Category Archives: Skywatch Line

This is the Dudley Observatory’s Skywatch Line for Monday and Tuesday March 8th, and 9th, written by Joe Slomka.

The Sun sets at 5:54 PM; night falls at 7:28. Dawn breaks at 4:43 AM and ends with sunrise at 6:17.

Monday’s Moon already rose and set by sunset. Tuesday’s 29-day-old Moon rises in Capricornus at 4:38 AM and sets at 1:52 PM, 15% illuminated. Wednesday’s Moon rises at 5:18 AM and appears 8% lit.

Monday’s night sky displays a glittering array for the beginner.

Three bright stars dazzle: Sirius (the Dog Star), Betelgeuse and Rigel in Orion, Aldebaran and Mars in Taurus. Mars continues to shrink and dim; it is now 6 arc-seconds in size and 1st magnitude in brightness. Mars sets shortly after Midnight. However, the main attraction is the asteroid Vesta. Vesta travels in the Main Belt, between Mars and Jupiter. It rises at 4:56 PM, is highest at 12:04 AM and sets at 7:12 AM.

Like planets and comets, asteroids have defined orbits about the Sun. Comets are ice and rock mixes, while asteroids are mostly rock. There are several types of asteroid. Some orbit between Jupiter and Mars, others accompany planets, and then there are interlopers from the far reaches of the solar system.

Vesta is the fourth dwarf planet to be discovered. It orbits the Sun every 3.6 years, and is past opposition, which occurred on March 4th. Like the first three asteroids, Vesta was temporarily named a planet, until astronomers realized its small size; it’s about 330 miles in diameter. Vesta is the brightest asteroid. It can be seen with binoculars from a dark, rural site. The Dawn spacecraft discovered layers of rock and metal. It also found that liquid water once flowed and that frozen water may lurk underground. Vesta was victim of an ancient collision; some pieces may have traveled to Earth as meteorites, which have a chemistry similar to Vesta’s.

Vesta currently inhabits the body of Leo, the Lion. Since it is currently in Opposition to the Sun and up all night, this is prime time to study this brightest of asteroids. It is located a bit above the 3rd magnitude star Theta Leonis (Chort), which forms the Lion’s hip. Monday at 7 PM, it shines about 21° above the Eastern horizon. Astronomy magazines and websites have finder charts for beginners.

The pre-sunrise southeastern sky contains similar treasures. The thin Moon rises in Sagittarius about 8° high. Capricornus exhibits 3 bright planets. Saturn rises first at 4:45 AM and glows with 0.7 magnitude. Jupiter follows 9° behind Saturn by rising at 5:08 AM and blazing with minus 2nd magnitude. Mercury brings up the rear by rising at 5:19 AM, shining with 0.52 magnitude and trailing Jupiter by 3°

This is Dudley Observatory’s Skywatch Line for Friday, March 5, through Sunday, March 7, written by Sam Salem.

On Friday, Sun rises at 6:24am and sets at 5:50pm; Moon rises at 12:31am and sets at 10:07am. Moon reaches its third quarter phase on Friday at 8:30pm. It will rise in the middle of the night, and then remain visible in the southern sky all morning. On Friday, the nearly half-lit Moon sits about three finger widths from the bright red giant star Antares in the constellation Scorpio in the southeastern sky before dawn.

This weekend Mercury will move close to much brighter Jupiter. Look for the two planets sitting low over the east-southeastern horizon after they rise together at about 5:15 a.m. At closest approach on Friday morning, Mercury will be located about 20 arcminutes to the upper left of Jupiter. The optimal viewing time for observers at mid-northern latitudes will be 5:45 to 6am, before the sky brightens fully. On Saturday, Mercury will reach its widest angle of 27 degrees west of the Sun, and peak visibility for the current morning apparition. Through a telescope, Mercury will exhibit a 57-per-cent-illuminated, waxing gibbous phase. Unfortunately, Mercury, Jupiter and Saturn will be harder to see, as they’re buried deeper in the morning twilight. The farther south you live, the more time before sunrise Mercury rises. Jupiter shines at magnitude -2.0, while Mercury reaches magnitude +0.1. Saturn sits nearby, just a little dimmer than Mercury at magnitude +0.7.

This weekend, watch Mars lying between the Hyades and Pleiades star clusters. The Hyades is also known as Caldwell 41, Collinder 50, or Melotte 25. It is the nearest open cluster and one of the best-studied star clusters. Located about 153 light-years away from the Sun, it consists of a roughly spherical group of hundreds of stars sharing the same age, place of origin, chemical characteristics, and motion through space. The Hyades is sufficiently close to the Sun that its distance can be directly measured by observing the amount of parallax shift of the member stars as the Earth orbits the Sun. The Hyades Cluster appears in the constellation Taurus, where its brightest stars form a “V” shape along with Aldebaran. However, Aldebaran is not part of the Hyades, as it is located much closer to Earth and merely happens to lie along the same line of sight.

Hyades and Pleiades form the Golden Gate of the Ecliptic, which is known for several thousand years. The Golden Gate of the Ecliptic is an asterism in the constellation Taurus. The two eye-catching open star clusters of the Pleiades and the Hyades form the two posts of a virtual gate at the two sides of the ecliptic line. The Planets, the Moon and the Sun are regularly passing through the Golden Gate of the Ecliptic. The Moon is the closest of these heavenly bodies to the Earth and it is inclined strong enough against the ecliptic. That’s why, in some occasions, the Moon covers the stars of the open star clusters or even pass outside of the golden gate.

This is Dudley Observatory’s Skywatch Line for Wednesday, March 3, and Thursday, March 4, written by Alan French.

A waxing gibbous Moon now rises late in the evening. The Moon will rise at 11:16 PM Wednesday and not until after midnight on Thursday, rising at 12:32 AM Friday morning.

The aurora or northern lights is one of nature’s most impressive sights. Although mostly associated with higher latitudes, like Alaska, northern Canada, and Scandinavia, displays sometimes push down into our area and, on rare occasions, even farther south. Auroras are caused by interactions between the solar wind and the Earth’s magnetic field.

The solar wind consists of charged particles, mostly electrons, protons, and alpha particles, streaming out from the Sun. This stream is deflected by and interacts with the Earth’s magnetic field. The interactions distort our magnetic field and can trap and accumulate charged particles in our planet’s magnetic field (magnetosphere). Further interaction between the solar wind and our magnetic field can cascade these particles down into denser atmosphere, where the collide with atoms and molecules with enough energy to produce light and treat us to beautiful aurora borealis (aurora australis in the Southern Hemisphere).

March is the most geomagnetically active month of the year, so this is a good time to watch for aurora. Look for a gentle glow, perhaps with some shafts of light stretching upward, low toward the north to northwest. A strong display will move higher in the sky, perhaps appearing as curtains of light and bright shafts of light extending toward the zenith. Some displays cover the entire sky.

Displays also vary in how active they are. The glowing curtains and shafts may be static or slow moving, or pulses of brighter light will move rapidly through them. Bright displays may be green, red, or purple. Fainter displays may not reveal color. The amount of structure and detail also varies. At a November display during a Landis Arboretum star party, a curtain of light high in the northwest looked to be made of innumerable pins of light laid side by side.

The best way to catch an aurora is simply to check the night sky evert clear night, especially toward the north to northwest, but that is not always practical or agreeable. Fortunately, there is a place on the web where you can check the space weather forecast and see if there is a chance for northern lights. The website is https://spaceweather.com/. While forecasts of geomagnetic storms and associated auroral activity are not guaranteed, they can alert you of better chances to catch a fine, memorable light show in the night sky.

This is Dudley Observatory’s Skywatch Line for Monday, March 1, and Tuesday, March 2, written by Alan French.

Now just past full, a bright, waning gibbous Moon rises after sunset. The Sun now sets at 5:45 P.M. On Monday night the Moon rises, due east, at 7:28 P.M. and on Tuesday it rises, slightly south of due east, at 8:43 P.M. The Moon will reach last quarter this coming Friday.

You’ve probably seen some of the fine photographs taken by the Perseverance rover on Mars, and perhaps some of the panoramas and 360-degree views created by stitching multiple photos together. One photo on the internet claimed to show Mars and its night sky, but it was actually the night sky as seen from Earth, digitally added. But what does the sky look like from Mars?

A Martian would see the same stars and constellations, but there would be differences from what we see. Our Earth’s axis points roughly toward Polaris, the North Star, so the stars appear to trace circles around Polaris as the Earth rotates. Mars is tipped on its axis at almost the same angle as our Earth, with Mars inclined 25.2 degrees compared to our Earth’s 23.4. Instead of being pointed toward Polaris, Mars’ axis is pointed toward a region in Cygnus that lacks bright stars. Mars’ north celestial pole lies almost 10-degrees north of Deneb, the brightest star in Cygnus, marking the end of the Swan’s tail. During a Martian night, all the stars circle around this point in northern Cygnus.

From our seat in the northern latitudes, constellations close to Polaris, like Cassiopeia, Ursa Minor and Ursa Major, Cepheus, and Draco never set and are above the horizon all night. From the northern hemisphere of Mars, at a similar latitude, Lyra, Cassiopeia, and Cygnus would all be circumpolar and never set. Perseverance is only 18 degrees north of the equator, so Lyra, Cassiopeia, and most of Cygnus dip below the rover’s horizon.

The view from Mars would feature the bright inner planet Earth, appearing as an evening or morning star. The Moon, when not nearly in line with Earth, would be visible by eye, appearing starlike by eye. Through a telescope both would show phases, like Venus and Mercury do from here.

Instead of a single large Moon, Mars has two small moons, Deimos and Phobos, in its sky. Phobos, the larger and closer moon, would appear, at its largest, about one-third the diameter of our Moon. Deimos, smaller and farther away from Mars, would be almost starlike. Because Phobos travels rapidly around Mars, it rises in the west and sets in the east, and makes two trips across the sky each Martian day. Its apparent size and phase change as it moves across the sky. Deimos spends about two-and-a-half days above the horizon.

From our vantage point here on Earth the Sun now lies in the constellation Aquarius. From Mars the Sun now lies in Sagittarius.

This is Dudley Observatory’s Skywatch Line for Friday, February 26, through Sunday, February 28, written by Sam Salem.

On Friday, Sun rises at 6:35am and sets at 5:41pm; Moon sets at 6:37am and rises at 4:57pm. Full Moon occurs on Saturday at 3:17am. The February full Moon, known as the Snow Moon or Hunger Moon, shines near the star Regulus in the constellation Leo. On Friday evening through the moonlight, Regulus is 7 degrees to the Moon’s upper right and Algieba is 7 degrees above the Moon. On Saturday, Denebola, Leo’s 2nd-magnitude tail tip, shines some 7 degrees left of the rising Moon after dark. At the vicinity of full Moon, the Moon rises around sunset, climbs highest in the sky around midnight, and sets around sunset. For us in the Northern Hemisphere, the February full Moon, like the August Sun, follows the high path of the summer Sun. Therefore, it stays out longer than 12 hours. The path of the Snow Moon across our sky is a welcome reminder of the longer summer days to come.

Mercury, Jupiter, and Saturn lurk very low in bright dawn. However, Jupiter and Saturn are getting a little higher and less difficult to see day by day. Mercury brightens while maintaining its position. Mercury nearly doubles in brightness to magnitude +0.3. Saturn is magnitude +0.7, while Jupiter, though lower, is much brighter at mag –2.0. Look very low in the east-southeast 20 or 30 minutes before sunrise. With the sky that bright, you will need binoculars.

Mars, at magnitude +0.8 under the Pleiades, continues to fade in the evening sky as it moves from constellation Aries into constellation Taurus. Look for it high in the west-southwest right after dark. Left of Mars shines Aldebaran, essentially the twin of Mars now in brightness as well as color. The gap between them shrinks to 15 degrees. They’ll pass 7 degrees apart in mid-March. Uranus, at magnitude 5.8 in western Aries, is roughly 20 degrees below Mars in early evening. In binoculars Uranus looks like a little pinpoint “star.”

On Friday, a nearly full Moon makes it difficult to track down dim objects, but plenty of bright targets remain, including the Great Cluster in Hercules M13. This massive, bright globular cluster is visible in the early morning hours before sunrise, when the Strongman Hercules is high in the East. You’ll find M13, which has a magnitude of 5.8, about 2.5 degrees south of magnitude 3.5 Eta (η) Herculis. This ancient group of stars spans 20′, which translates to more than 140 light-years at its distance of roughly 25,000 light-years. M13 is famous as the best Northern Hemisphere globular cluster. It contains hundreds of thousands of stars.

This is Dudley Observatory’s Skywatch Line for Wednesday, February 24, and Thursday, February 25, written by Alan French.

Approaching full, which it will reach early Saturday morning, an almost fully illuminated gibbous now rises before sunset and dominates the night sky. As darkness falls the Moon will be in the eastern sky. The Moon will travel high across the sky and will be highest at 10:22 Wednesday evening and 11:17 Thursday evening. With clear skies moonlight should nicely illuminate our snowy landscape.

On Thursday night the Moon will be in the constellation, Leo, the Lion. The Moon will lie 33-degrees above the eastern horizon at 7:00 P.M. and the star below the Moon, almost 10-degrees away, is Regulus, the brightest star in the constellation Leo, the Lion, and the 21st brightest star in the night sky. Like the majority of bright stars, Regulus is bright because it is one of our closer stellar neighbors, lying 77-1/2 light years from our Sun. The light you see now left the star around August, 1943.

Mars continues to grace the evening sky, but has faded considerably since late fall. On October 13, when Mars was at opposition, opposite the Earth from the Sun, it was 62.7 million kilometers from Earth. It is now 213.5 million kilometers away. Through a telescope it appears about one-quarter the diameter it did then. Looking at it a different way, signals from our spacecraft on and orbiting Mars took 3-1/2 minutes to reach Earth on October 13. Now they take almost 12 minutes to get here. This delay is why landings on Mars have to be handled by the craft’s onboard computers.

Look for reddish Mars high toward the southwest at 7:00 P.M. To its left and higher in the sky, you’ll find reddish Aldebaran, the star marking the eye of Taurus, the Bull, and one of the stars of the Winter Circle. Farther east and lower in the sky you’ll find the familiar patter of Orion, the Hunter.

Ten years ago, on February 24, 2011, the Space Shuttle Discovery was launched from Kennedy Space Center, headed to the International Space Station. Discovery landed at Kennedy Space Center on March 9, completing its 39th mission and final flight, having spent a total of 365 days in space during its career. Discovery is now at the Steven F. Udvar-Hazy Center in Virginia, part of the Smithsonian National Air and Space Museum.

This is Dudley Observatory’s Skywatch Line for Monday, February 22, and Tuesday, February 23, written by Alan French.

The technological success of Perseverance was exciting and it was a thrill to hear it was safely on Mars. While we couldn’t watch it directly, someone was carefully positioned and ready to take a quick look – the HiRISE (High Resolution Imaging Science Experiment) camera on the Mars Reconnaissance Orbiter. Through meticulous planning the HiRISE camera caught an image of Perseverance below its huge parachute as it descended toward Mars. You can see the image at HiRISE | The Descent of Perseverance (Mars 2020) (ESP_068281_9024 (uahirise.org).

Reaching first quarter last Friday, a waxing gibbous now dominates the evening sky. As the Sun sets look for a lovely Moon in the eastern sky. The Moon will be 79% illuminated on Monday night and 87% full on Tuesday. It will travel high across the sky both nights and will be up much of the night. It reaches full early next Saturday morning.

If you are up bright and early on Tuesday morning there is a lovely pass of the International Space Station (ISS) visible from our area just before 5 A.M.. We see satellites because they are up in sunlight while we are still down in the Earth’s shadow. Because the ISS is large it reflects a lot of sunlight and is the brightest satellite gliding through our skies. When high above the horizon it outshines the brightest stars and rivals the brightest planets.

Sometimes we can’t see the ISS pass entirely across the sky, because it either moves into or out of the Earth’s shadow while above the horizon. Tuesday morning’s pass has the ISS emerge from the shadow when 61-degeees above the south-southwestern horizon.

Just before 5 A.M. look high toward the south southwest for the bright, reddish star Arcturus. If you have the right star you’ll see a kite-shaped pattern of stars above it. The ISS, moving out of the Earth’s shadow and into view, will pass just to the left of Arcturus at 4:59:50. It will then move toward the northeast, passing close to bright Vega just before 5:01 A.M., and then pass through, Cygnus, the Swan, as it moves toward the horizon and fades from view. (Some of you may know Cygnus as the Northern Cross.)

This is Dudley Observatory’s Skywatch Line for Friday, February 19, through Sunday, February 21, written by Sam Salem.

On Friday, Sun rises at 6:46am and sets at 5:32pm; Moon sets at 12:35am and rises at 10:35am. The Moon completes the first quarter of its orbit around Earth at 1:47pm on Friday. The evenings surrounding first quarter are the best for seeing the lunar terrain when it is dramatically lit by low-angled sunlight. This first quarter phase will occur while the Moon is passing several degrees to the right of the triangular face of constellation Taurus, the large Hyades star cluster and the bright foreground star Aldebaran. Look for the bright Pleiades star cluster to the Moon’s right.

On Saturday evening, the pole-to-pole terminator boundary that divides the lit and dark hemispheres of the waxing gibbous Moon will fall just to the left of Rupes Recta, also known as the Lunar Straight Wall. This feature is very obvious in good binoculars and backyard telescopes. The rupes, Latin for “cliff”, is a north-south-aligned fault scarp that extends for 65 miles across the southeastern part of Mare Nubium. That’s the large dark region in the lower third of the Moon’s Earth-facing hemisphere. The Straight Wall is prominent a day or two after first quarter. It is obvious again just before third quarter. The Straight Wall is located due north of the prominent crater Tycho.

The Winter Hexagon, also known as the Winter Football and Winter Circle, is an asterism composed of the brightest stars in the constellations of Canis Major, Orion, Taurus, Auriga, Gemini, and Canis Minor. Stars Sirius, Rigel, Aldebaran, Capella, Castor & Pollux and Procyon form the asterism. After dusk, the huge pattern will stand upright in the southeastern sky, extending from 30 degrees above the horizon to overhead. The Milky Way passes vertically through the asterism. The waxing gibbous Moon will travel through the asterism from Saturday to Monday. At nightfall and early evening, look high overhead for the bright star Capella. This star marks the top of the Winter Circle. As Capella shines way overhead, the constellation Orion the Hunter is prowling in the southern sky. Draw a line downward through Orion’s Belt to find Sirius, the brightest star in the night sky. Sirius marks the bottom, or the southern tip, of the Winter Circle.

On Sunday night, the eastward orbital motion of the Moon will carry it towards and across the large open star cluster known as Messier 35, or the Shoe-Buckle Cluster. After dusk on Sunday, the waxing gibbous Moon will be positioned several finger widths to the lower right of the cluster. Hour by hour, the Moon will approach the cluster. By the time the Moon sets after 3am observers will see the Moon only a finger’s width below the cluster. Observers farther west will see the Moon pass across the cluster and leave it behind before moonset. M35 is the only Messier object in constellation Gemini. Look for it with binoculars near the foot of the Gemini star Castor. The cluster’s brightest stars can be resolved in 10X50 binoculars. Small telescopes will reveal some of the fainter stars. Bigger scopes at low magnifications show a field full of stars across the cluster. To best see Messier 35’s stars, hide the bright Moon beyond the upper edge of your binoculars’ field of view.

This is Dudley Observatory’s Skywatch Line for Thursday, February 18, written by Alan French.

This is the day the Perseverance rover and Ingenuity helicopter reach Mars, entering the Martian atmosphere at 3:48 P.M. EST. Their landing is a complex process and it takes about seven minutes for the spacecraft to get from the top of the atmosphere to the Martian surface. Similar landings have been called “Seven minutes of terror,” quite appropriate for today’s landing too.

About 10 minutes before entering the Martian atmosphere the spacecraft taking Perseverance to Mars will be jettisoned, freeing the cruise stage, carrying Perseverance and Ingenuity, to begin its descent. The cruise stage, with its protective heat shield leading, will enter the atmosphere at more than 12,000 mile per hour. After the craft is slowed sufficiently by the atmosphere, a large supersonic parachute will be deployed. Once deployed, the heat shield will separate from the craft.

With the heat shield gone, the cruise craft will use its radar and begin Terrain Relative Navigation – actively looking for a safe place to land Perseverance and Ingenuity. The landing site, Jezero Crater, is considered a good place to search for signs of past microbial life and is geologically interesting, but the region is also a risky place to land, hence the ability to search for and navigate to a safe landing spot.

Jettisoning the back-shield, including the parachute, retrorockets will fire to further slow and guide the craft to a safe landing. When it reaches an altitude of about 70 feet, the rover will separate from the rocket powered descent stage, and then a crane on the descent stage will lower the rover to the surface. The descent stage will then fly well away from the landing site. If all goes well the rover and helicopter will safely touch down at 3:55 PM EST.

You can watch the landing live at Watch NASA’s Perseverance Rover Land on Mars! – YouTube, on NASA Television, or find other live coverage with a search engine.

A lovely waxing crescent Moon, approaching first quarter, will be visible high toward the south southwest as darkness falls tonight. Although neither tonight’s weather nor the temperatures sound agreeable, the nights around first quarter are the perfect time to explore the Moon through a telescope or binoculars. Even steadily held binoculars will show the larger craters, and any modest spotting or astronomical telescope will show an amazing wealth of detail. Put “Exploring the Moon” on your bucket list for warmer weather and clear skies.

This is Dudley Observatory’s Skywatch Line for Monday, February 15, and Tuesday, February 16, written by Alan French.

The Sun now sets just before 5:30. The Moon was new last Thursday, so a waxing crescent Moon now graces the early evening sky. It will be a pretty sight in the west southwest under dark 7:00 PM skies. The Moon sets at 9:33 PM Monday and 10:34 PM Tuesday. The Moon will reach first quarter on Friday.

When the Moon is a crescent less than half of the side facing Earth is in sunlight and brightly illuminated, but it’s easy to see that the rest of Moon is also faintly visible. If you were on the visible part of the Moon you would see a waning gibbous Earth in your sky now, its light brightening the night portion of the Moon facing Earth. This faint illumination is called earthshine.

The United Arab Emirates’ Hope spacecraft successfully entered orbit around Mars on February 9 and has returned its first photo of the Red Planet. It will study the planet’s weather and climate.

China’s craft Tianwen-1 entered Martian orbit on February 10. In addition to studying the planet from the orbiter, Tianwen-1 carries a Martian rover, which will land on the planet in May or June. One of the main goals of the orbiter and rover is to map surface and subsurface ice.

The United State’s Perseverance rover, carrying the Ingenuity helicopter, will attempt to land on Mars at 3:43 P.M. EST on Thursday, February 18. It’s a busy time for Mars!