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Night Sky

Enjoy our starry night skies.
Be a considerate neighbor: reduce nighttime glare.
Shield your outside lights downward.
Let the stars light up the night.

February 2013 Night Sky

—Charlie Christmann

Dangerous skies

Our sky is full of debris left over from the formation of our solar system some four billion years ago. NASA currently knows about 1371 Potentially Hazardous Asteroids (PHAs)—those that are large enough to do major damage to our planet and come close enough to be a worry.

As I reported last month, on February 15, asteroid 2012 DA14 will pass inside the orbit of our geosynchronous satellites—around 21,497 miles over our heads. Closest approach will be at 12:26 p.m. Don’t bother to look for it, being only about 165 feet across, it will be too small to be seen without a telescope, and too dim to see in daylight. Its path will rapidly take it from south to north across the sky at a relative velocity of 17,493 miles-per-hour. 

2012 DA14 was discovered early last year by a Spanish observatory—though it has whizzed by Earth many times on its 366-day inclined orbit around the sun. Weighing in at 130,000 metric tons, it is small enough that there will be no effect on our planet. If it were to someday impact us, it would produce an explosion equivalent to 2.4 megatons of TNT. It would not destroy Earth, but it could flatten a city.

This asteroid crossed our path near the Moon’s orbit in February of 1918 and at twice the lunar distance in August of 2004. It will next menace Earth on February 16, 2046 when it could come as close as 39,041 miles. Astronomers will be watching this pass closely and making measurements to better pin down the asteroid’s orbit as it still poses a future threat.

My anniversary rock fizzles

A few years ago, I wrote about 99942 Apophis, an asteroid that would also pass very close to Earth in 2029. When first discovered in 2004, there was a flurry of fear as NASA predicted a small chance of a collision with Earth on April 13, 2029 (my wedding anniversary). Further observations ruled out that collision, but could not rule out an April 13, 2036 impact. As large as a modern super cruise ship, this space rock would equate to more than 500 megatons of TNT and could have disastrous implications if it were to hit Earth.

Current predictions show a miss of at least 18,300 miles in 2029. Uncertainties in 99942 Apophis’ size, surface characteristics, and spin make orbital predictions difficult. Sunlight pressure (like wind on a sail) can push the asteroid around.

Fortunately, Apophos has visited us recently and astronomers were able to make more measurements on its orbit. On January 10, 2013, this asteroid passed Earth at a distance of about nine million miles. According to Don Yeomans, manager of NASA’s Near-Earth Object Program, using measurements made by Pan-STARRS (Univ. of Hawaii) optical observatories, Goldstone Solar System Radar, and Magdalena Ridge (New Mexico Institute of Mining and Technology), the Earth will be safe in 2036, too.

If you plan to be around in April 2068 or October 2069, you might start worrying.

Over-hyped?

“Comet-Of-The-Century” astronomy buffs crow. The newly discovered Comet ISON is still near Jupiter, but may visit our neighborhood at the end of the year. Predictions are that this comet could be visible in daylight, similar in brightness to the moon.

Russian astronomers Vitali Nevski and Artyom Novichonok found the comet in September, 2012. It bears the name of their night-sky survey program, the International Scientific Optical Network.

Before it becomes the spectacle it is predicted to be, it has one major hazard to navigate—the sun. On November 28, 2013 it will pass through the solar atmosphere a mere million miles above the seething surface of the sun. It may not survive. Tidal forces and solar radiation have been known to destroy comets. Comet Elenin, broke apart and dissipated in 2011 as it approached the sun. Comet Lovejoy flew through the sun’s atmosphere in 2011 and not only survived intact; it wowed observers for weeks.

“Comet ISON is probably at least twice as big as Comet Lovejoy and will pass a bit farther from the sun’s surface,” notes Karl Battams of the Naval Research Lab. “This would seem to favor Comet ISON surviving and ultimately putting on a good show.

 If it survives its swing by the sun, Comet ISON will pass almost directly over the North Pole, making it a circumpolar object, visible all night—and maybe all day—long.

The Planets and Moon

  • Sunrise is from 7:00 a.m. to 6:35 a.m. this month and sets from 5:35 p.m. to 6:00 p.m.
  • Mercury is a morning star. Look hard in the twilight mid-month in the east. On the 8th, Mars is 0.3 degrees from Mercury.
  • Bright Venus rises about 6:25 a.m. ESE shining brightly at -4 magnitude.
  • Mars rises with Mercury this month in the east.
  • After sunset, Jupiter will be high and bright (-2.5 magnitude). Look for the Moon-Jupiter conjunction on the 17th.
  • Saturn rises around midnight this month in the ESE. The Moon nears Saturn on the 3rd.
  • On February 11, just after sunset, get out the binoculars. Carefully avoiding looking at the sun, find the very thin crescent Moon above the western horizon. Below the Moon will be Mercury, then Mars. Below those, near the horizon will be Neptune. If you have a telescope, you may be able to find Uranus above the moon. Venus will set before the sun. The arrangement of these many planets seen so close to the sun (conjunction) is very rare.
  • The Moon is new at 12:20 a.m. on the 10th and full at 1:26 a.m. on the 25th.

THE SONG OF THE NIGHT SKY

By observing carefully
The complex visual song
Played by the moon
The planets
And the stars
As they dance across the night sky

By noting their relative positions
Over the course of a night
From night to night
From month to month
From year to year

We can gather sufficient information
To determine

That we spin on a tilted axis
As we orbit the sun
In a galaxy we call The Milky Way

That the moon orbits us
And the time it takes

That the orbit of Mercury lies closest to the sun
Followed by Venus
Us
Mars
Jupiter
And Saturn

We can also determine

The time it takes each planet to orbit the sun
Relative to the year it takes us

We can predict

Conjunctions
Eclipses
The phases of Venus

With a small bit of optical assistance
We can observe

The phases of Venus
The moons of Jupiter
The rings of Saturn
Distant galaxies

—Jim Fish

 
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