THE USM SOUTHWORTH PLANETARIUM

207-780-4249     www.usm.maine.edu/planet

70 Falmouth Street     Portland, Maine  04103

43.6667° N                   70.2667° W 
Altitude:   10 feet below sea level

Founded January 1970

Julian date:  2458665.5

               "Because we're standing on ground that is still shrugging away the burden of the glacier that melted thousands of years ago;  because, being this close to the ocean, we're within a whisper's distance of whale song;  because we're sailing through the galaxy at half a million miles an hour; because thousands of souls will draw their first breaths in the next hour;  because we'll never exhaust all the world's possible harmonies; because the light and heat of a hundred thousand summers not yet realized now ascends through the turbulent layers of the furious Sun;  because the trillion uniquely  intricate snowflakes that have just fallen will go unobserved; because our supernatural minds contain hundreds  of acres of catacombs not yet explored; because the past is irretrievable, the future unknowable and the present ungraspable;  because arctic ice summits are cast into lustrous iridescence by auroral light at the same moment someone sniffs burnt August sand in the tropics; because our misery precipitates in cleansing tears and our exultations thunder into tectonic laughter....because of the thousands of other reasons not here mentioned and the thousands more I haven't even fathomed...am I one of the maudlin, dim-witted fools who doesn't believe that nothing is a miracle."

THE DAILY ASTRONOMER
Monday, July 1, 2019

July 2019 Night Sky Calendar

The word "month" derives from the word "moonth," the time period approximately equal to the completion of one lunar cycle: from new moon to new moon.       This actual time period, approximately equal to 29.5 days, is known as a "synodic month."     In July and in August, the new moon occurs around the first of the month so that the lunar cycle ages as the month, itself does:  new at the beginning, near full in the middle and almost back to new at month's end.  Along the way, the moon will block the Sun to produce a solar eclipse (we won't see it) and then a fortnight later, the moon will maneuver into Earth's shadow, creating a partial lunar eclipse (um, we won't see that event, either.)    We will also see the moon appear to move close to all five visible planets.   This month, Earth draws as far from the Sun as possible, Saturn reaches opposition, and Mercury moves into inferior conjunction (the last one prior to Mercury's next transit of the Sun.)    

MONDAY, JULY 1: MOON NEAR VENUS (BRONZE EVENT!)

Ordinarily, the close coupling of Venus and the moon would be awarded silver or even gold status.  This time, however, the Moon-Venus appulse warrants only a bronze medal as both worlds are lurking precariously close to the Sun in the eastern pre-dawn sky today.   The waning crescent moon (2% illuminated) and our sister planet will both rise just before 4:00 a.m.    By that time, nautical twilight will already be in progress and civil twilight, that period we call "pre-dawn," will begin less than half an hour later.     

TUESDAY, JULY 2:  NEW MOON

WOW!!

Hey, if we were in the southern part of the globe, we'd see a TOTAL SOLAR ECLIPSE today!

Alas, we're too far north to even see a partial solar eclipse.  (However, we're going to devote tomorrow's DA to this total solar eclipse, anyway, so we can begin to prepare for the total solar eclipse that we'll see in New England in 1743 days:  April 8, 2024)      Today, we'll see nothing: no eclipse, not even the moon.       Lunation cycle 1194 begins!

THURSDAY, JULY 4:   MOON NEAR MARS

During this festive holiday commemorating the war of ungrateful Yank aggression, we can see the thin waxing crescent moon (5% illuminated) close to the red planet Mars.   While Mars is not nearly as bright as Venus, it remains distinctly reddish and moderately bright.    See Mars and the moon in the western evening sky.  Both bodies will set by 10:15 p.m.

THURSDAY, JULY 4:  MOON NEAR MERCURY

If you can find Mars and the moon tonight, you can certainly see Mercury, as well.    The three M worlds (a technical term relating to planets with names starting with M), are gathered together in the western evening sky.    Though it is slightly brighter than Mars, Mercury is a bit more difficult to observe as it lacks Mars' reddish tint.  

THURSDAY, JULY 4:  EARTH AT APHELION!

"Aphelion?"    That is the point of greatest separation distance between Earth and the Sun.   ("Perihelion" is the point of least distance.)       If Earth's orbit were perfectly circular, the planet's distance from the Sun would remain constant throughout the year. However, Earth's orbital is a slightly eccentric ellipse, so its heliocentric distance varies continuously throughout every orbit.     Around July 4th, Earth reaches aphelion, its greatest distance.  Around January 3rd, Earth reaches perihelion, its least distance.   The Sun will be 152.1 million kilometers (about 94.5 million miles) from Earth today.    Around perihelion, the Sun's distance is 91.5 million miles.  

Aphelion vs. Perihelion:   As Earth travels along a slightly eccentric elliptical orbit, its distance from the Sun varies from a point of greatest distance, aphelion, to one of least distance, perihelion.    Earth reaches perihelion in early January and aphelion in early July.

FRIDAY, JULY 5:  MERCURY 0.2 DEGREES ENE OF MARS  (GOLD EVENT!!!)

Look into the southwestern evening sky tonight and find Mars and Mercury in close confines. Well, actually, apparently in close confines, as Mercury will be 61 million miles from Earth today, while Mars will be almost 240 million miles away.  Even though these planets are almost of equal brightness, one can distinguish between them because Mars will appear crimson, whereas Mercury will simply look white. 

TUESDAY, JULY 9:   FIRST QUARTER MOON

TUESDAY, JULY 9:  SATURN AT OPPOSITION (SILVER EVENT!!)

Today, the swift-footed Earth moves between lethargic Saturn and the Sun.      Were we to observe the solar system from an "aerial viewpoint," we would see the Sun, Earth and Saturn in a line.   Of course, Earth is about eight times closer to the Sun than it is to Saturn, today.   All the same, Saturn will be at its closest and brightest of 2019 right now!  Saturn will rise around sunset and will remain visible all night.   

SATURDAY, JULY 13:   MOON NEAR JUPITER

Wait a minute!    Why did we specify the angular separation between Mercury and Mars, but we only mention that the moon will be "near" Jupiter?   Simple:  the moon is a fast mover.  It shifts its position by half a degree an hour, equal to its own angular diameter.  The moon attains its minimum angular separation from another body for less than an hour as a consequence.  Whereas, for instance, on July 5th, Mercury and Mars will remain about 0.2 degrees apart for as long as they remain visible in our sky that night.     On the night of July 13th, we'll see the brilliant planet Jupiter and the gibbous moon (90% illuminated) close together throughout the evening.  Both of them will remain in the sky most of the night.

TUESDAY, JULY 16:  MOON NEAR SATURN

Up all night!    Tonight we'll see the full moon and the sixth planet appearing to travel together from dusk to dawn.     Even though Saturn reached opposition a week ago it will remain visible nearly all night.   Saturn is easier to see now that at any other time of year owing to its brightness and duration of visibility.   However, finding Saturn is even a bit easier tonight because it will be the bright "star" close to the full moon.

TUESDAY, JULY 16: FULL MOON!

And, dang it all to Dixie, today, part of the moon will move into Earth's shadow, but we here in the eastern arc of the United States will JUST miss the event.  The eclipse will be ending just before moon rise.    By this statement, we mean that the moon will be leaving the penumbra, the outer part of Earth's shadow, just as it rises.     The partial lunar eclipse will be visible in its entirety in Africa, most of Europe, the Middle East and many parts of Asia.    Even South America will see most of it. 

Always the Bride's Maid!     On July 14th the full moon will partially move into the inner part of Earth's shadow, called the "umbra."  We here in the eastern US will miss this event!   However, take heart, we will see the partial lunar eclipse on 21 November 2021!  

SUNDAY, JULY 21:  MERCURY AT INFERIOR CONJUNCTION

When a planet moves between Earth and the Sun, it is said to be in "inferior conjunction."   Mercury passes through inferior conjunction today and so, won't be visible.  However, the next time Mercury goes into inferior conjunction on November 11, 2019, it WILL be visible as it will then move directly across the Sun.  This Mercurian transit will be entirely visible here in the eastern US.  Hopefully, the sky will be clear, as it will be the last transit of Mercury we'll see until May 7, 2049!

THURSDAY, JULY 25:  LAST QUARTER MOON

SATURDAY, JULY 27:   CRESCENT MOON NEAR PLEIADES

Yes, well, the winter stars are returning to the pre-dawn eastern sky, but we don't have to pay much attention to them, at least not now.    Venture out to observe the sky in the wee hours and you'll see the waning crescent moon (26% illuminated) close to the Pleiades.  The moon won't be bright enough to totally obscure the Pleiades Star Cluster

PLANET WATCH

MERCURY is visible in the western evening sky during the early part of July.   However, by mid month, the first world will be too close to the setting Sun  to be observable.     VERDICT:   Try to find Mercury in early July.   Seek out Mercury on July 5th when it will be close to Mars!

VENUS.   July is not a favorable month for Venus.  The bright planet begins the month very low in the eastern pre-dawn sky.  By the second week, Venus vanishes!  However, our sister world will return to the western evening sky in September and will become a brilliant autumn sky beacon.   VERDICT:   Yeah, well, ok, you can try to find Venus if you're out before sunrise in early July.  Otherwise, wait until September to find Venus in the evening sky.

MARS is dimmer than it was this time last summer.    The fourth world will vanish into the western dusk by mid month.  Mars will then be on hiatus until late October, when it returns to the morning sky.    VERDICT:   Like Venus, Mars is best seen early in the month.   By mid month, Mars will then be out of sight until almost mid autumn  

JUPITER is big, bright, and up for most of the night.   Jupiter was at opposition on June 10th and now begins the evening in the eastern pre-dawn sky.  The behemoth planet remains visible until the onset of early twilight.  VERDICT:   Owing to its brilliance and position, Jupiter is quite easy to find throughout July.  Seek it in the evening and even well after midnight.

SATURN (PICK PLANET!)   Saturn isn't as bright as Jupiter, but as it passes into opposition this month, this planet is designated as the month's pick planet!   VERDICT:  See Saturn at any time of night!    Up around sunset and down by sunrise.