about six and one half degrees to Venus' left. Venus is the brightest, while Mercury pales in comparison. In a telescope, Mercury is about thirty percent illuminated, compared to Venus, which is approximately eighty-nine percent lit. Both planets display crescents for the observer to compare and contrast. Monday finds Mercury stationary; tomorrow it begins a slow slide into the Sun's glare.

The Albany Area Amateur Astronomers hold their monthly meeting on 7:30 PM Tuesday at the Schenectady Museum and Planetarium. The main topic is the annual Winter Star Party, recently held in the Florida Keys.

This is Dudley Observatory's Skywatch Line for Friday, February 15, through Sunday, February 17, written by Alan French.

The Moon was at first quarter last Wednesday and will be Full this coming Wednesday night, when we will be treated to a total lunar eclipse. This weekend the evening sky will be dominated by a waxing gibbous Moon. On Friday night the Moon will be close to Mars. If you look high toward the south at 7:00 PM you'll see reddish Mars to the lower left of the Moon. The Moon's eastward motion among the stars will gradually move it closer to Mars, and they will be just over one and a half degrees apart at 3:00 AM Saturday morning. They will be very low in the west northwest and less than an hour from setting.

Mercury, Venus, and Jupiter are all visible just before sunrise. Venus is rapidly sinking lower in the morning sky, and moving closer to Mercury each day. You can look for the trio in the east southeast any morning this weekend, but you'll need a good view down to the horizon, free of clouds and haze and natural obstructions, to catch sight of Mercury and Venus. If you do have a good view, Venus will be easy to spot by eye, but you may find binoculars helpful in sighting Mercury.

Look for the three planets at 6:00 AM. Jupiter will be the brightest “star” low in the southeast, eleven degrees above the horizon. Jupiter is in the constellation Sagittarius, the Archer. An obvious pattern of stars in this bright constellation form a teapot, with the spout to the right and the handle toward the left. Jupiter is above and left of the handle.

Venus is well to the lower left of Jupiter, brighter than the gas giant, and only four degrees above the horizon. Its brightness make it hard to miss. Mercury is to the lower left of Venus, and just above the horizon. Each morning finds Venus a bit lower, and Mercury a bit higher, so Mercury will be easiest to spot on Monday morning. As the light of the coming dawn brightens, Mercury moves higher into the sky, and may become easier to spot, but it is battle between the light of first magnitude Mercury and the morning twilight.

On Friday night the International Space Station will make a nice pass over the Capital District. With the space shuttle Atlantis docked, the ISS is even brighter than normal. It will appear at 6:16:34 PM coming up from the west northwestern horizon. The ISS will be highest when it reaches 77 degrees above the southwestern horizon at 6:19:23, and will vanish in the southeast at 6:22:12. The ISS will be brighter than the brightest stars, and it should be easy to spot as it glides among the stars – weather permitting, of course!

We have reached midwinter and the glittering spectacle of the bright winter constellations are fully displayed high in the southern sky at nightfall. To appreciate this marvelous display, dress in many layers of warm clothes. Don a warm hat, insulated gloves and boots, and sit in a comfortable lawn chair, facing south. For the first few minutes, allow your sight and mind to be overwhelmed by simply sweeping your unaided eyes back and forth across the field of bright objects. While the summer skies are distinguished by having three bright stars to form the "summer triangle", the winter skies boast seven stars to enclose the brightest collection of stars in such a small area anywhere in the skies visible from the Earth. These seven stars describe what is often called the "winter oval" or the "winter hexagon". Why refer to a loop of seven stars as a hexagon? Because two of the stars, Castor and Pollux, representing the heads of the Gemini twins, are close enough together to be considered as marking one corner of the hexagon. To pick out the hexagon, first locate Orion, the Hunter, one of the most familiar of all constellations. It is marked by a straight line of three evenly spaced bright stars that form the belt of the hunter. Two bright stars above the belt mark Orion's shoulders, and two more bright stars below the line mark the hunter's feet. Three fainter stars in a vertical line mark the sword hanging from Orion's belt.

From Sirius, move northeastward until you encounter another very bright white star named Procyon, in the constellation Canis Minor (the Little Dog). Moving northward toward Polaris the North Star, you'll run into the close twins, Castor and Pollux, mentioned above. From Pollux, the brighter of the two, move directly overhead to the brilliant yellow star Capella, part of the pentagon asterism that identifies the constellation, Auriga, the Charioteer. From Capella, proceed downward, or south, to the bright reddish star, Aldebaran, the eye of Taurus, the Bull. Continue downward and a bit left to the brilliant blue-white star Rigel in the foot of Orion and thence back to Sirius. Betelgeuse, the supergiant reddish star in Orion's shoulder, is near the center of the just-traced hexagon. This winter, the hexagon includes a bright guest object, the Red Planet Mars, located on a line halfway between Betelgeuse and Capella. Mars forms an almost perfect equilateral triangle with Betelgeuse and Aldebaran to produce the closest gathering of three bright reddish objects anywhere in the night sky.

This is the Skywatch Line for Monday and Tuesday, February Eleventh and Twelfth.
by Joe Slomka

The Sun sets at 5:19 PM, with night falling at 6:57. Dawn breaks at 5:21 AM, and ends with sunrise at 6:56.

The five-day-old Moon shines moderately high in the southwestern sky. Monday night has the Moon within the constellation Pisces; Tuesday finds it in Aries.

Mars glows in the twilight sky and is found between the horns of Taurus. Mars acts as the guide for several deep sky objects. It is only four and a half degrees above the telescopic object M-1, the Crab Nebula. It also is equally distant from M-35, a binocular open star cluster. Several other objects lie in nearby Auriga.

Saturn is also up at nightfall, but is best observed around midnight. It also lies within three degrees of several telescopic galaxies.

Jupiter rises a half-hour before Dawn, in the constellation Sagittarius. Jupiter is famous for the four moons that Galileo discovered in 1610. These are easily seen by binoculars in early twilight. However, a would-be observer might be confused on Wednesday morning. Jupiter appears to have a fifth satellite. Actually this outermost “moon” is really a star called Nu-1. Jupiter is now located in a very star-rich area and novice observers may be deceived.

Venus rises after Jupiter. It is far brighter than any star. Venus is about eighty-seven percent illuminated. Venus’ shape is caused by its gradual descent into the Sun’s glare; as a result we see only a part of the planet. Venus loses a degree a day in altitude and separation from once close Jupiter.

If the eastern horizon is unobstructed, Mercury may be spotted. Mercury is beginning a late winter dawn appearance. If you fail to spot it, it becomes easier as February progresses. Messenger, its first space probe since the 1970’s, recently visited Mercury. Once considered dead like the Moon, scientists discovered Mercury has a different history. The planet is apparently shrinking! It also has a magnetic field. Messenger flew past Mercury, and will make one more pass before orbiting the planet to make detailed explorations.

The New Moon is defined as that point in the Moon's orbital travel when it passes between the Earth and the Sun. Likewise, the Full Moon occurs when the Earth passes between the Sun and the Moon, and the Sun and Moon are opposite each other in the sky. An eclipse of the Sun can occur only at New Moon as the Moon passes between the Earth and the Sun, blocking out the Sun, and an eclipse of the Moon can occur only at Full Moon as the Earth passes between the Sun and the Moon, and casts its shadow on the Moon. Because of the tilt of the two orbital planes relative to each other, the Moon will spend half of its time above the Earth's orbital plane and the other half below. Thus, most of the time, the alignment of the three bodies will be imperfect, so the New Moon will appear to pass a little above or below the Sun, while the Full Moon will pass a little above or below the Earth's shadow and there will be no eclipse or other visual effect in either case.

This is the Skywatch Line for Monday and Tuesday, February Fourth and Fifth.
by Joe Slomka

The Sun sets at 5:12 PM, with night falling at 6:45. Dawn breaks at 5:29 AM; the Sun rises at 7:06.

As the Sun sets, only Mars is easily visible. The Red Planet glows high in the South. Mars now is fading and shrinking. By twilight’s end, it hovers between Taurus’, the Bull’s, horns. Last month, Mars stopped its westward motion. Now, it slowly picks up speed and heads east. Telescope users can find the Crab Nebula by looking four degrees below Mars.

While Mars attracts attention high in the southwest, Saturn is rising. The hours after midnight are the best time to observe Saturn, its moons and ring system.

Dawn skies find two bright planets low in the East. Jupiter rises first, followed by Venus about fifteen minutes later. Last month, Venus rose first, but now it is ending its winter apparition. Jupiter passed Venus and climbs higher daily. While Saturn is famous for its ring systems, Jupiter also has rings, as does Uranus and Neptune. However, it took the Hubble Telescope to discover Jupiter’s tenuous rings.

A very thin Moon crescent joins Jupiter and Venus in the East. Use binoculars to find it very low in the steadily brightening sky.

As the Sun sets, the giant constellation Orion appears. Canis Major, the Big Dog, follows at Orion’s heels. Sirius is among the closest stars to our Solar System, at 8.6 thousand light-years. Although stars seem fixed in our sky, they are actually traveling in different directions and different speeds. Sirius is one of these. In sixty thousand years, it will approach to 7.8 light-years and increase its brightness only marginally. Sirius is not a solitary star; it has a companion, appropriately nicknamed “The Pup.” This star closely orbits Sirius once every fifty years. This star is much smaller and dimmer than the primary. Sirius B is about the Earth’s size, but has the Sun’s mass. Sirius B, “The Pup’s” formal name, is still a bit too close. In a few years, amateur telescopes may spot The Pup, once Sirius’ brilliance is blocked.

Dudley Observatory's Skywatch Line for Friday, February 1, through Sunday, February 3, written by Alan French.

Just over one-half degree separated Venus and Jupiter on Friday morning. Although they are now moving apart as Venus moves eastward toward the Sun, the will remain a pretty pair for a while. On Sunday and Monday mornings they will be joined by the thin crescent old Moon, and form a beautiful trio in the predawn skies.

Look for Jupiter and Venus any morning this weekend toward the southeast one hour before sunrise. The Sun now rises at 7:08 AM, so look just after 6:00. On Saturday morning Venus and Jupiter will be just over one degree apart, with Venus to the left of Jupiter. A pretty crescent Moon will be well to their right and higher.

By Sunday morning Venus and Jupiter will be two degrees apart, and Venus will have moved lower in the sky and will be to the left of and below Jupiter. The Moon's eastward motion among the stars will have brought it closer to our planetary duo.

Monday morning at 6:00 AM will find a close trio of Venus, Jupiter, and a very slender old Moon. Venus and Jupiter will be three degrees apart, and the Moon will be below the pair. The Moon will be just above the horizon, so you'll need a good view to the southeast, unhindered by trees or buildings. If wait too long after 6:00, the Moon will have set.

The International Space Station, or ISS for short, will pass right over the Capital District early Sunday evening. With its large area, the ISS is the brightest satellite in the night sky, outshining all the stars. We will be giving some of the times for Sunday night's appearance in hours, minutes, and seconds.

On Sunday evening, look for the ISS, appearing as a bright star, moving up from the southwestern horizon at 5:16 PM. It will be highest at 5:18:39. After reaching its highest point it will move through the constellation Perseus, and then pass close to Capella, the brightest star in Auriga. The ISS will vanish below the east-northeastern horizon at 5:21:29.