Tuesday, January 31, 2012

More on the age of stars in Roanoke Skies

In the February installment of Roanoke Skies, www.roanoke.com/columnists/goss/, the ages of certain stars in our February evening sky were described using a timeline. How do stars form in the first place?

Astronomers and astrophysicists have studied the topic of stellar evolution for two hundred years, eventually arriving at a model that explains their observations. It really boils down to understanding in depth the processes of gravity, thermodynamics, and thermonuclear fusion.

The basic model of stellar formation begins with a nebula composed of gas that is many tens of light-years wide. The nebula is cold and contracts under its own very weak gravity. Perhaps the gravitational field of passing star or a shock wave from nearby hot stars initiates the collapse.

After a few hundred thousand years, the collapsed nebula forms a dense ball. As that ball contracts further, it heats. Once its core temperature reaches a million degrees or so, it begins thermonuclear reaction, i.e., it starts to fuse hydrogen into helium. A star is born.

The physics of stellar evolution is now largely well understood. Astronomers can determine a star's distance, motion through space, mass, diameter, rotational rate, intrinsic luminosity, surface temperature, and chemical composition. Most of this is accomplished through spectroscopy, which measures the star's spectrum, much as a prism reveals our sun's rainbow-like spectrum. This is simply amazing since the stars lie so far away.

Scientists developed their model by studying a great many stars. Then, they were able to deduce specific characteristics which occur at specific stellar ages. If they know a star's mass, distance, luminosity and composition, they can determine its approximate age.

Astronomers have found that high mass stars are very luminous and age very quickly living only a few million years. Rigel falls into that category. Lower mass stars aren't as luminous or as hot and don't age quickly, living 10 billion years. The sun falls into that group. Very low mass stars, the so-called red dwarfs, are not very hot (as stars go), and are not very luminous. They age extremely slowly, living one hundred billion of years. None of them can be seen with the unaided eye simply because of their low intrinsic luminosity, being about 1/100 as bright as that of the sun. Isn't it strange that every red dwarf that has ever formed is still dimly shining today because, compared to the lifetime of a red dwarf, the universe is relatively young at 13.7 billion years old.

Such is the view from our Earth...

"Use that 'Scope!"

"Use that 'Scope!" -- Saturday, February 4, 9:00 a.m .to noon, Moomaw Center, main campus Dabney Lancaster Community College, Clifton Forge. $20. Instructor: John Goss. Get a new telescope for Christmas and not sure how to use it? Learn how to use your new 'scope to find fun sky objects. Be sure to bring your telescope with you! To register, contact:

Judy Clark
Public Relations and Non-Credit Coordinator
Dabney S. Lancaster Community College
PO Box 1000
Clifton Forge, VA 24422
(540) 863-2863
(540) 863-2928 (Fax)
(540) 460-0187 (cell)

Such is our view from Earth...

Sunday, January 29, 2012

Watch Mars March

Every twenty-six months or so, Mars makes a bright appearance in our early evening sky. The Red Planet can be found climbing above the eastern horizon two hours after sunset. It is the brightest object in that part of the sky, almost matching Sirius, which shines in the south. During the next three months, Mars slowly moves westward through the constellation Leo, towards its bright star Regulus. After the middle of April, it reverses its apparent direction and begins moving away from Regulus.

Find the time to spot Mars as it marches through Leo!

Such is our view from Earth...

Friday, January 27, 2012

Our moon approaches Jupiter

Over the next few nights, the moon climbs higher, leaving Venus behind, and approaches Jupiter. On the 29th, the first quarter moon lies just to the west of the giant planet, and on the following night, it lies to the east of Jupiter. Bring out binoculars to look at the scene more closely. You will be able to see craters on the moon and the four large moons of Jupiter. Hold them steady and you may be rewarded with these interesting sights!

Such is the view from Earth...

Wednesday, January 25, 2012

Crescent Moon greets brilliant Venus

The moon and Venus always make a pretty combination. Tomorrow night, January 26, presents a great opportunity to see the two brightest evening objects come together in our western sky. Look to the west 45 minutes after sunset for their pairing. The moon will be sporting Earthshine, the back reflected sunlight off the nearly full Earth. This makes the lunar crescent appear dimly full. Use binoculars for a more magical effect!

Such is the view from Earth...

Sunday, January 15, 2012

December 2012, Doomsday, and the Mayan Calendar

It is 2012 on Planet Earth and all is well in the Celestial Neighborhood

There are fanciful stories floating on the Internet claiming that the Earth will face destruction in December 2012, more specifically on the winter solstice date of December 21. Three general causes are usually given, none of them have any validity and none of them make much sense.

1. The favorite reason maintains that a large, mysterious celestial body either will collide with the Earth destroying life as we know it, or will closely pass our planet causing catastrophic earthquakes.

2. A more bizarre assertion is that on the winter solstice the sun aligns with the center of the Milky Way galaxy causing the sun and the Earth to enter into a "galactic beam," possibly dragging the sun — with the Earth in tow — towards the center of the galaxy.

3. A third absurd claim contends that there will be an alignment of the planets resulting in upheavals on Earth caused by either devastating gravitational or strange magnetic forces, or by massive solar flares.

There is no scientific evidence to support any of these claims.

Here is what the scientific evidence does support:

A. No large body is approaching the Earth. No new large body has appeared in the solar system. No new body can be seen during daylight hours in the southern hemisphere — or the northern hemisphere, for that matter.

B. The sun does not align with the center of the Milky Way on December 21, 2012. The sun's position on the celestial sphere lies closest to the direction of the galactic center on December 18, not on the winter solstice, just as it has been over the past several decades. The position of the winter solstice on the celestial dome will never come into direct alignment with that of the galactic center. While the winter solstice point and the galactic center are located in the same general area of the sky, they are still over 6ยบ apart — about thirteen apparent full moon widths. In any case, the sun and the galactic center are located nowhere near each other in space with the sun on December 21 being about 91.5 million miles from Earth and the galactic center situated two billion times farther at 27,000 light-years away.

C. There are no unusual alignments of the planets in 2012. Planets sometimes appear close to one another in the sky, but viewed in three dimensional space, they are tens of millions to hundreds of millions of miles apart. While the sun has entered one of its periodic active phases, there is no reason to expect unprecedented solar disruptions.

Furthermore, there are claims that Earth’s imminent destruction by celestial agents is known to the governments of the world and that they are concealing this information for their own purposes. That assertion just doesn’t hold up to scrutiny. There are well over 100 professional observatories and over 10,000 amateur astronomers located across the globe who constantly search the skies for new and unusual celestial phenomena. No large approaching body could escape their attention. No government could silence them all.

A few outspoken people contend that the end of the world on December 21, 2012 was foretold by the ancient Mayans because, according to these people, the Mayan calendar ends on that date. Some professional archeologists who specialize in studying the Mayan civilization have concluded that one of the calendar's very long counting cycles, the 144,000 day "baktun," ends on December 21, 2012. (Not all authorities agree on this date, however.) This has prompted certain purveyors of doom to link the end of the thirteenth baktun to their own unsupported predictions that the world ends in December 2012. They ignore the fact that the calendar continues, without interruption, when the fourteenth baktun begins on the very next day after the thirteenth ends.

Such is our view from Earth...

Friday, January 13, 2012

Can you see Comet Levy?

Tonight before moonrise at 10:30 p.m., binocular uses can spot something a little different. 19 million mile distant Comet Levy lies about one binocular field of view below bright Jupiter. (Jupiter is the brightest object shining high in the southwest.) The comet should appear as a dim smudge. View it again on Saturday and Sunday nights. It will have moved.

The moon moves in our sky near Mars tonight. Then on Monday morning, the moon, sporting a third quarter phase, lies next to Saturn and Spica, forming a tight triangle with them. Saturn appears to its left while the similarly bright Spica sits just above the lunar half disk.

Such is our view from Earth...

Monday, January 9, 2012

Where are the planets?

The appearance of the celestial dome is always changing. Here is brief rundown of where the moon and the planets lie in the sky above us.

Moon: Just past full, it is a waning gibbous phase. As the week progresses, its "fattness" becomes less. It moves near Mars as they rise on the 12th and 13th.

Mercury: Rises an hour before the sun, and remains very low in the southeast just before sunrise. It will be difficult to spot.

Venus: Very bright starlike object in the west an hour after sunset. If it is clear, you can't miss it.

Mars: Appears as a bright star in the east after 11 pm. Can you notice its orange-red color?

Jupiter: As the sun sets, Jupiter lies very high in the south. It is easily the brightest object in that area of the sky.

Saturn: Won't rise in the east until 2 am. It sits to the left of a slightly dimmer object, the star Spica. Bright Mars lies far to their upper right.

As a bonus celestial sight: The ever popular constellation Orion with its two bright stars, Betelgeuse and Rigel, can be found after 7 p.m. climbing in the east.

Such is our view from Earth...

Thursday, January 5, 2012

Perihelion today

Our Earth moves in an elliptical orbit around the sun. It may seem strange with our recent cold winter weather, but today our planet reaches its annual minimum distance to the sun — called perihelion. Our distance now is about 91.4 million miles, which about 3 million miles closer, or about 3% closer, than in July. Therefore, the January sun appears a little brighter in our sky than the July sun! Odd.

such is our view from Earth...

Tuesday, January 3, 2012

Quadrantid Meteor Shower: 1/04/12 after 2 am

The waxing gibbous moon tonight sits just to the east of bright Jupiter. As they set around 2 a.m., the Quadrantid Meteor Shower takes hold in the northeastern sky. (The center of the radiant is located just south of the tip of the handle of the Big Dipper.)

From a dark location, upwards of 60 meteors per hour might be seen under good conditions. Keep warm and relax in a comfortable chair while watching for these swift streaks of light. Binoculars are not necessary, nor even useful. How many do you count?

...such is the view from our Earth