Skywatch Line for Wednesday, May 12, and Thursday, May 13, 2021

This is Dudley Observatory’s Skywatch Line for Wednesday, May 12, and Thursday, May 13, written by Alan French.

Having reached new on Tuesday, a young, slender, crescent Moon is a difficult target on Wednesday night, but higher and easier by Thursday. On Thursday evening it will be close to Mercury and provide a nice landmark to aid spotting the innermost planet. If you have trouble spotting the Moon or Mercury, binoculars may bring success. Once located in binoculars, they should be easier to spot by eye.

The Sun sets at 8:09 on Wednesday night and at 8:10 Thursday. Look for the Moon 30 to 40 minutes after sunset on Wednesday, 40 to 50 minutes after sunset on Thursday. (Times are given for Schenectady.)

For measuring angular distances in the sky, a fist held at arm’s length spans 10 degrees across the knuckles. Also held at arm’s length, the first three fingers, held together span 5 degrees across their tips, and the pinkie spans 1 degree.

To spot the very slender, 1.2% illuminated, crescent Moon on Wednesday night you’ll need an unobstructed view of the west northwestern horizon and skies clear to the horizon. At 8:40 PM the Moon will be 4 degrees above the horizon and 29-1/2 hours old. Venus will be less than a degree away from the Moon, to its right (north) and a little higher. Mercury will be 11 degrees above and slightly left of the Moon, past the 11 o’clock position. By 8:50 the Moon will be just under 3 degrees above the horizon. It will set at 9:11.

By Thursday evening the Moon’s eastward motion among the stars will have brough it higher in the sky and not far from Mercury. The Moon’s movement around our Earth will also have increased the sunlit portion we see, showing us a 4.1% sunlit Moon. The Moon will be just under 11 degrees above the horizon at 9:00 PM and Mercury will lie 3 degrees to the Moons right and slightly lower in the sky. With clear skies the pair should make a lovely sight. Moonset is at 10:12.

In 1840 the Director of the Paris Observatory suggested that mathematician Urbain Le Verrier study the motion of Mercury and build a model of the planet’s movement based on the laws of motion and gravitation developed by Sir Isaac Newton. Le Verrier published his initial results in 1843. His predictions for the November 9, 1848, transit of Mercury across the Sun were a test of his model. When they proved inaccurate, Le Verrier further refined his model. He suggested the orbit of Mercury was being perturbed by a small planet inside its orbit. Similar calculations by Le Verrier helped with the discovery of Neptune in 1846, giving astronomers confidence in his prediction and inspiring them to search for Vulcan.

Although a French amateur astronomer claimed to have spotted the proposed planet, Vulcan, crossing the Sun’s face in 1859, and there were other claimed sightings, Le Verrier’s inner planet did not exist. The discrepancies in Mercury’s orbit were later explained by Einstein’s Theory of Relativity.

This is Dudley Observatory’s Skywatch Line for Wednesday, May 12, and Thursday, May 13, written by Alan French.

Having reached new on Tuesday, a young, slender, crescent Moon is a difficult target on Wednesday night, but higher and easier by Thursday. On Thursday evening it will be close to Mercury and provide a nice landmark to aid spotting the innermost planet. If you have trouble spotting the Moon or Mercury, binoculars may bring success. Once located in binoculars, they should be easier to spot by eye.

The Sun sets at 8:09 on Wednesday night and at 8:10 Thursday. Look for the Moon 30 to 40 minutes after sunset on Wednesday, 40 to 50 minutes after sunset on Thursday. (Times are given for Schenectady.)

For measuring angular distances in the sky, a fist held at arm’s length spans 10 degrees across the knuckles. Also held at arm’s length, the first three fingers, held together span 5 degrees across their tips, and the pinkie spans 1 degree.

To spot the very slender, 1.2% illuminated, crescent Moon on Wednesday night you’ll need an unobstructed view of the west northwestern horizon and skies clear to the horizon. At 8:40 PM the Moon will be 4 degrees above the horizon and 29-1/2 hours old. Venus will be less than a degree away from the Moon, to its right (north) and a little higher. Mercury will be 11 degrees above and slightly left of the Moon, past the 11 o’clock position. By 8:50 the Moon will be just under 3 degrees above the horizon. It will set at 9:11.

By Thursday evening the Moon’s eastward motion among the stars will have brough it higher in the sky and not far from Mercury. The Moon’s movement around our Earth will also have increased the sunlit portion we see, showing us a 4.1% sunlit Moon. The Moon will be just under 11 degrees above the horizon at 9:00 PM and Mercury will lie 3 degrees to the Moons right and slightly lower in the sky. With clear skies the pair should make a lovely sight. Moonset is at 10:12.

In 1840 the Director of the Paris Observatory suggested that mathematician Urbain Le Verrier study the motion of Mercury and build a model of the planet’s movement based on the laws of motion and gravitation developed by Sir Isaac Newton. Le Verrier published his initial results in 1843. His predictions for the November 9, 1848, transit of Mercury across the Sun were a test of his model. When they proved inaccurate, Le Verrier further refined his model. He suggested the orbit of Mercury was being perturbed by a small planet inside its orbit. Similar calculations by Le Verrier helped with the discovery of Neptune in 1846, giving astronomers confidence in his prediction and inspiring them to search for Vulcan.

Although a French amateur astronomer claimed to have spotted the proposed planet, Vulcan, crossing the Sun’s face in 1859, and there were other claimed sightings, Le Verrier’s inner planet did not exist. The discrepancies in Mercury’s orbit were later explained by Einstein’s Theory of Relativity.

Skywatch Line for Monday May 10th and Tuesday May 11th, 2021

This is the Dudley Observatory’s Skywatch Line for Monday Tuesday May 10th, and 11th, written by Joe Slomka.

The Sun sets at 8:06 PM; night falls at 10:03. Dawn breaks at 3:40 AM and ends with sunrise at 5:37.

Monday’s Moon sets at 7:08 PM. Tuesday, it rises, in Aries, at 5:18 AM and sets at 8:09 PM; Wednesday, it rises at 6:08 AM. Tuesday’s Moon, in Taurus, is at apogee (furthest from Earth); its located 406,512 km (252,595 mi)- the most distant for this year. Tuesday’s Moon is also “New,” which means that its illuminated side faces away from our planet, assuring that the sky will be dark for observation.

Mars remains the only easily spotted planet. Inhabiting Gemini, it rises during daytime, glows with first magnitude and shrinks to about 4.5 arc-seconds. By 9 PM, the Red Planet is about 35° high in the West and sets at 12:06 AM. Mercury and Venus are beginning to become visible. In Taurus, they lie low on the western horizon and may require an unobstructed horizon and binoculars. Mercury is highest shining with minus zero magnitude, almost 7 arc-seconds in size and sets at 9:54 PM. Venus is about 9° to Mercury’s lower right and only 5° above the horizon. Venus blazes with minus 3rd magnitude and sized almost 10 arc-seconds. Venus sets at 9:01 PM.

Asteroid 4Vesta still rides Leo’s back, shining with 7th magnitude, it is best observed at 8:33 PM, when it is highest at 64° and sets at 3:40 AM. Finder charts are available from astronomical websites.

The pre-dawn sky also begins to show off planets. Saturn rises first, in Capricornus, at 1:53 AM; the Ringed Planet shines with zero magnitude, and almost 17 arc-seconds. By 4 AM, it is 18° high in the South-east. Jupiter, in Aquarius, follows by rising at 2:36 AM, glaring with minus 2nd magnitude, it appears about double Saturn’s size. By 4 AM, it hovers about 14° high and about 16° to Saturn’s lower left. Both planets are well situated for observation.

Saturn for its famous rings and Jupiter for its 4 moons.

Both planets set during daytime.

At 9 PM, turn your attention to the close star Porrima. The Latin name refers to a Goddess of Prophesy. The star lies above Spica, in Virgo, and Denebola, Leo’s tail. Porrima is a double star. Both stars are nearly identical. They are about the same brightness, third magnitude, and the same mass, about 1.5 times the Sun. They are sun-like, but significantly brighter and warmer. Like the Sun, Porrima and its companion are main sequence stars, fusing hydrogen into helium. Porrima was among the first double star systems discovered. Sir John Herschel calculated its orbit in 1833. They share a highly elliptical orbit, which makes one cycle in about 169 years. An observer, with high power eyepieces in the telescope, can see them about 1.7 arc seconds apart.

Skywatch Line for Friday, May 7, through Sunday, May 9, 2021

This is Dudley Observatory’s Skywatch Line for Friday, May 7, through Sunday, May 9, written by Sam Salem.

On Friday, Sun rises at 5:41am and sets at 8:03pm; Moon rises at 4:15am and sets at 4:04pm.

Mercury is now easily spotted in twilight if you have a good view to the west-northwest. Venus, despite its brightness, can still be tricky to spot as it sits 8 degrees below. Mars sits higher in the west as night falls. Little Mars is approaching the base of the Arch of Spring, the long line from Procyon on the left to Capella on the right.

Jupiter, at magnitude –2.2, and Saturn, at magnitude +0.7, sit at dim constellation Capricornus. They rise more than an hour before the first light of dawn. As dawn begins, spot them in the southeast. Saturn sits 16 degrees to Jupiter’s right or upper right.

The Diamond of Virgo is some 50 degrees tall and extending over five constellations. It now stands upright in the south after the stars come out. Start with Spica, its bottom. Upper left from Spica is bright Arcturus. Almost as far upper right from Arcturus is fainter Cor Caroli, 3rd magnitude. The same distance lower right from there is Denebola, the 2nd-magnitude tail tip of Leo. And then back to Spica. The bottom three of these stars, the brightest, form a nearly perfect equilateral triangle. If you have a dark sky, or using binoculars, look halfway from Cor Caroli to Denebola for the very large, sparse Coma Berenices star cluster. It spans some 4 degrees, about the size of a ping-pong ball held at arm’s length.

Now shift your gaze to the Virgo Cluster. The cluster contains as many as 2,000 galaxies, dozens of which are visible with amateur telescopes under dark sky conditions during spring evenings. The cluster spans nearly a fist’s diameter of sky on the border between Virgo and Coma Berenices. The brightest member is the elliptical galaxy Messier 49, which is located a generous palm’s width to the lower right of the bright star Vindemiatrix, or Epsilon Virginis. Using low magnification, aim your telescope mid-way between Vindemiatrix and the bright star Denebola. That region contains a large number of bright galaxies, including the Messier objects M84 and M86 through M91.

Markarian’s Chain is a stretch of galaxies that forms part of the Virgo Cluster. The chain is a spectacular smoothly curved line of galaxies spanning 1.5 degrees. It arcs to the upper left from M84. Charles Messier first discovered two of the galaxies, M84 and M86, in 1781. The other galaxies seen in the chain were discovered by William Herschel and are now known primarily by their catalog numbers in John Louis Emil Dreyer’s New General Catalogue, published in 1888. It was named after the Armenian astrophysicist, Benjamin Markarian, who discovered their common motion in the early 1960s.

Skywatch Line for Wednesday, May 5, and Thursday, May 6, 2021

This is Dudley Observatory’s Skywatch Line for Wednesday, May 5, and Thursday, May 6, written by Alan French.

The Moon reached last quarter this past Monday so a waning crescent Moon is now moving toward new and rising before sunrise. On Thursday morning a 25% illuminated Moon rises at 3:55 and by Friday it will appear only 17% sunlit and rise at 4:16 AM. With the Moon rising so late we’re in for some nice, dark moonless skies.

The terms first and last quarter Moon tend to cause confusion. People sometimes interpret them to mean one quarter of the Moon will be in sunlight and brightly illuminated. In reality half the visible face of the Moon is sunlit. The terms actually refer to the Moon’s position in its orbit around the Earth.

The Moon is considered to start a trip around Earth when it reaches new, roughly between our Earth and the Sun, with the sunlit face entirely away from us. At new the Moon is invisible, unless it happens to pass between the Earth and the Sun, when parts of Earth will see a solar eclipse. When the Moon reaches first quarter it has completed one-quarter of its trip around Earth. When it reaches last quarter, also called third quarter, it has completed three-quarters of its trip around Earth. At both phases we see half the visible face in sunlight.

When the skies are clear and moonless, it’s a good idea to make a habit of checking the night sky low in the north to northwest for signs of Northern Lights. Although websites like https://spaceweather.com/ can alert you to increased chances for aurora, keeping your eye on the sky is the best guarantee of catching a display. Displays often start as faint glows or curtains of light low in the north to northwestern skies. They may feature shafts of light extending higher into the sky. Some displays are rather static, while others may be very dynamic. A major display can be bright and vivid and involve most of the sky, something not to be missed and worth some vigilance. (Although dark, moonless skies are best for most auroral displays, this writer saw a fine display from Worcester, MA, with a bright, gibbous Moon in the sky.)

For those of us in the Northern Hemisphere, May is the best chance to spot Mercury this year. The innermost planet is now following the Sun across the sky and is visible after sunset. It moves farther from the Sun each day, so appears higher in the sky, but it is also fading. It will be farthest from the Sun on May 17, but just over a magnitude fainter than now.

In addition to clear skies, you’ll need a good view to the west northwest to northwest. (Mercury will be in the same direction as the setting Sun.) The Sun now sets at 8:02 PM. At 8:32 on Wednesday night Mercury will be 10-1/2 degrees above the horizon. By 8:45 it will be 8 degrees high but the sky will be darker. By Thursday it will be one-half degree higher at these times. For reference, a fist held at arm’s length spans 10 degrees across the knuckles.

As it gets later, the western skies will continue to darken, but Mercury will also be lower, where our view is through a thicker layer of our atmosphere and more haze. The optimal time to look is between 8:30 and 9:00 PM. With good sky conditions Mercury is easily visible by eye, but binoculars can make the hunt easier and success more assured. Once located, Mercury is easier to spot without optical aid. Mercury sets at 9:39.

If you have clear skies and an exceptionally good view to the horizon, free of clouds and haze, you may see Venus below and a bit right (north) of Mercury and closer to the horizon. Venus sets at 8:55.

Skywatch Line for Monday May 3rd and Tuesday May 4th, 2021

This is the Dudley Observatory’s Skywatch Line for Monday Tuesday May 3rd, and 4th, written by Joe Slomka.

The Sun sets at 7:59 PM; night falls at 9:51. Dawn breaks at 3:53 AM and ends with sunrise at 5:45.

The Last Quarter Moon rose at 2:21 AM in Capricornus, and appeared 48% illuminated and set at 11:41. Tuesday’s Moon, in Aquarius, rises at 2:58 AM, appears 30 arc-minutes in size, 38% lit and sets at 12:50 PM.

Mars rises, in Gemini, during daytime, is near minimum with 1.6 magnitude and a small 4.6 arc-seconds. By 8:30 PM, it lies about 40° above the southwestern horizon and becomes lower daily. Asteroid 4Vesta remains the only other easily visible solar system object, still riding the back of Leo. Vesta rose at 1:49 PM and shines with 7th magnitude. It is highest at 9 PM when it is due South and 64° altitude; Vesta sets at 4:07 AM.

Also, in the western twilight sky, the constellation Taurus (the Bull) poses challenges for the observer. Venus rises during daytime, blazes with minus 4th magnitude and appears about 10 arc-seconds in size. By 8 PM, it lies about 7° low; however, its brilliance should attract attention; it sets at 8:43. Brilliant Venus points to the other challenge object, Mercury. The elusive planet also rose during daylight, glows with minus zero magnitude, appears a smaller 6 arc-seconds, about 75% lit, 13° high and sets at 9:22 PM. Both planets hug the western horizon, require an unobstructed horizon and may need binoculars.

The pre-dawn eastern sky presents a dramatic scene. Saturn rises first in Capricornus at 2:20 AM, glowing with zero magnitude, and is moderately sized at 16 arc-seconds. Jupiter follows, rising in Aquarius, bright with minus 2nd magnitude and appears twice as large as Saturn. Neptune shares Aquarius, glows with 8th magnitude and only 2 arc-seconds. As mentioned above, the Moon rises at 2:58 AM. Tuesday, the early riser will witness Saturn, Jupiter and the Moon forming a close triangle. By 4 AM, both Saturn and Jupiter will be quite obvious and about 9° apart from the Moon; Neptune, dimmer, lies 23° below Jupiter and may be difficult to spot in the rapidly brightening sky. All three planets set during daytime.

Saturn is the showpiece of any star party. Saturn is not the only planet that has rings. Jupiter, Uranus and Neptune were discovered to display rings by space-borne probes. Now, a new member joins the club. Last year, the European Space Organization (ESO) announced that Chariklo, an asteroid, possesses rings. This was an accidental finding. The ESO had several observatories study Chariklo as it occulted (or eclipsed) a star – to determine its size and shape. When they studied the results, the star was occulted three times. First it flickered; secondly the asteroid blacked it out; thirdly, it flickered again. Astronomers deduced that two rings surrounding Chariklo caused the flickering. Chariklo is a Centaur asteroid; it is rock, enclosed by a fuzzy comet-like halo of gas. The occultation revealed that it is the largest Centaur – 160 miles in diameter.

Skywatch Line for Friday, April 30, through Sunday, May 2, 2021

This is Dudley Observatory’s Skywatch Line for Friday, April 30, through Sunday, May 2, written by Sam Salem.

On Friday, Sun rises at 5:51am and sets at 7:55pm; Moon rises at 8:27am.

The month of May presents the year’s best month for spotting the solar system’s innermost planet, Mercury, in the evening sky. However, you’ll want to find an unobstructed horizon in the direction of sunset to maximize your chances of catching it. Mercury isn’t difficult to spot because it’s dim. Rather, Mercury often eludes detection, because sits low in the west at sunset and then follows the Sun beneath the horizon before true darkness falls. Mercury shines at its brightest for the month in early May, and then slowly dims each day thereafter. Throughout the first week of May, Mercury shines at a negative magnitude, or brighter than a 1st-magnitude star. But even as Mercury dims, it climbs farther away from the Sun each day, to reach its greatest elongation from the Sun on May 17. At that time, Mercury’s brilliance will match that of 1st-magnitude star. This means that chances are that you may well see Mercury with the eye alone, despite the glow of evening twilight. Even with ideal seeing conditions, binoculars enable you to catch Mercury all the sooner after sunset.

Most likely, you won’t see Venus early in the month, as it sits rather close to the glare of sunset throughout the first week of May. Day by day, however, Venus will climb upward, away from the sunset glare.

On Friday, Uranus is in conjunction with the Sun at 4pm. The distant ice giant hasn’t been visible for most of the month, but it will soon return, appearing in the morning sky by late May.

Arcturus is the brightest star high in the east these evenings. Spica shines lower right of it by about three fists at arm’s length. To the right of Spica by half that distance is the distinctive four-star constellation of Corvus, the springtime Crow.

The large constellation Ursa Major, the Big Bear spans the zenith after dusk in late April. The Big Dipper is the most familiar asterism within the constellation. Three Leaps of the Gazelle is another easily seen, but lesser-known pattern in that constellation. Spaced along a line spanning nearly 30 degrees of the sky, three pairs of medium-bright stars resemble a gazelle’s tracks, or perhaps the toes of the bear. In each pairing, the stars are separated by about a thumb’s width. The most westerly stars, Kappa and Iota UMa, or Al Kaprah and Talitha, are found by extending a line drawn diagonally through the Big Dipper’s bowl from Megrez to Merak. The central pair, Mu and Lambda UMa, or Tania Borealis and Australis, sit midway between the Big Dipper’s bright star Dubhe and Algenubi in Leo. The most easterly duo, Xi and Nu UMa, or Alula Borealis and Australis, are close to a line extended south from Dubhe through Merak. The word Alula arises from Arabic for “first leap,” while Tania means “second,” and Talitha means “three.”

On May 1,1949, the Dutch-American astronomer Gerard Kuiper discovered Nereid, the second satellite of Neptune, the outermost and the third largest of Neptune’s known satellites. Nereid’s orbit is the most highly eccentric of any planet or satellite in the solar system. Its distance from Neptune varies from 1,353,600 to 9,623,700 kilometers. Nereid’s odd orbit indicates that it may be a captured asteroid or Kuiper Belt object. The name, Nereid, from Greek methology, refers to the sea nymphs who dwell in the Mediterranean Sea, the 50 daughters of Nereus and Doris. The name Nereids means “Daughters of Nereus” but also “the Wet Ones” from nêros the Greek word for “wet”.

Skywatch Line for Wednesday, April 28, and Thursday, April 29, 2021

This is Dudley Observatory’s Skywatch Line for Wednesday, April 28, and Thursday, April 29, written by Alan French.

The Moon was full last Monday, so a waning gibbous Moon rises after sunset now. The Sun sets at 7:54 PM. Moonrise is at 10:11 Wednesday night and 11:29 Thursday night. It will reach last quarter early next Monday afternoon, having completed three-quarters of its trip around the Earth, from new Moon to new Moon.

Sunrise is at 5:53 AM. If you’re up early, between 4:30 and 5:00, look for bright Jupiter low toward the southeast. The obvious but fainter yellowish star higher in the sky and to Jupiter’s right, 15-degrees away, is Saturn.

Even in Earth’s neighborhood, our solar system, distances are hard to comprehend. A popular aid is to make or imagine a scale model, but a model that has the planet’s sizes and their distances from the Sun on the same scale is not small. A popular model, where 1 inch represents 100,000 miles and 1 yard represents 3.6 million miles, reduces the Sun to the size of the bowling ball and has a peppercorn sized Earth 26 yards away. On this scale our Moon would be a small pinhead just under 2-1/2 inches away from Earth.

All four of the outer gas giants, in our scale model, are larger than our Earth’s peppercorn. Our model would require a chestnut sized Jupiter, Saturn the size of a filbert, and peanuts for Uranus and Neptune. (More precisely, the Earth would be 0.08 inches in diameter, Jupiter 0.9 inches, Saturn 0.75 inches, and Uranus and Neptune 0.3 inches across.)

The scale model Jupiter is, on average, 134 yards from the Sun, while Saturn is 247 yards from it. If we made a model for now, Jupiter would lie 137 yards from our Earth and Saturn would be 288 yards away, almost the length of three football fields.

Neptune is also in the morning sky, but it is never visible by eye. Binoculars, at least, and a detailed star chart are needed to spot it. (Uranus is sometimes bright enough to be spotted by eye under dark skies.) Neptune lies 24 degrees to Jupiter’s lower left now. On our model it averages 778 yards from our Sun and is now 790 yards away from Earth.

In our model, our next closest stellar neighbor, Proxima Centauri, would lie 4000 miles from our bowling ball Sun!

If you are up early on Thursday morning you can watch the ISS (International Space Station) glide across the northwestern sky. Look for it, a moving star, low in the west at 5:16 AM, passing below bright Arcturus, the brightest star in Boötes. At 5:17 it will be passing below the kite shaped pattern of stars outlining Boötes and heading toward the Big Dipper’s handle in the northwest. After passing through the handle, it will be above the Dipper’s bowl at 5:18 and then glide down toward the northeastern horizon, fading from view a bit after 5:21.

Skywatch Line for Monday April 26th and Tuesday April 27th, 2021

This is the Dudley Observatory’s Skywatch Line for Monday and Tuesday April 26th, and 27th, written by Joe Slomka.

The Sun sets at 7:51 PM; night falls at 9:39. Dawn breaks at 4:09 AM and ends with sunrise at 5:57.

Monday’s Full Moon rises at 7:27 PM in Virgo; by 8 PM it is 4° high in the East, 33° in size, and sets at 6:23 AM, Tuesday. Tuesday’s Moon is found in Libra, about the same size as Monday, slightly slimmer, rises at 8:48 PM and sets at 6:57 AM, Wednesday. Because of the Moon’s elliptical orbit, it monthly comes closest to Earth. This occurs on Tuesday, generating “perigean spring tides” – high tides which may pose danger for oceangoing craft.

Red Planet Mars is the only easily seen evening planet.

It rises in Gemini at 9:02 AM, glows with first magnitude, about 4 arc-seconds in size, 93% illuminated. and sets at 12:25 AM. By 9 PM, it is about 35° high in the western sky. Mars is only 4° away from the star cluster M35; both should fit in a low power telescope or binocular field.

Mercury and Venus make a fleeting appearance in the western sky. Found in Aries, they pose a challenge for the observer. Both are close to the setting Sun. Mercury blazes with minus first magnitude and Venus with minus third magnitude. Both are about 4° high; avoid looking directly at the Sun. An unobstructed western horizon and binoculars are helpful. Both set by 8:30 PM.

Asteroid 4Vesta continues to ride Leo’s back. It shines with 7th magnitude and appears about 7° from the bright star Regulus. Vesta rises in the afternoon, is highest at 9:24 PM and sets at 4:39 AM. It is 64° high at 9:24 PM, 57° at 11 PM and 48° at midnight.

The first artificial satellite, Sputnik, was launched in 1957. A series of military and scientific satellites followed. However, long before Sputnik, Arthur C. Clarke, a novelist, screenwriter and physicist, had a dream. In 1947, he published a paper predicting that a satellite placed in a special orbit could act as a relay for radio signals. Clarke predicted that, if you launched a satellite to orbit high above the Earth at the same speed as the Earth’s, the satellite would appear to be stationary in the heavens. In May 1960, NASA first launched Echo, a silvered Mylar balloon, which literally bounced signals across the Atlantic. On July 10, 1962, AT&T launched Telstar, a true relay station. Telstar received and retransmitted signals between the US and Europe. Today, many such satellites crowd our skies and make worldwide television, telephone and Internet service routine. Telstar also paved the way for commercial services like Dish TV and satellite radio services.

Skywatch Line for Friday, April 23, through Sunday, April 25, 2021

This is Dudley Observatory’s Skywatch Line for Friday, April 23, through Sunday, April 25, written by Sam Salem.

On Friday, Sun rises at 6:01am and sets at 7:47pm; Moon sets at 4:33am and rises at 3:35pm. Look upper left of the Moon on Friday, by less than fist at arm’s length for 2nd-magnitude Denebola, the tail star of Leo. Nearly four fists left of the Moon shines brighter Arcturus, the leading star of Bootes. On Saturday evening, Arcturus shines about three fists left of the Moon. Look below the Moon by hardly more than half that distance, and a bit left, to find Spica, the brightest star of Virgo.

Immediately after sunset this weekend, look just above the west-northwestern horizon, where Mercury will be climbing past much brighter Venus. On Saturday, Mercury will be positioned a thumb’s width to Venus’ lower right. On Sunday and Monday Mercury will ascend to Venus’ upper right. The best viewing times will be at about 8pm. It won’t be easy to observe these two planets, even with binoculars. You’ll need an unobstructed horizon in the direction of sunset and clear skies to view these planets in the glow of evening twilight. The Northern Hemisphere has the advantage because Mercury and Venus stay out longer after sunset at more northerly latitudes. For our area, Mercury-Venus set about 35 minutes after the Sun. Day by day, both Mercury and Venus will climb up higher in the sky at sunset and will stay out longer after sundown. Mercury, the faster-moving planet, will soar above Venus in the evening twilight for the next month until Mercury reaches its greatest elongation, or maximum angular distance from the setting Sun, on May 17. After that, Mercury will descend downward, toward the sunset, as Venus continues its climb upward, away from the setting Sun.

Mars, at magnitude +1.4, is now crossing from Taurus into Gemini constellation. It shines in the west after dark.

Jupiter and Saturn sit low in the southeast just before and during early dawn. They are floating nearby in dim constellation of Capricornus. Jupiter grabs the eye at magnitude –2.1. Saturn glows a thirteenth as bright at magnitude +0.7. Catch Saturn a little more than a fist at arm’s length to Jupiter’s right or upper right before dawn grows too bright.

An hour or two before sunrise, look for Vulpecula the Fox in the eastern sky, just to the right of the more famous constellation Cygnus the Swan. Hidden within Vulpecula is Brocchi’s Cluster, also known as the Coathanger. To find it, first locate bright star Albireo, or Beta [β] Cygni, the Swan’s head. Draw an imaginary line 3.3 degrees south and you’ll hit 4th-magnitude star Anser, or Alpha Vulpeculae. Continue that line about 4.5 degrees in the same direction and you’ll land on the Coathanger. Six stars form the line at the bottom of the hanger, while four stars create the curved hook. Wide-field binoculars will give you the best views. The relatively faint, magnitude 8.8, open cluster NGC 6802 lies just east of the Coathanger asterism. Use larger binoculars or a small scope to help observing this irregular scattering of stars.

The Lyrid meteor shower will last until the end of the month, so you might continue to see more shooting stars as the shower winds down over the next week. Lyrid meteor shower peaked on Thursday morning, although the bright Moon will hinder your viewing until shortly before sunrise.

Skywatch Line for Wednesday, April 21, and Thursday, April 22, 2021

This is Dudley Observatory’s Skywatch Line for Wednesday, April 21, and Thursday, April 22, written by Alan French.

The Moon was at first quarter, appearing half-full, early Tuesday night. On Wednesday night the Moon, 68% illuminated, will be high in the southeast as darkness falls. By Thursday it will be 77% in sunlight but not as high in the sky, having risen 72 minutes later.

With the Moon crossing high in the sky and not far past first quarter this is an excellent time to observe the Moon. Any modest telescope will show a wealth of details and even steadily held binoculars will provide a nice view. Shadows are longest along the terminator, the line between sunlight and darkness, so this is where detail stands out in bold relief.

With the Moon between new and full, the terminator is the sunrise line. If you spend time watching, or check every once in a while, you’ll see the rising Sun slowly bringing new mountain tops and crater rims into view, appearing just into the darkness. It’s fun to catch the floor of a crater slowing being revealed by the light of the rising Sun.

On April 21, 1972, Apollo 16’s Lunar Module, piloted by astronaut Charles Duke and carrying Commander John Young, became the second mission to land in the lunar highlands. They explored and secured samples in the area around the landing site. They also deployed the Apollo Lunar Surface Experiment Package (ALSEP). On April 22 they drove the Lunar Rover to Stone Mountain, where they continued their explorations and sample taking.

They departed from the lunar surface on April 24. Apollo 17, which carried Eugene Cernan and Harrison Schmitt to the lunar surface in December, 1972, was the last time humans visited the Moon.