Mercury-Jupiter Conjunction of Friday March 5, 202

Eric Saltmarsh


If you went outside just after dawn on Friday, you were treated to a close conjunction of the planets Mercury and Jupiter, in the constellation Capricorn. The planets rose together in the ESE about 5:15am MST.

On that morning, Mercury and Jupiter were separated by only 0.6 degrees. Jupiter, at magnitude -2.0, is the brighter planet, with dimmer Mercury at magnitude 0.6. Saturn, magnitude 0.7, is also in the vicinity, to the pair’s upper right.

If you look for these planets on more than one morning, notice how quickly Mercury and Jupiter appear to converge before conjunction, then separate afterward. Mercury is the real speedster here since, by virtue of its proximity to the Sun, it has a much higher orbital speed than distant, sluggish Jupiter.

These relationships are explained by Johannes Kepler’s three laws of planetary motion, published early in the 17thcentury:

  1. The orbit of a planet is an ellipse, with the Sun at one of the two foci.
  2. A line segment joining a planet and the Sun sweeps out equal areas during equal intervals of time.
  3. The square of a planet’s orbital period is proportional to the cube of the length of the semi-major axis of its orbit.

Cutting to the chase, Kepler’s laws confirm that planets orbiting closer to the Sun travel faster than planets farther from the Sun.

In the case of Mercury and Jupiter, Mercury, the innermost planet, travels around the Sun at 107,000 miles per hour versus Jupiter’s 29,000 miles per hour. Mercury’s orbit is much smaller than Jupiter’s, as well. Since a year is the time it takes a planet to complete one revolution around the Sun, a year on Mercury is equivalent to 88 Earth-days. A year on Jupiter is equivalent to 11.9 Earth-years.

Mercury & Jupiter, Tuesday March 2
Mercury & Jupiter, Tuesday March 2
Mercury & Jupiter, Wednesday March 3
Mercury & Jupiter, Wednesday March 3

Both phots were taken at the same time. Jupiter is higher on the 3rd because it rises earlier each day. Mercury looks like it hasn’t moved in the last 24 hours, but in actuality, it has reduced its apparent distance from Jupiter by one-third.

 

 

 

Mars & The Pleiades
Mars (lower left) passing beneath the Pleiades in Taurus on March 1, 2021

This week, Mars, ‘the Red Planet,’ is making a close passage beneath the Pleiades star cluster. It will be 17 years before Mars and the Pleiades hook up again, so take a moment and check this out while they’re still close together. You can find Mars and the Pleiades just past overhead as darkness falls. They set in the WNW around midnight.

Currently, Mars shines at magnitude 0.9, not nearly as bright as it was at opposition last fall. But, its reddish-yellow color creates a fine contrast with the blue stars of the Pleiades.

About 450 light-years away, the Pleiades (a.k.a., the Seven Sisters) is the closest open star cluster to our solar system. There are 1,000 to 3,000 stars in this dipper-shaped cluster. The stars of the cluster are less than 100 million years old and are considered to be of intermediate age. The brightest stars are hot blue stars, however, most of the Pleiades are faint stars at the red end of the spectrum.

Faint wisps of reflection nebulae, like blue cirrus clouds, seem to surround the brightest stars in the cluster. The nebulae is believed to be unrelated to the cluster, the stars just passing through the dust clouds as they travel together through space. A small telescope or camera-mounted star-tracker is needed to photograph the nebulae

The Pleiades in Mythology

Ancient stories of the Pleiades abound. In Greek mythology, the Pleiades are the seven daughters of the titan Atlas and the sea-nymph Pleione.

In one version of the myth, these seven sisters committed suicide when their father, Atlas, was eternally doomed to shouldering the heavens, as punishment for his part in the ‘Battle of the Gods,’ a decade-long war for control of the universe, fought between the titans or old gods and the new Olympian gods (the Olympian gods won).

After Atlas was forever occupied holding up the sky, the hunter Orion pursued each of his daughters. Zeus, the Sky god and head of all gods on Mount Olympus, placed the Seven Sisters in the sky to keep Orion at bay. Zeus then placed Orion in the sky, where the hunter chases in vain the seven daughters of Atlas across the firmament (unbeknownst to the ancient Greeks, the Pleiades star cluster is moving toward Orion!).

According to one Native American tale, seven young Kiowa women were surrounded by bears. Appealing to the Great Spirit, the ground beneath the women’s feet began to rise, freeing them from their predators. The bears clawed at the new cliffs beneath the flat-topped ground where the women safely resided. As the bears gouged the sides of the cliffs, the ground rose higher, pushing the women into the sky as stars. The butte where the women were saved from the bears is now known as Devils Tower, located in northeastern Wyoming.

In India, the stars are known as Krittika, the six mothers of the six-faced war god, Murugan. To the Japanese, the star cluster is known as ‘Subaru,’ which means clustering or unifying.

In the Lascaux Caves in southwestern France, an ancient pictograph portrays the Pleiades as a six-starred dipper cluster in the shoulder of a bull (Taurus). This rock painting is estimated to be 17,000 years old.

Mars and the Pleiades This Week

Mars will be slightly closer to the Pleiades over the next two nights, making its closest approach on Wednesday (March 3). The planet will then move away from the cluster as it heads for neighboring Gemini.

No optical aid is necessary to view Mars and the Pleiades, although binoculars will help. It’s best to view this spectacle shortly after dark, before Mars and the Pleiades descend into the glare of the prison lights and the light dome of Santa Fe and communities just to the north.

Mars (lower left) and the Pleiades (upper right) on March 1, 2021. The star trails, due to the length of exposure, help show the color contrast between reddish-yellow Mars and the blue stars in the cluster. Reflection nebulae can barely be discerned, especially near the star, Merope (the lower left star in the ‘dipper’).
The constellations Leo (upper right) and the faint, but beautiful Coma Berenices (left of center) grace the spring skies. The glow above the tree is the Zodiacal Light (sunlight reflecting off of interplanetary dust particles). The lighting on the tree and land around it is compliments of the lights at the intersection of Avenida Vista Grande and Route 285. ©Eric Saltmarsh

“Spring constellations are relatively lacking in bright stars, star clusters, and nebulae since we’re looking away from the Milky Way.”

The March Night Sky

– Eric Saltmarsh

The March night sky opens with Leo, the first spring constellation, rising in the east as darkness falls. By month’s end, Virgo pursues Leo into the sky after sunset, followed by Libra, which rises about 11pm MDT.

Spring constellations are relatively lacking in bright stars, star clusters, and nebulae since we’re looking away from the Milky Way. However, what they lack in clusters and nebulae, they more than make up for by offering a window beyond the Milky Way, where other galaxies abound. By studying other galaxies, we can learn about the evolution of our own. Unfortunately, you need a good-sized telescope to view most of these far away objects.

Galaxies beyond our own offer a special glimpse into the universe’s distant past. While most objects within the Milky Way are tens to thousands of light-years away from Earth (a light-year is the distance light travels in one year – 5.9 trillion miles), galaxies are millions, even billions of light-years distant.

The light we see from a galaxy, say 100 million light-years away, left that galaxy 100 million years ago – long before there was life on Earth. Now let’s suggest that this hypothetical galaxy had a cataclysmic explosion within its core, say 20 million years ago. We won’t know about that until light from that event reaches us, 80 million years from now. The scale of the universe boggles the mind.

The farthest known galaxy is 13 billion light-years away. The light we receive from that galaxy tonight, left the galaxy only about 500 million years after the ‘Big Bang’ – the creation of the universe. So, studying distant galaxies not only teaches us about the evolution of galaxies, but about the evolution of the universe, as well.

March Planets

March opens with speedy Mercury and sluggish Jupiter making a tight planetary pair in the dawn sky. They will be at conjunction (closest to one another) on March 5th. This is a very favorable pairing of the two planets since Mercury is close to its greatest western elongation, meaning that it’s about as far from the Sun as it gets.

The two planets rise in early dawn, about 5:20am MST. Saturn isn’t far away, just to the upper right of the Mercury-Jupiter pair. By the 10th of the month, the two planets will be well-separated, with Jupiter continuing to rise earlier and Mercury heading back toward the Sun. By month’s end, Jupiter follows Saturn into the pre-dawn sky. Mercury is now a difficult object, rising at about 6:25am MDT.

Fading Mars opens March near the Pleiades star cluster in Taurus. The Moon passes close to Mars on the evening of the 19th.

Venus is too close to the Sun to be seen this month.

March 5, 2021 Jupiter Mercury Conjunction
Jupiter & Mercury are close together in the March 5 early morning sky. Graphic courtesy EarthSky.Org
Vega, Deneb, & Circumpolar Stars
In this photograph, stars within the yellow arc are circumpolar. The arc is part of a circle encompassing all circumpolar stars seen from our location. Vega and Deneb are not circumpolar here, but they’re high enough in the northern sky that, in late fall/early winter, they set in the northwest after sunset and rise in the northeast before the next sunrise. ©Eric Saltmarsh

March Spotlight: Circumpolar Stars

From the northern hemisphere, Polaris (a.k.a., North Star, Pole Star) seems to stand still in the sky, while the rest of the stars revolve around it. It sits less than one degree from the ‘North Celestial Pole,’ the point directly above Earth’s North Pole. While there are stars closer to the North Celestial Pole than Polaris, they’re all very faint.

While many stars seen from our area rise and set due to the Earth’s rotation, those near Polaris rotate around it, remaining visible all night, all year. These are known as ‘circumpolar stars.’

If we were at the equator, Polaris would be sitting on the north horizon, never appearing to move. However, because Santa Fe sits 35 degrees north of the equator, Polaris appears 35 degrees above the north horizon. As a result, any stars within a radius of 35 degrees of Polaris are circumpolar, as seen from our latitude.

March Night Sky Events

March 3: Mars passes 2.6 degrees from the Pleiades star cluster.

March 5: Mercury and Jupiter are in conjunction, rising together during dawn.

March 6: Mercury is at its farthest from the Sun in the dawn sky (greatest western elongation), in Capricorn, to the lower left of Jupiter. It forms a nice pair with Jupiter during the first week or so.

March 13: New moon.

March 19: The first quarter Moon passes close to Mars in the constellation Taurus.

March 20: Vernal equinox occurs at 6:27am MDT. The Sun is directly over the equator, moving north. This is the first day of spring in the northern hemisphere.

March 28: The full Crow Moon occurs at 12:49pm MDT in the constellation Virgo.

March 31: By month’s end, Jupiter and Saturn rise before dawn in the constellation Capricorn.

Circumpolar stars
Due to the long exposure, the stars appear as lines since they’re constantly rotating around the North Celestial Pole. Polaris is the closest bright star to the North Celestial Pole. But, since it’s not right on the pole, it endlessly circles it, like all the other stars in the photo. ©Eric Saltmarsh

 

Disabled train against the circumpolar stars
A disabled train engine facing due south provides an interesting foreground object as circumpolar stars rotate around Polaris (top center). The glow to the left of the train is light pollution from the Santa Fe area. ©Eric Saltmarsh

 

Canopus above the "Galisteo Wave"
Canopus is the bright white star trail to the upper left of Cerro Pelon (a.k.a., ‘the Galisteo Wave’). Notice how the stars near Canopus rise and set without ever straying far from the southern horizon. Because Canopus is so far south, it sets only 2.5 hours after it rises

Don’t Overlook Our Southern Skies

 – Eric Saltmarsh


One of the aspects of our local skies that I love is our view to the south. There are numerous locations that offer unrestricted access to the southern sky, right down to the horizon.

Objects near the southern horizon don’t receive much attention because they’re low in the sky to most northern hemisphere observers and because only 10% of the world’s population lives south of the equator, where the southern sky is best seen.

Since we live at 35 degrees north latitude (about the same as San Luis Obispo, California and Raleigh, North Carolina) and have dark skies that allow us to view stars right down to our low southern horizon, we can see 55 degrees of sky below the celestial equator (the celestial equator is an imaginary line in the sky, directly above the Earth’s equator). We can’t see the entire southern sky, but we can see more than half of it.

If you go outside after dark this week, there are a number of interesting objects you can find low in the south. One is Canopus, the second brightest star in the night sky, which currently rises in the SSE, about 7pm MST. Canopus is a white star of magnitude -0.74, situated in the constellation Carina. It’s only outshone by Sirius.

While Canopus truly is the second brightest star, its brilliance lacks luster because it never appears more than three degrees above the horizon, as seen from Santa Fe. Canopus’ proximity to the horizon causes us to view it through more atmosphere than a star overhead, significantly dimming it.

Open clusters in the constellation Puppis
Open clusters in the constellation Puppis. NGC 2546 is left of center; NGC 2451 is right of center; NGC 2477 is the indistinct glow to the lower left of NGC 2451.

Three open star clusters (i.e., NGC 2451, NGC 2477, and NGC 2546) sit close together within the winter Milky Way, in the constellation Puppis. NGC (New General Catalogue) 2451 and NGC 2546 appear as neighboring broad clusters of stars, visible to the unaided eye and easily viewed in binoculars. The third cluster, NGC 2477, is a compact group of 300 stars that requires a small telescope to resolve.

A favorite object of mine is Omega Centauri, a large globular cluster located in the constellation Centaurus. Globular clusters are tight balls of myriad stars, held close to one another by gravity. They’re old objects that form halos around a galaxy’s core. Comprised of 10 million stars, omega Centauri is the largest globular cluster in our galaxy.

Omega Centauri is visible to the unaided eye from the 285 Corridor, but – owing to our latitude – it never rises more than 8 degrees above the southern horizon. For centuries prior to the invention of the telescope, this ‘fuzzy star’ was an object of speculation to ancient astronomers.


There are many other objects worthy of our attention that never climb far above our southern horizon. Fortunately, our southern horizon is fairly flat and relatively free of light pollution, so we can view stars and deep sky objects in the southern sky – at least for the time being.

The sky visible from a planet orbiting a star at the center of the omega Centauri globular cluster
Imagine the sky visible from a planet orbiting a star at the center of the Omega Centauri globular cluster

Last fall, the ‘summer Milky Way,’ the brightest portion of the Milky Way that includes the center of our galaxy, appeared to slowly disappear into the sunset. However, its disappearance had nothing to do with its own movement or that of the Sun’s. The summer Milky Way’s disappearance into the solar glare was due to the movement of the Earth, as it orbits the Sun.

Copernicus figured this out in the mid-16th century when he proposed that the Earth orbited around the Sun instead of vice versa and that the stars were in the background, far beyond the Sun and the Earth.

You may be wondering how the Milky Way could have disappeared when it’s clearly visible in the southeast in February, as soon as darkness takes hold. That quandary is due to the fact that we are viewing the Milky Way from inside it.

The Milky Way is a spiral galaxy – a relatively flat disk consisting of a core and several arms that spiral around it. There are between 100 billion and 400 billion stars in the Milky Way, the Sun being one of them.

Our solar system sits in one of the Milky Way’s outer arms. This arm is known as the Orion arm. The Milky Way we see on February evenings, stretching from the southeast horizon, passing overhead, then dropping down to the northwest horizon, is a combination of the Orion and Perseus arms of the galaxy, sometimes called the ‘winter Milky Way.’ At this time of year, we’re looking away from the center of the galaxy.

Before dawn today, we had clear, dark skies – the first clear morning in some time. As I set up my camera and my eyes became dark-adapted, I was heartened to see the summer Milky Way rising on its side, just above the horizon. The Earth had moved far enough along its orbit around the Sun to bring the summer Milky Way back into the night sky, albeit at 4:30am MST!

 – Eric Saltmarsh

February opens with the winter constellations well-placed in the sky as darkness descends. Brilliant stars abound in mid-winter, dominated by Sirius, the brightest star in the night sky. In early February, 11 of the brightest 25 stars in the entire night sky are visible around 9pm MST (8pm MST in late February).

Once darkness sets in, the Orion and Perseus arms of our galaxy, appear as a faint, narrow cloud of stars, spanning the sky from the northwest to the southeast horizons, passing through numerous constellations, including Cygnus, Cassiopeia, Perseus, Auriga, Gemini, Orion, Monoceros, Canis Major, and Puppis.

While not as glorious as the ‘summer Milky Way’ (located toward the center of our galaxy), the winter Milky Way is still a sight to behold on a dark night and one that can’t be enjoyed by many in the US, due to light pollution.

February Night Sky Spotlight:

Orion is one of the most well-known constellations in the sky, named for a hunter in Greek mythology. This month, it’s visible for much of the night.

Orion’s body is depicted by a large rectangle of bright stars. The lower right star is the blue-white Rigel, the seventh brightest star in the night sky.

Diagonally opposite Rigel is red-orange Betelgeuse, marking one of Orion’s shoulders. Betelgeuse is known

as a semi-regular variable star, meaning that its brightness waxes and wanes over a somewhat predictable period. A bright star in its own right, Betelgeuse varies between being the fifth and 23rd brightest star in the night sky.

Betelgeuse is a red giant, a cooling star that‘s burned through its hydrogen and is nearing the end of its stellar life. If our Sun was replaced by swollen Betelgeuse, the Earth would not exist because Betelgeuse’s width would extend to the orbit of Jupiter.

Two years ago, Betelgeuse was in the news because it dimmed significantly and then didn’t brighten when expected (it has since returned to ‘normal’ behavior). The prevailing theory is that the dimming was caused by a large dust cloud, expelled from the star.

In the middle of the rectangle depicting Orion’s body are three fairly bright stars forming a rough line. This is Orion’s belt. A line extended downward from the belt stars roughly points to dazzling, blue-white Sirius. A line drawn in the opposite direction roughly points to red Aldebaran, the brightest star in neighboring Taurus.

Just below Orion’s belt is his sword, consisting of a compact row of four ‘stars.’ The brightest of these appears indistinct. It’s not a star, it’s a giant cloud of dust and gas, known as the Orion Nebula. The nebula is a stellar birthplace of about 700 stars.

Above Betelgeuse is a group of faint stars that form Orion’s club-wielding right arm. A portion of the Milky Way runs through the upraised arm and club. Beginning at Orion’s opposite shoulder (the star Bellatrix), is a faint curving line of stars that denotes Orion’s shield (some artist renderings show Orion holding an animal pelt instead of a shield). A compact triangle of stars between and just above Betelgeuse and Bellatrix marks the hunter’s head.

February Night Sky Planets:

The plethora of planets seen earlier this winter have, for the most part, departed the evening sky. Mars is still visible in Aries after dark, but it’s noticeably fainter than it was several months ago, since the distance between Earth and Mars is increasing.

At the beginning of February, Venus, Saturn, and Jupiter create a short conga line, but are difficult objects to find in the brightening dawn. By month’s end, Saturn and Jupiter have moved farther west of the Sun and are easily viewed in the early dawn, joined by elusive Mercury. Venus has moved closer to the Sun and isn’t visible.

February Night Sky Events:

February 5: Midwinter.

February 10: The waning crescent Moon joins Saturn, Jupiter, Venus, and Mercury in Capricorn, in the ESE, just before sunrise. Binoculars will be needed to find these objects in the strong glare of dawn.

February 11: New moon.

February 18: The first quarter Moon passes just below Mars in the constellation Aries. Notice how the Moon pulls away from Mars as the evening progresses. The two objects will be visible until they set together, just after midnight.

February 24: The waxing gibbous Moon passes close to the Beehive Cluster in Cancer. Binoculars will be needed to view the open cluster in the strong moonlight.

February 27: Full moon occurs at 1:19am MST in the constellation Leo.

 

– Eric Saltmarsh