planets 2018 Archives

July 18, 2018 by David Dickinson

Enter the Red Planet: Our Guide to Mars Opposition 2018

Mars Dust Storm — A dusty view of Mars from July 11th. Image credit and copyright: Waskogm.

Have you checked out Mars this season? Mars reaches opposition on July 27th at 5:00 Universal Time (UT) shining at magnitude -2.8 and appearing 24.3” across—nearly as large as it can appear, and the largest since the historic opposition of 2003. We won’t have an opposition this favorable again until September 15^th, 2035.

Mars starts this week near the +4th magnitude star Psi Capricorni, loops westward through retrograde briefly into the astronomical constellation of Sagittarius the Archer in late August before heading back into Capricornus in September.

Mars opened up 2018 just 4.8” across, trekking through the early dawn sky. What a difference a few months make: Mars broke 15” arc seconds—a maximum size for an unfavorable opposition near aphelion—on May 30^th, and now dominates the summer sky around midnight.

Path of Mars — The path of Mars from July through September 2018. Credit: Starry Night.

There’s one downside, however, to the 2018 opposition of Mars: it’s occurring very nearly as far south along the ecliptic as it can. This is great news for observers in Australia, South Africa and South America, as the Red Planet rides high near the zenith at local midnight. Up north, however, we are still looking at Mars through the murk of the atmosphere lower to the horizon. For example, here in Norfolk, Virginia at latitude 37 degrees north, we never see Mars rise more than 29 degrees altitude above the southern horizon this season.

Down with Dust Storms

Does Mars seem a bit… peachy colored to you this season? It’s not your imagination: a planetary dust storm is indeed underway. It’s the middle of autumn for northern hemisphere of Mars, and this seems to be shaping up to be one of those oppositions where the planet, though at its closest, presents a featureless, dust-shrouded disk. This seems to be the case roughly every third opposition or so… our best hope now is that it may clear in the coming final weeks of July. We checked out Mars over the past weekend, and could just spy the pole cap and some slight detail under a veil of haze.

Curiosity dust storm — The Curiosity rover’s dusty view from late June. Credit: NASA

Despite the depiction of Martian dust storms in science fiction blockbusters such as The Martian as furious and unrelenting, these storms are actually pretty mild-mannered, barely able to chase a leaf before them through the tenuous Martian atmosphere, if deciduous trees grew on Mars. One thing Martian dust storms can do, however, is coat solar panels with a battery-killing film, and it has yet to be seen if the aging Opportunity rover will awaken and phone home from Meridiani Planum.

Unlike the Earth, Mars has a markedly elliptical orbit, varying from 1.7 (AU) astronomical units from the Sun at aphelion to 1.4 AU near perihelion. This all means that not every opposition of Mars is equal; in fact, Mars can range from 55 million to 102 million kilometers from the Earth near opposition and appear 13.8” to 25.1” across, depending on where it’s at in its orbit. And although Mars laps the Earth roughly every 26 months, a cycle of favorable oppositions repeat every 15 years.

Mars 2018 — Still dusty… Mars from July 16th. Image credit and copyright: Shahrin Ahmad.

In 2018, Mars reaches opposition on July 27th at 5:00 UT/1:00 AM EDT 57.8 million kilometers from the Earth, then makes its closest approach four days later on July 31^st at 8:00 UT/4:00 AM EDT, 57.6 million kilometers distant. Why the discrepancy? Well, opposition is simply reckoned as the point where an outer planet reaches an ecliptic longitude of 180 degrees opposite from the Sun. Mars, however, is still headed inward towards perihelion on September 16^th, while Earth just came off of aphelion on July 6^th.

Visually, Mars can on occasion “go yellow” and present a saffron color even to the naked eye if a planetary wide sandstorm is underway. At the eyepiece, the most prominent feature is always the pole cap, a white dollop on the planet’s pumpkin hued limb. Crank up the magnification, and dark patches come into view, as Mars is the only planet in the solar system presenting an actual surface available for amateur scrutiny. Mars has a day very similar to Earth’s at only 37 minutes longer in duration, meaning that if you observe Mars at the same time every evening, you’ll see nearly the same longitude of the planet turned towards you, shifted 10 degrees westward. A great tool for comparing what features on Mars are currently turned Earthward is Mars Previewer.

Can you spy Mars… daytime? This month is a good time to try, as it currently shines brighter than Jupiter. The easiest thing to do is lock on to it with a telescope near dawn as it sets to the west and the Sun rises in the east, then simply track it into the daytime sky. We’ve seen Mars in 2003 and again this year while the Sun is still above the horizon… having the Moon nearby also helps, though of course, Mars is very close to the horizon at sunset/sunrise right at opposition.

And speaking of which, viewers in Europe, Africa, Asia and Australia are in for a special treat on the evening of July 27^th, as a total eclipse of the Moon occurs just 15 hours after Mars passes opposition. Ironically, this is also a Minimoon eclipse, as the Moon also passes apogee just 14 hours prior to entering the Earth’s shadow. Expect to see the Red Planet just seven degrees from the blood red Moon at mid-eclipse (more on the eclipse next week).

eclipse vs mars — Mars versus the total lunar eclipse on the night of July 27th. Credit: Stellarium

The Moon won’t occult (pass in front of) Mars again until November 16^th, 2018 for the very southernmost tip of South America. Stick around until July 26^th, 2344 AD, and you can witness the Moon occulting the planet Saturn during an eclipse, though you’ll have to journey to southern Japan to do it.

But you may not have to wait that long… stick around until April 27th, 2078, and you can witness the Moon occult Mars… during a penumbral lunar eclipse:

The April 27th, 2078 occultation of Mars… during a penumbral lunar eclipse. Credit: NASA/GSFC/Occult 4.2/Starry Night

This current evening apparition of Mars ends over a year from now on September 2^nd, 2019, as Mars reaches solar conjunction on the farside of the Sun.

Finally, opposition is a great time to try and check the tiny Martian moons Phobos and Deimos off of your life list. These two moons were actually discovered by Asaph Hall from the United States Naval Observatory’s newly installed 26-inch refractor during a favorable parihelic apparition of Mars in 1877.

Shining at magnitude +12.4 (Deimos) and +11.3 (Phobos), seeing these moons would be a cinch… were it not for the presence of Mars shining a million times brighter nearby. Your best bet is to construct an occulting bar eyepiece (we’ve used a thin strip of foil and a guitar string affixed to an eyepiece to accomplish this) or simply place brilliant Mars just out of view. Phobos orbits once every 7.7 hours and substends 20” from the disk of Mars, while Deimos goes around Mars once every 30.35 hours and journeys 66” with each elongation from the Martian disk. PDS rings node or a good planetarium program such as Starry Night or Stellarium will show the current orientation of the Martian moons, aiding in your decision of whether or not to take up the quest.

Don’t miss out on Mars this opposition season… it’ll be almost another two decades before we get another favorable view.

Read all about viewing the planets, from observation to imaging and sketching in our new book: The Universe Today Guide to the Cosmos out October 23^rd, now available for pre-order.

May 31, 2018 by David Dickinson

Planets on Parade: Saturn at Opposition 2018

2018 planets — Saturn, Mars and Jupiter all beckon this summer. Image credit and copyright: Sharin Ahmad (@shahgazer)

We’re in the midst of a parade of planets crossing the evening sky. Jupiter reached opposition on May 9th, and sits high to the east at dusk. Mars heads towards a fine opposition on July 27th, nearly as favorable as the historic opposition of 2003. And Venus rules the dusk sky in the west after the setting Sun for most of 2018.

June is Saturn’s turn, as the planet reaches opposition this year on June 27th, rising opposite to the setting Sun at dusk.

In classical times, right up until just over two short centuries ago, Saturn represented the very outer limit of the solar system, the border lands where the realm of the planets came to an end. Sir William Herschel extended this view, when he spied Uranus—the first planet discovered in the telescopic era—slowly moving through the constellation Gemini just across the border of Taurus the Bull using a 7-foot reflector (in the olden days, telescopes specs were often quoted referring to their focal length versus aperture) while observing from his backyard garden in Bath, England on the night of March 13th, 1781.

vesta — Looking east tonight at sunset… note Vesta to the upper left. Credit: Stellarium.

Orbiting the Sun once every 29.5 years, Saturn is the slowest moving of the naked eye planets, fitting for a planet named after Father Time. Saturn slowly loops from one astronomical constellation along the zodiac to the next eastward, moving through one about every two years.

path of saturn — The path of Saturn through 2018. Image credit: Starry Night Education software.

2018 sees Saturn in the constellation Sagittarius the Archer, just above the ‘lid’ of the Teapot asterism, favoring the southern hemisphere for this apparition. Saturn won’t cross the celestial equator northward again until 2026. Not that that should discourage northern hemisphere viewers from going after this most glorious of planets. A low southerly declination also means that Saturn is also up in the evening in the summertime up north, a conducive time for observing. Taking 29-30 years to complete one lap around the ecliptic as seen from our Earthly vantage point, Saturn also makes a great timekeeper with respect to personal life milestones… where were you back in 1989, when Saturn occupied the same spot along the ecliptic?

Saturn also shows the least variation of all the planets in terms of brightness and size, owing to its immense distance 9.5 AU from the Sun, and consequently 8.5 to 10.5 AU from the Earth. Saturn actually just passed its most distant aphelion since 1959 on April 17^th, 2018 at 10.066 AU from the Sun.

Saturn’s in 2018 Dates with Destiny

Saturn sits just 1.6 degrees south of the waning gibbous Moon tonight. The Moon will lap it again one lunation later on June 28th. Note that the brightest of the asteroids, +5.7 magnitude 4 Vesta is nearby in northern Sagittarius, also reaching opposition on June 19^th. Can you spy Vesta with the naked eye from a dark sky site? 4 Vesta passes just 4 degrees from Saturn on September 23rd, and both flirt with the galactic plane and some famous deep sky targets, including the Trifid and Lagoon Nebulae.

Saturn reaches quadrature 90 degrees east of the Sun on September 25th, then ends its evening apparition when it reaches solar conjunction on New Year’s Day, 2019.

Saturn is well clear of the Moon’s path for most of this year, but stick around: starting on December 9^th, 2018, the slow-moving planet will make a great target for the Moon, which will begin occulting it for every lunation through the end of 2019.

It’s ironic: Saturn mostly hides its beauty to unaided eye. Presenting a slight saffron color in appearance, it never strays much from magnitude -0.2 to +1.4 in brightness. One naked eye observation to watch for is a sudden spurt in brightness known as the opposition surge or Seeliger Effect. This is a retro reflector type effect, caused by all those tiny iceball moonlets in the rings reaching 100% illumination at once. Think of how the Full Moon is actually 3 to 4 times brighter than the 50% illuminated Quarter Moon… all those little peaks, ridges and crater rims no longer casting shadows do indeed add up.

And this effect is more prominent in recent years for another reason: Saturn’s rings passed maximum tilt (26.7 degrees) with respect to our line of sight just last year, and are still relatively wide open in 2018. They’ll start slimming down again over the next few oppositions, reaching edge-on again in 2028.

Even using a pair of 7×50 hunting binoculars on Saturn, you can tell that something is amiss. You’re getting the same view that Galileo had through his spyglass, the pinnacle of early 17^th century technology. He could tell that something about the planet was awry, and drew sketches showing an oblong world with coffee cup handles on the side. Crank up the magnification using even a small 60 mm refractor, and the rings easily jump into view. This is what makes Saturn a star party staple, an eye candy feast capable of drawing the aim of all the telescopes down the row.

If seeing and atmospheric conditions allow, crank up the magnification up to 150x or higher, and the dark groove of the Cassini division snaps into view. Can you see the shadow of the disk of Saturn, cast back onto the plane of the rings? The shadow of the planet hides behind it near opposition, then becomes most prominent towards quadrature, when we get to peek around its edge. Can you spy the limb of the planet itself, through the Cassini Gap?

Though the disk of Saturn is often featureless, tiny swirls of white storms do occasionally pop up. Astrophotographer Damian Peach noted just one such short-lived storm on the ringed planet this past April 2018.

Saturn’s retinue of moons are also interesting to follow in there own right. The first one you’ll note is +8.5 magnitude smog-shrouded Titan. Larger in diameter than Mercury, Titan would easily be a planet in its own right, were it liberated from its primary’s domain.

Though Saturn has 62 known moons, only six in addition to Titan are in range of a modest backyard telescope: Enceladus, Rhea, Dione, Mimas, Tethys and Iapetus. Two-faced Iapetus is especially interesting to follow, as it varies two full magnitudes in brightness during its 79 day orbit. Arthur C. Clarke originally placed the final monolith in 2001: A Space Odyssey on this moon, its artificial coating a beacon to astronomers. Today, we know from flybys carried out by NASA’s Cassini spacecraft that the leading hemisphere of Iapetus is coated with dark in-falling material, originating from the dark Phoebe ring around Saturn.

iapetus — Two-faced Iapetus as imaged by Cassini. Image credit: NASA/JPL/Space Science Institute.

Owners of large light bucket telescopes may also want to try from two fainter +15th magnitude moons: Hyperion and Phoebe.

Fun fact: Saturn’s moons can also cast shadows back on the planet itself, much like the Galilean moons do on Jupiter… the catch, however, is that these events only occur around equinox season in the years around when Saturn’s rings are edge-on. This next occurs starting in 2026.

Cassini finished up its thrilling 20 year mission just last year, with a dramatic plunge into Saturn itself. It will be a while before we return again, perhaps in the next decade if NASA selects a nuclear-powered helicopter to explore Titan. Until then, be sure to explore Saturn this summer, from your Earthbound backyard.

Love to observe the planets? Check out our new forthcoming book, The Universe Today Ultimate Guide to Viewing the Cosmos – out on October 23rd, now up for pre-order.

April 11, 2018 by David Dickinson

New Saturn Storm Emerging?

Are you following the planets this season? The planetary action is about to heat up, as Jupiter, Saturn and Mars all head towards fine oppositions over the next few months.

Spying the Storms of Saturn

Astrophotographer Damian Peach raised the alarm on Twitter this past week of a possible bright storm emerging of the planet Saturn. The spot was noticeable even with the naked eye and in the raw video Peach captured, a sure sign that the storm was a biggie.

Though outbursts of clusters of white spots on the surface of Saturn aren’t uncommon, it’s rare to see one emerge at such a high latitude. The storm had faded considerably the next observing session Peach performed on April 5th, though observers should remain vigilant.

Saturn Storm 2 — A storm subsiding? The followup view a few days later on April 5th. Image credit and copyright: Damian Peach.

It’s sad to think: Cassini and our eyes in the outer solar system are no more… and the situation will probably remain this way for some years to come. Juno also wraps up its mission at Jupiter (pending extension) this year, and New Horizons visits its final destination Ultima Thule (neé 2014 MU69) on New Year’s Day 2019, though it’ll likely continue to chronicle its journey through the outer realms of the solar system, much like the Voyager 1, 2 and Pioneer 10, 11 missions, also bound to orbit the galaxy, mute testaments to human civilization. But even though proposals for Europa Clipper, a nuclear-powered quad-copter for Saturn’s moon Titan, and a Uranus and/or Neptune Orbiter are all on the drawing board, the “gap decade” of outer solar system exploration will indeed come to pass and soon.

But dedicated amateur astronomers continue to monitor the outer solar system for changes. This month sees Saturn rising around 1:30 AM local and transiting highest to the south for northern hemisphere observers at 6:00 AM local, just before sunrise. Saturn crosses the constellation Sagittarius in 2018, bottoming out at its most southerly point this year for its 29 year path around the Sun. Saturn currently shines at +0.4 magnitude, extending 40” across (including rings) as it heads towards a fine opposition on June 27th. After opposition, Saturn formally crosses into the dusk sky. The amazing rings are an automatic draw, but last week’s storm admonishes us not to forget to check out the saffron-colored disk of Saturn itself as well. For example, I’ve always wondered: why didn’t we see the hexagon before? It’s right there festooning the northern hemisphere cap, plain as day in modern amateur images… to be sure, we’re in a modern renaissance of planetary astrophotography today, what with image stacking and processing, but surely eagle-eyed observers of yore could’ve easily picked this feature out.

And the view is changing as well, as Saturn’s rings reached a maximum tilt in respect to our line of sight of 27 degrees in 2017, and now head back towards edge-on again in 2025. And be sure to check out Saturn’s retinue of moons, half a dozen of which are easily visible in a telescope at even low power.

Finally, here’s another elemental mystery poised by Saturn related to the current storm, one that Cassini sought to solve in its final days: how fast does Saturn rotate, exactly? The usual rough guesstimate quoted is usually around 10.5 hours, but we’ve yet to pin down this fundamental value with any degree of precession.

One thing’s definitely for sure: we need to go back. In the meantime, we can enjoy the early morning views of the most glorious of the planets in our Solar System.

February 26, 2018 by David Dickinson

Venus Returns to the Dusk Sky

The changing phases of Venus, from the 2013 apparition. Credit and copyright: Shahrin Ahmad (@Shahgazer)

Where have all the planets gone? The end of February 2018 sees the three naked eye outer planets – Mars, Jupiter and Saturn — hiding in the dawn. It takes an extra effort to brave the chill of a February morning, for sure. The good news is, the two inner planets – Mercury and Venus – begin favorable dusk apparitions this week, putting on a fine sunset showing in March.

Venus in 2018: Venus begins the month of March as a -3.9 magnitude, 10” disk emerging from behind the Sun. Venus is already over 12 degrees east of the Sun this week, as it begins its long chase to catch up to the Earth. Venus always emerges from behind the Sun in the dusk, lapping the Earth about eight months later as it passes through inferior conjunction between the Sun and the Earth as it ventures into the dusk sky.

Follow that planet, as Venus reaches greatest elongation at 45.9 degrees east of the Sun on August 17th. Venus occupies the apex of a right triangle on this date, with the Earth at the end of one vertice, and the Sun at the end of the other.

Not all elongations of Mercury or Venus are equal, but depend on the seasonal angle of the ecliptic, and whether they occur near aphelion or perihelion. Credit: Dave Dickinson

Mercury joins the fray in early March, as the fleeting innermost world races up to meet Venus in the dusk. March 4th is a great date to check Mercury off of your life list, as the -1.2 magnitude planet passes just 66′ – just over a degree, or twice the span of a Full Moon – from Venus. Mercury reaches greatest elongation 18.4 degrees east of the Sun on March 15^th.

And the Moon makes three on the evening of March 18th, as Mercury, Venus and the slim waxing crescent Moon form a line nine degrees long.

The Moon, Venus and Mercury – looking west at dusk on March 18th. Credit: Stellarium

It’s a bit of a cosmic irony: Venus, the closest planet to the Earth, is also eternally shrouded in clouds and appears featureless at the eyepiece. The most notable feature Venus exhibits are its phases, similar to the Moon’s. Things get interesting as Venus reaches half phase near greatest elongation. After that, the disk of Venus swells in size but thins down to a slender crescent. Venus’s orbit is tilted 3.4 degrees relative to the ecliptic, and on some years, you can follow it right through inferior conjunction from the dusk to the dawn sky. Unfortunately, this also means that Venus usually misses transiting the disk of the Sun, as it last did on June 5-6^th, 2012, and won’t do again until just under a century from now on December 10-11^th, 2117.

Small consolation prize: Mercury, a much more frequent solar transiter, will do so again next year on November 11-12th, 2019.

Amateur astronomers have, however, managed to tease out detail from the Venusian cloudtops using ultraviolet filters. And check out this amazing recent image of Venus courtesy of the Japanese Space Agency’s Akatsuki spacecraft:

Venus in the ultraviolet courtesy of JAXA’s Akatsuki spacecraft. Credit: JAXA/Akatsuki/ISAS/DARTS/Damia Bouic

It’s one of our favorite astro-challenges. Can you see Venus in the daytime? Once you’ve seen it, it’s surprisingly easily to spy… the main difficulty is to get your eyes to focus in on it without any other references against a blank sky. The crescent Moon makes a great visual aid in this quest; although the Moon’s reflectivity or albedo is actually much lower than Venus’s, it’s larger apparent size in the sky makes it stand out. Key upcoming dates to see Venus near the Moon around greatest elongation are April 17^th, May 17^th, June 16^th, July 15^th, and Aug 14^th.

Apparitions of Venus also follow a predictable eight year cycle. This occurs because 13 orbits of Venus very nearly equals eight orbits of the Earth. For example, Venus will resume visiting the Pleiades star cluster during the dusk 2020 apparition, just like it did back before 2012.

Phenomena of Venus

When does Venus appear half illuminated to you? This stage is known as dichotomy, and its actual observed point can often be several days off from its theoretical arrival. Also keep an eye out for the Ashen Light of Venus, a faint illumination of the planet’s night side during crescent phase, similar to the familiar sight seen on the crescent Moon. Unlike the Moon, however, Venus has no nearby body to illuminate its nighttime side… What’s going on here? Is this just the psychological effect of the brain filling in what the eye sees when it looks at the dazzling curve of the crescent Venus, or is it something real? Long reported by observers, a 2014 study suggests that a nascent air-glow or aurora may persist on the broiling night side of Venus.

All thoughts to ponder, as you follow Venus emerging into the dusk sky this March.