See what's up in the night sky for August 2019, including stargazing events and the moon's phases, in this Space.com gallery courtesy of Starry Night Software.
Monday, September 2 before 11 p.m. EDT - Great Red Spot on Jupiter
Due to Jupiter's rapid 10-hour rotation period, its Great Red Spot (or GRS) is only observable from Earth during a predictable three-hour window every 2nd or 3rd night. The GRS will be easiest to see using a medium-sized, or larger, aperture telescope on an evening of good seeing (steady air). For observers in the Americas, the Great Red Spot will be crossing the planet on Monday evening, September 2 from dusk to 11 p.m. EDT.
Wednesday, September 4 from 9:21 to 11:33 p.m. EDT – Io's Black Shadow and GRS on Jupiter
From time to time, the little round, black shadows cast by Jupiter's four Galilean moons become visible in backyard telescopes as they cross (or transit) the planet's disk. On Wednesday, September 4 from 9:21 to 11:33 p.m. EDT, observers in the Americas can watch Io's shadow transit Jupiter, accompanied by the Great Red Spot.
Thursday, September 5 at 11:10 p.m. EDT - First Quarter Moon
After the moon has completed the first quarter of its orbit around Earth, the relative positions of the Earth, sun, and moon cause us to see it half-illuminated - on its eastern side. At first quarter, the moon always rises around noon and sets around midnight local time, so it is also visible in the afternoon daytime sky. The evenings around first quarter are the best times to see the lunar terrain dramatically lit by low-angled sunlight.
Thursday, September 5 evening - First Quarter Moon near Jupiter
In the southern sky on the evening of Thursday, September 5, the first quarter moon will be positioned less than four finger widths to the upper right (or 4 degrees to the celestial northwest) of the bright planet Jupiter. The moon and Jupiter will both fit within the field of view of binoculars (red circle). If you watch the pair over several hours, starting at dusk, you will see the moon's orbit carry it closer to the planet.
Friday, September 6 evening - Neptune Kisses Phi Aquarii
In the southeastern sky on the evenings around Friday, September 6, the orbital motion of the dim, blue planet Neptune (red line with dates and times labeled) will carry it very close to a reddish, naked-eye star named Phi (φ) Aquarii. On both Thursday and Friday, the planet will appear within one arc-minute of the star, placing them close together in the field of view of a telescope at high power (red circle). A large telescope might also reveal Neptune's large moon Triton.
Sunday, September 8 evening - Bright Moon near Saturn
In the southern sky after dusk on Sunday evening, September 8, the planet Saturn will be positioned a palm's width to the right (or 6 degrees to the celestial west) of the bright, waxing gibbous moon. The pair will cross the sky together for most of the night. If you check on them over several hours, starting at dusk, you will see the moon's orbit carry it farther from the planet and the rotation of the sky lift the moon higher than Saturn. Hours earlier, observers in eastern Africa, Madagascar, southern Indonesia, western and northern Australia, western Micronesia, and western Melanesia can see the moon occult Saturn.
Monday, September 9 from 8:30 to 11:30 p.m. EDT - Great Red Spot on Jupiter
Due to Jupiter's rapid 10-hour rotation period, its Great Red Spot (or GRS) is only observable from Earth during a predictable three-hour window every 2nd or 3rd night. The GRS will be easiest to see using a medium-sized, or larger, aperture telescope on an evening of good seeing (steady air). For observers in the Americas, the Great Red Spot will be crossing the planet on Monday evening, September 9 from 8:30 p.m. to 11:30 p.m. EDT.
Tuesday, September 10 overnight - Neptune at Opposition near Phi Aquarii
On Tuesday, September 10, Neptune will be directly opposite the sun in the sky. At opposition, Neptune will be closest to Earth for the year, slightly brighter and larger in telescopes, and visible all night long. The dim, magnitude 7.8, blue planet will be located among the stars of eastern Aquarius, just 7.5 arc-minutes (approximately one-quarter of the moon's apparent diameter) to the right (or celestial west) of the naked-eye star Phi (φ) Aquarii. Both Neptune and that star will appear together in the field of view of a backyard telescope at medium power.
Thursday, September 12 after sunset - Venus Kisses Mercury
After sunset on the evenings around Thursday, September 12, the inner planets Mercury and Venus will appear very close together. After the sun has completely disappeared, look just above the western horizon for bright Venus sitting about half a finger's width (20 arc-minutes, or two-thirds of the full moon's diameter) above dimmer Mercury. Due to Mercury's faster orbital motion, Mercury will be to Venus' lower right on Thursday and to Venus' lower left on Friday. The two planets will appear together in binoculars and backyard telescopes at low power (red circle). Observers at low latitudes will see the planets more easily, in a darker sky.
Saturday, September 14 at 12:33 a.m. EDT - Full Harvest Moon
The September full moon, traditionally known as the "Corn Moon" and "Barley Moon", always shines in or near the stars of Aquarius and Pisces. Full moons always rise around sunset and set around sunrise. Because this is the closest full moon to the autumnal equinox in 2019, it is also the Harvest Moon. On the evenings around its full phase, the moon usually rises about 50 minutes later each night. But the shallowly sloping evening ecliptic around the equinox causes Harvest Moons to rise at almost the same time each night – only delayed by as little as 10 minutes, depending on your latitude. This phenomenon traditionally allowed farmers to work into the evening under bright moonlight — hence the name.
Tuesday, September 17 overnight – Bright Waning Moon meets Uranus
In the eastern late-evening sky on Tuesday, September 17, the waning gibbous moon will be positioned about a palm's width below (or 5.5 degrees to the celestial southeast of) the blue-green planet Uranus. While the bright moon will overwhelm much dimmer Uranus, you can take note of where the planet is compared to the surrounding stars, and try looking for it after the moon moves away on subsequent evenings.
Wednesday, September 18 from 8:41 to 11:10 p.m. EDT – Europa's Black Shadow crosses Jupiter
From time to time, the little round, black shadows cast by Jupiter's four Galilean moons become visible in backyard telescopes as they cross (or transit) the planet's disk. On Wednesday, September 18 from 8:41 to 11:10 p.m. EDT, observers in the Americas can watch Europa's shadow transit the northern hemisphere of Jupiter. In the eastern portion of the continent the planet will set shortly before the transit is complete, but observers farther west will see the entire event.
Wednesday, September 18 evening — Saturn Stands Still
On Wednesday, September 18, Earth's faster orbit will cause Saturn to end a westward retrograde loop with respect to the distant stars (red path with labelled dates) and resume its regular eastward motion. Look for the yellowish, magnitude 0.4 planet in the lower part of the southern sky, among the stars of northeastern Sagittarius.
Thursday, September 19 after midnight — Moon Tackles Taurus
When the waning gibbous moon rises in the east at about 10:30 p.m. local time on Thursday, September 19, it will be positioned several finger widths to the upper right of the large triangular grouping of stars that form the face of Taurus the bull. During the night, the moon's orbital motion (green line) will carry it towards the bright, orange-tinted star Aldebaran, which marks the bull's eastern eye.
Friday, September 20 from 7:40 to 9:52 p.m. EDT – Io's Black Shadow crosses Jupiter
From time to time, the little round, black shadows cast by Jupiter's four Galilean moons become visible in backyard telescopes as they cross (or transit) the planet's disk. On Friday, September 20 from 7:40 to 9:52 p.m. EDT, observers in the Americas can watch Io's shadow transit Jupiter.
Saturday, September 21 at 10:41 p.m. EDT — Last Quarter Moon
At its last quarter phase, the moon rises around midnight and remains visible in the southern sky all morning. At this phase, the moon is illuminated on its western side, towards the pre-dawn sun. Last quarter moons are positioned ahead of the Earth in our trip around the sun. About 3½ hours later, Earth will occupy that same location in space. After this phase, the waning moon will traverse the last quarter of its orbit around the earth, on the way to new moon.
Sunday, September 22 pre-dawn — Moon passes Messier 35
In the eastern pre-dawn sky of Sunday, September 22, the waning last quarter moon will pass two finger widths to the lower right (or 2 degrees to the celestial south) of the bright, open star cluster known as Messier 35. That cluster sits near the toes of Castor, Gemini's more westerly twin.
Monday, September 23 at 3:50 a.m. EDT – Equinox
On Monday, September 23 at 3:50 a.m. EDT, the sun will cross the celestial equator moving southward, marking the autumnal equinox in the Northern Hemisphere and the beginning of autumn. On the equinoxes in March and September, day and night are of equal length and the sun rises due east and sets due west.
Tuesday-Wednesday, September 24 and 25 pre-dawn — Crescent Moon Passes the Beehive
In the eastern pre-dawn sky on the mornings of Tuesday, September 24 and Wednesday, September 25, the waning crescent moon will hop over the large, bright, open star cluster known as the Beehive, Praesepe, and Messier 44. On Tuesday, the moon will be positioned about a palm's width to the upper right (celestial west) of the cluster. The following morning, the moon's orbital motion will place it about the same distance to the lower left (celestial east) of the Beehive. Observers in Asia will see the moon pass through the cluster (green line).
Wednesday, September 25 after midnight — Vesta Reverses Direction
On Wednesday, September 25, the Earth's orbital motion will cause the large asteroid designated (4) Vesta to commence a westerly retrograde loop among the distant stars of Taurus. After dark, use binoculars or a backyard telescope to look for the magnitude 7.3 object sitting about a fist's diameter (9 degrees) to the right (or celestial west) of the naked-eye star Gamma Tauri, which marks the bull's chin.
Friday, September 27 pre-dawn — Morning Zodiacal Light for Mid-Northern Observers
For about half an hour before dawn during moonless periods in September and October annually, the steep morning ecliptic favors the appearance of the zodiacal light in the eastern sky. This is reflected sunlight from interplanetary particles concentrated in the plane of the solar system. During a two-week period that starts just before the September new moon, look above the eastern horizon, near the stars of Leo, for a broad wedge of faint light rising from the horizon and centered on the ecliptic (marked by green line). Don't confuse it with the Milky Way, which is sitting further to the southeast.
Saturday, September 28 at 2:26 p.m. EDT — New Moon and Large Tides
At its new phase, the moon is travelling between Earth and the sun. Since sunlight can only reach the far side of the moon, and the moon is in the same region of the sky as the sun, the moon becomes completely hidden from view. Because the moon's closest approach to Earth (perigee) will occur only 16.5 hours before this new moon, the combined gravitational tugs of the sun and moon pulling from the same direction in space will generate large tides on Earth for several days.
Saturday, September 28 after sunset — Mercury meets Spica near Venus
After dusk on the evenings around Saturday, September 28, observers at low latitudes can see the planet Mercury pass a generous finger's width to the upper right of the bright, naked-eye star Spica in Virgo. At visual magnitude -0.24, Mercury will appear approximately three times brighter than magnitude 0.95 Spica. Both the star and the planet will fit together in the field of a backyard telescope at medium power (red circle), but wait until the sun has completely disappeared from view before aiming your telescope or binoculars at them. To assist in your search, much brighter Venus will be positioned a palm's width to the right (or celestial west) of Mercury and Spica.
Sunday, September 29 after sunset — Crescent Moon near Mercury and Venus
Immediately after sunset on Sunday, September 29, the very young crescent moon will form a triangle with Mercury and Venus. Dim Mercury will be positioned low over the horizon and almost a palm's width (or 5 degrees) to the lower left of the moon. Much brighter Venus will be a similar distance to the moon's lower right. After the sun has completely disappeared, use binoculars (red circle) to find the moon, and then sweep lower for the two planets. Observers at low latitudes will see the trio more easily, in a darker sky.