A Southern solar Eclipse, Earth Approaches Sol, Evening Gas Giants Gleam, and Touring the Triangle!
Earth at Aphelion
On Thursday, July 4, Earth will reach aphelion, its maximum distance from the sun for this year. The aphelion distance of 152.1 million km is 1.67% farther from the sun than the average Earth-sun separation of 149.6 million km, which scientists call one Astronomical Unit (AU). Earth’s perihelion, our minimum distance from the sun, will occur next January 4. At that time, the sun will be 147.1 million km from Earth. As you can see, our seasonal temperatures are not produced by our distance from the sun — but by the amount of sunshine we receive in a day. And that is controlled by the amount that Earth’s axis points toward (or away from) the sun.
The Moon and Planets
The moon will be returning to the evening sky this week, to join the two bright gas giant planets Jupiter and Saturn. But first, we’ll get a new moon on Tuesday morning that will also feature a Total Solar Eclipse visible in the Southern Hemisphere! Here are the Skylights!
Early risers on Monday morning (Oh, Canada Day!) will get one last chance to see the old crescent moon before it meets the sun. At the same time, you can look for very bright Venus sitting a palm’s width to the moon’s left (celestial northeast). Both objects will be immersed in the pre-dawn twilight. They’ll rise shortly before 5 am local time. While the moon will show a slim crescent, Venus will appear nearly fully illuminated in a telescope. This is because the moon is closer to Earth than the sun, while Venus is on the far side of the sun from Earth.
At Tuesday morning’s new phase, the moon will be travelling between Earth and the sun. Since sunlight is only reaching the far side of the moon, and the moon is in the same region of the sky as the sun, the moon will be completely hidden from view — except when it passes directly in front of the sun!
This new moon will feature a total solar eclipse visible inside a narrow path that crosses the southern Pacific Ocean and southern South America. A partial eclipse will be seen across most of the southern Pacific Ocean (almost reaching the coast of Antarctica) and most of South America. The period of totality will reach a maximum of 4m33s in the South Pacific, about 1,080 kilometers north of Easter Island at 19:22:57.9 GMT (Greenwich Mean Time). The first landfall for the moon’s shadow will occur on the Chilean coast, 50 kilometers north of La Serena, at 20:39 GMT, when totality will last for 2m36s and the sun will be at 14° altitude. The eclipse will end near the coast of Argentina, just south of Buenos Aires. Those of us not located where we can see the partial or total eclipse, NASA TV and several YouTube channels.
The young crescent moon will re-appear on Wednesday evening after sunset. At that time, it will share the northwestern sky with Mars and Mercury. The trio, which will fit within the field of view of binoculars, will set by 10 pm local time. Observers in the eastern tip of Africa, the Arabian Peninsula, most of Asia, and Micronesia will see the moon occult Mars.
For the rest of the week, the moon will continue to wax fuller and climb away from the sun, landing on Friday evening just a few finger widths to the right (northwest) of the bright, white star Regulus in Leo (the Lion). The moon will end next weekend approaching its first quarter phase, among the stars of Virgo (the Maiden). The weekend evenings will be particularly good times to look at the moon while its terrain is dramatically lit by slanting rays of sunlight!
Dim, reddish Mars and brighter Mercury are still hanging out together just above the northwestern horizon after sunset this week. The best time to look for them falls between 9:30 and 9:45 pm local time. They’ll set by about 10:15 pm local time. Look for dimmer Mars sitting four finger widths to the right of brighter Mercury. (Take care that the sun has set before attempting to view them using binoculars or a telescope.) You can also look for the bright stars Castor and Pollux of Gemini (the Twins) sitting to the right of the two planets.
The blazingly-bright object that you’ve been seeing in the southeastern evening sky recently is mighty Jupiter. We are recently past Jupiter’s biggest and brightest appearance for 2019. This week Jupiter will be visible from dusk to almost 4 am local time.
From time to time, the small, round black shadows cast by Jupiter’s four Galilean moons become visible in amateur telescopes as they cross (or transit) Jupiter’s disk. On Thursday, July 4 from 10:36 pm to 12:48 am EDT, observers in the Eastern half of North America can watch Io’s shadow transit Jupiter. As a bonus, the Great Red Spot will be crossing the planet from dusk until approximately 11 pm.
Due to Jupiter’s rapid 10-hour rotation period, the Great Red Spot (or GRS) is only observable from Earth every 2nd or 3rd night, and only during a predictable three-hour window. The GRS will be easiest to see using a medium-sized, or larger, aperture telescope on an evening of good seeing (steady air). If you’d like to see the Great Red Spot in your telescope, it will be crossing the planet on Monday evening from 10 pm until 2 am EDT. More GRS viewing opportunities will occur on Thursday from dusk to 11 pm EDT, and on Saturday night from 10 pm to 1 am EDT.
This week, yellowish Saturn will be rising in the east-southeast before dusk and remaining visible all night long. Its position in the sky is just to the left (east) of the stars that form the teapot-shaped constellation of Sagittarius (the Archer). Saturn is quite a bit dimmer than Jupiter. To find it, look about 3 fist diameters to the lower left (east) of Jupiter. Dust off your telescope! Once the sky is dark, even a small telescope will show Saturn’s rings and several of its brighter moons, especially Titan! Because Saturn’s axis of rotation is tipped about 27° from vertical (a bit more than Earth’s is), we can see the top surface of its rings, and its moons can appear above, below, or to either side of the planet. During this week, Titan will migrate counter-clockwise around Saturn, moving from Saturn’s lower left tonight (Sunday) to the right of the planet next Sunday. (Remember that your telescope will flip the view around.)
For night owls, distant and dim, blue Neptune is in the southeastern pre-dawn sky, among the stars of Aquarius (the Water-Bearer). The planet will be rising shortly after midnight local time this week. You’ll find the magnitude 7.9 planet sitting a thumb’s width to the left (east) of a medium-bright star named Phi (φ) Aquarii.
Blue-green Uranus will be rising at about 2 am local time this week. It is sitting among the stars of Aries (the Ram) and is just a palm’s width above the head of Cetus. The large main-belt asteroid Vesta is nearby — a palm’s width below Uranus. Look for Vesta sitting only half a finger’s width below the modest star Xi (ξ) Ceti (and also named Al Kaff al Jidhmah). They will appear together in the field of view of a backyard telescope.
Venus is bright enough to see within the pre-dawn twilight sky that surrounds it, but it is sitting very low in the northeast — sinking ever-closer to the rising sun. Venus will be rising at about 4:40 am local time all week.
The Summer Triangle
When you are out on the next clear night, be sure to look for the three bright and beautiful blue-white stars of the Summer Triangle asterism, which shine high in the eastern sky every July. Once you have it identified, you can find some treasures within it, and follow its progress across the night sky until late fall.
Find an open area and face east. Almost straight overhead is the bright star, Vega. It’s the fifth brightest star in the entire night sky and one of the first stars to appear after dusk. Now look for the other two corners. Altair is not as bright as Vega and sits about 3.5 outstretched fist diameters (34°) to the lower right of it. The third star, Deneb, is about 2.5 fist diameters (24°) to the lower left of Vega and higher up than Altair. It’s a very big triangle!
Can you see the four fainter stars forming a small parallelogram just below Vega? It’s about a thumb’s width wide and a few finger widths long. This shape is the body of the musical harp that makes up the constellation of Lyra (the Lyre). Vega marks the top of the instrument’s neck. Vega’s visual magnitude, or brightness, is the zero reference point for the scale of star brightness values. Objects brighter than Vega have values lower than zero, and vice versa. Spica, the star near Jupiter this summer, has a value of about 1, making it 2.5 times dimmer than Vega. (It’s a logarithmic scale.)
Vega also makes a little triangle with two other dim stars, each about a finger’s width apart. The star to Vega’s upper left is Epsilon Lyrae, also known as the Double Double. Can you tell it’s actually two stars tight together? Try using binoculars. In a telescope, each star splits again!
The bright star Deneb marks the tail of great Cygnus (the Swan). A faint star about two fist diameters (22°) to its right, in the middle of the Summer Triangle is Albireo, a colourful double star that marks the swan’s head. A widely spaced string of modest stars running up-down traces out the swan’s wings. (Look closer to Deneb than Albireo for them — swans have long necks!) The brighter star in the middle of the wing span is Sadr, marking the swan’s belly. If you are in a dark location, you should also be able to see that the Milky Way runs right through Cygnus, as if she is about to land for a swim on that celestial river!
The most southerly of the triangle’s corners is marked by Altair — the head of the great eagle Aquila. In fact, its name translates from “the flying eagle”. At only 16.8 light-years distance, Altair is one of the nearest bright stars — so close that its surface has been imaged! The star also seems to be spinning 100 times faster than our sun, probably generating an equatorial bulge. Like Cygnus, the Aquila the eagle is oriented with its wingtips up-down. The tail bends to the lower right. Two little stars named Terazed (above) and Alshain (below) sit on either side of Altair, like a balance. As a matter of fact, these two little stars’ names derive from an old-fashioned scale balance.
Grab your binoculars and look about midway between Vega and Altair for a little grouping of stars called The Coathangar. (Hint: For North American observers, it’s oriented with the hook downwards to the west.) Finally, have a look for two little constellations in the area. Sagitta (the Arrow) comprises five faint stars running left-right, above Altair. The three on the right (west) end form the feathers. Below Sagitta, and about 13° to the left of Altair is cute little Delphinus (the Dolphin). Four stars form a diamond-shaped body and another star to the lower right marks the tail flukes! The star names for Delphinus include a very interesting story. Look it up!
There’s one assitional small constellation inside the Summer Triangle, but its dim stars make it difficult to make out. It’s called Vulpecula (the Fox), and it sits about a palm’s width above and parallel to Sagitta. Two birds, a dolphin, and a fox! (And — there’s the lizard Lacerta just to the east and a little foal Equuleus below Delphinus!) Enjoy your tour of the triangle and visit to this celestial zoo!
Astronomy Skylights for the week of June 30th, 2019 by Chris Vaughan.
Keep looking up, and enjoy the sky when you do. I love questions and requests — so, send me some!