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

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

On Friday, the Sun rises at 5:42am and sets at 8:22pm; Moon sets at 5:23am and rises at 8:23pm. Full Moon occurs at 4:20pm on Friday. This is the smallest full Moon of 2018 as the Moon is also at apogee, or farthest point in its orbit around the Earth. Total eclipse of the Moon occurs on Friday but not for the Americas. This will be the longest total lunar eclipse of the 21st century with totality lasting 1 hour 43 minutes. The eclipse will be viewed in Europe, Africa, and much of Asia. The Moon, orbiting Earth, is in opposition to the Sun at full Moon. When Moon is in exact opposition, a lunar eclipse occurs.

Mars reached opposition Thursday night. However, Mars will be closest to Earth, and its absolute biggest and brightest on the night of July 30-31. A planet is in “opposition” when it is opposite to the Sun as seen from Earth. Opposition occurs for superior planets orbiting outside Earth’s orbit. These planets are Mars, Jupiter, Saturn, Uranus, Neptune, and dwarf planets. A planet in opposition is visible almost all night, rising around sunset, culminating around midnight, and setting around sunrise. Opposition occurs at the point in planet’s orbit where it is roughly closest to Earth, making it appear larger and brighter.

The evening sky features four of bright planets along the ecliptic from west to east. Westernmost is the “evening star” Venus at magnitude –4.2. Jupiter, at magnitude –2.1, shines in the south-southwest at dusk and sets a little before 1am. Saturn, at 0.2-magnitude, transits the meridian at roughly 10:45pm, when it’s due south and in prime position for telescopic inspection. Mars outshines Jupiter, gleaming at magnitude –2.8. Mars is visible all night and highest in the south at around 1:00am. Mars will maintain its peak size of 24.3 arcseconds for about a week around its closest approach on the night of July 30-31. The dust that still cover the Martian globe has started to thin, allowing faint, low-contrast views of some dark surface features.

The first large, stable mass of liquid water has been detected on Mars. An Italian team using ground-penetrating radar found a 12-mile wide lake about a mile beneath the planet’s southern ice cap. There has been evidence of recent water activity but never of stable bodies of water. The team discovered the lake while analyzing a radar survey that was done between 2012 and 2015 by the Mars Express orbiter spacecraft.

Friday is the grand opening of the new observatory building at miSci. The new observatory holds a modern 14-inch telescope. The celebration will run from 6:00 pm to 11:00 pm with solar observing, Night sky observing, hands on activities, and Planetarium shows. Check the Dudley Observatory website for more information.

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

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

With the 97% illuminated, waxing crescent Moon rising at 6:57 p.m. in Sagittarius, set your sights on the brighter celestial objects these nights. After sunset, look for Venus about 15 degrees over the western horizon, shining at magnitude -4.3. Continue to look toward the western horizon at 9:14 p.m., when the -1.7 magnitude International Space Station emerges from below Venus. Follow the ISS as it continues on a northerly trek through Leo, and continues past Ursa Major, before crossing through Cassiopeia, and disappearing into the northeast. The third brightest object on this night is Mars, shining at magnitude -2.77. Mars rises in the southeast at 9 p.m. in the constellation Capricornus. Mars reaches opposition Thursday, and will be at its peak visibility for the year, and at its brightest since 2003. While Mars is rising, look for Jupiter about 20 degrees over the southwestern horizon in the constellation Libra. On this night of bright objects, look for Saturn, shining at magnitude 0.16, 10 degrees to the south of the Moon. Thursday night, the nearly Full Moon, will rise about an hour earlier than Mars, and the two will be separated by 10 degrees.

A surprisingly bright comet is now passing the constellation Auriga. After a second outburst in two weeks, Comet c/2017 S3 (PanSTARRS) is now a binocular target. This 8th magnitude comet may be as bright as 3rd magnitude in August, when it reaches perihelion. Auriga’s brightest star, Capella, rises in the northeast around 2 a.m., signaling the appearance of its host constellation. Look for Comet C/2017 S3 (PanSTARRS) 10 degrees to the lower left of Capella. Future positions for this comet can be found on the website at

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

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

The Sun sets at 8:25PM; night falls at 10:28. Dawn begins at 3:34 AM and ends with the Sun rising at 5:37.

The evening sky is full of planets. Mercury lies very low in the West. In Leo, it shines with 1st magnitude and appears about 10 arc-seconds in size and 22% illuminated. However, it is about 2º above the western horizon and needs an unobstructed view before it sets at 9:11 PM. Venus appears about 22º to Mercury’s upper left. Venus, also in Leo, blazes with minus 4th magnitude, appears about twice as large as Mercury, and is 60% lit. It sets at 10:22 PM.

Jupiter, high in the southwest, still inhabits Libra. It also glares with minus 2nd magnitude and is best observed at 7:34 PM. Telescopic observers can witness the Jovian moon Io disappear behind the planet on Monday at 9:22 PM and also see Io’s shadow leave the planet’s face at 10:03 PM. Jupiter recently made headlines. On July 17th, the Minor Planet Center announced that Scott Sheppard (Carnegie Institution for Science) publicized the discovery of 12 new moons for Jupiter. Of the 12, nine orbit Jupiter opposite to the planet’s spin (retrograde). One moon, nicknamed Valetudo, spins with Jupiter, but at a 34º angle to the equator; in addition, Valetudo crosses paths with the other retrograde moons. This brings the total moon count for Jupiter at 79 and 185 for the whole Solar System; only Mercury and Venus are moonless. Jupiter sets at 12:43 AM.

Saturn, in Sagittarius, shines with zero magnitude moderately high in southeastern skies. Wednesday, it lies about 6º south of the Moon. Saturn is best viewed at 11 PM and sets at 3:42 AM.

Mars, in Capricornus, rises about 9:04 PM. It reaches Opposition on Thursday night. The Red planet shines with minus 3rd magnitude, appears about 24 arc-seconds in size, the maximum for this appearance, and about 10º high in the southeast. NASA reports the dust storm still rages, limiting views of the planet. Mars sets after sunrise.

Neptune, in Aquarius, rises about 10:19 PM, and is best studied at 4:02 AM. Uranus, in Aries, glows with 6th magnitude and rises at 12:06 AM. Both require detailed sky charts to locate them.

The 11-day-old Moon is already up by sunset. In Ophiuchus, it blazes with minus 11th magnitude, appears 88% lit and is best observed at 10:07 PM. Tuesday’s Moon, in Sagittarius, is brighter and larger. It is best observed at 10:55 PM. The Moon sets at 2:20 AM Tuesday and at 3:42 AM on Wednesday.

As appropriate for the racing season, two horses appear by midnight. The largest horse is, of course, Pegasus. The smallest is Equuleus. This dim constellation is easy to find. Pegasus flies upside down and is easily identified as a Great Square. Two thin star chains sweep northward from the upper left. If one sweeps across the chains, binoculars show a large hazy oval; this is revealed, in telescopes, to be the Andromeda Galaxy – about two and a half million light years distant, accompanied by two smaller satellite galaxies. You can see it with the naked eye under dark rural skies. Pegasus’ neck flows from the lower right corner and angles up. Equuleus is the small angular line of stars West of Pegasus’ nose. A globular star cluster, M 15, lies exactly halfway between Pegasus’ nose and Equuleus. This too is easily seen in binoculars.

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

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

On Friday, the Sun rises at 5:35am and sets at 8:28pm; the waxing gibbous Moon sets at 12:43am and rises at 2:12pm. The first quarter Moon occurred on Thursday at 3:52pm. On Friday evening, the waxing gibbous Moon is positioned just three degrees north of Jupiter. The Moon will be closest to Jupiter at around 11:15pm. Lunar Straight Wall, or Rupes Recta, can be seen on Friday evening using a telescope. The Straight wall is a linear fault on the Moon in the southern part of the Mare Nubium. The Rupes Recta casts a wide shadow that gives it the appearance of a steep cliff when the Sun illuminates the feature at an oblique angle. This takes place about day 8 of the Moon’s orbit.

The 0.8-magnitude Mercury is wrapping up its current apparition and sets one hour after the Sun. Venus gleams at magnitude –4.2 due west at dusk. Jupiter, at magnitude –2.2, is already past the meridian at sundown. Aim your scope at Jupiter early to spot it higher in the sky to increase your chances of experiencing steady seeing conditions. You don’t have to wait until dark to observe Jupiter as the planet shows up well at dusk, soon after sunset. Jupiter belts and the Great Red Spot are more pronounced when contrasted against a deep blue, twilight sky.

Saturn, at magnitude 0.1, culminates around 11:15pm this weekend. Saturn hangs low in the south. Shift your scope to catch Saturn rings on full display, just one degree shy of their maximum tilt. This makes the Cassini division easier to sight.

The excitement is mounting as we count down to Mars’ most favorable opposition since 2003. Mars reaches opposition next week, and, at magnitude –2.7, noticeably outshines Jupiter. Mars rises around 9:15pm and hits the meridian a little after 1:30am. Mars’ disk this weekend spans 23.7 arc seconds, which is only a hair shy of the maximum it will attain during closest approach on July 31. However, Mars hangs low in the sky and the dust storm obscure virtually all Mars’ surface markings, no matter how powerful the telescope you use. Watch and hope that the dust settles soon.

This week, the International Astronomical Union’s Minor Planet Center published the orbits for 12 newfound Jovian moons, bringing Jupiter’s total to 79 moons. The team at Carnegie Institution for Science, along with collaborators at the University of Hawaii and Northern Arizona University were able to spot a bit fainter objects than anyone has been able to go in the past. This led the team to the discovery of Jupiter’s 12 new moons. Three of the new moons travel in sync with Jupiter’s rotation, or in prograde orbit. The other 9 have backward, or retrograde, orbits. The smallest newly discovered moon, Valentudo, has a prograde orbit that crosses the retrograde moon orbits, setting the stage for possible moon-moon collision.

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

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

The two innermost planets nearest to the Sun, Mercury and Venus, are low over the western horizon after sunset. Mercury is currently 0.744 astronomical units (69,159,120 miles) away from Earth, or 74.4% of the distance of the Earth to the Sun. Venus is 0.921 astronomical units (85,612,298 miles) away from Earth. You might be asking, how is Mercury closer to Earth than Venus. The reason is that Venus is currently at a greater angular distance from Earth than Mercury. Both Mercury and Venus’elliptical orbits are taking them toward Earth. The easily visible outermost planets, Mars, Jupiter and Saturn, will all be observable after Mars rises at 9:30 p.m. in the constellation Capricornus. Saturn can be found in Sagittarius, while Jupiter resides in Libra.. Mars is 0.396 astronomical units (36,810,499 miles) from Earth, Jupiter is 5.007 astronomical units (465,429,727 miles) from Earth, and Saturn is currently 9.116 astronomical units (847,385,139 miles) from Earth.

The First Quarter phase of the Moon occurs at 3:52 p.m. Thursday. Moonset occurs at 39 minutes past midnight. As you are observing the First Quarter Moon with half of its surface in sunlight, and half in darkness, think about the temperature difference of each side. The sunlit portion of the Moon can reach 280 degrees Fahrenheit. Since there is no atmosphere on the Moon to retain the heat, when the surface slips into darkness, the temperature drops to 280 degrees Fahrenheit below zero. The coldest place in the solar system is the permanently shadowed southwestern edge of the Hermite Crater in the northern polar zone of the Moon. The temperature in the crater can reach -412°F. The hottest place in the solar system, with the exception of solar flares, is in the lowlands of Venus, where the temperature can reach 900°F.

The Albany Area Amateur Astronomers invite you to join them for their monthly club meeting Thursday night, beginning at 7:30 p.m. at miSci in Schenectady.

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

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

The Sun sets at 8:31 PM; night falls at 10:38. Dawn begins at 3:23 AM and ends with the Sun rising at 5:31.

The 4-day-old Monday’s Moon blazes with minus 7th magnitude near Leo’s tail. The Moon is about 21% illuminated and about 22º high; it sets at 11:12 PM. Tuesday’s Moon is brighter and larger in our instruments, migrates to Virgo, 31% lit and about 27º high; it sets at 11:43.

Mercury is quite low on the southwestern horizon. It shares Leo with Venus, gleams with zero magnitude, but is only 6º above the horizon. Mercury is notorious for being difficult to observe; the astronomer must have an unobstructed western view. Mercury becomes lower daily, setting at 9:38 PM. Venus dazzles with minus 4th magnitude, is about 18 arc-seconds in size and appears about 64% lit. It, too is low, about 15º at Civil Dusk and sets at 10:34 PM.

Jupiter still clings to Libra, shining with minus 2nd magnitude and a huge 40 arc-seconds in size. It is best observed, high in the South, at about 8 PM and sets at about 1:10 AM. Jupiter always presents something for the telescopic observer. Monday, at 10:53 PM, the Jovian Moon IO reappears from behind the giant planet; at 11:23 PM, the Great Red Spot (a giant storm) can be seen centered on the planet.

Saturn rises before Sunset and, by Civil Dusk, shines with zero magnitude, appears a medium 18 arc-seconds in size and about 16º high. It, and its famous rings, are best viewed at about 11:35 PM. Saturn sets at 4:11 AM.

Asteroid 4Vesta now grows dimmer daily. In Ophiuchus, the tiny space rock glows with 6th magnitude and is about 25º high. It is best placed for observation at 11:35 PM; however, Vesta requires detailed sky maps to be located. Vesta sets at 3:32 AM.

Mars, in Capricornus, rises at about 9:35 PM and shines with minus 2nd magnitude. Mars continues to brighten and enlarge in our instruments in preparation for its July 27th opposition and closest approach to Earth on the 31st. This opposition is made difficult due to Mars’ low altitude in the sky, but also to the continuing global dust storm. Planetary scientists still report minimal viewing of surface features. Some express hope that there are indications that it might abate, but most experts think it will take months for Martian skies to clear. Mars is highest at 1:58 AM.

Neptune, in Aquarius, glows with 8th magnitude and rises near the star Phi Aquarii at 10:43 PM and is best observed at 4:26. Uranus rises in Aries at 12:33 AM, shines with 6th magnitude and a tiny 3.5 arc-seconds. By Civil Dawn, it is about 46º high. Like Vesta, Neptune and Uranus also require detailed sky maps to assist the observer.

Summer constellations are quite evident. If you live in rural areas, the Milky Way stretches from the northern horizon, overhead, to Sagittarius in the South.

A binocular observer has a choice of objects. He can sweep the Milky Way and wonder at the myriad of stars. Our galaxy resembles a Frisbee. The Milky Way is actually the rim of our Galaxy. Globular clusters of stars surround the galaxy center like Christmas ornaments. Many of these tightly packed star cities can be seen in binoculars. For example, M4 is only a binocular field away from Antares, the heart of Scorpius. Another is the pair on either side of the tip of Sagittarius’ teapot top. Both M22 and M28 are beautiful binocular objects.

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

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

On Friday, the Sun rises at 5:29am and sets at 8:33pm. The new Moon occurred on Thursday at 10:48pm. As twilight fades on Saturday, try to locate the tiny crescent Moon over Mercury very low in the west and to the lower right of Venus. Your best view may be about 45 minutes after sunset. The waxing crescent Moon will be about 2 degrees right of Venus on Sunday early evening. This is close enough for the pair to look good in binoculars or a small scope used at low power.

All five naked-eye planets are viewable before midnight this weekend. Mercury is at greatest elongation from the Sun on Thursday. Mercury sits roughly 6 degrees below and right of Venus, low in the west-northwest during twilight. Due to the shallow angle the ecliptic makes with the horizon at this time of year, Mercury is now slightly lower at dusk than it was at the end of June. Jupiter is already past the meridian as twilight fades in the southwest. At the same time, Saturn is ascending in the south-southeast. Saturn culminates soon after midnight. Mars rises in the southeast horizon around 10:30pm. Mars has brightened considerably as it nears its July 31 close approach. This week Mars shines at magnitude –2.5 and features a disk spanning 22.8 arc seconds. A global dust storm has rendered most Martian surface details indistinct or invisible. Hopefully, the storm will abate soon and Mars observers will be rewarded with best views of the planet since 2003.

Watch satellites slowly drifting across the sky during deep twilight this weekend. You will be able to see them as the Sun is still shining brightly there at altitude of these satellites. The most known human-made satellite object currently in orbit is the International Space Station (ISS). It circles the Earth every 90 minutes at an altitude of 400 kilometers. If you’ve ever wondered about a “bright light” moving west to east at night, there’s a good chance it’s the ISS. The ISS isn’t the only brightly reflective space satellite. Iridium satellites can also put on an impressive display. Unlike the space station, Iridium satellites produce a relatively brief flare that fades away after a few seconds. This is a particularly good weekend for sighting the space station in the morning sky. If you want to catch the ISS or an Iridium flare, there are a number of on-line resources. Use NASA’s Spot the Station site.  Select your location and the site produces a timetable of upcoming ISS passes.  The Heavens Above site lists ISS passes as well as the timings for Iridium flares. The site provides ISS Interactive, a real-time 3D Visualization ISS-eye view of the Earth.

One hour after sunset this weekend, as twilight fades further and the stars are coming out, try to locate the two brightest stars of summer, Vega and Arcturus. They are about equally near the zenith, The very pale bluish white Vega sits toward the east. The pale yellow-orange Arcturus shines toward the southwest.
Sunday marks the 53rd anniversary of the Mariner 4 closest approach to Mars. The satellite sent a transmission of the close-up photograph of Mars, consisting of 8.3 dots per second of varying degrees of darkness. The transmission lasted for 8.5 hours. The satellite was 134 million miles away from earth and 10,500 miles from Mars. The spacecraft provided key information about how to safely deliver future missions to the Martian surface. Far outlasting its planned eight-month mission, the spacecraft lasted about three years in solar orbit, continuing long-term studies of the solar wind and making coordinated measurements with Mariner 5 spacecraft.

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

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

The 2% illuminated, waning crescent Moon sets at 7:14 p.m. Wednesday. The Moon will reach its New phase at 10:48 p.m. Thursday. Lunar perigee, the Moon’s closest distance to Earth during this lunar cycle, occurs at 4:28 a..m. Friday. The combination of lunar perigee so closely following the New Moon will cause higher, and lower, than normal tides. This difference in tides is caused by the Moon’s close proximity, and alignment with the Sun, gravitationally causing the oceans to bulge higher than average on the Moon’s side of the Earth. As the Earth rotates under the bulge of water, tides rise, and as that same area rotates away from the bulge, tides subside.

Five planets are easily visible in the night sky. Look for Mercury low over the northwestern horizon before it sets at 9:35 p..m.. Mercury is 43% illuminated, and will reach its greatest eastern elongation, 26 degrees from the Sun, on Thursday. Venus will be 12 degrees over the western horizon as Mercury is setting. A telescopic view of -4.10 magnitude Venus will reveal it is 66% illuminated. Look for -2.24 magnitude Jupiter 30 degrees over the south-southwestern horizon. Thursday night, Jupiter’s Moon Io, and its shadow, will cross the face of the planet from 10:35 p.m. until 11:34 p.m., when Io’s transit ends. Saturn, just past its opposition, and still 100% illuminated will be in the sky all night. Look for the ringed planet in the constellation Sagittarius, above the south-southeastern horizon before midnight. Last up is 98 % illuminated, -2.49 magnitude Mars. Mars rises in Capricornus at 10:00 p.m., and sets after sunrise.

On July 11, 1801, astronomer Jean-Louis Pons discovered his first comet. During his lifetime, Pons discovered, or co-discovered 37 comets, more than any other person. The July 11,1801 discovery was shared with Charles Messier, who reported seeing the comet the next day. Pons’ first discovery was Messier’s last. Pons continued to discover comets almost every year until his sight failed in 1827. Comet C/2017 S3 (PANSTARRS) suddenly brightened recently. Observers reported the green comet exploded from 12th magnitude to 9thmagnitude and expanded in size to almost double the width of Jupiter. This visitor from the Oort Cloud was expected to be seen with the naked eye in August, but is currently only visible through binoculars and telescopes. You can find the location of Comet C/2017 S3 (PANSTARRS) for any given day using the Heavens-above website.

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

This is the Dudley Observatory Skywatch Line for Monday and Tuesday, July 9th and 10th written by Joe Slomka.

The Sun sets at 8:35 PM; night falls at 10:46. Dawn breaks at 3:15 AM and ends with the Sun rising at 5:26.

Bright planets shine in this evening’s twilight. In the West, Mercury, in Cancer, glows with 0.4 magnitude, appears about 8 arc-seconds in size, and looks about half lit. Its low, 8º altitude, means that it sets quickly at 9:57 PM. Mercury is in its descending mode, which means that it gets lower on the horizon daily. Venus, which lies about 16º to Mercury’s upper left, blazes with minus 4th magnitude and appears about 2/3 illuminated. Binocular and telescopic observers will note that Venus snuggles up 1º to Regulus, the brightest star in Leo. At Civil Dusk, Venus is about 17º high; it sets at 10:46.

The Eastern horizon has its own share of bright planets. Jupiter, in Libra, is found due South at Civil Dusk. It blazes with minus 2nd magnitude is a large 40 arc-seconds in size and about 32º high. It is highest at 8:28 PM. Binocular observers will see Jupiter still close to Libra’s brightest star, Zubenelgenubi. Tuesday, telescopic observers can witness the Jovian moon Ganymede begin to cross the planet’s face at 12:13 AM. Later Tuesday, they will see the Great Red Spot (a giant storm) at 10:13 PM. Jupiter sets at 1:34 AM.

Twilight also reveals Saturn, in Sagittarius; it shines with zero magnitude an is about 22º high in the southeast. Saturn is quite low and presents a challenge for astronomers to see details of its marvelous ring system. Saturn is highest at about Midnight and sets at 4:37 AM. At about 10º to Saturn’s upper right lies the asteroid 4Vesta, in Ophiuchus. It still shines with 5th magnitude and is about 25º high during twilight. Those seeking to find Vesta should utilize detailed sky charts from astronomical media. It sets at 3:57.

Mars, 33º to Saturn’s lower left, rises at 10:04 PM, shines with minus 2nd magnitude, is 22 arc-seconds in size and 98% lit. Mars continues to become brighter and larger, in preparation for its July 27th Opposition. This is normally prime time for people to study Martian geography; however, the global Martian dust storm remains unabated, enabling planetary scientists to track weather on a close planet. Mars is best observed at 2:31 AM.

Neptune rises in Aquarius at 11:15 PM and is best viewed at 4:53 AM. Uranus, in Aries, shines with 5th magnitude, is 3.5 arc-seconds in size and is about 25º high by Dawn.

The waning Moon occupies Taurus both days. Tuesday, the 26-day-old Moon rises at 3:06 AM, blazes with minus 5th magnitude and is about 11% lit. Wednesday, it rises at 3:55 AM, gleams with minus 3rd magnitude and is about 5% lit. Wednesday’s Moon is the last easily spotted old Moon.

Vesta was the goddess of the hearth. Roman homes had hearths for cooking and heat; in fact, the hearth was her shrine. Romans said daily prayers to her in thanksgiving for food and heat. The household fire must never go out. Should the fire extinguish, a new fire could only be started from another holy hearth or Vesta’s temple fire. At the temple, six Vestal Virgins, unmarried women, tended to the sacred fire day and night. They enjoyed great esteem and were granted important privileges. Vestalia was a religious festival when the Vestal Virgins would clean the temple and relight the flame with a magnifying glass. Special cakes were baked and offered to Vesta.

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

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

On Friday, the Sun rises at 5:24am and sets at 8:37pm; the Moon rises at 12:52am and sets at 1:27pm. The Moon reached last-quarter phase on Thursday at 3:51am. Watch the waning crescent Moon, Pleiades star cluster, and bright star Aldebaran in dark eastern skies before dawn on Sunday. Aldebaran is the brightest star in the constellation Taurus the Bull. The Pleiades cluster is fainter, especially as darkness gives way to dawn.

Earth reaches its most distant point from the Sun, aphelion, on Friday at 1:46pm. The word aphelion comes from the Greek words apo meaning away and helios, for the Greek god of the Sun. Earth’s tilt causes the seasons, not Earth’s distance from the Sun. However, Earth’s varying distance from the Sun does affect the length of the seasons. Earth is always farthest from the Sun in early July during northern summer and closest in January during northern winter. That’s because, at our farthest from the Sun, Earth is traveling most slowly in its orbit. That makes summer the longest season in the Northern Hemisphere and winter the longest season on the southern half of the globe. Meanwhile, winter is the shortest season in the Northern Hemisphere, and summer is the shortest in the Southern Hemisphere.

Mercury is coming to the end of its brief evening apparition. Venus, shining at magnitude –4.1, can be spotted minutes after sundown. Mercury sets at 10:03pm and Venus sets at 10:51pm, on Friday night. Like Mercury, Jupiter is winding down its current apparition. The magnitude –2.3 planet is already at the meridian when the Sun sets. Look early to catch Jupiter at its best. Jupiter sets around 1:50am this weekend. Saturn, at magnitude zero, rises around 7:45pm, culminates slightly before 1am, and sets around 4:55am this weekend. Mars rises in the southeast around 10:15pm and reaches the meridian at 3:15am. Mars is only weeks away from its close opposition. Now it exactly matches Jupiter’s brightness and its disk has grown to 21.6 arc seconds diameter.

The darkest sky settles in at around 1am. That’s the ideal hour to enjoy the globular clusters that congregate in and around the Milky Way. The constellations Sagittarius and Ophiuchus harbor seven globulars each. Of the 14 globular clusters scattered across this region, M22, in Sagittarius is the most rewarding. This cluster is a delight in any size telescope. Glowing at magnitude 5.1, M22 is the brightest Messier globular. Locating M22 is straightforward. Using your binoculars or finderscope, you’ll find M22 about 2½ degrees northeast of 2.8-magnitude Lambda (λ) Sagittarii, the star marking the top of the Sagittarius Teapot. Also, you can catch a second globular, M28, in the same finder field one degree northwest of Lambda. At magnitude 6.8 and half the size of M22, M28 is not nearly as impressive an object.