Skywatch Line for Friday, April 27 through Sunday, April 29, 2018

This is Dudley Observatory’s Skywatch Line for Friday, April 27 through Sunday, April 29, written by Sam Salem.

On Friday, the Sun rises at 5:56am and sets at 7:52pm; the waxing gibbous Moon sets at 5:04am and rises at 5:23pm. Full Moon occurs on Sunday at 8:58pm. The Full Moon in April is the Pink Moon, from the pink flowers “phlox” that bloom in the early spring. Other names for this full Moon include Sprouting Grass Moon, Fish Moon, Hare Moon, and the Old English/Anglo-Saxon name is Egg Moon. On Friday and Saturday, the Moon is in front of the constellation Virgo and close to Spica, Virgo’s brightest star. However, the glare of the waxing gibbous Moon may make it difficult to see Spica these next few nights.

Venus, at magnitude -3.9, is visible shortly after sundown, and doesn’t set until around 10:00pm. Jupiter, shining at magnitude –2.5, appears in the east-southeast around 9:00pm. Jupiter is highest at around 2:00am. Saturn, at magnitude 0.4, rises a little before 1:00am, while Mars, at magnitude –0.3, is up an hour later. Saturn’s rings are an easy target even in a small telescope. Mercury is at its greatest western elongation of 27 degrees west of the Sun on Sunday. Due to the shallow angle the ecliptic makes with the horizon at dawn at this time of year, Mercury is a challenging find even with binoculars.

Double stars are telescopic sight relatively immune to lunar light pollution this full-Moon weekend. You can split Regulus, the leading light in Leo, in a small scope even at low magnification. Regulus’ companion, at 8.2 magnitude, lies 176 arc seconds northwest of the 1.4 magnitude main star. Next aim your telescope north right at the pole star, Polaris. Alpha Ursae Minoris is also a striking double star that spans a range of brightness. However, the Polaris pair isn’t nearly as widely separated as Regulus’. The 2.1-magnitude pole star is accompanied by a 9.1 magnitude companion, 18.6 arc seconds away. That close separation, together with the brightness difference, makes spotting the secondary star such a delight.

Saturday marks the birthday of astronomers Francis Baily and Jan Oort.
Born on April 28 1774, the English astronomer Francis Baily contributed in describing the striking optical effect of what is now called “Baily’s Beads”. The optical effect is an arc of bright spots briefly seen during solar eclipse, immediately before and after totality. It is due to the light shining through the Moon’s irregular surface features. Baily also contributed to revising the British Nautical Almanac and several star catalogs.
Born on April 28 1900, the Dutch astronomer Jan Hendrik Oort was one of the most important figures in 20th-century efforts to understand the nature of the Milky Way Galaxy. Oort measured the rotation of the earth’s galaxy and hypothesized an “Oort Cloud” of predominantly icy planetesimals proposed to surround the Sun to as far as somewhere between 50,000 and 200,000 Astronomical Units (0.8 and 3.2 light years). In 1927, Oort analyzed motion of distant stars, found evidence for differential rotation and founded the mathematical theory of galactic structure. After World War II, he led the Dutch group that used the 21-cm line to map hydrogen gas in the Galaxy. In 1950, Oort proposed the now generally accepted model for the origin of comets.

Skywatch Line for Wednesday, April 25th, and Thursday, April 26th, 2018

This is the Dudley Observatory Skywatch Line for Wednesday, April 25th, and Thursday, April 26th, written by Louis Suarato.

The 80% illuminated, waxing gibbous Moon rises at 3:16 p.m. Wednesday. Astronomical Twilight begins at 8:56 p.m., when the Sun is 12 degrees below the horizon. At this time it is dark enough to see most stars and other celestial objects. This is when you’ll notice the Moon is positioned between the constellations Leo and Virgo, and between their brightest stars, Regulus and Spica. Try to catch Venus when is well above the horizon, and before it sets at 10:01 p.m. in the west-southwest. Venus will be 4 degrees to the left of the Pleiades star cluster. Our neighboring planet, and the “Seven Sisters” should be able to be seen in the same field of view through most binoculars, and should be an attractive photography image.

About 25 degrees above Venus and the Pleiades, is the constellation Auriga. Auriga is the 21st largest constellation best seen from October through April. Auriga contains several bright objects, including Capella, the third brightest star in the northern celestial hemisphere, and the northernmost first magnitude star. Capella is comprised of 4 stars in two binary pairs. Two are yellow giant stars, which orbit each other every 104 days. The second pair are small, faint, cool red-dwarf stars. Capella is 42.9 light-years from our Sun. Auriga is also the home of three bright open star clusters, M36, M37, and M38. M36 is a cluster of about 60 stars, shining from magnitudes between 9 and 14. M36 is 4,100 light-years away. Four degrees to the west of M36 is open cluster M37. M37 is the brightest and largest of the three star clusters. This cluster consists of over 500 stars, with about 150 above 12th magnitude in brightness. M38, also known as the Starfish Cluster, can be found 3 degrees to the upper right of M36. M38 is the faintest of the three open clusters. All three open star clusters can be seen through binoculars and small telescopes. When viewing these star clusters, you are looking away from the Milky Way Galaxy’s center. Their elliptical orbit takes 219.3 million years, coming as close as 19,600 light-years to the galactic center, and as far as 30,700 light-years.

Jupiter rises at 8:55 p.m. in Libra. At 1:22 p.m. Wednesday, Jupiter’s largest moon, Ganymede, is eclipsed by the planet. At 9:21 Thursday night, Europa is eclipsed by the solar system’s largest planet. Saturn rises in Sagittarius 47 minutes after midnight, followed by Mars about an hour later. Saturn now shines at magnitude 0.38, while Mars has brightened to magnitude -0.26.

Skywatch Line for Monday and Tuesday, April 23rd and 24th, 2018

This is the Skywatch Line for Monday and Tuesday, April 23rd and 24th.

The Sun sets at 7:46 PM; night falls at 9:33. Dawn begins at 4:13 AM and ends with the Sun rising at 6 AM.

The Moon and Venus are main attractions in the evening. Monday’s 9-day-old Moon blazes near Leo’s front paw, shines with minus 10th magnitude and appears about 63% illuminated. Tuesday’s Moon is slightly brighter, and fuller, about 74% lit. Tuesday’s Moon lies between Leo’s legs and belly. Tuesday, the Moon sets at 3:22 AM, Wednesday at 3:59 AM.

Venus, moderately low in the West, gleams with minus 4th magnitude and appears about 90% lit. Binocular and naked eye viewers will see the Pleiades star cluster about 3 ½ º above Venus on both nights. Venus sets about 10 PM.

Jupiter rises at 9 PM, during Astronomical Dusk. At minus 2nd magnitude, it is the brightest object in Libra, low in the southeast. By Midnight, it is about 25º high; providing telescopic detail of its intricate cloud systems. In addition, Tuesday’s Midnight affords telescopic views of the Great Red Spot (an Earth-sized storm). Wednesday permits views of the moon Europa’s shadow beginning to cross Jupiter’s face at 2:10 AM, followed by the moon itself at 2:53 AM. The shadow leaves Jupiter at 4:26 AM, followed by Europa at 5:01 AM.

Dawn sees Jupiter accompanied by Saturn, in Sagittarius, which rose at 12:51 AM. Saturn shines at zero magnitude and appears about 17 arc-seconds in size. The Ringed Planet lies about 49º east of Jupiter. Saturn is surrounded by several star clusters, easily seen with binoculars. Mars, also in Sagittarius, rises about 1:43 AM, about 11º east of Saturn. It shines at minus zero magnitude, about 88% illuminated and about 10 arc-seconds in size. In pre-dawn hours it is well placed for observation. Six degrees above Saturn, Asteroid 4Vesta, also in Sagittarius, shines with 6th magnitude, but appears a tiny 0.4 arc-seconds is size. It rises at 12:10 AM and is highest at 5:04 AM. However, 4Vesta requires detailed finder charts, found in astronomy magazines and websites.

Neptune, in Aquarius, returns in the brightening sky. It rises at 4:16 AM, glowing at 8th magnitude, about 2.2 arc-seconds in size and about 13º above the eastern horizon. As the month progresses, it should become easier to find. Mercury, in Cetus, rises at 5:11 AM, shining at 0.8 magnitude, about 35% crescent. However, it is about 3º high and presents a challenge for the early observer. Even when at its highest on April 29th, it is less than 10º in altitude.

Last week, we discussed Saturn’s moon Iapetus; today, let us consider another Saturnian moon – Enceladus. Jupiter owns 67 moons; Saturn commands a fleet of 62 satellites, 8 of which are visible in amateur telescopes. Sir William Herschel discovered Enceladus in 1789 and named it for one of the mythical Giants that fought the Greek gods. Enceladus is medium sized, about 504 KM (313 mi) in diameter and orbits Saturn in 1.37 days. NASA’s Cassini space probe revealed an ice-covered world, with strange blue “tiger stripes.” Planetary scientists soon realized that there was an ocean beneath the ice. They witnessed water spouting from those “stripes.” Like Jupiter’s moon Europa, Enceladus is being squeezed by Saturn’s huge gravity and heating the interior, causing the venting. As Cassini’s 12-year mission wrapped up, NASA dared to have Cassini make close passes on several moons. A pass through Enceladus’ vapor revealed salt and silica nanoparticles, which were picked up by the water’s contact with hot interior rocks. Hot rocks should leach oxygen from seawater leaving molecular hydrogen gas; a subsequent flyby of Enceladus verified its existence. Molecular hydrogen creates a chemical imbalance that may be conducive to life. Astrobiologists are not claiming life, but only the conditions that may make it possible.

Skywatch Line for Friday, April 20 through Sunday, April 22, 2018

This is Dudley Observatory’s Skywatch Line for Friday, April 20 through Sunday, April 22, written by Sam Salem.

On Friday, the Sun rises at 6:06am and sets at 7:44pm; the waxing crescent Moon rises at 9:41am and sets at 12:55am on the following day. First quarter Moon occurs on Sunday at 5:46pm. The first quarter Moon passes 1.5 degrees south of the Beehive Cluster (M44) late Sunday night. Lunar X near crater Werner is visible in all of North America at 5pm on Sunday. The Lunar X, also known as the Werner X, is a clair-obscur effect in which light and shadow create the appearance of a letter ‘X’ on the rim of the Blanchinus, LaCaille and Purbach craters. Refer to a lunar map to help you locate the craters. The X is visible only for a short time before the first quarter Moon, slightly below the lunar terminator.

One hour after sunset, watch Venus gleaming at magnitude –3.9 among the bright stars of the winter sky in the west. Climbing higher into view at nightfall are the comparatively dim constellations of spring and the prominent stars Regulus, Spica and Arcturus. Jupiter, at magnitude -2.5, joins a little before 10:00pm. Jupiter reaches its height, due south, around 2:15am. Jupiter shifts over to the southwest an hour before sunrise, while Mars, at magnitude –0.1, and Saturn, at magnitude 0.4, approach the meridian. The two planets reside in constellation Sagittarius.

On Sunday, the Lyrid meteor shower peaks in the predawn hours. The shower’s radiant point is just right of the blue-white star Vega, the brightest star in the constellation Lyra, the Harp. Vega rises above the horizon little after 8pm. It climbs upward through the night. The higher Vega climbs into the sky, the more meteors you’re likely to see. Under good conditions you can expect to see about 10 to 15 meteors per hour at its peak. Fortunately this year, the rather wide waxing crescent moon on the Saturday and Sunday mornings, and the last quarter Moon on Monday morning will set before the Lyrid shower presents its greatest display in the predawn sky.

The Moon rides high on the ecliptic over this weekend, which makes this a good time to use a telescope to explore the crater trio of Theophilus, Cyrillus, and Catharina. These intriguing formations are among the most eye-catching on the Moon, especially when the terminator is nearby, as it is on Friday evening. All three craters are big, ranging in size from 98 to 110 kilometers across, and positioned on the western shore of Mare Nectaris. Notice how the Catharina’s wall is slightly more worn down and less distinct than those of its neighbors. Look at how Catharina’s floor is peppered with small craterlets. Throughout the Moon’s history a steady rain of impacts has battered its surface.. As a result, the older a given feature is, the less well defined it is, and the more heavily cratered it tends to be. The greater number of little craters on the floor of Catharina indicates it’s older than its neighbors. Refer to a lunar map to help you locate the Moon craters.

Saturday is the “spring” International Astronomy Day. Astronomy Day is a worldwide event observed each spring and fall. Local astronomical societies, planetariums, museums, and observatories will be sponsoring public viewing sessions, presentations, workshops, and other activities to increase public awareness about astronomy and our wonderful universe. The Dudley Observatory offers a number of activities from 11am to 9pm that day. Check the Dudley website link below for more information.

National Astronomy Day 2018

Skywatch Line for Wednesday, April 18th, and Thursday, April 19th, 2018

This is the Dudley Observatory Skywatch Line for Wednesday, April 18th, and Thursday, April 19th, written by Louis Suarato.

The 12% illuminated, waxing crescent Moon sets at 10:38 Wednesday night. After sunset, the Moon forms a triangle with the Pleiades star cluster and Venus. Look about 12 degrees north of the Moon for the Pleiades, and 8 degrees below the Pleiades for Venus. All planets, with exception of Venus, rotate clockwise. Venus rotates counter-clockwise, and unlike other planets, the Sun rises in the west and sets in the east. Venus rotates at a relatively slow speed of 4 miles per hour, or once every 243 Earth days. Venus orbits the Sun once every 224.7 Earth days, making a Venusian day longer than its year. If you were on the surface of Venus, you would experience a sunrise and sunset only once every 1.08 years. Uranus is different than other planets in that it rotates on its side. That means that for 42 years Uranus’ south pole face the Sun, and for 42 years, Uranus north pole faces the Sun. This unique rotation provides each pole with 42 years of continuous sunlight or darkness. Thursday night, the Moon will be 2 degrees below Taurus’ brightest star, Aldebaran.

Jupiter rises at 9:26 p.m. in Libra. Almost simultaneously, Jupiter’s largest moon, Ganymede, is occulted by the planet. Ganymede’s occultation ends at 10:39 p.m. as the moon reappears from behind the pole of the gas giant. Saturn rises at 1:15 a.m. in Sagittarius, followed by Mars 42 minutes later. Before dawn, the two planets are high in the south-southeast. Mars, slightly brighter than Saturn, is on the left. The red and ringed planets are separated by about 10 degrees. Saturn becomes stationary on Wednesday, and begins its retrograde, or westward motion. Saturn is also at aphelion, its furthest distance from the Sun since 1959.

The Albany Area Amateur Astronomers invite you to join them Thursday evening at miSci, beginning at 7:30 p.m., for their monthly meeting. The guest speaker is Dr. E. Bruce Watson, professor of Earth and Environmental Sciences at RPI. Dr. Watson specializes in the geochemistry of deep Earth in the lower crust and upper mantle. His topic will be “Ancient Crystals in the Early Earth”. Dr. Watson is a graduate of the University of New Hampshire and earned his Ph.D. from MIT. Dr. Watson has over 300 publications to his name.


Skywatch Line for Monday and Tuesday, April 16th and 17th, 2018

This is the Skywatch Line for Monday and Tuesday, April 16th and 17th.

The Sun sets at 7:39 PM; night falls at 9:22. Dawn begins at 4:27 AM and ends with the Sun rising at 6:10.

Venus, in Aries, is the brightest object in the darkening western sky. It blazes with minus 4th magnitude, appears about 91% lit and lies about 16º above the horizon. It sets at 9:41 PM.

The one-day-old Monday’s Moon lies 13º below Venus and about 2º above the horizon. It shines with 2nd magnitude and appears as a thin 1º crescent. It sets at 8:23 PM. Binocular and telescopic observers can see this very young Moon if they have an unobstructed horizon. This writer once caught a similarly young moon using both binoculars and telescope. Tuesday’s Moon is brighter, about 5% lit, about 13º high and sets at 9:34 PM.

Jupiter, in Libra, rises about 9:32 PM and blazes at minus 2nd magnitude. It is a best observed at 2:29 AM. Telescopic viewers can see the Great Red Spot (a giant Jovian storm) at 11:19 PM Monday and at 5:06 AM on Wednesday. They can also witness the moon Europa’s shadow begin to cross the planet’s face at 11:36 PM on Tuesday, followed by Europa itself at 12:37 AM Wednesday; Europa’s shadow exits at 1:51 AM Wednesday, followed by Europa at 2:45 AM.

Sagittarius houses three Solar System members. Saturn rises at 1:19 AM, shining with zero magnitude and about 10 arc-seconds in size. Saturn is at aphelion (most distant from the Sun) and also it is stationary in our sky. Note its position. Saturn soon begins retrograde motion, which means that it travels westward. Saturn is also high enough for telescopes to capture its rings and moons.

Mars rises about a half-hour after Saturn. It shines with minus zero magnitude, appears about 10 arc-seconds in size and 88% illuminated. It is best studied before Dawn and large enough to begin to show surface features. Dwarf Planet Pluto, which is too small and faint for most amateur telescopes, lies about 5º east of Mars.

Asteroid 4Vesta is the final inhabitant of Sagittarius. Rising at 12:33 AM, it shines with 7th magnitude about 28º above the eastern horizon. It is best observed at 5:28 AM. However, its small apparent size requires the use of detailed finder charts from astronomical media.

If the astronomer sees meteors streaking from the constellation Lyra, he is witnessing the beginning of the annual Lyrid meteor shower. Although it peaks on April 22nd, meteors may occasionally appear before that date.

Saturn is high in the Dawn sky. Besides the rings, Saturn has sixty-one moons. One of these, Iapetus, has puzzled observers for centuries. Iapetus is bright when it is on one side of Saturn, but markedly darker when on the other.

Recently, two groups of astronomers think they have figured it out. Iapetus is tidally locked to Saturn, just like the Earth’s Moon – showing the same side to the planet. The leading side of Iapetus sweeps up debris from a newly discovered (and invisible to amateurs) ring. Thus, one side looks like it was covered in chocolate dust, while the trailing side is as white as snow (really ice). In addition, the dust, warmed by sunlight, melts the ice beneath, which flows to the trailing side and re-freezes. Iapetus has a 79.3-day orbit and is visible in amateur telescopes. Astronomy programs and websites assist the observer.

Skywatch Line for Friday, April 13 through Sunday, April 15, 2018

This is Dudley Observatory’s Skywatch Line for Friday, April 13 through Sunday, April 15, written by Sam Salem.

On Friday, the Sun rises at 6:17am and sets at 7:36pm; the waning crescent Moon rises at 5:24am and sets at 5:03pm. New Moon occurs on Sunday at 9:57pm.

The winter constellations are crowded into the west during early evening. Venus gleams at magnitude –3.9 and sits roughly 10 degrees above the horizon one hour after sunset. Jupiter, at magnitude –2.4, clears the east-southeast horizon after 10:00pm. Wait a few hours for the planet to gain some elevation before you turn your scope on it. Jupiter reaches the meridian around 3:15am. Saturn is up shortly after 2:00am and Mars joins it some 20 minutes later. The space between the two planets is starting to grow after they have been keeping each other company for the past several weeks. Both planets are located in constellation Sagittarius and are closely matched in brightness. Saturn gleams at magnitude 0.4, while Mars is a little brighter at magnitude 0.1.

This weekend head over to constellation Cancer, the Crab, the faintest constellation of the Zodiac. Cancer, the Crab, lies between the two brightest starts of Gemini, Castor and Pollux, and Leo’s brightest star Regulus. Try to locate the open cluster M44, also known as the Beehive Cluster in Cancer. M44 is a fine binocular object that’s easy to locate. The one-degree-wide clump of stars is parked midway and a little west of a line joining Delta and Gamma Cancri. At magnitude 3.9, Delta is Cancer’s brightest star. Another delightful open cluster is M67. Nicknamed the King Cobra Cluster, M67 is an open cluster located in the constellation Cancer. It can be found roughly halfway and slightly above the imaginary line connecting the bright stars Regulus in constellation Leo and Procyon in constellation Canis Minor. Under a dark sky the little stellar gathering is visible in steadily held binoculars as a fuzzy patch. M67 is one of the oldest known open clusters and the single oldest open cluster listed by Messier in his catalogue. The estimated age of M67 is in the range from 3.2 to 5 billion years. Open clusters are typically younger and the stars tend to disperse over time, usually before they reach this age. For example, the Beehive Cluster M44 is only 600 million years old.
Constellation Cancer is also home to a number of fine double stars, including Iota Cancri. Iota is a striking sight in small telescopes. It features a 4.1-magnitude yellow star contrasting with a 6.0-magnitude blue companion, separated by a generous 31 arc seconds. The two are easily split in any scope used at low power. The double star is located 7 degrees north of the M44, Beehive Cluster.

Saturday marks the 389th. birthday of the Dutch physicist and astronomer Christiaan Huygens who founded the wave theory of light, discovered the true shape of the rings of Saturn, and contributed to the study of the action of forces on bodies., In 1655, Huygens discovered the first moon of Saturn, later named Titan, using a lens he ground for himself. In 1656, he patented the first pendulum clock, which he developed to enable exact time measurement while observing the heavens. Cristiaan Huygens developed theories on centrifugal force in circular motion, which influenced Sir Isaac Newton in formulating his Law of Gravity. Huygens also studied and drew the first maps of Mars. On January 14, 2005, a NASA space probe, named after Huygens, landed on Titan.

Skywatch Line for Wednesday, April 11th, and Thursday, April 12th, 2018

This is the Dudley Observatory Skywatch Line for Wednesday, April 11th, and Thursday, April 12th, written by Louis Suarato.

The 18% illuminated, waning crescent Moon sets at 2:57 p.m. Wednesday. The Moon rises again, 13% illuminated at 4:57 Thursday morning. Mercury follows the Moon, rising 43 minutes later, 20 degrees from the Sun. With a diameter of 3,032 miles, Mercury is smaller than the two largest moons in the solar system. Jupiter’s largest moon, Ganymede, has a diameter of 3,274 miles, and Titan, Saturn’s largest moon, is 3,201 miles wide. Jupiter’s moon, Callisto has a diameter that is only 37 miles smaller than Mercury, and Io is 68 miles smaller. Venus is low in the west after sunset, 22 degrees elongated from the Sun.

Jupiter rises at 9:58 p.m. in the constellation Libra. Two hours after Jupiter rises, the Great Red Spot begins its transit across the face of the planet. This cyclonic storm has been raging on Jupiter for at least 350 years. With winds estimated at 400 miles per hour, the Great Red Spot is two to three times the size of Earth. Only the winds of Uranus, at 560 miles per hour, and those of Neptune, at 1,500 miles per hour, are stronger. Saturn and Mars rise overnight in Sagittarius, now separated by 4 degrees. Earth continues to close on Mars this month, coming to within 79 million miles on April 30th, with the red planet increasing in magnitude to -0.4.

Thursday is the 50th anniversary of the fall of the Schenectady meteorite. On April 12, 1968, at around 8:30 p.m., a meteorite hit a house in Glenville, NY. The 383.3 gram (approximately 10 ounces) meteorite was discovered on April 14th when the owner, Joseph Kowalski noticed the damage to his roof. Kowalski donated the meteorite to the Schenectady Museum, now known as miSci. According to the U.S. Meteorological Society, two other meteorites have been found in, or near, the Capital Region. A .5 ounce meteorite was found in Bethlehem in 1859, and in 1863, a 3.3 pound meteorite was found in Rensselaer County’s Tomhannock Creek.

The Schenectady meteorite will be on display April 21st at miSci for National Astronomy Day.

Skywatch Line for Monday and Tuesday, April 9th and 10th, 2018

This is the Skywatch Line for Monday and Tuesday, April 9th and 10th.

The Sun sets at 7:30 PM; night falls at 9:11. Dawn begins at 4:42 AM and ends with the Sun rising at 6:22.

The twilight sky has only one bright planet – Venus. Located in Aries, the planet shines with minus 4th magnitude, appears a medium size of 11 arc-seconds and is about 93 percent illuminated. Moderately low in the western sky, it sets at 9:23 PM.

Jupiter rises in Libra and is the brightest object in the constellation. Jupiter rises at 10:03 PM, and by midnight, is 17 degrees high in the eastern sky. Telescopic observers can see the Great Red Spot (a giant storm) at 10:34 PM Monday, and at 4:21 AM on Wednesday. They can also, at 11:17 PM on Tuesday, witness the moon Europa’s shadow leave the Jovian surface, followed by the moon itself at 12:29 AM. Jupiter is best observed at 3:00 AM.

Dawn sees Sagittarius as the site of the main attractions. Saturn rises 1:46 AM, shining at 0.5 magnitude, 17 arc-seconds in size and 21 degrees high in the western sky. The Ringed Planet lies about 47 degrees east of Jupiter. Binocular observers can see the rings tilted nearly to maximum – 25.5 degrees. They can also see Saturn 1 degree above globular star cluster M-22, 4 degrees from globular star cluster M-28 and 3 degrees below open star cluster M-25. Telescopic observers can, at 4:00 AM Tuesday, see 5 Saturnian moons clustered about the planet.

Mars also inhabits Sagittarius, rising at 2:09 AM, shining at zero magnitude and 9 arc-seconds in size. It appears about 88 percent illuminated. Mars is gradually growing brighter, larger, and beginning to be worthy of studying surface features. Sagittarius has one more visitor, 4Vesta. This asteroid is 512 km (312 mi) in diameter and is appropriately small in our telescopes. It rises at 12:55 AM and shines with 7th magnitude, within most amateur telescopes. Observers should consult websites and magazines for detailed finder charts.

Finally, the Moon rises in Capricornus at 3:47 AM Tuesday, and 4:22 AM on Wednesday. It shines at minus 8th magnitude and is 31 percent phase on Tuesday, and 22 percent on Wednesday.

Earlier, we mentioned that Saturn and Mars lie quite close to several star clusters. Throughout the night, star clusters abound. In early evening, we find the Pleiades above the shoulders of Taurus. The Bull’s face is made of another star cluster, the Hyades. The nearby constellation Auriga harbors three clusters. Finally, Cancer contains the Beehive and M 67.

All these are called “Open Clusters.” They appear to contain, at most, a few hundred stars, which are widely spaced and irregularly shaped. Open clusters are relatively young, less than a billion years old. They reside in the disk of a galaxy and are relatively small, about 50 light-years across.

There is another class of star clusters, called “Globular Clusters.” Globular clusters are usually found around galaxy halos and central bulges.
Globulars may contain up to a million stars and are quite large, in a sphere about 100 light-years across. These stars are quite old.

If tonight’s weather is clear, binoculars can show many Open Clusters. Just dress warmly and observe the Hyades, Pleiades and the nearby pentagon shaped constellation Auriga.

Skywatch Line for Friday, April 6 through Sunday, April 8, 2018

This is Dudley Observatory’s Skywatch Line for Friday, April 6 through Sunday, April 8, written by Sam Salem.

On Friday, the Sun rises at 6:29am and sets at 7:28pm; Moon rises at 12:47am and sets at 10:30am. Last quarter Moon occurs on Sunday at 3:17am. The last quarter Moon aligns with the closest apogee of the year, at 404,144 km distance. Apogee is the Moon’s most distant point from Earth in its monthly orbit. This Sunday, the half-lit last quarter Moon almost exactly aligns with lunar apogee. This is the year’s closest coincidence of quarter Moon and lunar apogee, with the two events taking place less than two hours apart.

Venus gleams at magnitude –3.9 in the early evening even as it sits low in the west at dusk. Jupiter, at magnitude –2.4, rises a little before 11pm. Mars and Saturn rise more or less together around 2:45am. The two planets are less than three degrees apart in northern Sagittarius and closely matched in brightness. Mars glows at magnitude 0.2, while Saturn is only a bit fainter at magnitude 0.5. On Saturday morning, Saturn will be the closer of these two planets to the Moon, as the Moon will pass just north of Saturn.

The 5.1-magnitude open cluster, M35, in constellation Gemini is easy to find as it’s located just above the westernmost foot of the Twins, marked by 2.9-magnitude Mu (μ) and 3.3-magnitude Eta (n) Geminorum. 10×50 binoculars show a few individual cluster members in M35. A more powerful telescope has the ability to resolve many more stars. Try to spot M35’s celestial neighbor, the 8.6-magnitude cluster NGC2158. It’s a tough catch in binoculars, but a small scope has no trouble pulling in little NGC2158 in a reasonably dark sky. The two clusters are physically similar but look quite different to us because one is much nearer to Earth than the other. M35 is the closer cluster at roughly 2,800 light-years. It’s only one-fifth the distance of NGC2158.

On April 6, 1852, Edward Sabine announced that the 11 year sunspot cycle was “absolutely identical” with the geomagnetic cycle. Sabine was an Irish geophysicist, astronomer, and explorer, who made extensive pendulum measurements to determine the shape of the Earth, and established magnetic observatories to relate sunspot activity with disturbances in terrestrial magnetism.

Sunday marks another anniversary related to sunspot discovery. On April 8 1947, the largest sunspot group recorded was observed on the Sun’s southern hemisphere. Its size was estimated at 7 billion square miles, or an area of 6100 millionths of the Sun’s visible hemisphere. Sunspots are areas of somewhat cooler surface than the surrounding solar gases, and appear as dark spots on the solar surface. Astronomers measure the sizes of sunspots as millionth fractions of the Sun’s visible area. Typically, a big sunspot measures 300 to 500 millionths. The entire surface area of the Earth is only 169 millionths of the solar disk.