Skywatch Line for Friday, November 17 through Sunday, November 19, 2017

This is Dudley Observatory’s Skywatch Line for Friday, November 17 through Sunday, November 19, written by Sam Salem.

On Friday, Sun rises at 6:50am and sets at 4:31pm; Moon rises at 5:42am and sets at 4:31pm, at the time of sunset. New Moon occurs on Saturday at 6:42am.

Saturn, at magnitude 0.5, is about 10 degrees above the southwest horizon, as dusk begins. Mars, shining at magnitude 1.7, is gaining altitude as it grows in size and brightness in the morning sky. The red planet climbs to about 20 degrees above the southeast horizon an hour before sunrise. Jupiter, at magnitude –1.7, rises almost an hour before the Sun. Venus, at magnitude –3.9, rises a few minutes after Jupiter.

Watch for Leonid meteors in the hours before dawn on Saturday. Fortunately this year, the meteor shower occurs on new Moon dark night. The radiant point of the shower is constellation Leo, the Lion. Therefore, the meteors in this annual shower are named for this constellation. The Leonids are famous for storming at various times throughout history. The first great meteor storm in modern times was the Leonid shower of November 1833. That famous shower had a major effect on the development of the study of meteors. Meteors were thought to be atmospheric phenomena, like rain or snow. The Leonid meteor storm of 1833 helped prove that meteors in annual shower originate in comets. In 1865, astronomers discovered a comet, which was named Comet Tempel-Tuttle. The comet’s orbit around the Sun was found to be about 33 years. As predicted, there was another Leonid meteor storm in November 1866. Earth crosses the orbital path of Comet Tempel-Tuttle every year. Debris from this comet burns up in the Earth’s upper atmosphere to create the annual Leonid shower. It’s only when the comet is near Earth that we see a Leonid storm. That happened last in 1966, when North Americans enjoyed a Leonid storm numbering 100,000 shooting stars per hour. No heightened meteor activity is anticipated for the Leonid meteor shower this year. That’s because the Tempel-Tuttle comet of the Leonid shower is not nearby. The comet’s next expected perihelion is in May 20, 2031. That’s when we expect the next Leonid storm. This year, in a dark, moonless sky, you might see up to 10 to 15 meteors per hour. On a dark night, we typically see the most Leonid meteors streaking the sky in the hour before dawn because that’s when the radiant point of the shower, constellation Leo the Lion, is found highest in the sky. Leo rises over eastern horizon around 1am. Leo then climbs upward and westward, reaching its highest point in the southern sky around 6:30am.

The Dutch astronomer, Hendrik Christoffel Van de Hulst, was born in November 19, 1918. In 1944 he had predicted that the amount of neutral atomic hydrogen in interstellar space would be so great as to produce a measurable signal at radio wavelength of 21 centimeters. Shortly after the end of the war several groups set about to test this prediction. The 21-cm line of atomic hydrogen was detected in 1951, first at Harvard University followed within a few weeks by others. The discovery led to a breakthrough in astronomical research, which at that time was limited to conventional light.


Skywatch Line for Wednesday, November 15th, and Thursday, November 16th, 2017

This is the Dudley Observatory Skywatch Line for Wednesday, November 15th, and Thursday, November 16th, written by Louis Suarato.

The 10% illuminated, waning crescent Moon shares the pre-dawn sky with Mars, Jupiter, and Venus. Wednesday morning, Mars will be 3 degrees south of the Moon. Also, on Wednesday morning, an extremely bright -3.5 magnitude, International Space Station will appear at 5:06 a.m. above Ursa Minor. The ISS will then sail on through the Big Dipper and continue toward the eastern horizon where it will pass very close to the crescent Moon, and Virgo’s brightest star, Spica. Jupiter rises at 5:29 a.m., followed by Venus, 10 minutes later. Thursday,Jupiter will be about 7 degrees below a thinner crescent Moon.If you’ve never viewed asteroid Vesta, Thursday morning may provide the opportunity to locate it when this 7th magnitude asteroid will be 1 degree above the crescent Moon.

One of the most prominent constellations in the Autumn sky is Pegasus, the winged horse of Greek mythology. Pegasus is the 7th largest constellation, featuring its “Great Square”, which is comprised of four 2nd magnitude stars. Beginning from the easternmost, upper star and moving clockwise, these stars are: Alpheratz, also known as Alpha Andromedae. As its name indicates, Alpheratz is actually part of the constellation Andromeda. The star to the right of Alpheratz is Scheat, which is Arabic for shin. Below Scheat is Markab. To the left, or east of Markab is Algenib, the dimmest star in the Great Square. The only Messier object in Pegasus is the globular star cluster, M15. Discovered by Jean-Dominique Maraldi in 1746, M15 is one of the oldest known globular clusters, estimated to be 12 billion years old. This globular cluster has a diameter of 175 light-years and is about 33,600 light-years from Earth. This densely packed star cluster is estimated to be the home of over 100,000 stars.

The Albany Area Amateur Astronomers invite you to join them for their monthly meeting to be held at miSci in Schenectady beginning at 7:30. This month’s speaker will be Dr. James Johnson, who will be giving a presentation about Earth’s Precession. The Albany Area Amateur Astronomers also invite you to join them for their last star parties of the year to be held, weather permitting, Friday and Saturday nights at the Landis Arboretum in Esperance, NY.

Skywatch Line for Monday and Tuesday, November 13th and 14th, 2017

This is the Skywatch Line for Monday and Tuesday, November 13th and 14th.

The Sun sets at 4:34 PM; night falls at 6:11. Dawn begins at 5:07 AM and ends with the Sun rising at 6:46.

Saturn is the easiest planet to see in the twilight sky. It lies moderately low in the southwestern constellation of Ophiuchus; it shines with zero magnitude about 13 degrees above the horizon and sets at 6:38 PM. Saturn is slowly descending into the Sun’s glare; now is the time for last looks.

Mercury is beginning an appearance 15 degrees below Saturn. Also in Ophiuchus, it peeks above the southwestern skyline, shines with minus 0.3 magnitude and appears about 81 percent illuminated. Mercury sets at 5:24 PM.

While Saturn sets, Neptune, still in Aquarius, shines at 8th magnitude near the bright star Hydor. Uranus, also still residing in Pisces, has moved slightly. It now is about 3 degrees above the brighter star Mu Piscium. Mu Piscium shines with 4th magnitude about 3 degrees below Uranus. Mu Piscium is also an interesting double star. The two stars lie about 3 arc-minutes apart, within the ability of most moderately sized telescopes. Neptune is best observed at 7:15 PM and sets at 12:51 AM. Uranus is best seen at 9:57 PM and sets at 4:38 AM.

Mars rises about 3:29 AM in Virgo. The Red Planet shines at 1st magnitude, appears about 4 arc-seconds in size and about 96 percent lit. The bright, 3rd magnitude, star Porrima glows about 3 degrees above Mars.

Tuesday’s Moon rises also in Virgo and blazes at minus 6th magnitude. The 26-day-old Moon is about 15 percent crescent and rose at 2:37 AM. Wednesday’s Moon also lies in Virgo, appears thinner and about half the size of Monday’s Moon and rises at 3:40 AM.

Civil Dawn presents a dramatic scene for early rising astronomers. Venus rises in Virgo about 16 degrees below Mars at 5:32 AM. Venus dazzles at minus-4th magnitude and appears about 97 percent lit. Jupiter, also in Virgo, rises at the same time and blazes at minus 1st magnitude. The two easily fit in a binocular or telescope field. They are separated by 1 degree on Tuesday, and 2 degrees on Wednesday. Follow them and note that Jupiter rises while Venus sinks as the month goes on.

Followers of the Skywatch Line know that the Milky Way, which tonight stretches from horizon to horizon, represents the rim of our galaxy. They also know that the faint glow in Andromeda is that of a giant galaxy, similar to ours. However, these “island universes” are not isolated from each other. Their gravitational fields clump galaxies into groups. The Local Group is made of our Milky Way, Andromeda, M 33 in Triangulum, and about a dozen other galaxies. This group is traveling together through space. Some galaxies also interact with each other. A prime example is M 51, off the Big Dipper’s Handle. Telescopes show one galaxy seemingly stealing material from another. Some astronomers think that giant galaxies like our own grow by absorbing smaller ones. Colliding galaxies are common telescopic sights. It is thought that two spiral galaxies will merge to form an elliptical galaxy. In fact, in about three billion years, Andromeda and the Milky Way will probably collide and merge. The result will be a giant galaxy marked by very active star formation

Skywatch Line for Friday, November 10 through Sunday, November 12, 2017

This is Dudley Observatory’s Skywatch Line for Friday, November 10 through Sunday, November 12, written by Sam Salem.

On Friday, Sun rises at 6:42am and sets at 4:37pm; Moon sets at 12:52pm and rises at 11:23pm; Last Quarter Moon occurs at 3:36pm.

On Friday night, view the Moon coupling up with Regulus, the brightest star in the constellation Leo the Lion. Watch for the Moon and Regulus before dawn, when the two objects will be highest up for the night. The Moon will pass Regulus after a few more days, and then will be traveling toward planets Mars, Venus and Jupiter. Regulus is the only first-magnitude star to sit almost on the ecliptic, the Sun’s annual path in front of the constellations of the Zodiac. Wake up before the Sun then use the Moon, Regulus, and the early morning planets Venus and Jupiter to help you envision the ecliptic over the next several days. The planets orbit the Sun, and the Moon orbits Earth, on nearly the same plane that Earth circles the Sun. Therefore, the Moon and planets are always found on or near the ecliptic.

Saturday night and early hours of Sunday are expected to be the peak time of the North Taurid meteor. This shower has been known to produce very bright meteors. Hopefully, the waning crescent Moon won’t too greatly intrude on this year’s shower. You can watch this shower before the Moon rises, which won’t be until after midnight. You might not see any more than five North Taurids an hour. It’s not the number of Taurids that makes this shower amazing, it’s the fireball or bright meteors it produces. Both the North and South Taurids are known for having a high percentage of extra-bright meteors. To increase your chances of seeing really bright meteors, watch in the hours around midnight. That’s when the radiant point, in the constellation Taurus the Bull, will be well above the horizon. You don’t need to identify this constellation to see the meteors. They will appear all over the sky. Still, it helps to know when the radiant rises. Taurus rises over the northeast horizon around 7 to 8 pm. Find a dark place to observe. This shower will be active for another month or so. By then the waning crescent Moon will make moonlight less of a factor.

Before sunrise on Monday, watch for the super-close pairing of the sky’s two brightest planets, Venus and Jupiter, low in the eastern sky at dawn. Venus and Jupiter will come closest together on the sky’s dome on Monday and Tuesday morning. Venus and Jupiter will be snuggling close together on both dates, close enough to easily fit inside the same binocular field, or a single field of view in a low-powered telescope. At their closest, Venus and Jupiter will be 0.3 degrees apart. That’s less than the apparent diameter of the Moon. Also, don’t miss the waning crescent Moon swinging by these planets later this week. Venus and Jupiter rise better than an hour before the Sun. Jupiter will climb higher up in the morning sky day by day while Venus will plunge sunward day by day.

Saturday marks the birthday of the American astronomer Vesto Melvin Slipher.
Born on November 11 1875, Slipher’s observations of the extraordinary radial velocities of spiral galaxies, from 1912 to 1925, provided the first evidence supporting the expanding-universe theory. Slipher spectroscopically measured the displacement of galaxies spectral lines by the Doppler effect by which the wavelength of light from an object moving away from an observer were shifted toward the red end of the spectrum. Earlier, Slipher had determined the rotation periods of some of the planets by spectroscopic means. With Lowell in 1912, he found out that Uranus had a rotation period of 10.8 hours.

Skywatch Line for Wednesday, November 8th, and Thursday, November 9th, 2017

This is the Dudley Observatory Skywatch Line for Wednesday, November 8th, and Thursday, November 9th, written by Louis Suarato.

The 75% illuminated, waning gibbous Moon sets at 11:05 a.m. Wednesday, and will return 71% illuminated at 10 p.m., providing you with at least 4 hours of a moonless sky. The Moon orbits Earth once every 27.322 days, traveling at the speed of 2,287 miles per hour. There are four types of lunar months. An anomalistic month is the time it takes for the Moon to orbit Earth from one perigee to the next. An anomalistic month is 27 days, 13 hours, 18 minutes and 37.4 seconds. A nodical month is the time it takes the Moon to pass through a node, or Earth’s plane, and return. A nodical month is 27 days, 7 hours, 43 minutes and 11.5 seconds. A sidereal month is the time it takes the Moon to orbit the Earth using the stars as a reference point. A sidereal month is 27 days, 7 hours, 43 minutes and 11.5 seconds. A synodical month is measured by the time it take the Moon to circle the Earth using the Sun as a reference point, or completing the full cycle of phases. A synodical moth is 29 days, 12 hours, 44 minutes and 2.7 seconds.

Saturn will only be 13 degrees above the southwestern horizon after sunset. Mercury is lower on the horizon, and will be a challenge to see. Mercury and Saturn will meet for a conjunction toward the end of the month. Mars rises at 3:35 a.m. in the constellation Virgo, followed by Venus about 2 hours later, its distance from the Sun gradually decreasing. Jupiter is slowly moving away from the Sun, moving toward a very close conjunction with Venus in the middle of the month.

November 9th is the birth date of astronomer Carl Sagan. Born in 1934, Sagan was instrumental in the American space program, consulting and advising NASA in the 1950’s, and briefing astronauts before their missions to the Moon. Sagan made astronomy popular through his hundreds of articles and over two dozen books. His series “Cosmos” was one of the most-watched public television shows in history, seen by more than 500 million people in 60 countries.

Skywatch Line for Monday and Tuesday, November 6th and 7th, 2017

This is the Skywatch Line for Monday and Tuesday, November 6th and 7th.

Now that Daylight Savings Time has ended, the Sun sets at 4:41 PM; night falls at 6:18. Dawn breaks at 5 AM and ends with the Sun rising at 6:37.

Saturn, in Ophiuchus, is still the easiest planet to observe, though it is slowly sinking. Binoculars and telescopes show its rings, which appear deformed by our ever-convective atmosphere. The zero-magnitude planet stands about 15 degrees above the western horizon at Civil Dusk and sets at 7:03 PM.

Mercury, in Scorpius, peeks above the western horizon about 23 degrees below Saturn. Mercury is brighter at minus 0.3 magnitude and 86 percent illuminated. Note that diving Saturn approaches climbing Mercury this month. Mercury is beginning a Fall appearance in the evening sky. It sets at 5:20 PM.

Twilight’s end reveals tiny Neptune, in Aquarius near the star Hydor. The small 8th magnitude planet is best observed at 7:43 PM. Uranus, in Pisces, is brighter and slightly larger near the star Omicron Piscium. It is best observed at 10:25 PM. Neptune sets at 1:15 AM; Uranus sets at 5:03 AM. Both require detailed charts from astronomy media and websites.

The 18-day-old Moon rises in Taurus on Monday at 7:08 PM. It blazes at minus 11.5 magnitude, is about 87 percent lit and 28 degrees above the horizon. Tuesday, the Moon is a bit dimmer, 79 percent lit and rises in Gemini at 8:06 PM. The Moon is best observed at 2:40 AM on Tuesday and at 3:41 AM on Wednesday; it sets during daylight.

The variable star Algol, in Perseus, dims at 9:16 PM on Tuesday. Algol varies its light every 2.9 days; the star dims from second to third magnitude, a process that takes about 5 hours from dimming to brightening.

Virgo contains all the morning planets. Mars rises in pre-dawn 3:34 AM, near the bright star Porrima. First magnitude Mars appears as a tiny red dot about 15 degrees above the eastern horizon. Venus blazes at minus 4th magnitude and appears almost “full”, having risen at 5:16 AM. Venus helps find Mars, since it is brighter and about 19 degrees below the Red Planet. Jupiter rises at 5:49 AM, glows at minus 1st magnitude and about 30 arc-seconds in size; binoculars may help find it amid the rising Sun’s glare.

By 10 PM, the constellation Auriga is well up in the East. Auriga resembles a pentagon or home plate. The brightest star is Capella and is found in the upper right corner. The opposite corner is the more obscure 1st magnitude star Menkalinan – “shoulder of the charioteer.” Menkalinan, a member of Auriga, is actually connected to the Big Dipper – Ursa Major.

Five of the Big Dipper’s stars formed together from the same gas cloud. Menkalinan also formed from that same cloud; it sails through space along with its Big Dipper brothers. It shares the same color, brightness, speed and direction. It is also the same distance from Earth – 82 light years. Menkalinan is easy to find. It is opposite Capella, on the eastern top portion of the pentagon.

Skywatch Line for Friday, November 3 through Sunday, November 5, 2017

This is Dudley Observatory’s Skywatch Line for Friday, November 3 through Sunday, November 5, written by Sam Salem.

On Friday, Sun rises at 7:33am and sets at 5:45pm; Moon sets at 6:30am and rises at 5:55pm, shortly after sunset. On Sunday at 2:00am, daylight time officially comes to an end and standard time begins.

Full Moon occurs on Saturday at 1:23am. The full Hunter’s Moon, the 2nd-largest full Moon this year, will parade across the sky from dusk till dawn. The Hunter’s Moon is the name for the full Moon that immediately follows the full Harvest Moon. The full Harvest Moon fell on October 5. The Hunter’s Moon, like the Harvest Moon, is famous for dusk-till-dawn moonlight for a few nights in a row. That means there’s a somewhat shorter-than-usual time between successive moonrises for the next few nights.

Venus, at magnitude –3.9, is gradually losing altitude. It rises 90 minutes ahead of the Sun. Mars, at magnitude 1.8, is climbing higher and higher in the dawn.

On Sunday, the Moon and star Aldebaran cross the night sky from evening until dawn. The Moon occults Aldebaran, the brightest star in the constellation Taurus the Bull. This occultation is visible from much of North America, Greenland, Iceland and northern Europe. The almost-full waning gibbous Moon might make it tough to see Aldebaran and the nearly Pleiades star cluster. From our area, occultation begins a couple of minutes after 8:00pm and ends a couple of minutes before 9:00pm. During occultations such as this one, which occur when the Moon’s phase is waning, the star’s reappearance tends to be more dramatic.

On this full Moon weekend, use your telescope to scan the entire circumference of the Moon limb. You will notice a trace of shadow detail, especially on Friday and Sunday nights when the phase is a little shy of full. This weekend, libration effects favorably tilt the Moon’s north pole toward us. That means you’ll get to glimpse features in the extreme north that are usually hidden from sight. Over the course of a lunar cycle we can see more than 50% of the Moon’s surface from Earth. This is because of a combination of effects known as “librations” of the Moon. Libration is a slow rocking back and forth of the Moon as viewed from Earth, permitting an observer to see slightly different halves of the surface at different times. The eccentricity of the Moon’s orbit around Earth, the slight inclination between the Moon’s axis of rotation to the plane of its orbit around Earth, and the small daily oscillation due to Earth’s rotation cause the lunar libration. Although the Moon always presents us with the same face towards the Earth, due to its rotation and revolution being tidally locked to the same period, the combined effect of all these different librations allows us over time to see some 59% of the Moon’s surface.

The real attraction of a full Moon is the complex shading of light and dark, ranging from dull grey to brilliant white. Ray craters in particular stand out. The most eye-catching of them all is Tycho. The 85-kilometre-wide impact feature boasts impressively long, bright rays that span two-thirds of the lunar disk. Use steadily held binoculars or a small telescope to observe Tycho’s rays. Inspect Tycho itself with a telescope at moderate magnification and you’ll easily see a dark halo encircling the crater.

Skywatch Line for Wednesday, November 1st, and Thursday, November 2nd, 2017

This is the Dudley Observatory Skywatch Line for Wednesday, November 1st, and Thursday, November 2nd, written by Louis Suarato.

November begins with the 94% illuminated, waxing gibbous Moon rising in the constellation Pisces at 4:51 p.m. Wednesday. Saturn will be less than 15 degrees above the southwestern horizon after sunset. Your best view of planets occurs in the morning, with Mars and Venus at opposite sides of Virgo before sunrise. If you are up and out early Wednesday morning, look for the International Space Station to emerge out of the dark at 5:23 a.m., to the upper right of Mars in the constellation Hydra. This -1.2 magnitude pass will continue over Mars and into the east-northeastern horizon, passing over Arcturus in the constellation Bootes. A brighter -2.5 magnitude ISS pass begins at 6:57 a.m. originating from the western horizon. Follow the ISS as it passes by the Pleiades star cluster, through Perseus, and over the Double Cluster and Cassiopeia, before heading toward the glow of sunrise.

With the Moon approaching its Full phase, you may want to concentrate your viewing on the brightest celestial objects in the sky opposite the Moon. After 8 p.m., Aquila, the eagle, and Cygnus, the swan, will be diving toward the west-southwestern horizon. Aquila’s brightest star, Altair, is a member of the summer triangle, and the 12th brightest star in the night sky. Above Altair is another member of the Summer Triangle, Deneb, in Cygnus. Deneb is the 19th brightest star in the sky, and also forms the head of the asterism known as the Northern Cross. As the result of the Earth’s wobbling motion, or axial precession, Deneb will replace Polaris as the pole star around the year 9800 AD. Between Deneb and Altair are two open star clusters, NGC 6871, on the neck of the swan, and NGC 6940, below its left wing. If you follow an imaginary line connecting these two star clusters southward, you’ll come to the globular cluster M15. Discovered by Jean-Dominique Maraldi in 1746, M15 is estimated to be 12 billion years old, making it one of the oldest known globular clusters. M15 has an absolute magnitude of -9.2, giving it a luminosity of 360,000 times brighter than our Sun. The absolute magnitude of a celestial object is calculated as if the object were 32.6 light-years, or 10 parsecs, away. This dense globular cluster has a diameter of approximately 175 light-years, and contains more than 100,000 stars.

November 2 is the birth date of astronomer Harlow Shapley. Born in 1885, Shapley was known as the “Modern Copernicus” for discovering the Sun’s position in the Milky Way Galaxy. Prior to Shapley’s calculations, it was commonly thought that our galaxy was the universe, but Shapley correctly proclaimed that our galaxy was part of a much larger universe. Shapley worked at the Mt. Wilson Observatory. It was on November 2, 100 years ago, that the 100-inch Hooker telescope saw its first light. The hooker telescope remained the world’s largest until 1949, when it was surpassed by the 200-inch Hale telescope.

Skywatch Line for Monday and Tuesday, October 30th and 31st, 2017

This is the Skywatch Line for Monday and Tuesday, October 30th and 31st.

The Sun sets at 5:50 PM; night falls at 7:25. Dawn begins at 5:53 AM, and ends with sunrise at 7:08.

Civil Twilight presents only the Moon and Saturn. The 10-day-old Moon, in Aquarius both nights, blazes at minus 11th magnitude, appears 78 percent illuminated, 24 degrees high on Monday and best observed at 9:20 PM. Tuesday finds the Moon 86 percent lit and best observed at 10 PM. The Moon sets at 3:03 AM on Tuesday, and at 4:09 AM on Wednesday.

Saturn, in Ophiuchus, appears moderately low in the Southwest, shining at zero magnitude and setting at 8:28 PM.

Nightfall finds already risen Neptune in Aquarius, but almost impossible to see, because the brilliant Moon is only 2 degrees away on Monday, obscuring the dim, distant planet. Tuesday, the Moon will be more distant, but still intense and making locating Neptune difficult. Neptune sets at 2:42 AM.

Uranus, in Pisces, should be easier to see. It is located near the star Omicron Piscium, shines at 5th magnitude, 3.7 arc-seconds in size, is best placed for viewing at 11:54 PM and sets at 6:32 AM.

Sunday, asteroid 2 Pallas reached opposition, which means it is in line with the Earth and Sun. Located in the constellation Fornax (the Furnace), it glows with 8th magnitude and is 20 degrees high in the East at Midnight. Asteroid 7 Iris is at Opposition Monday night in Aries, shining at 7th magnitude and about 68 degrees high by Midnight.

Neptune, Uranus, 2 Pallas and 7 Iris require detailed finder charts, available from astronomy websites.

Mars rises in Virgo at 4:38 AM, during Dawn, shines at 2nd magnitude and appears 97 percent lit. Venus, also in Virgo, rises at 5:58 AM, blazes at minus 4th magnitude and appears almost as illuminated as Mars. Venus appears about 10 degrees above the eastern horizon, and stands about 4 ½ degrees below the bright star Spica.

Dwarf Planet Eris was one of the first Kuiper Belt objects discovered, and one of the reasons for Pluto’s demotion. The technique that Chilean observatories used is a very low tech one. They knew that the Moon would occult, or eclipse, Eris. They accurately timed the disappearance and reappearance. This is a very common method for amateur astronomers to assist professionals. An organization named IOTA publishes dates, times, and places where an asteroid can be witnessed eclipsing a star. Amateur astronomers then observe the event by accurately timing it and noting their GPS location coordinates. Results are sent to IOTA’s headquarters. If enough widely separated observers report in, the size and rough shape of the asteroid can be determined. IOTA is one of the earliest examples of citizen science – the alliance of professionals and amateurs that advance the science of Astronomy.

Skywatch Line for Friday, October 27 through Sunday, October 29, 2017

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

The evening sky’s sole naked-eye planet is Saturn. However, the 0.5-magnitude planet is losing ground to twilight. As the sky begins to darken, Saturn sits some 15 degrees above the south-southwest horizon where views of its famous ring system will likely be blurred by Earth’s churning atmosphere. Early risers have two planets to enjoy, though neither is much to look at in a scope, at least for now. Mars is first up, rising around 5 a.m., local daylight time. At magnitude 1.8, the red planet is barely brighter than Polaris and has an apparent diameter of just 4 arc seconds—scarcely bigger than distant Uranus! Mars’ brightness and size will greatly increase, but not for many months yet. The second dawn world is Venus. Gleaming at magnitude –3.9, it pops up roughly one hour after Mars. Despite its prominence, Venus is a disappointing telescopic target at the moment, appearing as a small gibbous disc when viewed at medium power. Still, the brilliant planet is a lovely naked-eye sight set against morning twilight.

On Friday, Sun rises at 7:24am and sets at 5:55pm; First Quarter Moon at 6:22pm; Moon sets at 12:00am.
On Friday evening the moon is at or near its first quarter phase, which means the moon’s disk is 50% illuminated by sunshine and 50% engulfed in the moon’s own shadow. First quarter moon arrives on October 27, at 6:22 p.m. EDT
Half the moon is always illuminated in space. In other words, the moon has a day side and a night side, just as Earth does. Due to the angle between the sun, Earth and moon, we’re seeing about equal portions of its day side and night side tonight. Because the moon is now waxing, we’re bound to see more of its day side each evening until the night that the moon turns full on the night of November 3-4.
The part of the moon that isn’t in sunlight is often called the moon’s dark side. Just realize that – because of the moon’s motion around Earth – the portion of the dark side that we see from Earth constantly changes.
There is a permanent far side of the moon. But there is no permanent dark side of the moon, because any given lunar location experiences night for about two weeks, followed by about two weeks of daylight.
The moon does rotate on its axis. But billions of years of Earth’s strong gravitational pull have slowed it down such that today the moon takes as long to rotate as it does to orbit once around Earth. Astronomers would say that the moon is tidally locked with Earth. For that reason, one side of the moon always faces Earth, but it is not always dark – as you can see just by looking at the sky tonight.
Incidentally, the moon’s gravitational effects on Earth are much smaller, but – given billions of years of time – the Earth will slow down and keep one face always toward the moon.

Lunar Straight Wall on Saturday evening. Rupes Recta is a linear fault on the Moon, in the southeastern part of the Mare Nubium at 22.1°S 7.8°W. The name is Latin for straight cliff, although it is more commonly called the Straight Wall.[1] This is the most well-known escarpment on the Moon,[2][3] and is a popular target for amateur astronomers.[3] [4]
When the sun illuminates the feature at an oblique angle at about day 8 of the Moon’s orbit, the Rupes Recta casts a wide shadow that gives it the appearance of a steep cliff. The fault has a length of 110 km, a typical width of 2–3 km, and a height of 240–300 m. Thus although it appears to be a vertical cliff in the lunar surface, in actuality the grade of the slope is relatively shallow.
To the west of this escarpment is the crater Birt, which is about 17 km in diameter. Also to the west is the Rima Birt rille. At the southern end is a group of hills often called the “Stag’s-Horn Mountains”, although this name is not officially recognized by the IAU. Northeast of the escarpment is the land cape of Promontorium Taenarium.
To the northeast is the crater Alpetragius, and to the east is Thebit.

From 1969 to 1972, Apollo astronauts had left laser reflectors on the moon’s surface, enabling astronomers to measure the moon’s distance from Earth with great accuracy. Although the moon’s distance from earth varies each month because of its eccentric orbit, the moon’s mean distance from Earth is nonetheless increasing at the rate of about 3.8 centimeters (1.5 inches) per year. That’s about the rate that fingernails grow. Tidal friction with the Earth’s oceans is responsible for this long-term increase of the moon’s distance from Earth. It’s causing the moon to spiral into a more distant orbit. Tidal friction also slows down the Earth’s rotation, lengthening the day by about 1 second every 40,000 years. Hence, the number of days in a year is slowly diminishing over the long course of time. Simulations suggest that at the time of the moon’s formation some 4.5 billion years ago, the moon was only about 20,000 to 30,000 kilometers (12,000 to 18,000 miles) from Earth. Way back then, Earth’s day might have been only 5 or 6 hours long. That would mean over 1,400 days in one year! However, astronomers suspected the moon was receding from Earth before the heyday of the Apollo astronauts. Edmund Halley’s (1656 to 1741) studies of ancient solar and lunar eclipses suggested the possibility, as well. George Howard Darwin (1845 to 1912) is credited for figuring out mathematically how tidal friction affects the moon’s orbit. Studies in fossilized coral indicate that the Earth had spun faster upon its rotational axis when the moon was closer to Earth. Millions of years ago, days on Earth were shorter yet more abundant. For instance, around 900 million years ago, there were about 480 18-hours days in one year. Around 400 million years ago, there were about 400 22-hour days in one year. Looking into the future, astronomers expect longer days but fewer of them in one year.
If the lifetime of the Earth-moon system lasts long enough (which is doubtful), it is projected that after many billions of years, the same sides of the Earth and moon would face one another. In other words, the Earth’s rotational period and the moon’s orbital period would equal one another, representing a period of 47 days. At that time, the Earth/moon distance would expand to some 336,000 miles of 560,000 km, exceeding the present distance of 238,855 miles or 384,400 km by nearly 150%. As you view our companion world tonight, ponder on the rich history and intriguing future of our planet Earth and its wayward moon!

Tonight – just in time for the upcoming season of Halloween and the Day of the Dead – look for the Demon Star in the constellation Perseus the Hero.
That star is Beta Persei, or Algol, pronounced AL-gul. The name Algol comes from an Arabic term for head of the ghoul or head of the demon. This chart showed you how to use the constellation Cassiopeia to locate Perseus in the northeast in the evening sky. The brightest star in Perseus is Alpha Persei, whose proper name is Mirfak.
If you can find Perseus and Mirfak, you can find Algol, too!
Also, as darkness falls this evening, look for the planets Venus and Saturn in your southwest sky.
As darkness falls this evening, look for the planets Venus and Saturn. They’re in the southwest as viewed from Earth’s Northern Hemisphere, more northwest as viewed from the Southern Hemisphere.
Algol is a very interesting star. It’s known to vary in brightness in a way that’s extremely regular. The cycle lasts exactly 2 days, 20 hours and 49 minutes. For a few hours during the cycle, Algol’s brightness falls far below normal, then returns to normal. All the while, the star remains visible to the eye.
Algol’s brightness variation is not due to some special quality of a single star. Instead, this is a multiple star system, where one star regularly passes in front of another as seen from our earthly perspective.
Thus Algol is what’s called an eclipsing variable star.
Thousands of these stars are known, but Algol is perhaps the most famous of this class because its periodic dip in brightness can be seen with the eye alone, and because the cycle is relatively short.
The ancient stargazers had no knowledge of multiple star systems, but possibly they did notice this star’s brightness change. Perhaps the brightness change is why, throughout parts of the ancient world, the star Algol was associated with demons or monsters. The Greeks and Romans identified the star with the Head of Medusa, a fearful monster with snakes in place of hair. The star has also been called the Ghoul Star.
High northern latitudes see Perseus by nightfall or early evening. Observers farther south may have to wait till mid-evening to catch Perseus and the Demon Star, aka Algol, in the northeastern sky.
Bottom line: The best-known star in the constellation Perseus is Algol, its name coming from the Arabic for head of the demon.

The October 27 – 29 weekend features a waxing Moon lighting up the evening sky. So why not spend some time doing a little lunar exploring? There’s lots to see whenever the Moon is up, but on Friday evening the terminator lies near the spectacular crater trio of Ptolemaeus, Alphonsus and Arzachel.
What makes these craters so interesting is that each one has a distinctive appearance. Northernmost is 164-kilometre-wide Ptolemaeus—the biggest of the bunch. Notice its smooth mare-covered floor. Immediately south of Ptoelmaeus is 108-km-diameter Alphonsus, which features a curious north-south ridge. Last is Arzachel, arguably the most conventional of the three. Spanning 96 km rim-to-rim, Arzachel has a classic “complex crater” appearance with its terraced rim and central mountain peak. Also interesting is 40-km-wide Alpetragius, which is nestled between Alphonsus and Arzachel. Alpetragius has an usually large, rounded central mountain. It looks, as lunaphile Charles A. Wood notes, like a nest with a single egg inside. This weekend, take a moment to look in on these craters this weekend and notice how dramatically their appearance changes with increasing illumination.

First U.S. astronomy expedition views eclipse. October 27 1780, the first U.S. astronomical expedition to record an eclipse of the sun observed the event which lasted from 11:11 am to 1:50 pm. The observers left about three weeks earlier, on 9 Oct from Harvard College, Cambridge, Mass., for Penobscot Bay, led by Samuel Williams. A boat was supplied by the Commonwealth of Massachusetts the four professors and six students. Although the U.S. was at war with Britain, the British officer in charge of Penobscot Bay permitted the expedition to land and set up equipment to observe the predicted total eclipse of the sun. The expedition was shocked to find itself outside the path of totality. They saw a thin arc of the sun instead of its complete obscuration by the moon.

October 29 1991, space probe Galileo become the first human object to fly past an asteroid, Gaspra, making its closest approach at a distance of 1,604 km, passing at a speed of 8 km/sec (5 mi/sec). The encounter provided much data, including 150 images, which showed Gaspra has numerous craters indicating it has suffered numerous collisions since its formation. Gaspra is about 20-km long and orbits the Sun in the main asteroid belt between Mars and Jupiter. Gaspra, asteroid 951, was discovered by Ukrainian astronomer Grigoriy N. Neujamin (1916) who named it after a Black Sea retreat. In the photograph (left), subtle color variations have been exaggerated by NASA to highlight changes in reflectivity, surface structure and composition.