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July 2009

Skywatchers’ Guide for July 2009

PLANETS

This sky chart shows Saturn, Regulus and the western evening sky 45 minutes after sunset on July 4 from the Desert Southwest. This sky chart is most useful for the continental United States, Hawaii, southern Canada and northern Mexico.

This sky chart shows Saturn, Regulus and the western evening sky 45 minutes after sunset on July 4 from the Desert Southwest. This sky chart is most useful for the continental United States, Hawaii, southern Canada and northern Mexico.

This sky chart shows Saturn, Regulus, Mercury, the Moon and the western evening sky 40 minutes after sunset (at around 8 p.m.) on July 24 from the Desert Southwest. This sky chart is most useful for the continental United States, Hawaii, southern Canada and northern Mexico.

This sky chart shows Saturn, Regulus, Mercury, the Moon and the western evening sky 40 minutes after sunset (at around 8 p.m.) on July 24 from the Desert Southwest.

This sky chart shows Jupiter, the Moon, and the southern sky on July 13 at around 11 p.m. MST from southern Arizona. This sky chart is most useful for the continental United States, Hawaii, southern Canada and northern Mexico.

This sky chart shows Jupiter, the Moon, and the southern sky on July 13 at around 11 p.m. MST from southern Arizona.

This sky chart shows Venus, the Moon, and the eastern sky on July 19 at around 4:15 a.m. MST from southern Arizona. This sky chart is most useful for the continental United States, Hawaii, southern Canada and northern Mexico.

This sky chart shows Venus, the Moon, and the eastern sky on July 19 at around 4:15 a.m. MST from southern Arizona. This sky chart is most useful for the continental United States, Hawaii, southern Canada and northern Mexico.

HIGHLIGHTS: Saturn, in the eastern evening sky, is losing altitude in the western sky, but its rings can still be viewed in a telescope. The rings of Saturn appear very thin, as we view them nearly edge-on from Earth. Three planets, Venus, Mars and Jupiter, are widely spaced in the east to southern area of the morning twilight sky, with Mercury a difficult object near the horizon in early July.

Early July 2009 offers the best, last chance quality telescope views of Saturn and its ring system this year. The ringed planet is highest in evening twilight during the first half of this month. By the second half of July Saturn sinks to below 20 degrees in altitude in the evening twilight. On July 1 Saturn sets at around 11:20 p.m., but by 9:26 p.m. on July 31 for southern Arizona. The ringed planet is somewhat dimmer this year (compared to previous years) because its rings are more edge-on. Saturn is a 1st magnitude and 17 arc second wide star-like object.

Saturn’s rings continue to narrow very slowly as we view them more edge-on. Even so the rings are open enough to discern in a good quality telescope. The ringed world continues eastward or ‘direct’ motion, drifting farther but very slowly each night from Leo’s brightest star, Regulus. Also, the 3.5 day old waxing crescent Moon is nearest (8 degrees from) Saturn in our sky on Friday evening July 24.

Bright Jupiter continues to gain altitude and rise earlier each night this July in the southeastern sky. Jupiter rises by 10:15 p.m in early July, by 9:15 p.m in mid-July and around 8:30 p.m. in late July. Jupiter is high enough for quality telescopic viewing, starting 2.5 hours after these rise times. The best time to view Jupiter (when it is highest and when the atmosphere is most stable) is in the pre-dawn hours after midnight. All July long the giant planet is easily seen over one hour before sunrise, well above the southwestern horizon. Also all Jupiter is in the same low power telescope field with faint, bluish Neptune (the two are just over 48 arc minutes apart the first 10 days or so of July). Telescopes at low power with a one degree field or more can easily view both planets at a single glance (bluish-green Uranus is some 30 degrees east of Jupiter in Pisces, the Fish). Jupiter is located in the constellation of Capricornus, the Sea Goat, and is the brightest star like object that is high in the southern sky during morning twilight. The Moon will rise above and west of Jupiter just before 10 p.m. on Thursday, July 9 and rise with but along side (and east of) Jupiter on Friday, July 10.

The best views of any planet should be when it is highest in the sky, but viewing is dependent on atmospheric stability and conditions, and of course, the quality and size of the telescope used. Large, high quality amateur telescopes in good “seeing” (stable atmospheric conditions) will best reveal any features on a planet’s disk.

The brilliant planet Venus starts the month closely grouped with faint Mars during the dawn twilight, above the eastern horizon. The two drift farther apart each morning in our dawn sky between the Hyades and Pleiades clusters in Taurus, the Bull. Venus and Mars are four degrees apart at the beginning of July, but widen to 16 degrees apart by the end of July. Brilliant white Venus is some 22 degrees above the eastern horizon in the morning twilight, one hour before sunrise. It drifts northward in our sky each morning and is at nearly peak altitude this month. Venus will be slightly higher in August. Look for the thin waning crescent Moon (26 days old) to group close to Mars on Saturday, July 18, while a thinner 27-day-old Moon will lie some 7 degrees apart from Venus in our sky in the dawn twilight of Sunday morning, July 19. Mars is still a long ways off from Earth (hence its faintness compared to Venus) and so is currently an unremarkable object in a telescope.

Elusive Mercury is largely lost in the glare of the Sun, but might be seen very early in the month in the bright dawn twilight, or the last few days of July in the bright evening twilight. In very clear skies and an unobstructed horizon Mercury might be visible during the first few days of July in the bright dawn twilight, 30 minutes before sunrise. Mercury might also be seen with binoculars in a difficult evening apparition starting July 20 this month. Mercury on the morning of July 1 is bright (at -1.0 magnitude) but just 5 degrees in altitude 30 minutes before sunrise above the the east-northeastern horizon. It loses about a degree in altitude each morning. For those who want to try for the elusive planet starting July 21 in the evening, Mercury is extremely low, just 1-2 degrees above the west-northwestern horizon, starting 20 minutes after sunset. Mercury on July 21 is bright at -1.1 magnitude but slowly dims and creeps higher each evening. For a binocular challenge in clear skies, the razor thin 1 day old crescent Moon will lie nearest and left (east) of Mercury on July 22. Mercury reaches 4 degrees in altitude by July 30, 30 minutes after sunset, but is dimmer then at -0.5 magnitude.

Visitors to Flandrau’s 16-inch telescope should note that Saturn is visible in the telescope during public hours, and other celestial objects will be shown in the telescope, weather permitting. Flandrau’s main exhibit hall and planetarium is now closed to the public and to school groups due to state budget cuts (the Mineral Museum is open by appointment only) but our Observatory remains open for viewing during public hours from 7-10 p.m., weather permitting, Wednesday through Saturday nights (excluding select holidays).

Finally, remember that in spotting planets there is a general rule: ’stars twinkle, planets don’t’. This is because stars are point sources of light; therefore starlight is easily disturbed and shifted by air currents in the Earth’s atmosphere. However when looking at Mercury or Mars this month, note that they appear to twinkle somewhat; however, this twinkling is of a slower nature than that of the bright stars.

JULY EVENING STARS

The northern evening sky in early July at 10:30 p.m., in middle July at 9:30 p.m. and in late July at 8:30 p.m. The “pointer stars” of the Big Dipper, Dubhe and Merak, point down to the ‘North Star’, Polaris.

The “pointer stars” of the Big Dipper, Dubhe and Merak, point down to the ‘North Star’, Polaris.

This sky chart shows much of the western half of the sky at 10:30 p.m. in early July, at 9:30 p.m. in middle July and at 8:30 p.m. in late July.

This sky chart shows much of the western half of the sky at 10:30 p.m. in early July, at 9:30 p.m. in middle July and at 8:30 p.m. in late July.

The bright stars Antares and Vega provide a color contrast in the bright summer Milky Way. This sky chart shows the sky in early July at 9:45 p.m. and in middle July at 8:45 p.m.

The bright stars Antares and Vega provide a color contrast in the bright summer Milky Way. This sky chart shows the sky in early July at 9:45 p.m. and in middle July at 8:45 p.m.

The Big Dipper is easy to find in July, high in the northern half of the evening sky. Look for the Big Dipper high in the north 1 hour after sunset. Take the two end stars off of the bowl (the ‘pointer stars’) and point down to Polaris, the North Star. Polaris is a star of ordinary brightness, and marks the end of the handle of the Little Dipper. Polaris can also be found about 30 degrees (or 3 fists) above the northern horizon. Polaris stays put in the sky; to the eye it doesn’t appear to move. This is because Earth’s axis is pointed toward Polaris in space.

Bright stars of the July evening sky (1 hour after sunset) include ruddy Antares in the south, the bright yellow star Arcturus high overhead, and the blue star Spica, high in the southwest. Locate the bright yellow star Arcturus and the blue star Spica by recalling, “Follow the arc (of Big Dipper’s handle) to Arcturus and drive a spike to Spica”, or simply “Arc to Arcturus and spike to Spica”. Although Spica is said to mark the spike or ear of wheat in the hand of Virgo, it really looks like the bottom of a group of stars in Virgo that make up a diamond or kite shape.

High above the northeastern horizon in early July one hour after sunset is bright Vega, the brightest star of the summer sky. Blue-white Vega high in the northeastern sky contrasts sharply with Antares, the baleful red super-giant star of summer, now above the southern horizon in early July evenings. Throughout July the orange-red twinkling of Antares enlivens the southern sky, giving reason to its name “the rival of Mars”. From the southern United States Antares does not get very high, only about 30 degrees (or three fists held at arm’s length) above the southern horizon (due to its location in the southern sky). From Australia, though, Antares can be seen overhead in June and July. Antares is the brightest part of a most impressive scroll of stars, sort of like a long letter “S” fallen halfway forward. In this case the “S” stands for the constellation it is part of: Scorpius.

The Milky Way Prominent in the Late Night Hours!

The Milky Way is brightest in the south during July and August evenings. This sky chart shows the southern sky as seen looking toward the south in early July at 11:30 p.m., in middle July at 10:30 p.m. and in late July at 9:30 p.m.

The Milky Way is brightest in the south during July and August evenings. This sky chart shows the southern sky as seen looking toward the south in early July at 11:30 p.m., in middle July at 10:30 p.m. and in late July at 9:30 p.m.

Look for the Milky Way to rise late on moonless July evenings. It will be brightest around the constellation Scorpius, the Scorpion in the south. The Milky Way, the galaxy of stars, gas and dust our solar system resides in, is prominent all summer long, and is brightest after 10 p.m. in early July, but by late July can be seen well at the end of evening twilight. To see it, you’ll need to get away from city lights to a dark location, and look on a night when there’s not much interference from the moon. The Milky Way will appear as a “cloudy” band stretching clear across the sky. High power binoculars and telescopes reveal the Milky Way to be clouds of stars, millions of them, with attendant star clusters and gas clouds making up some of the “fuzzier” spots you’ll see.

MOON PHASES
The July Full (Buck/Thunder) Moon will rise on the evening of Monday, July 6 and set on the morning of Tuesday, July 7. This full moon is the second lowest in the sky this year, and should appear deceptively large to many people. The July last quarter Moon occurs on Wednesday morning July 15. The July new moon occurs on Tuesday, July 21. The July 2009 first quarter Moon will occur on Tuesday evening, July 28. These dates and times are for southern Arizona, and are not necessarily Greenwich Mean Time dates, the moon phase dates used for calendars.

Note: Additional information can be accessed by phone at Flandrau Science Center’s Astronomy Newsline at (520) 621-4310 or as a menu option at 621-S-T-A-R.

Graphics done using Starry Night Pro, Starry Night Enthusiast and Adobe Photoshop. To purchase Starry Night Pro or Enthusiast, go to http://StarryNight.com

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