and Sunset Times for
The period from sunrise to sunset decreases by 39 minutes during July. However, the progression of twilight provides nearly two extra hours of daylight each day. Astronomical twilight begins when the sun is eighteen degrees below the horizon. When the sun rises to twelve degrees below the horizon, about 45 minutes later, nautical twilight begins. Shapes and color become apparent. By the time civil twilight arrives, 35-40 minutes later, the sun provides adequate light for most any activity, even though it is still six degrees below the horizon. The reverse progression occurs at dusk.
On July 4 a waxing gibbous moon appears high in the southern sky at twilight with Antares (Scorpius) to its right. A full moon rises on July 7 at 9:13pm. Actual time varies depending upon surrounding terrain. If the moon appears to darken after midnight, it is due to a penumbral lunar eclipse. Any object that casts a shadow creates a central dark shadow called the umbra and an outer half shadow called the penumbra. During a penumbral lunar eclipse, the moon is not in a direct line with the earth and sun. It is, however, close enough that, from earth, we see the moon through the earth’s penumbral shadow. The eclipse begins at 12:37am (July 8) and ends at 2:39am. Greatest darkening occurs at 1:38am. On July 9 the waning gibbous moon rises before midnight with Jupiter to its left. Last quarter moon occurs July 15. On July 18 early risers will experience a clustering in the eastern sky of the Pleiades, Mars, and a waning crescent moon, with Venus above and to the left. New moon occurs July 21. At twilight on July 24 a thin crescent moon appears below Saturn low in the western sky. On July 27 the waxing moon appears in the southwestern sky near Spica (Virgo). First quarter moon occurs July 28. On the evening of July 30 the waxing gibbous moon again pairs with Antares (Scorpius), this time to its left and in the southwestern sky.
The last week of July provides two good meteor showers. The Southern Delta Aquarid Meteor Shower stretches from July 18 to August 18 and could produce 10-20 meteors per hour. Best viewing will be July 28-29 after midnight when the moon has set. The radiant for this meteor shower is the constellation Aquarius which rises in the southeastern sky after midnight. Overlapping this meteor shower is the beginning of the Perseid Meteor Shower. The Perseids will not peak until August 12; but it is a stong meteor event, so look for early meteor activity. Its radiant, Perseus, rises about two hours after Aquarius. Look for meteors after July 23 in the northeastern sky. A third meteor shower, the Alpha Capricornids, peaks earlier in the month and will be compromised by a waning full moon rising in the eastern sky around midnight. Capricorn, its radiant, has a boomerang shape and will be almost due south after midnight.
On July 4 the earth reaches aphelion, the farthest point in its orbit from the sun. Earth’s distance from the sun at aphelion is about 2.8 million miles farther than it is at perihelion, which is the nearest point to the sun in its orbit. The increase in distance is a reminder that the warm summer season is a result of the earth’s tilted axis pointing toward the sun, not its distance from the sun. The reverse is true for the southern hemisphere. Aphelion occurs during its winter season, and perihelion occurs during its summer season.
THE MILKY WAY GALAXY
Summer is the best time to enjoy the Milky Way. Trace it from north to south through Cassiopeia, Cygnus, and Aquila. Then look into the center of our galaxy as your eyes follow the Milky Way to the southern horizon. The dense nebula of stars and star dust spreads across the southern sky through Sagittarius and Scorpius. The center of the Milky Way Galaxy lies in the center of Sagittarius about 26,000 light years away.
Jupiter - The bright, white light of Jupiter is visible from dusk until dawn throughout July. It rises before midnight in the southeastern sky with Capricornus, and shines strongly in the southwestern sky at dawn. (Magnitude -2.6)
Mars - Look for the red-orange glow of Mars in the morning sky. It rises after 3:00am, preceding Venus in the eastern sky. Mars is in Taurus this month where it nearly matches the faint orange brightness of Aldebaran to its east. Each morning Mars advances higher in the sky distancing itself from Venus. (Magnitude +1.1)
Saturn - Look low in the western sky for Saturn’s pale-yellow light at Leo’s hind flank. Saturn sets in the western sky as Jupiter rises in the southeastern sky. By month’s end, Saturn may be too low to observe without a high, clear vantage point. (Magnitude +1.3)
Venus - The brilliant yellow-white light of Venus appears in the eastern sky about the same time that astronomical twilight brightens the morning sky. Venus is in its gibbous phase with about 66% of its face lit by the sun. (Magnitude -4.4)
Note: Apparent magnitude values range from -4 to +6 for most planets and visible stars. The lower the value the brighter the object. A decrease of 1.0 magnitude is 2.5 times brighter.
Note: Hold your hand at arm’s length to measure apparent distances in the sky. Adjust for the size of your hand. The width of the little finger approximates 1.5 degrees. Middle, ring, and little finger touching represent about 5 degrees. The width of a fist is about 10 degrees. The hand stretched from thumb to little finger equals 20 degrees. The diameter of both the full moon and the sun spans only 0.5 degree.
Primary Sources: USGS, U.S. Naval Observatory,
The Summer Triangle dominates the eastern sky. Bright stars Deneb (Cygnus), Vega (Lyra), and Altair (Aquila) to the south mark its three points. Deneb and Altair are 1st magnitude stars. Vega, the brightest, is a 0 magnitude star.
CONSTELLATIONS this MONTH
Hold the star chart high above
your head and match the compass directions to the direction
you are facing.
Adjust the star chart by orienting Ursa Major (Big Dipper) to match its position
in the sky.
The star chart approximates the
night sky from astronomical twilight to midnight. As the night
and the month progress, the constellations will shift toward