The month of August offers incredible night sky events, weather permitting, of course.
The southwest monsoon season is in full swing this summer, compromising stargazing, but delivering much needed water to New Mexico. Photo taken July 6, 2021.
Saturn is in opposition to the Sun and closest to Earth on August 2nd. Jupiter’s opposition follows on the 19th. Both planets will be bright (Jupiter being the brighter of the two) and visible all night.
The Perseid meteor shower, one of the best showers of the year, peaks on the night of August 12th and pre-dawn of the 13th. With the waxing crescent moon setting around 10:30pm MDT, observing conditions will be perfect for viewing about a meteor per minute, weather permitting.
‘Stargazer’ watches a Perseid meteor explode as it slams into the Earth’s atmosphere. Photo taken August 12, 2020, Santa Fe, NM.
The Summer Milky Way is well-positioned for evening viewing on clear, dark nights. As darkness falls in early August, the Milky Way will span the sky from the southern to the northeastern horizons. By month’s end, it will have shifted a bit, reaching from the SSW to the NNE horizons, passing almost overhead. Darkness occurs about 40 minutes earlier than in early August, making the Milky Way visible earlier in the evening.
Mercury opens August behind the Sun. By month’s end, it’s visible during evening twilight in Virgo, setting an hour after the Sun. Since the ecliptic is tilted toward the southwest, Mercury doesn’t get very high during this evening apparition.
Venus begins the month easily visible in Leo. By the end of the month, it moves higher in the sky and shifts east, into Virgo, setting as night begins (about 9:05pm MDT).
Mars begins August near Regulus, in Leo, but it’s almost on the opposite side of the Sun from Earth and is thus faint and hidden in twilight glare all month.
Jupiter reaches opposition to the Sun and closest to Earth on August 19th. See ‘August Spotlight’ for further details.
Saturn reaches opposition on August 2nd and is visible all night in the constellation Capricornus. This month is the best time to view Saturn for the remainder of the year since it’s close to Earth and its rings are wide open.
Jupiter (the bright ‘star’ on the left) and Saturn (2:30 from Jupiter, above the horse sculpture) follow the Summer Milky Way into the night sky, as they both approach opposition in August. Photo taken July 8, 2021.
The planet Jupiter has attracted attention since humans began gazing at the night sky. It’s usually the second brightest object in the night sky, excluding the Moon (Venus is the brightest; once every 15-17 years, Mars can briefly outshine Jupiter).
Jupiter is exceedingly bright now because it’s almost at its closest distance to Earth. Opposition (the time when the Sun, Earth, and planet line up, with Earth in the middle) occurs on the 19th of August. At that time, Jupiter will shine in Aquarius at magnitude -2.9. The next few weeks offer our best chance to view Jupiter until it next reaches opposition in September 2022.
To the unaided eye, Jupiter shines like a brilliant white pearl, rising around sunset and setting around sunrise. A small telescope will reveal Jupiter’s four largest moons, called the Galilean Moons. These four large moons were discovered and determined to be satellites of Jupiter by Galileo Galilei, when he turned his new telescope on Jupiter in 1610. I find it rewarding to watch these moons nightly, since they slowly change position relative to Jupiter and to each other.
Jupiter and its four Galilean moons. Photo taken with a Canon digital camera and 600mm lens.
Ganymede, the largest of the four moons, is slightly larger than the planet Mercury. Calisto is smaller than Mercury, but much larger than Earth’s Moon. Io is about the same size as our Moon, while Europa is a bit smaller.
Since Jupiter orbits the Sun just beyond the asteroid belt, its gravity has captured a number of small asteroids that strayed too close to the giant planet. Currently, there are 79 known moons of Jupiter, all but the four Galilean Moons being small and beyond the reach of small telescopes.
Sometimes, Jupiter captures objects and gobbles them up. One well-observed instance occurred in the early 1990s, when a comet was gravitationally captured by Jupiter. The comet broke apart before colliding with the planet, leaving a series of black disturbances in Jupiter’s upper atmosphere.
The dark splotches in Jupiter’s atmosphere mark the sites where pieces of Comet Shoemaker-Levy 9 slammed into Jupiter’s atmosphere. The Great Red Spot is visible at the lower left. Photo by NASA Hubble Telescope and copied from scientificamerican.com.
If you look closely at Jupiter through a small telescope, you’ll notice that it’s a bit wider at the equator than it is at the poles. This is due to the rapid rotation of the planet. Even though Jupiter’s diameter is about 11 times Earth’s, it spins once on its axis (a.k.a., a day) in just under 10 hours, versus 24 hours for an Earth day. This rapid rotation causes Jupiter’s atmosphere to noticeably bulge at the equator.
You’ll also observe faint horizontal bands crossing the planet. These are cloud patterns at the top of Jupiter’s atmosphere, caused by the planet’s rapid rotation and high winds. While most of Jupiter’s atmosphere is composed of hydrogen and helium, the visible clouds at the top of the atmosphere are mainly ammonia. The dark colored atmospheric bands are called ‘belts;’ the lighter colored ones are ‘zones.’
Detailed photographs of Jupiter’s weather at the top of the atmosphere, taken with telescopes and satellites, reveal these belts and zones to be incredibly complex swirling patterns and colors. One atmospheric feature that can be seen in a small to medium-sized telescope is a reddish oval called the ‘Great Red Spot.’ The Great Red Spot is a storm that has been continuously observed from Earth for over 300 years.
A close-up of Jupiter’s dynamic atmospheric belts and zones, photographed by NASA’s Juno orbiter.
Some astronomers consider Jupiter to be a ‘failed star’ since its atmosphere is mainly composed of hydrogen and helium, similar to the Sun, but lacks sufficient mass and pressure for the process of atomic fusion to occur. While true, the planet developed from the accretion of rocks and ice, like other planets in the solar system, not the compression of gas and dust that leads to star formation, like the Sun.
Thus, the solar system’s largest planet shines by reflected sunlight, rather than by light produced by internal thermonuclear reactions. Regardless, Jupiter is a breathtaking sight, whether viewed with the unaided eye or a telescope. Enjoy observing the planet and its four largest moons while it’s close to Earth (a mere 365 million miles at its closest on the night of August 19th).
August Night Sky Events:
August 1-31: The Zodiacal Light is visible about an hour before dawn. The Zodiacal Light is sunlight from the not yet risen Sun reflecting off of interplanetary dust particles. Clear, dark skies are required to see this faint light.
Zodiacal light glows over Galisteo before dawn, June 30, 2020. Venus is rising in the center, below the Pleiades star cluster. Mars is the bright object in the upper right quadrant.
August 2: Saturn is at opposition to the Sun and closest to Earth, visible all night long in the constellation Capricornus.
August 8: New moon.
August 12-13: The Perseid meteor shower peaks on the night of the 12th and morning of the 13th. This could be a great shower this year since the Moon sets around 10:30pm on the 12th. At peak, the shower could produce in excess of 60 meteors per hour.
August 19: Jupiter is at opposition to the Sun, shining at magnitude -2.7, near the Capricornus-Aquarius border.
August 22: Full moon occurs at 6:02am MDT. Since this is the third of four full moons in a three month period, it’s known as a ‘blue moon’ (as in, “once in a blue moon”). Blue moons occur about every 2.7 years.
An almost full moon rises before sunset. Distant wildfires spewed small particles into the atmosphere, contributing to the Moon’s faded appearance and yellowish color. Photo taken July 22, 2021.