By “Astro” Mark Laurin
Let’s have a picnic. Let’s go to the park, run in the grass, and feel summer between our toes. Across the land, the call went out to one and all. Summer is coming! Summer is coming! Cometh one by hazy lazy long days, or cometh two by the cool waters that swell around your ankles, calves, and knees. On Wednesday, June 21st, at 8:57am Mountain Time summer arrives. A cheer will rise and be heard throughout the northern hemisphere, summer is here!
Indeed, the summer solstice is important, essential, and required by the movement of the cosmos. So much so, that much of this month’s What’s Up Above? stargazing calendar of events involves this event. The Summer Solstice is line item #1 on our Solar System’s invisible balance sheet. The northern hemisphere get summer, and the southern hemisphere gets winter. The northern hemisphere has its longest day; and the southern hemisphere has its shortest day. Each is opposite, and each requires the other. As stargazers, we know this balance well. When winter grips the northern hemisphere, we witness the spectacular sparkles of dazzling gems shivering under layered blankets of wool. Our ventures outside are momentary. Summer releases us from winter’s cold grip. Now, we can linger longer outside at night. We lie on woolen blankets, now spread out open under a canopy of night. It’s as if we’re floating on a celestial summer river. Peering up we see a glowing Milky Way, simmering glistening stars, and stalwart planets. They are beckoning you. And now that you’re there, here’s some objects to view this June.
The Summer Solstice, June 21st
The word “solstice” comes from the combination of two Latin words, “sol” (the Sun) and “sistere” (to stand still). In the northern hemisphere, on the 21st, this appears to happen as the Sun, close to 90 degrees north of the horizon, and directly overheads crosses the Tropic of Cancer. It appears to be in the same location in the sky the day before the solstice and then the day after the solstice. During that period, for those living on the Tropic of Cancer, at noon, the Sun does indeed appear to stand still directly overhead. And it’s all because of the Earth’s tilt and orbit around the Sun. This is a consequence of the Sun reaching its northernmost path in the sky. At the solstice, Earth’s North Pole is at its maximum tilt to the Sun, approximately 23.4 degrees. Which is why the Solstice is the longest day of the year. We can expect roughly 16 hours of daylight on the day of the Summer Solstice. And if you live near the Arctic Circle, the party never ends – I mean the Sun never sets. Sadly, after that date the Sun begins its long sojourn south, and hence the daytime shortens.
Venus, Mars, a Gas Giant, and a Sextuple Star System Join the Solstice Celebration, June 21st
Who wouldn’t want to join the Summer Solstice celebration? Not you, not I, nor the planets Venus or Mars; nor a gas giant call Pollux, or a sextuplet star system named Castor. At the finish of the day, a true mix of celestial friends will cheer the Sun as it breaks the finish line ribbon after a long day of shining.
From your location look to the western horizon on the solstice day around 30 minutes after the sunset. Approximately 20 degrees above the cardinal direction west you will spy a spectacular three-way conjunction of Venus, Mars, and the fresh and new crescent Moon. Recall that for us on Earth, a conjunction is when two or more astronomical objects have the same right ascension (similar to latitude), and in many cases the same ecliptic longitude. Then we see holding the halves of finish line ribbon the brightest stars in constellation Gemini, the twin brothers, Pollux and Castor. In both Greek and Roman mythology, the twin are known together as the Dioscuri. Their mother was Leda (an Aetolian princess) and had different fathers; one mortal and the other divine. Pollux, the son of Zeus, and Castor the son of Tyndareus, the king of Sparta. Pollux pleaded with Zeus to make is brother Castor immortal so they can stay together through eternity. Zeus obliged and transformed the brothers into the constellation of Gemini, the twins. How can you tell the twins apart? Pollux on the left will have an orange / yellow hue to it, while Castor on the right will appear white-ish.
Vega Rises to Recognize the Solstice, June 21st
We’ve been looking west at sunset this evening of the Summer Solstice, so now it’s time to do the hokey pokey and turn yourself around. Look to the east-northeast horizon and invite the 5th brightest star in the night sky to our solstice celebration. Vega is the alpha star (the brightest, most prominent) in the constellation Lyra and is no secret to astronomers. Austin Gulliver, wrote in The Astrophysical Journal that “Vega is arguably the next most important star in the sky after the Sun.” Why? Vega was the northern pole star around 12,000 BCE, and will again be the northern hemisphere’s pole star around the year, 13,727. Who knew? Next, Vega was the first star (other than the Sun) to be photographed in 1850. Additionally, Vega was among the first stars to have its distance estimated through parallax measurement. Interestingly, Vega is ten times smaller than our Sun, yet 2 times more massive. For stars, bigger isn’t always better. Behemoth stars burn fast, bright, and furious. Despite the size difference and burn rate, both the Sun and Vega are approaching midlife.
The Milky Way Returns, June 7th
The month of June brings to a close Galaxy Season. It is a period of time in the stargazing year when the Milky Way almost disappears below the horizon. The “disappearance” giving us a gateway to see distance galaxies that are usually obscured from view. Indulge a step back to ask the question: What is the Milky Way?
The Milky Way is a Galaxy. It is a barred spiral galaxy, like a large pinwheel. It is our Galaxy and inside this barred spiral galaxy we find our solar system. (The Sun, Planets, Moons, Dwarf Planets, Asteroids, Comets, and Belts.) The Milky Way Galaxy is approximately 13.6 billion years old. The spirals of the bar originate from the galactic center of our Galaxy. These long spiraling arms fan out with some having spurs. Earth reside in the Orion Spur, of the Sagittarius Arm. We live approximately 26,000 light-years away from the Milky Way’s galactic center, and all of the objects in our Galaxy revolve around the galactic center. And remember, a light-year is just shy of 6 trillion miles! Yowza! For our solar system to make one revolution around the Milky Way’s galactic center takes 250 million years. Better pack a lunch for that trip.
And when you look up at the night sky in June you also see the Milky Way. Specifically you see the Orion Spur as a hazy band of white light. This results from unresolved stars (blurry), dust, and gases. Brighter regions through the band appear as soft patches of light know as start clouds. Dark regions within the band is interstellar dust that blocks out the light from background stars shining through. Cultural mythologies concerning the Milky Way are varied and rich. The Babylonian believed the Milky Way is created from the severed tail of the primeval salt water dragoness, Tiamat. In Greek lore, Zeus places his son, born by a mortal woman, on Hera’s breast while she slept so the baby will drink her divine milk and become immortal. It no surprise that Hera wakes up and sees she is nursing an unknown baby. She pushes the baby away, spilling her milk and in doing so creates the band of light known as the Milky Way. The Romans called it the Via Galactica, or “road made of milk.” Thus in all these ways, our home in the universe became known as the Milky Way.
So sway away fellow stargazers be it in your terra firma hammock or nocturnal chaise lounge. Get outside on the Summer Solstice. The day and night of June 21st is significant in for many reasons and in many and varied cultures recognized through rituals and festivals. Ergo, all the more reason for you to run through the grass, float on a river, sift sand through your toes, and then relax by tilting your head back and looking up to enjoy these wonders of the night sky. Blend your longest day of the year into a balmy summer night under the celestial sphere. It’s June. Summer is coming! Dive in.
Clear skies to you!