Skywatcher's Guide: July-September 2023

The names given to July's full Moon by various indigenous American tribes include the Buck Moon and Thunder Moon (Algonquin), the Peaches Moon (Natchez), the Killer Whale Moon (Haida), and the Rain Moon (San Ildefonso).

Earth at aphelion (farthest from the Sun), at a distance of 1.01668 AU, or 94.5 million miles (152 million kilometers), compared to the average of 93 million miles (150 million kilometers). This results in a 3.4% difference in the apparent diameter of the solar disk between aphelion and perihelion (Earth's closest point to the Sun)—not that anyone would easily notice just by looking.

The Moon reaches the last quarter at 6:48 pm PT, when it's below the horizon, and we don't see it until it rises around 1 am on the morning of the 10th. In the following week, the Moon becomes a waning crescent as it moves closer into alignment with the Sun, rising gradually closer to dawn.

Summer begins…on Mars, which is still visible very low in the west just after sunset, near much brighter Venus. See the Planets section for observability and summer temperatures.

New Moon. Visual sighting of the first thin crescent after this new Moon marks the start of Muharram, the first month in the moon-based Islamic calendar. This sighting is possible just after sunset on the 18th from much of the Americas and (if conditions are perfect) in most of Africa.

The Moon reaches the first quarter at 3:07 pm PT, when it's already visible in the daytime sky, low in the southeast. By sunset, it has moved to the south-southwest, and it sets at midnight.

Peak of the annual Delta Aquarid meteor shower, which averages 20 meteors per hour. Unfortunately, the light of a waxing gibbous Moon interferes with viewing. Details in Highlights.

August's full Moon is also known as the Sturgeon Moon (from the Algonquin), the Mulberries Moon (from the Natchez), the Women's Moon (from the Choctaw), and the Blueberry Moon (from the Ojibway).

Last quarter Moon at 3:28 am PT—about 3½ hours after it rises in the east-northeast. Jupiter is nearby, separated by 3° of arc (6 times the apparent width of a full Moon).

Peak of the annual Perseid meteor shower, usually one of the best showers of the year. Will we be able to see it? Details in Highlights.

The new Moon occurs at 2:38 am PT/5:38 am ET. Sighting of the first thin crescent after this marks the start of Safar, the second month of the lunar-based Islamic calendar. This observation is challenging because such a thin crescent is easily lost in the glow of evening twilight, but is possible for the continental US, South America, Africa, parts of the Middle East, and southern India on the 17th.

Moon at first quarter, rising roughly around 3 pm in the afternoon, making it visible in the south at nightfall against the stars of Scorpius the Scorpion.

Full Moon rising at sunset near Saturn against the stars of Aquarius the Water-Carrier. Since the last full Moon was on August 1 and the Moon's cycle of phases is 29½ days long, this full Moon is occurring before the last day in August, making this the second full Moon of the month. By one definition, that means this can be referred to as a "blue Moon," but there's another definition of the term that you can learn more about in Highlights.

Last quarter Moon rises at about midnight against the stars of Taurus the Bull. By dawn, it's located high in the south and remains visible in the daytime sky, weather-permitting, until it sets around 3 pm.

New Moon. Sighting of the first young crescent after this new Moon marks the start of Rabi' al-Awwal, the third month of the Islamic lunar calendar. This sighting is possible just after sunset on the 16th from much of the US, South America, Africa, the Middle East, India, and Australasia.

The Moon reaches first quarter at 12:32 pm PT, located in Sagittarius the Archer, low in the south at sunset and setting in the southwest just before midnight.

Autumnal equinox, or the beginning of the fall season for the Northern Hemisphere at 11:50 pm PT (which is 2:50 am ET on the 23rd). More fall facts in Highlights.

Full Moon, also known as the Mulberry Moon by indigenous Americans of the Choctaw nation, the Salmon Spawning Moon by the Haida, and the Moose-Calling Moon by the Micmac. A popular name still used today—the Harvest Moon—comes from the Algonquin.