Sky Smorgasbord


Artist’s conception of the Spitzer Space Telescope against the infrared sky.

Credit: NASA/JPL

Saturday evening, March 4, an exciting close encounter between the nearly-first-quarter Moon and the bright star Aldebaran will occur. Their juxtaposition will be visible, if skies are clear, across most of the continental United States. Aldebaran, in the constellation Taurus, is the brightest star ever blocked from our view as Earth’s satellite travels its monthly orbit against the backdrop of zodiac stars. Although this event, known as a lunar occultation, may be seen with naked eyes, binoculars are a big help when watching the action. Aldebaran, 67 light years from the Solar System, is a giant star with a diameter about 25 times that of the Sun.

Aldebaran’s size and distance ensure its light will not be instantaneously chopped from view as the Moon passes between us and the star’s disk. Instead a brief period of fading starlight less than a second in duration may be discerned by sharp eyed observers. The star will disappear as it is covered by the dark portion of the Moon’s northern edge.

For observers in the middle of New York City, the March 4th occultation of Aldebaran is predicted to begin at 11:10:51 p.m. Then the Moon is low in the western sky, 16° above the horizon. As the Moon orbits eastward relative to this star, Aldebaran will reappear at the illuminated side of the northern lunar limb about 11:31:05 p.m. Given the 35 mile extent of the city, starting and finishing times for the occultation may vary by a minute or more depending on your location. Observers should start looking for the Moon and Aldebaran at least five minutes before times indicated. Occultation times for other locales around North America may be found at Rob Robinson’s occultation website.

For viewers along a razor thin strip of geography at the northern limit of the occultation’s zone of visibility, hills and valleys at the edge of the Moon may provide dramatic glimpses of Aldebaran as the Moon’s rough topography alternately blocks, then quickly reveals starlight. This effect may be seen by observers precisely stationed along a line stretching from the Pacific Northwest to Rhode Island. Locally, the line of grazing occultation passes just south of Oneonta and north of Hartford, passing through the northern Catskills. The International Lunar Occultation Timing Association provides detailed maps and suggestions for identifying sites along the event’s “graze line.”

The remarkable discovery of seven Earth sized planets orbiting within the “Goldilocks” zone of a 39 light year-distant dwarf star known as TRAPPIST-1 was recently revealed in the journal Nature. The story elicited enormous interest, reported above the fold on the front page of The New York Times, and featured by media worldwide. During a 20-day period beginning last September 19, the Spitzer Space Telescope provided nearly continuous infrared monitoring of the star, culminating recent studies of its fascinating planetary system.

Because Earth-sized planets of the TRAPPIST-1 system orbit a star barely larger than Jupiter, dimming of starlight as the planets pass between their host star and us provides more noticeable effects than when Earth-sized planets in other systems transit far larger stars. Not only is timing of events at TRAPPIST-1 more precisely discernable, there is also greater potential for future spectral study of planetary atmospheres if they exist, as analysis abilities evolve. In the not too distant future, that might provide evidence of life (or lack thereof) on these planets. 

One of the charms of astronomy is an ability to go outdoors and point up toward distant objects that are subjects of historic discoveries past and present.

Soon after learning about recent discoveries at the TRAPPIST-1 system, I wondered where it’s located in the sky and the Spitzer Space Observatory website provided coordinates in Aquarius. It happens that in March the Sun is also in Aquarius and on Sunday March 5, the Sun and the TRAPPIST-1 planetary system are at nearly the same direction in our sky. Their minimum angular separation occurs at about 3:48 p.m. EST that day. The Sun’s disk is then just half a degree of arc (its own apparent diameter) north of the newly famous star and its seven intriguing planets.

Of course never stare at the Sun, but if you’re out and about on the afternoon of March 5, you might point slightly beneath the Sun, and share with someone the story of that extraordinary star system.

Daylight Saving Time begins 2 a.m. Sunday March 12, and we “spring forward,” gaining an extra hour of daylight at the end of the work day and one hour less light during early morning.

Spring officially begins in the northern hemisphere at 6:29 a.m. EDT Monday the 20th of March. At that time, the Sun is directly above a point on the equator at longitude 24° 52' East in the Democratic Republic of the Congo, about 500 miles west of Lake Victoria.