Skywatch Line for Friday, August 11 through Sunday, August 13, 2017

This is Dudley Observatory’s Skywatch Line for Friday, August 11 through Sunday, August 13, written by Sam Salem.

On Friday, Sun rises at 5:58am and sets at 8:03pm; Moon rises at 10:19pm. Last quarter Moon occurs on Monday at 9:15PM.

One hour after sunset, magnitude –1.8 Jupiter hangs just a little more than 10 degrees above the southeast horizon, while Saturn, magnitude 0.3, is already at the meridian and starting to lose altitude. In the morning sky, Venus, at magnitude –4.0, continues its long-running apparition. It rises well before astronomical twilight begins and is a dominant sight at dawn. Venus will continue as “morning star” all through summer and to the end of fall.

Friday and Saturday nights present the peak nights of the Perseid meteor shower. Watch from late evening till dawn on both nights. The greatest number of meteors typically fall in the hours before dawn, and on a moonless night you can often spot 50 or more meteors per hour. This year the bright waning gibbous Moon lights up the morning hours, intruding on the annual Perseid meteor display. Perseids are well worth watching because a good percentage of these meteors should be bright enough to overcome moonlit glare. The Perseids are known to be colorful meteors. According to NASA’s Meteoroid Office, the Perseids have more fireballs than any other major shower. The constellation Perseus is the radiant for the annual Perseid meteor shower. But you don’t need to know the constellation Perseus to watch the Perseid meteor shower. The Perseids fly every which way across the starry heavens. The radiant sits low in the northeast sky at evening and climbs upward throughout the night. The higher that the radiant is in your sky, the more Perseid meteors you’re likely to see. The radiant is highest before dawn. The earliest historical account of Perseid activity comes from a Chinese record in 36 AD, where it was reported that “more than 100 meteors flew in the morning.” The Perseid meteors happen around this time every year, as Earth in its orbit crosses the orbital path of Comet Swift-Tuttle. Dusty debris left behind by the comet smashes into Earth’s upper atmosphere, lighting up the nighttime as fiery Perseid meteors.

The faint constellation Ophiuchus, the Serpent Bearer appears in the south to southwest sky on August and September evenings, above the bright star Antares, the brightest in the constellation Scorpius, the Scorpion. Planet Saturn appears near Antares, somewhat brighter than Scorpius’ brightest star. Saturn shines in front of the constellation Ophiuchus and will continue to do for several more months. Ophiuchus’ brightest star, Rasalhague, marks the of Ophiuchus’, the Serpent Bearer, Head. Rasalhague is from the Arabic word (ras-al-hawwa) which means the Head of the Serpent Collector.

Saturday marks the anniversary of the discovery of the first of two moons of Mars. On August 12 1877, American astronomer Asaph Hall discovered the first of two moons of Mars. He named the first Deimos. Five days later, on August 17 1877, he observed a second moon, which he named Phobos. In Greek mythology, these are the sons of Ares (Mars) and Aphrodite (Venus). Deimos is Greek for “panic” and phobos is Greek for “fear.” These moons are composed of carbon-rich rock like C-type asteroids and ice. Their densities are so low that they cannot be pure rock. Both are heavily cratered. They are probably asteroids perturbed by Jupiter into orbits that allowed them to be captured by Mars.

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

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

Now that Daylight Savings Time is in effect, the Sun sets at 7 PM; night falls at 8:34. Dawn breaks at 5:34 AM and ends with sunrise at 7:08.

Two bright and one dim planets appear in the darkening western sky. Venus, in Pisces, is the brightest and lowest at 13 degrees altitude. It glares at minus 4.3 magnitude, is large in our instruments at 56 arc-seconds, but shows only a very thin crescent at 5.6 percent. It sets at 8:44 PM. Mars, in Aries, is second brightest at first magnitude and appears nearly full, but is a tiny 4 arc-seconds in size; it hovers 31 degrees above the western horizon. It sets at 10:21 PM. Uranus, in Pisces, is dimmest at sixth magnitude, appears smaller than Mars in our telescopes and is 21 degrees high; it sets at 9:27 PM.

The just-passed-full Moon rises at 8:13 PM in Virgo and blazes at minus 12th magnitude. Tuesday finds it rising in Virgo at 9:14 PM. The rising Moon will blot out most deep-sky objects, like galaxies and nebulas. However, the Moon will not obscure the giant planet Jupiter, which also rises in Virgo at 9:11 PM. Jupiter, the Moon and Virgo’s bright star Spica will form an attractive triangle Tuesday night.

Jupiter shines at minus 2.4 magnitude and appears a large 43 arc-seconds in size. The giant planet remains up all night. Astronomers can have a double treat from Jupiter. The Great Red Spot, a giant storm, will be visible at 3:18 AM and at 11:09 PM on Tuesday. Jupiter’s moon Europa disappears behind the giant planet at 4:37 AM also on Tuesday.

Twilight affords a challenge object, the asteroid 4Vesta. It’s about one-and-a-half degrees below the star Upsilon Geminorum. It shines at seventh magnitude and is a tiny 0.4 seconds in size, requiring detailed star charts from astronomy media. Observers should try before the Moon gets too high in the sky.

Saturn rises in Sagittarius at 2:40 AM. It shines at 0.5 magnitude and presents a modest 16 arc-seconds in our telescopes. Saturn is best observed before Dawn breaks at 5:34 AM; it should be far enough from the Moon to enjoy views of its rings.

March 17 is the 362nd anniversary of Christian Huygens’ discovery of the Saturnian moon Titan. Christian Huygens was a Seventeenth Century scientific giant. He made discoveries in the fields of: astronomy, game theory and horology (time). He improved spherical telescope lenses; today, astronomers still use Huygens eyepieces. He observed the 1661 transit of Mercury across the Sun, worked on laws of gravity and light, invented the first projector, the first pendulum clock and improved the pocket watch. While Galileo first observed Saturn through a telescope, he was confused by the rings, which he called “ears.” Huygens, observing Saturn with a fifty-power telescope, was the first to call them a ring; later observers discovered gaps in the rings. Huygens even published a book on extra-terrestrial life.

For his many accomplishments, Huygens was honored. The Cassini space probe of Saturn carried the Huygens lander. Asteroid 2801 was named for him, as were a crater on Mars and a mountain on the Moon.

Skywatch Line for Friday, December 30, through Sunday, January 1, 2017

This is Dudley Observatory’s Skywatch Line for Friday, December 30, through Sunday, January 1, written by Sam Salem.

On Friday, the Sun rises at 7:26am and sets at 4:31pm; the 2% illuminated Waxing Crescent Moon sets at 6:09pm.

Mars rises above-left of Venus in the evening. One hour before sunrise, Jupiter, at magnitude -1.9, is roughly due south, in Virgo, above the bright star Spica. Saturn is a bit tricky to see. It doesn’t rise until after 6:30 am in the southeast horizon, when twilight is brightening the dawn sky. Look for the Waxing Crescent Moon and the nearby Venus, on Sunday after sunset, Watch for the Waxing Crescent Moon to pass by Venus and Mars over the next several evenings.

Mars and Neptune have a rare and close conjunction on New Year’s Eve. They will appear roughly 11 arc minutes apart, which is about 1/3 the apparent size of the full Moon. Mars glides south of the pale-blue, 8th-magnitude dot of Neptune. The later you look, the closer the pair will be. The longer you wait, the lower they’ll be.

The moonless nights this weekend offer an opportunity for deep sky observing. Look for constellation Auriga, the charioteer. Auriga is home to three open clusters: M36, M37 and M38. These stellar clumps are members of the Milky Way Galaxy. Locating Messier 36 is relatively easy once you locate the constellation of Auriga. Looking roughly like a pentagon in shape, start by identifying the brightest of these stars, Capella. Due south of it is the second brightest star which shares its border with Beta Tauri, El Nath. By aiming binoculars at El Nath, go north about 1/3 the distance between the two. Note the two very visible clusters of stars in this area, Binoculars will reveal the pair in the same field, as will telescopes using lowest power. The dimmest of these is M38. About 2 1/2 degrees to the southeast, which is about a finger width, locate the much brighter M36, more easily resolved in binoculars and small scopes. If you continue roughly on the same trajectory about another 4 degrees southeast, you will find open cluster M37. This galactic cluster will appear almost nebula-like to binoculars and very small telescopes. It comes to perfect resolution with larger scopes. The easiest target is M36, as it’s the most compact member of the trio. In a telescope, M36 displays a striking, spider-like appearance with rows of faint stars radiating from the cluster’s center.

The New Year begins with Sirius’ culmination at the midnight hour. December 31 is the official midnight culmination of Sirius, the brightest star in the nighttime sky, when it is highest in the sky at midnight. The midnight culmination of Sirius by the clock may be a little bit off, depending on how far east or west you live from the meridian that governs your time zone. For our area, Sirius reaches transit altitude of 30 degrees south one minute after midnight on the New Year’s Eve. Sirius is out for most of the night. It rises at 7pm and sets around 5am that night.

On January 1, 1972, the Coordinated Universal Time (UTC) was adopted worldwide. UTC is determined from six primary atomic clocks that are coordinated by the International Bureau of Weights and Measures located in France. The abbreviation – UTC – was chosen as an international compromise between the initials of the English language form “coordinated universal time” and the French “temps universel coordonné.” Leap seconds are added to UTC periodically, about once each 18 months, so the highly accurate atomic clock time matches the time measured by Earth’s rotation, which is very slightly variable due to tidal forces with the Moon.

Skywatch Line for Friday, September 16, through Sunday, September 18, 2016

This is Dudley Observatory’s Skywatch Line for Friday, September 16, through Sunday, September 18, written by Sam Salem.

The Full Moon occurs at 3:05pm on Friday. The Harvest Full Moon rises shortly after sunset, at 7:11pm, and sets shortly before sunrise, at 6:14am. The Harvest Moon is the full Moon closest to the Fall Equinox. Every Full Moon rises around the time of sunset, and on average each successive moonrise comes about 50 minutes later daily. But when a full Moon happens close to the Fall Equinox, the Moon (at our latitude) rises only about 30 to 35 minutes later daily for several days before and after the full Harvest Moon. It happens because the Moon’s orbital path makes a narrow angle with the evening horizon near the Fall Equinox. In the nights after the full Harvest Moon, the Moon rises in the east relatively soon after sunset making it seem as if there are several full Moons for a few nights in a row. That fact was important to farmers in earlier times. It meant there was no long period of darkness between sunset and moonrise for several days after full Moon. Farmers could work on in the fields, bringing in the crops by moonlight, hence the name “Harvest Moon”.

Lunar sightseeing can be done during this full Moon weekend. The most striking detail seen along the lunar terminator would be absent when the Moon is full. However, you can use your telescope to scan the entire circumference of the limb and notice a trace of shadow detail, especially on Saturday and Sunday nights when the phase is a little past full. The Moon is very bright when it’s full. For comfortable observing, use a Moon filter to cut the brilliance without eliminating detail. Because there are no shadows at full Moon, the dark and light areas seen are variations in the reflectivity of different parts of the Moon. The biggest difference is between the dark maria (the lunar “seas”) and the light highlands. This is due to the compositions of the two surfaces. When the Moon is full, the great crater Tycho is one of the most noticeable lunar features. It features impressively long bright rays that span two-thirds of the lunar disc. Inspect Tycho with a telescope at moderate magnification and you’ll easily see the dark halo that encircles the crater. Inspect the lunar disk for more ray craters, including Copernicus, Proclus, Kepler and Aristarchus.

Spica, the brightest star in constellation Virgo, is about 3 degrees lower right of Venus on Saturday and Sunday, soon after sunset. Spica sets at 7:53pm and Venus sets at 8:03pm on Saturday.

Shortly before sunrise, follow Capella and Sirius into daylight. Look up north for Capella, the brightest star in constellation Aurigae and look up south for Sirius, the brightest star in the night sky.

Skywatch Line for Monday and Tuesday, July 4th and 5th, 2016

This is the Skywatch Line for Monday and Tuesday, July Fourth and Fifth.

The Sun sets at 8:36 PM; night falls at 10:50. Dawn breaks at 3:09 AM and ends with the Sun rising at 5:23.

Monday is auspicious for several reasons, all astronomical. Three weeks ago, the Earth experienced the Summer Solstice, when the Sun is highest in the sky and daylight is longest. On the Fourth of July, the Earth is at aphelion: its furthest from the Sun – 94 million miles or 152 million kilometers. The northern hemisphere undergoes hot summers because Earth is tilted, and that tilt points to the Sun and its warming rays. Ironically, the Northern Hemisphere is warmest when Earth is furthest from the Sun.

The Moon exhibits a “New” phase at 7:01 AM. This means that the Moon rises and sets with the Sun, and is hidden in the solar glare. Tuesday, the Moon rises later and also sets later, at 9:24 PM, when the it is only 3 percent illuminated and a degree above the western horizon.

Three planets are more easily observed. Jupiter is first to appear in the darkening sky. It is in Leo about 27 degrees above the western horizon and blazes at minus 1.9 magnitude. Observers should study Jupiter as early as possible, before it becomes too low for useful views. Jupiter sets before Midnight.

Mars, in Libra, shines at minus 1.3 magnitude. Mars is now receding in Earth’s rearview mirror, dimming by one-half and also shrinking in our eyepieces. Mars still forms the western point of a celestial triangle. It lies about 18 degrees from Saturn and 16 degrees above the bright red star Antares, in Scorpius. It also now has resumed “direct” (eastward) motion and slowly creeps toward Saturn. Mars is best seen at about 9:22 PM, and sets at 2 AM.

Saturn, the eastern part of the triangle, is still in the dim constellation of Ophiuchus and about six degrees above Antares. Saturn is best observed about 10:40 PM. Both Mars and Saturn are favorites at star parties and a treat for first time sky watchers. Saturn sets at 3:22 AM.

Eighth magnitude Neptune rises in Aquarius at 11:22 PM. This gas giant planet appears as a tiny blue-green dot amid the stars, and requires a detailed sky chart from astronomical media. Similar looking Uranus, in Pisces, glows slightly brighter at 5.8 magnitude. It, too, requires detailed finder charts and rises about 12:55 AM.

The Fourth of July is famous for fireworks. In the year 1054 Nature staged her own fireworks show. Chinese astronomers saw a new star in Taurus. Eyewitness accounts said it “shone like a comet.” The “guest star” shone in daylight for 23 days and was visible nightly for a year and a half. Many textbooks remark that no one in Europe or the Mid-East observed it. However, North American Natives noticed it and made rock carvings depicting it. Charles Messier made it the first in his list of false comet objects. We now know the Crab Nebula is a supernova – the remnant of a star that blew up. It shone with the brightness of 500 million suns and produced a pulsar, a residue body that spins rapidly and emits regular radio pulses.

Skywatch Line for Friday, June 24, through Sunday, June 26, 2016

This is Dudley Observatory’s Skywatch Line for Friday, June 24, through Sunday, June 26, written by Sam Salem.

The Sun rises at 5:18am on Friday and sets at 8:38pm. The Waning Gibbous Moon is 78% illuminated on Friday. In the next days the Moon rises after nightfall and sets westward direction after sunrise. On Sunday, the moon rises at 12:03am and sets at 11:48am. This weekend, look at the Moon, at the same time every day, and watch it climbing higher and higher up into the morning sky. The last quarter occurs on Monday at 2:19pm.

Mercury rises at 4:22 am on Friday. Mercury is having a very low partition in the dawn. Look for it above the east-northeast horizon 30 or 20 minutes before sunrise.

Jupiter appears high in the west as the darkness falls and remains in the sky until midnight. Jupiter shines at magnitude -1.9 in Leo the Lion.

Mars and Saturn rise before sunset. Mars, now of -1.6 magnitude in Libra, is still an attractive object to observe even with a small telescope. Saturn, of +0.1 magnitude, is about 20 degrees left of Mars at dusk with Antares to its lower right. Mars sets around 2:45am and Saturn sets around 4:09am on Saturday morning.

Sunday night is a good time to look for Pluto. The distant dwarf planet passes south of the third magnitude star Pi (p) Sagittarii in northeastern Sagittarius. You will need an 8-inch telescope or larger to spot the +14.1 magnitude dim world.

It’s summer time. Late sunsets combined with the long summer twilights reduce the time for dark sky observation. Darkness begins when the Sun dips 18 degrees below the horizon. The Sun’s position in the sky is defined by its declination and right ascension, which are similar to the latitude and longitude. After sunset, the Sun continues to move along its line of declination. The circles of declination intersect the horizon at a shallow angle around the solstice. Leading to longer twilight, as Earth must spin a while longer before the sun reaches the -18 degrees. The lines of declination curve upward as the Sun moves back toward dawn after a few hours of darkness.

June 26, 1730 is the birth date of Charles Messier. The French astronomer is best known for his famous astronomical catalog known as the “110 Messier Objects”. Messier’s job as a comet hunter led him to continually come across fixed fuzzy objects in the night sky which could be mistaken for comets. He compiled the list in collaboration with his assistant to help comet hunters distinguish between the comets they were looking for and the non-comet, permanent fuzzy objects, in the night sky. The catalogue consists of star clusters, nebulae, and galaxies. Messier did his observing with a 4-inch refracting telescope from a hotel in downtown Paris. Messier designations of celestial objects, from M1 to M110, are still used by astronomers today. The relative brightness of the Messier objects makes them popular objects for amateur astronomers.

Skywatch Line for Friday, December 25, through Sunday, December 27, 2015

This is Dudley Observatory’s Skywatch Line for Friday, December 25, through Sunday, December 27, 2015, written by Alan French.

We have a rare Christmas full Moon to enjoy. It has been 38 years since there was a Full Moon on Christmas, the last being in 1977. The wait for the next Christmas Full Moon will not be as long – only 19 years.

Reaching full very early Christmas day, the Moon will rise at 5:09 pm Friday. Look for it toward the east northeast as it peaks above the horizon. With the proper choice of foreground this rising Christmas full moon would make a fine photo.

A rising full Moon can be a lovely sight. With its light passing through a thicker layer of atmosphere and more of the shorter wavelengths toward the blue end of the spectrum scattered, it is often orange. Its shape can also be distorted, often giving it a flattened appearance. An illusion also makes it appear larger when near the horizon.

The Moon will be due south and highest at 12:36 am Saturday morning, but catch it when you can – it will be a pretty sight among the bright stars of winter all night.

A bright waning gibbous Moon will rise at 6:09 pm Saturday and 7:11 pm Sunday.

Mercury is an elusive target. Because it orbits close to the Sun it can never appear high in the dark sky, and only makes brief excursions into the early morning or evening twilight skies. Right now Mercury is in the evening sky and can be spotted as darkness falls.

Look for Mercury at 5:15pm toward the southwest. It will be just under five degrees above the horizon, so you’ll need a good clear view to the southwest. Haze or clouds over hang near the horizon and might make it impossible to spot by eye. If so, try finding it by scanning the horizon with binoculars.

If the weather is uncooperative or you are unable to find Mercury, keep trying on following nights. Mercury is slowing fading, but it is also slowly moving higher into the evening sky, reaching just less than seven degrees above the horizon on the first days of January.