July 2014 Skywatching


Video Source

During the early evening hours of July and August, an assembly of stars arches across the sky.  During the evening it slowly marches westward.  Even from dark skies, it appears as a cloudy ribbon of light stretching from south to north.  When your eyes are well-adjusted you can see brighter sections and apparent gaps.  Through binoculars the ribbon resolves into a celestial stream of stars, glowing clouds along with striking voids.  This is our celestial home, the Milky Way galaxy.  From within the celestial community, we see our sidereal neighbors and a glowing rim that holds the far-off cities and states of seemingly innumerable stars.

The time-lapse video above shows the slow westward dance of the Milky Way from our planet’s rotation.  Leave the bright lights of the cities and travel into the country on moonless evenings.

Earth

earth_140703

Our planet reaches its farthest distance (aphelion) from the sun on July 3 at 7 p.m.  At this time we are 94.5 million miles from the sun.  The chart above shows the orbits of Venus, Earth, and Mars with the planets’ positions as they appear on July 3.  (Click the image to see it larger.)  Notice the shapes of the orbits.  Venus’ orbit is nearly a circle, less than 0.6% from perfection.  Planet Earth’s orbital shape is about 2% from the circular perfection.  Mars’ orbit is obviously not a circle as it is 9.3% from being a circle.

The sun’s distance from the sun varies throughout the year.  At the closest point (perihelion) on January, we were over 3 million miles closer to the sun.

Sun

As the annual distance variation, the first thought is that the seasons are caused by this effect, though our planet is farther away from the sun during the hottest time of the year in the northern hemisphere.  The season cycle is from our planet’s tilt.  The sun’s changing rising and setting points along the horizon combined with the lengthening and shortening of the daylight hours are the effects of this tilt.

july_daylight_2014

This chart shows the hours of daylight for July 2014 in the blue section of the chart. The red line shows the length of daylight throughout the year. Calculated from data from the U.S. Naval Observatory.

The daylight hours in mid-northern latitudes decreases  nearly 45 minutes during the month.  By July’s end early risers will notice the sun rises a little later than early in the month.  The chart above shows the changing daylight hours during July.

Moon

NASA Photo

NASA Photo

Phase Date/Time Moonrise Moonset
First Quarter 07/05/14 (6:59 a.m.) 1:23 p.m. 12:45 a.m. (07/06)
Full Moon 07/12/14 (6:25 a.m.) 7:35 p.m. (7/11) 5:47 a.m. (07/12)
Last Quarter 07/18/14 (9:08 p.m.) 12:11 a.m. (7/19) 2:00 p.m. (7/19)
New Moon 07/27/14 (5:42 p.m.) 5:32 a.m. 7:49 p.m.

Times are Central Daylight Time for Chicago, Illinois, from US Naval Observatory calculations. (For mjb)

Evening Sky

Jupiter rapid fades into bright sunlight during the month moving behind the sun (conjunction) on July 24.  It appears in the morning sky next month with Venus.

mars_sat_140701

Saturn and Mars appear in the southern sky during the month as shown here on July 1.

Mars and Saturn appear in the southern sky during July.  Mars begins the month about 5.5 degrees to the upper right of Spica.  During the month, Mars eastward motion carries it past the star.

mars_lune_140705

The moon moves into the region early in the month.  On July 15, the First Quarter moon is less than a half degree (one full moon diameter) to the lower left of Mars while the planet is 4 degrees from Spica.

sat_moon_140707

A few  nights later, the moon moves appears about 1.7 degrees below Saturn.

mars_spica_140712

Mars passes within about 1 degrees of Spica on the evening of July 12.  The separation is slightly larger than about the size of two full moons.

mars_spica_140731

During the month, Mars moves quickly eastward compared to the starry background. The separation between Mars and Spica is easily observed. By month’s end they are about 9 degrees apart.

Morning Sky

Venus continues as a brilliant Morning Star.  It rises about 2 hours before the sun in the northeastern sky.  On July 11, Venus rises north of the sunrise position and continues rising north of sunrise until it disappears into bright sunlight in October.  Read more about Venus as a Morning Star.

ven_moon_140724

Venus and the waning crescent moon appear together in the predawn skies during twilight on July 24.  Find a clear horizon to view the pair.

Mercury appears in the eastern morning sky throughout most of the month.  This elusive planet appears during twilight and never in a dark sky.  On July 12 it reaches its greatest angular separation from the sun.

mer_moon_140725

The waning crescent moon may provide some assistance in locating Mercury.  During bright morning twilight on July 25, the moon appears about 5 degrees to the lower right of Mercury while Mercury is 9 degrees to the lower left of Venus.

Solar System

Solar System July 2014

The chart above shows the planets’ positions on July 15, 2014.  Mars and Saturn appear on the evening side of the sky with Mercury and Venus in the morning.  Jupiter is behind the sun as visible from earth.  Notice that it is on the noon line meaning that it is in the sky during the day and not visible in the bright sunlight.

 

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: