Catch Jupiter Homing in on Venus Through June

Getting closer... Venus, Jupiter, the Moon and an iridium flare on the night of May 26th, 2015. Image credit and copyright: Chris Lyons

Are you ready to hear an upswing in queries from friends/family and/or strangers on Twitter asking “what are those two bright stars in the evening sky?”

It’s time to arm yourself with knowledge against the well-meaning astronomical onslaught. The month of June sees the celestial action heat up come sundown, as the planet Jupiter closes in on Venus in the dusk sky. Both are already brilliant beacons at magnitudes -1.5 and -4 respectively, and it’s always great to catch a meeting of the two brightest planets in the sky.

June 5th
Looking west on the evening of June 5th from latitude 30 degrees north… Image credit: Stellarium

Be sure to follow Venus and Jupiter through June, as they close in on each other at a rate of over ½ a degree—that’s more than the diameter of a Full Moon—per day.

June 20th
…and looking west on the evening of June 20th…

Venus starts June at 20 degrees from Jupiter on the first week of the month, and closes to less than 10 degrees separation by mid-month before going on to a final closing of less than one degree on the last day of the June. Th climax comes on July 1st, when Venus and Jupiter sit just over 20’ apart—2/3rds the diameter of a Full Moon—on July 1st at 3:00 UT or 11:00 PM EDT (on June 30th). This translates to a closest approach on the evening of June 30th for North America.

July 1st
… and finally, looking westward on the evening of July 1st.

Venus starts the first week of June forming a straight line equally spaced with the bright stars Castor and Pollux in the astronomical constellation Gemini. On June 12-13, Venus actually nicks the Beehive cluster M44 in the constellation Cancer, a fine sight through binoculars.

Credit: Starry night Education software
The apparent paths of Venus versus Jupiter through the month of June. Credit: Starry Night Education software

Jupiter and Venus will then be joined by the Moon on the evening of June 20th to form a skewed ‘smiley face’ emoticon pairing. Not only is the pairing of Venus and the crescent Moon represented on many national flags, But the evening of June 20th will also be a great time to try your hand at daytime planet spotting before sunset, using the nearby crescent Moon as a guide.

The daytime view of Venus, the Moon and Jupiter of the evening of June 20th. Image Credit: Stellarium
The daytime view of Venus, the Moon and Jupiter of the evening of June 20th. Image Credit: Stellarium

The Moon will actually occult Venus three times in 2015: On July 19th as seen from the South Pacific, on October 8th as seen from Australia and New Zealand, and finally, on December 7th as seen from North America in the daytime.

This conjunction of Venus and Jupiter occurs just across the border in the astronomical constellation of Leo. As Venus can always be found in the dawn or dusk sky, Jupiter must come to it, and conjunctions of the two planets occur roughly once every calendar year. A wider dawn pass of the two planets occurs this year on October 25th, and in 2019 Jupiter again meets up with Venus twice, once in January and once in November. The last close conjunction of Venus and Jupiter occurred on August 18th, 2014, and an extremely close (4’) conjunction of Venus and Jupiter is on tap for next year on August 27th. Check out our nifty list of conjunctions of Venus and Jupiter for the remainder of the decade from last year’s post.

The view through the telescope on the evenings June 30th and July 1st will be stunning, as it’ll be possible to fit a 34% illuminated 32” crescent Venus and a 32” Jupiter plus its four major moons all in the same low power field of view. Jupiter sits 6 astronomical units (AU) from Earth, and Venus is 0.5 AU away on July 1st.

30 FoV
Looking at Jupiter and Venus on July 1st using a 30 arc minute filed of view. Image credit: Starry Night Education Software

And just think of what the view from Jupiter would be like, as Venus and Earth sit less than 3 arc minutes apart:

View from jupiter
The view from Jupiter on July 1st looking at the Earth. Image credit: Starry Night Education software

Venus reaches solar conjunction this summer on August 15th, and Jupiter follows suit on August 26th. Both enter the field of view of the European Space Agency’s Solar Heliospheric Observatory (SOHO) LASCO C3 camera in mid-August, and are visible in the same for the remainder of the month before they pass into the dawn sky.

But beyond just inspiring inquires, close conjunctions of bright planets can actually raise political tensions as well. In 2012, Indian army sentries reported bright lights along India’s mountainous northern border with China. Thought to be reconnaissance spy drones, astronomers later identified the lights as Venus and Jupiter, seen on repeated evenings. We can see how they got there; back in the U.S. Air Force, we’ve seen Venus looking like a ‘mock F-16 fighter’ in the desert dusk sky as we recovered aircraft in Kuwait. Luckily, cooler heads prevailed during the India-China incident and no shots were exchanged, which could well have led to a wider conflict…

Remember:  Scientific ignorance can be harmful, and astronomical knowledge of things in the sky can save lives!

Observing Challenge: The Moon Brushes Past Venus and Covers Mercury This Week


The summer astronomical action heats up this week, as the waning crescent Moon joins the inner planets at dawn. This week’s action comes hot on the tails of the northward solstice which occurred this past weekend, which fell on June 21st in 2014, marking the start of astronomical summer in the northern hemisphere and winter in the southern. This also means that the ecliptic angle at dawn for mid-northern latitude observers will run southward from the northeast early in the morning sky. And although the longest day was June 21st, the earliest sunrise from 40 degrees north latitude was June 14th and the latest sunset occurs on June 27th. We’re slowly taking back the night!

The dawn patrol action begins tomorrow, as the waning crescent Moon slides by Venus low in the dawn sky Tuesday morning. Geocentric (Earth-centered) conjunction occurs on June 24th at around 13:00 Universal Time/9:00 AM EDT, as the 8% illuminated Moon sits 1.3 degrees — just shy of three Full Moon diameters — from -3.8 magnitude Venus. Also note that the open cluster the Pleiades (Messier 45) sits nearby. Well, nearby as seen from our Earthbound vantage point… the Moon is just over one light second away, Venus is 11 light minutes away, and the Pleiades are about 400 light years distant.

Jun 24 5AM Starry Night
Looking east the morning of Tuesday, June 24th at 5:00 AM EDT from latitude 30 degrees north. Created using Starry Night Education software.

And speaking of the Pleiades, Venus will once again meet the cluster in 2020 in the dusk sky, just like it did in 2012. This is the result of an eight year cycle, where apparitions of Venus roughly repeat. Unfortunately we won’t, however, get another transit of Venus across the face of the Sun until 2117!

Can you follow the crescent Moon up in to the daytime sky? Tuesday is also a great time to hunt for Venus in the daytime sky, using the nearby crescent Moon as a guide. Both sit about 32 degrees from the Sun on June 24th. Just make sure you physically block the dazzling Sun behind a building or hill in your quest.

From there, the waning Moon continues to thin on successive mornings as it heads towards New phase on Friday, June 27th at 8:09 UT/4:09 AM EDT and the start of lunation 1132. You might be able to spy the uber-thin Moon about 20-24 hours from to New on the morning prior. The Moon will also occult (pass in front of) Mercury Thursday morning, as the planet just begins its dawn apparition and emerges from the glare of the Sun.

The position of the Moon and Mercury post-sunrise on the morning of June 26th. Credit: Stellarium.

Unfortunately, catching the event will be a challenge. Mercury is almost always occulted by the Moon in the daytime due to its close proximity to the Sun. The footprint of the occultation runs from the Middle East across North Africa to the southeastern U.S. and northern South America, but only a thin sliver of land from northern Alabama to Venezuela will see the occultation begin just before sunrise… for the remainder of the U.S. SE, the occultation will be underway at sunrise and Mercury will emerge from behind the dark limb of the Moon in daylight.

The ground track of the June 26th occultation. Credit: Occult 4.0.

Mercury and the Moon sit 10 degrees from the Sun during the event. Stargazer and veteran daytime planet hunter Shahrin Ahmad based in Malaysia notes that while it is possible to catch Mercury at 10 degrees from the Sun in the daytime using proper precautions, it’ll shine at magnitude +3.5, almost a full 5 magnitudes (100 times) fainter than its maximum possible brightness of -1.5. The only other occultation of Mercury by the Moon in 2014 favors Australia and New Zealand on October 22nd.

This current morning apparition of Mercury this July is equally favorable for the southern hemisphere, and the planet reaches 20.9 degrees elongation west of the Sun on July 12th.

You can see Mercury crossing the field of view of SOHO’s LASCO C3 camera from left to right recently, along with comet C/2014 E2 Jacques as a small moving dot down at about the 7 o’clock position.

Mercury (arrowed) and comet E2 Jacques (in the box) as seen from SOHO. (Click  here for animation)

And keep an eye on the morning action this summer, as Jupiter joins the morning roundup in August for a fine pairing with Venus on August 18th.

The Moon will then reemerge in the dusk evening sky this weekend and may just be visible as a 40-44 hour old crescent on Saturday night June 28th. The appearance of the returning Moon this month also marks the start of the month of Ramadan on the Islamic calendar, a month of fasting. The Muslim calendar is strictly based on the lunar cycle, and thus loses about 11 days per year compared to the Gregorian calendar, which strives to keep the tropical and sidereal solar years in sync. On years when the sighting of the crescent Moon is right on the edge of theoretical observability, there can actually be some debate as to the exact evening on which Ramadan will begin.

Don’t miss the wanderings of our nearest natural neighbor across the dawn and dusk sky this week!

Seeing in Triplicate: Catching a Rare Triple Shadow Transit of Jupiter’s Moons

Hubble nabs a triple shadow transit in this false color image taken in 2004. Credit: NASA/HST.

The planet Jupiter is always fascinating to watch. Not only do surface features pop in and out of existence on its swirling cloud tops, but its super fast rotation — once every 9.9 hours — assures its face changes rapidly. And the motion of its four large Galilean moons is captivating to observe as well. Next week offers a special treat for well-placed observers: a triple shadow transit of the moons Callisto, Europa and Ganymede on the evening of June 3rd.

The view at 19:00 UT/3:00 PM EDT on June 3rd. Credit: Starry Night Education Software.
The view at 19:00 UT/3:00 PM EDT on June 3rd. Credit: Starry Night Education Software.

Now for the bad news: only a small slice of the planet will witness this rare treat in dusk skies. This is because Jupiter starts the month of June 40 degrees east of the Sun and currently sets around 11 PM local, just 3 hours after local sunset. Never fear, though, it may just be possible to spy a portion of this triple transit from North American longitudes with a little careful planning.

The action begins on June 3rd at 15:20 Universal Time as Callisto’s shadow slides on to the disk of Jupiter, to be followed by Europa and Ganymede’s shadow in quick succession hours later. All three shadows are cast back onto the disk of Jupiter from 18:05 to 19:53 UT, favoring European and African longitudes at sunset.  The final shadow, that of Ganymede, moves off the disk of Jupiter at 21:31 UT.

The hemisphere of the Earth facing towards Jupiter from the beginning of the triple shadow transit to the end. the red line marks the day/night terminator. Credit: Stellarium.
The hemisphere of the Earth facing towards Jupiter from the beginning of the triple shadow transit to the end. the red line marks the day/night terminator. Credit: Stellarium.

The following video simulation begins at around 15:00 UT just prior to the ingress of Callisto’s shadow and runs through 22:00 UT:

Triple shadow transits of Jupiter’s moons are fairly rare: the last such event occurred last year on October 12th, 2013 favoring North America and the next won’t occur until January 24th, 2015. Jean Meeus calculated that only 31 such events involving 3 different Jovian moons either transiting Jupiter and/or casting shadows onto its disk occur as seen from Earth between 1981 and 2040. The June 3rd event is also the longest in the same 60 year period studied.

The 1:2:4 orbital resonance of the Jovian moons Io, Europa and Ganymede. Credit: Wikimedia Commons.
The 1:2:4 orbital resonance of the Jovian moons Io, Europa and Ganymede. Credit: Wikimedia Commons.

Can four shadow transits occur at once? Unfortunately, the answer is no. The inner three moons are in a 1:2:4 resonance, meaning that one will always be left out of the picture when two are in front. This also means that Callisto must be included for any triple shadow transit to occur. Next week’s event sees Callisto, Europa and Ganymede crossing in front of Jupiter and casting shadows onto its disk while Io is hidden behind Jupiter in its enormous shadow. Callisto is also the only one of the four large Jovian moons that can “miss” the disk of Jupiter on certain years, owing to the slight inclination of its orbit to the ecliptic. Callisto thus doesn’t always cast a shadow onto the disk of Jupiter, and we’re currently in the middle of a cycle of Callisto shadow transits that started in July of 2013 and runs through July 2016. These “Callisto transit seasons” occur twice during Jupiter’s 11.8 year orbit, and triple shadow transits must also occur within these periods.

So, what’s a North American observer to do? Well, it is possible to spot and track Jupiter with a telescope in the broad daylight. Jupiter rises at around 9:20 AM local in early June, and the waxing crescent Moon passes 5.4 degrees south of it on June 1st. The Moon stands 30 degrees from the planet on June 3rd, and it may be juuusst possible to use it as a guide to the daytime event. A “GoTo” telescope with precise pointing will make this task even easier, allowing you to track Jupiter and the triple shadow transit across the daytime sky from North American longitudes. But be sure to physically block the blazing June Sun behind a building or structure to avoid accidentally catching its blinding glare in the eyepiece!

The orientation of Jupiter the Moon and the Sun at 4PM EDT on June 3rd. Credit: Stellarium.
The orientation of Jupiter, the Moon and the Sun at 4PM EDT on June 3rd. Credit: Stellarium.

Do the shadows of the moons look slightly different to you? A triple shadow transit is a great time to compare them to one another, from the inky hard black dot of the inner moons Europa and Io, to the diffuse large shadow of Callisto. With practice, you can actually identify which moon is casting a shadow during any transit just by its size and appearance!

A study of three multi-shadow transits: last year's (upper left) a double shadow transit from early 2014 (upper right) and 2004 (bottom. Photos by author.
A study of three multi-shadow transits: last year’s (upper left) a double shadow transit from early 2014 (upper right) and 2004 (bottom). Photos by author.

Shadow transits of Jupiter’s moons also played an interesting role in the history of astronomy as well. Danish astronomer Ole Rømer noted that shadow transits were being observed at slightly different times than predicted depending on the distance of Jupiter and the Earth, and made the first rough calculation of the speed of light in 1676 based on this remarkable insight. Celestial navigators were also intrigued for centuries with the idea of using the phenomena of Jupiter’s moons as a natural clock to gauge longitude. It’s a sound idea in theory, though in practice, it proved tough to make accurate observations from the pitching deck of a ship at sea.

Jupiter captured near the daytime Moon. Photo by author.
Jupiter captured near the daytime Moon. Photo by author.

Miss the June 3rd event? There’s still two fine opportunities to see Jupiter do its impression of the Earth-Moon system and appear to have only one satellite – Callisto – on the evenings of May 30th and June 7th.

From there, Jupiter slides lower into the dusk as June progresses and heads towards solar conjunction on July 24th.

Let us know if you manage to catch sight of this rare event!

-Send those shadow transit pics in to Universe Today at our Flickr forum.

Catch the Moon pairing with Mercury & Venus Tonight

Looking west at sunset from latitude 30 degrees north. The ecliptic and Mercury's orbit along with a 10 degree field of view outlined for reference. All graphics created by the author using Starry Night).

If you’ve never seen Mercury, this week is a great time to try.

Over the past few weeks, observers worldwide have been following the outstanding tight triple conjunction of Mercury, Venus and Jupiter low to the west at dusk.

Jupiter has exited the evening sky, headed for conjunction with the Sun on June 19th. I caught what was probably our last glimpse of Jupiter for the season clinging to the murky horizon through binoculars just last week. If you’re “Jonesin’ for Jove,” you can follow its progress this week through superior conjunction as it transits the Solar Heliospheric Observatory’s LASCO C3 camera.

This leaves the two innermost worlds of our fair solar system visible low to the west at dusk. And tonight, they’re joined by a very slender waxing crescent Moon, just over two days after New phase.

The Moon, Venus and Mercury as seen from 30 degrees north tonight at 9PM EDT.
The Moon, Venus and Mercury as seen from 30 degrees north tonight at 9PM EDT.

The evening of June 10th finds a 4% illuminated Moon passing just over 5 degrees (about 10 Full Moon diameters) south of Venus and Mercury. Venus will be the first to appear as the sky darkens, shining at magnitude -3.9 and Mercury will shine about 40 times fainter above it at magnitude +0.3.

Ashen light, also known as Earthshine will also be apparent on the darkened limb of the Moon. Another old-time term for this phenomenon is “the Old Moon in the New Moon’s Arms.” Ashen light is caused by sunlight being reflected off of the Earth and illuminating the nighttime Earthward facing portion of the Moon. Just how prominent this effect appears can vary depending on the total amount of cloud cover on the Earth’s Moonward facing side.

....and the orientation of the Moon, Mercury and Venus on the night of June 12th and ~9PM EDT.
….and the orientation of the Moon, Mercury and Venus on the night of June 12th and ~9PM EDT.

This week sets the stage for the best dusk apparition of Mercury for northern hemisphere viewers in 2013. Orbiting the Sun every 88 Earth days, we see Mercury either favorably placed east of the Sun in the dusk sky or west of the Sun in the dawn sky roughly six times a year. Mercury’s orbit is markedly elliptical, and thus not all apparitions are created the same. An elongation near perihelion, when Mercury is 46 million kilometers from the Sun, can mean its only 17.9 degrees away from the Sun as viewed from the Earth. An elongation near aphelion, 69.8 million kilometers distant, has a maximum angular separation of 27.8 degrees.

This week’s greatest elongation of 24.3 degrees occurs on June 12th. It’s not the most extreme value for 2013, but does have another factor going for it; the angle of the ecliptic. As we approach the solstice of June 21st, the plane of the solar system as traced out by the orbit of the Earth is at a favorable angle relative to the horizon. Thus, an observer from 35 degrees north latitude sees Mercury 18.4 degrees above the horizon at sunset, while an observer at a similar latitude in the southern hemisphere only sees it slightly lower at 16.9 degrees.

Venus and the Moon make great guides to locate Mercury over the next few nights. It’s said that Copernicus himself never saw Mercury with his own eyes, though this oft repeated tale is probably apocryphal.

We also get a shot at a skewed “emoticon conjunction” tonight, not quite a “smiley face” (: as occurred between Jupiter, Venus and the Moon in 2008, but more of a “? :” Stick around until February 13th, 2056 and you’ll see a much tighter version of the same thing! A time exposure of a pass of the International Space Station placed near Mercury and Venus could result in a planetary “meh” conjunction akin to a “/:” Hey, just throwing that obscure challenge out there. Sure, there’s no scientific value to such alignments, except as testimony that the universe may just have a skewed sense of humor…

Through the telescope, Venus currently shows a 10” diameter gibbous phase, while Mercury is only slightly smaller at 8” and is just under half illuminated. No detail can be discerned on either world, as a backyard telescope will give you the same blank view of both worlds that vexed astronomers for centuries. These worlds had to await the dawn of the space age to give up their secrets. NASA’s MESSENGER spacecraft entered a permanent orbit around Mercury in 2011, and continues to return some outstanding science.

Both planets are catching up to us from the far side of their orbits. Mercury will pass within 2 degrees of Venus on June 20th, making for a fine wide field view in binoculars.

And now for the wow factor of what you’re seeing tonight. The Moon just passed apogee on June 9th and is currently about 416,500 kilometers or just over one light second distant. Mercury meanwhile, is 0.86 astronomical units (A.U.), or almost 133 million kilometers, or about 7 light minutes away. Finally, Venus is currently farther away from the Earth than the Sun at 1.59 A.U.s, or about 13.7 light minutes distant.

All this makes for a great show in the dusk skies this week. And yes, lunar apogee just after New sets us up for the closest Full Moon of 2013 (aka the internet sensation known as the “Super Moon”) on June 23rd. More to come on that soon!