06/30/2003
July Skies - by Dick Cookman
Highlights: The Martian Chronicle, Planets of July, Clusters and Clouds of Sagittarius, Milky Way, July Moon
Focus Constellations: Cygnus, Vulpecula, Sagitta, Aquila, Scutum, Sagittarius, Scorpius, Serpens Cauda, Ophiuchus
The Martian Chronicle
Earth and Mars are rapidly converging at a rate of 25,000 miles per hour, and are expected to reach their closest approach on August 27, 2003. Amateur astronomers with modest telescopes are already reporting they can see surface features such as the polar ice caps with greater clarity. At their closest, the two planets will only be 56 million km apart; the closest they've been for 60,000 years. The planet is currently visible in the morning sky, and rises in Aquarius before midnight on July 1st. Over the course of the month it will move into the evening sky as it rises before 10 Pm on July 31st. It will be hard to miss since it will be brighter than everything except the Moon.
The view of Mars shown here was obtained from Malin Space Science Systems (www.msss.com.) They assembled it from MOC daily global images obtained on May 12, 2003. At that time, the northern hemisphere was in early autumn, and the southern hemisphere in early spring. At the left/center of this view are the four large Tharsis volcanoes: Olympus Mons, Ascraeus Mons, Pavonis Mons, and Arsia Mons. Stretching across the center of the globe is the ~5,000 kilometers (~3,000 miles) long Valles Marineris trough system. The seasonal south polar carbon dioxide frost cap is visible at the bottom of this view. A dust storm sweeps across the plains of northern Acidalia at the upper right. North is up, east is right, sunlight illuminates the planet from the left.
In July, Mars increases brightness by 0.9 magnitude, from -1.4 to -2.3, so it will appear 2.3 times as bright at the end of the month as it does at the beginning. Mars' apparent width in the telescope eyepiece will increase from 16.7 arcseconds to 22.2 arcseconds, a figure exceeded only by Jupiter and Venus at its widest.
Planets of July
As Mars joins the evening planets, Jupiter makes its exit. Jupiter sets at 10:45 PM during the last stages of twilight at the beginning of July and is lost in twilight when it sets before 9:00 PM by the end of the month. Dim Neptune and Uranus are in Capricornus and Aquarius respectively so they remain candidates for observation during July evenings.
Venus, Saturn, and Mercury rise just before the sun at the beginning of July. By month's end, Saturn shines brightly in the east during the last two hours before dawn, and Mercury joins Jupiter and the waxing crescent moon in the glow of sunset.
Clusters and Clouds of Sagittarius
Deep sky objects are among the jewels of summer. Our best evening view of Sagittarius is in July and August when it is highest above the southern horizon. Sagittarius lies between Earth and the nucleus of the Milky Way Galaxy, it is within the Sagittarius Spiral Arm which is the arm next inward from the Orion Spiral Arm in which Earth resides. As a result, the Globular and Open Star Clusters and nebulous Clouds of gas and dust that dominate the nucleus and spiral arms of the galaxy are abundant. They include 15 Messier Objects, the most in any constellation, and binoculars or a small telescope reveal numerous interesting clusters and nebulae.
The open clusters include M-18, M-21, M-23, M-24, and M-25. Globular Clusters of Sagittarius include M-22, M-28, M-54, M-55, M-69, M-70, and M-75. The Nebulae are M-8 (Lagoon Nebula), M-17 (Omega, Horseshoe or Swan Nebula), and M-20 (Trifid Nebula).
Sagittarius was considered by the Greeks to be the "Archer," but it looks suspiciously like a tea kettle to me. The steam from the western spout is made up of the nebulae M-8, and M-20, and the Open star Clusters M-21 and M-23. The bottom of the kettle has the Globular Star Clusters M-54, M-70 and M-69 while two more, M-28 and M-22 are near the peak of the lid. The Omega Nebula and the Open Star Clusters M-18, M-24 and M-25 rise farther above the lid, and the last two globular Star Clusters M-55 and M-75 lie below and behind the eastern handle of the tea kettle respectively.
Milky Way
From Scorpius and Sagittarius in the south, the Milky Way Galaxy can be traced northward high in the eastern sky through Ophiuchus, Serpens Cauda,Scutum, Aquila, Sagitta and Vulpecula then overhead to Cygnus. These constellations define the arc which includes the Earth and Sun's forward direction of movement in the Milky Way disk (Cygnus) and the direction inward toward the center of the disk (Sagittarius.)
These constellations collectively include 33 of Messier's list of 109 prominent deep-sky objects, making this arc the most Messier-rich segment of our view of the disk of the entire Milky Way Galaxy. There are 17 Globular Star Clusters, 11 Open Star Clusters, and 5 Nebulae. Since twice that many Messier Objects reside outside the confines of the disk, the rest of the Milky Way disk includes no more than ten Messier deep-sky objects.
If you live in town, grab your scope and head for a place where night skies are dark. Otherwise, if you are lucky enough to live where people have not polluted the night with unnecessary and unwanted light, an 8" diameter telescope will gather sufficient light to provide absolutely spectacular views of these deep sky wonders. (See www.darksky.org.)
July Moon
The July Full Moon at 3:20 PM EDT is referred to as the "Hay" or "Buck" or "Thunder" Moon. It is named because the antlers of buck deer sprout during summer. It is known as the Full Thunder Moon because of the summer storm season.
The Pomo People of California call it the "Moon when Acorns Appear" to remember that when Earth Elder reached into the water covering the newly created world, he gathered mud and placed it on Turtle's back. He then shaped the Stars and Sun. He thought about what would most help the people who he planned to create and made the Great Oak with twelve overarching limbs. As he sat below it he thought of food for the people and acorns started to form. Now the people wait for the time of year when the Sun is hottest to gather the Seventh Moon's harvest of acorns.
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