This weekend, and the second weekend in July, "Manhattanhenge" once again returns to New York City. Images, my full write-up, times, and other details are posted on our Manhattanhenge page.

As you may know, Manhattanhenge takes place on two consecutive days, twice a year, when the setting Sun aligns precisely with the Manhattan street grid, creating radiant sunsets that burst across our brick and steel canyons, simultaneously illuminating both the north and south sides of every street. A rare and beautiful sight.

Unnoticed by many, the sunset point actually creeps day to day along the horizon: northward until the first day of summer, then returning southward until the first day of winter. In spite of what pop-culture tells you, the Sun rises due east and sets due west only twice per year - the first day of spring and of autumn. Every other day, the Sun rises and sets elsewhere on the horizon.

While we are on the subject, when viewed from all latitudes north of the Tropic of Cancer (23.5 degrees north latitude), the Sun always rises at an angle up and to the right, and sets and an angle down and to the right. That's how you can spot a faked sunrise in a movie: it moves up and to the left. Filmmakers are not typically awake in the morning hours to film an actual sunrise, so they film a sunset instead, and then time-reverse it, thinking nobody will notice.

The consecutive days for Manhattanhenge identify when half the Sun's disc and when the entire Sun's disc is setting on the grid. If the Sun were to set perpendicular to the horizon then these would be the same day. But since the Sun's path angles down and to the right, and shifts slightly from one day to the next, we get two days of Manhattanhenge, a half-sun sunset (my personal favorite for photographs) and full-sun sunset.

People in the eastern United States will get a great opportunity, weather permitting, to see the Space Shuttle Discovery launched into orbit Wednesday evening, March 11.

The Shuttle flight (STS-119) will be the 28th to rendezvous and dock with the International Space Station (ISS) and the glow of its engines will be visible along much of the Eastern seaboard of the United States.

To reach the ISS, Discovery must be launched when Earth's rotation carries the launch pad into the plane of the ISS's orbit. For mission STS-119, on March 11 that will happen at 9:20:10 p.m. ET, resulting in NASA's first Shuttle flight of 2009 and its second consecutive nighttime (the previous shuttle flight, last November 14, was also a nighttime launch). This launch will bring the Shuttle's path nearly parallel to the U.S. East Coast.

What to expect

For most locations, Discovery will be visible by virtue of the light emanating from its three main engines. It should appear as a very bright, pulsating, fast-moving star, shining with a yellowish-orange glow.

Based on previous night missions, the brightness should be at least equal to magnitude -2; somewhat brighter than Sirius, the brightest star in the sky, which shines brilliantly in the south-southwest during the evening hours. Observers who train binoculars on the Shuttle should be able to see the rapidly moving shuttle resembling a tiny V-shaped contrail.

In the Southeast United States, depending on a viewer's distance from Cape Canaveral, Discovery will become visible anywhere from a few seconds to 2 minutes after it leaves Pad 39-A. The brilliant light emitted by the two solid rocket boosters will be visible for the first 2 minutes and 4 seconds of the launch out to a radius of some 520 statute miles from the Kennedy Space Center.

No matter where you're located, keep in mind that the Shuttle will not get very high above the horizon. In most cases, it will range from roughly 5 to 10 degrees. To get an idea of how high this is, make a fist and hold it out at arm's length. Place the bottom of your fist on the horizon; the top of your fist is 10 degrees

By location:

Southeast U.S. coastline:

Anywhere north of Cape Canaveral, I suggest viewers initially concentrate on the south-southwest horizon (if you are south of the Cape, look low toward the north-northeast).

Mid-Atlantic region:

Look toward the south about 3 to 6 minutes after launch.

Northeast (Washington, Philadelphia, New York, Boston):

Concentrate your gaze low toward the south or south-southeast about 6 to 8 minutes after launch. Of course, as the shuttle gets closer, its azimuth very quickly swings over to the southeast, where in most cases, the point of maximum altitude occurs. I suspect most people will be scanning the horizon from south-southeast in the final couple of minutes of powered ascent . . . if so, you shouldn't miss out on sighting Discovery.

Discovery will seem to flicker, then abruptly wink-out 8 minutes and 23 seconds after launch as the main engines shut-down and the huge, orange, external tank is jettisoned over the Atlantic at a point about 870 statute miles uprange (to the northeast) of Cape Canaveral and some 430 statute miles southeast of New York City. At that moment, Discovery will have risen to an altitude of 341,600 feet (64.7 statute miles), while moving at more than 17,000 mph and should be visible for a radius of about 770 statute miles from the point of Main Engine Cut Off, or MECO.

Should the launch of Discovery be scrubbed on Wednesday, March 11, the launch will be rescheduled on a daily basis, but the time of the launch will occur roughly 23 minutes earlier for each day the launch is delayed (launch window times through March 16).

Before hoping to see the Shuttle streak across your local sky, make sure it has left the launch pad! Watch a television news outlet to verify that Discovery has been launched, or you can watch the launch on your computer via streaming video from NASA-TV.

Good Luck!

Without a question of doubt, the most spectacular celestial sight during these final days of November is reserved for the early evening sky. One of my astronomy mentors, Dr. Ken Franklin (1923-2007), a former Chairman and Chief Astronomer here at the Hayden Planetarium often made reference to our dynamic and ever-changing night sky.  Such an eloquent description certainly fits our current evening sky, as we now have a celestial summit meeting in the making in the western evening twilight.

The highlight will be the gradual approach relative to each other of the two brightest planets—Venus and Jupiter—with the waxing crescent Moon joining them on the first evening of December.  For the remainder of November, skywatchers will observe Jupiter and Venus slowly converge on each other in the southwestern sky, right after sunset.  Venus and Jupiter will appear a similar distance apart on both the evenings of November 30 and December 1.  The moment of closest approach will actually come during the early morning hours of December 1, unfortunately when this dynamic duo is below the horizon for North America.  They'll be separated by just over 2°, which corresponds to roughly one-half the distance that separates Pollux from Castor, the Twin Stars of Gemini (The width of your fist, held at arm’s length roughly corresponds to 10°).

The pinnacle, however, will come on early on Monday evening, December 1.

Every once in a while, something will appear in the night sky that will attract the attention of even those who normally don't bother looking up.  It's likely to be that way on that Monday evening when a slender crescent Moon, just 15% illuminated, will appear in very close proximity to Venus and Jupiter.

People who are unaware, or have no advance notice, will almost certainly wonder, as they cast a casual glance toward the Moon on that night, what those two large, silvery stars happen to be?  Sometimes, such an occasion brings with it a sudden spike of phone calls to local planetariums, weather offices, and even police precincts.  Not a few of these calls excitedly inquire about the UFOs that are hovering closely in the vicinity of our natural satellite.

A very close conjunction of the crescent Moon and a bright star or planet can be an awe-inspiring naked-eye spectacle. Those involving Venus, Jupiter and the Moon—the three brightest objects in the night sky—always attract the greatest attention of all. Ken would have called it, A beautiful celestial tableau!

The English poet, critic, and philosopher, Samuel Taylor Coleridge (1772-1834) used just such a celestial sight as an ominous portent in his epic, The Rime of the Ancient Mariner.  In addition, there are juxtaposed crescent Moon and star symbols that have appeared on the flags of many nations, including Turkey, Pakistan, Malaysia, Algeria, Mauritania, and Tunisia.

Earthshine

Also on Monday evening, you may be able to see the full globe of the Moon, its darkened portion glowing with a bluish-gray hue interposed between the sunlit crescent and not much darker sky.  This vision is sometimes called the old Moon in the young Moon's arms. Leonardo da Vinci (1452-1519) was the first to recognize it as what we now call Earthshine.

As seen from the Moon, the Earth would loom in the sky nearly 3.7 times larger than the Moon does for us.  In addition, the land masses, the oceans, and clouds make the Earth a much better reflector of sunlight as compared to the Moon.  In fact, the Earth's reflectivity varies as clouds, which appear far more brilliant than the land and seas, cover greater or lesser parts of the visible hemisphere.  The result is that the Earth shines between 45 and 100 times more brightly than the Moon.  The Earth also goes through phases, just as the Moon does for us, although they are opposite from what we see from Earth.  The term for this is called complementary phases.

On Thanksgiving Day, for example, when the Moon is New for us, as seen from the surface of the Moon, the Earth appears Full. A few nights later, as the sliver of a crescent Moon begins to appear in our western twilight sky, its entire globe may be glimpsed.  Sunlight is responsible for the slender crescent, yet the remainder of the Moon appears to shine with a dim blush-gray tone. That part is not receiving sunlight, but shines by virtue of Earthlight: the nearly full Earth illuminating the otherwise dark lunar landscape. So Earthshine is really sunlight which is reflected off Earth to the Moon and then reflected back to Earth.

Venus and Jupiter

Those using binoculars or a small telescope will certainly enjoy the almost three-dimensional aspect of the Moon, but Venus will be rather disappointing appearing only as a brilliant blob of light, for right now, it's a small, featureless gibbous disk.  That will change in the coming weeks, however, as Venus approaches Earth and the angle it makes between us and the Sun allows it to evolve into a half-Moon phase in mid January, and a lovely crescent phase of its own during the latter part of February and March.  Jupiter on the other hand is a far more pleasing sight with its relatively large disk, cloud bands and its retinue of bright Galilean satellites.

No question about it.  It will hardly be an evening spending time watching TV!  If the weather is clear between about 5 and 7 p.m. next Monday, be sure to get out and take a look.