Category Archives: sky

International Observe the Moon Night September 18th

The Sky This Week, 2010 September 14 -21 — Naval Oceanography Portal

In celebration of our closest neighbor in space, the evening of the 18th has been designated as the first annual International Observe the Moon Night (InOMN). … Information on InOMN, including charts depicting Luna’s appearance on the 18th, may be found on the official website.

The Sky This Week, 2010 September 14 -21 — Naval Oceanography Portal

youll see an attractive triangle in the southwest with Mars and Venus forming the base and Saturn the apex

The Sky This Week, 2010 July 27 – August 3 — Naval Oceanography Portal

As you wait for the sky to darken in the hours after sunset, keep an eye on the southwestern sky, where three planets are participating in one of the best series of conjunctions for the year.  The objects in question are Venus, Mars, and Saturn, and they will spend the next couple of weeks playing a celestial version of “leapfrog” during the twilight hours.  As the week opens, both Venus and Mars lie to the west of Saturn.  By the end of July Mars overtakes and passes the more distant ringed planet, with closest approach between the duo falling on the evening of the 31st.  In the meantime, dazzling Venus is chasing down both objects, and by the end of the week you’ll see an attractive triangle in the southwest with Mars and Venus forming the base and Saturn the apex.  Looking ahead to August, Venus blows by Saturn on the 7th, then passes Mars on the 18th.   

All of this activity in the early evening sky sets the stage for the entrance of Jupiter, who rises just as Saturn and his companions set.  By the end of the week you should see Old Jove in the east at around 11:00 pm, and by midnight he should be high enough to train the telescope in his direction.  Jupiter will become an easier target as August passes, rising about four minutes earlier each night.  He’s still missing his prominent South Equatorial Belt of dark clouds, but this in turn helps to accentuate the famous Great Red Spot, which is the planet’s most famous feature.

The Sky This Week, 2010 July 27 – August 3 — Naval Oceanography Portal

The Sky This Week, 2010 July 20 – 27 Naval Oceanography Portal

The Sky This Week, 2010 July 20 – 27 — Naval Oceanography Portal

The late twilight of the evening sky finds the beginnings of a planetary “traffic jam” in the southwest.  Venus will be the most obvious planet as the light of early evening fades, and she is steadily closing in on ruddy Mars and gold-hued Saturn.  I happened to view Venus shortly before she set last weekend from down on the Northern Neck of Virginia.  Thanks to a flat horizon, thin clouds, and haze, the normally dazzling white planet was glowing like a single orange-red coal in a dying campfire.  She spends the week in restless pursuit of Mars and Saturn, which are gearing up for their own conjunction next week. 

The late night sky now welcomes the bright glow of Jupiter, who is doggedly rising about four minutes earlier each night.  Old Jove reaches the first stationary point in the current apparition on the night of the 23rd, pausing for a few days in his eastward motion before seeming to back up toward the west over the course of the next four months.  Late night skywatchers are now enjoying the view of the giant planet in their telescopes.  Soon he’ll be delighting even those of us with early bedtimes.

The Sky This Week, 2010 July 20 – 27 — Naval Oceanography Portal

A Sphere of Finite Dimensions

The Sky This Week, 2010 June 15 – 22 — Naval Oceanography Portal 

The summer solstice occurs on June 21st at 7:28 am EDT.  At this moment the center of the Sun’s disc stands directly overhead at a point on the Tropic of Cancer in the southeastern corner of Algeria.  A few hours earlier Old Sol stood virtually overhead in the Egyptian city of Aswan, known to the Greek astronomer Eratosthenes in about 240 BCE as Syene.  Eratosthenes also knew that on the summer solstice in Alexandria, Egypt the Sun was just over seven degrees from the zenith.  Having traveled by camel from Syene to Alexandria, he estimated the distance between the two cities and used geometry to estimate the circumference of the Earth.  His result was remarkably close to our modern value if we make certain assumptions about the units that he used.  Still, his method proved that the Earth was indeed a sphere of finite dimension.  For most of us, the solstice passes more or less unnoticed except as the marker of the longest day of the year.  However, many ancient cultures revered the day, as evidenced by Neolithic and Paleoamerican sites throughout the world.

The Sky This Week, 2010 June 15 – 22 — Naval Oceanography Portal

Happy Solstice to all!