Fall heralds the return of stargazing, The Sky Guy’s astronomy column: Back in black

The Sky Guy

Posted: Sunday, September 03, 2006

PlanetsPluto

A very bright Jupiter can be seen very low in the Southwest just after sunset. And a very bright Venus is visible very low in the east just before sunrise.

Better situated is Saturn: it’s best seen by commuters along the Sterling Highway on their way to Anchorage as it appears just above the Kenai Mountains during the predawn and dawn hours. There is another bright object nearby, which is the star Regulus in the constellation Leo.

September provides the best chance to see the faint planets Uranus and Neptune, hence the supplied charts of Aquarius and Capricorn. On a very clear night without haze, you need to look very low on the southern horizon (the best is at the Kenai river beach looking south along Cook Inlet). First find the bright Summer Triangle high in the south and the Square of Pegasus in the southeast — the Triangle points toward the western end of Capricorn and the Square’s right side toward the eastern end of Aquarius. Now use binoculars, consult the accompanying diagrams and find those groups of triple stars. From there find the other brighter stars in the diagrams, then greenish Uranus and bluish Neptune.

StarsPluto

To first orientate yourself first, find the Big Dipper low in the northwest, then extend the dipper’s last two stars high into the north to find Polaris, the North Star, and the Little Dipper. With the Big Dipper on one side of Polaris, find the constellation Cassiopeia, a nicely shaped W, on the other side of Polaris high in the northeast. Back to the Big Dipper, follow the curve of its handle toward the bright red giant Arcturus low in the west with its constellation of Bootes above, appearing as a kite or cone shape. Notice the bowl-shaped Corona Borealis to its upper left.

Prominently high overhead and extending to the south is the Summer Triangle, made up of the three bright stars — Vega, Deneb and Altair. Deneb’s constellation of Cygnus, the Swan, in a cross shape is easily seen; Vega’s small, rectangular-shaped Lyra, the Harp, is prominent as well; while Altair’s Aquila or Eagle may be depicted by its wings. Just on the upper left of Altair is the dolphin-shaped small constellation Delphinus. Also prominent in the

southeast are the Great Square of Pegasus, and low in the northeast is bright-yellowish Capella with its pentagon-shaped constellation Auriga.

By morning, constellations have rotated toward the west with some of them having set while other have risen in the east. Those are Orion, Taurus, Gemini, Cancer and Leo, as well as the planets described above.

Have fun observing, I’m looking forward to hopefully clear skies this winter and the astronomy class I’ll be teaching this fall.

Pluto

For those following the news that Pluto has been demoted in status to a “dwarf planet,” here’s an explanation of what happened:

The following is the International Astronomical Union’s official definition on planets and other objects orbiting our sun. The definition got 237 “yeah” votes and 157 “nay” votes (60 percent vs. 40 percent) among 424 astronomers present at the time of voting Aug. 24 at the meeting of the IAU in Prague, Czech Republic, out of 2,411 registered at the conference. The vote took place on the last day of the conference, hence rather few people voted:

“(1) A “planet” [1] is a celestial body that: (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighborhood around its orbit.

(2) A “dwarf planet” is a celestial body that: (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape [2], (c) has not cleared the neighborhood around its orbit, and (d) is not a satellite.

(3) All other objects [3] except satellites orbiting the Sun shall be referred to collectively as “Small Solar System Bodies.”

Footnotes: {1] The eight planets are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.

[2] An IAU process will be established to assign borderline objects into either “dwarf planet” and other categories.

[3] These currently include most of the Solar System asteroids, most Trans-Neptunian Objects (TNOs), comets, and other small bodies.

The IAU further resolves:

Pluto is a “dwarf planet” by the above definition and is recognized as the prototype of a new category of trans-Neptunian objects.

Astronomers seem to be divided about the decision as well as about Pluto’s status. As Pluto had been designated a planet for 75 years, in my opinion, the decision by the IAU to demote it to dwarf planet status is too new and the vote too contentious that the last word has not been spoken about it. So, for at least the near future, I go along with my preference, which is that I continue labeling it as a planet. There’s not really a rationale behind it why I prefer Pluto being a planet — other than its long status as such — but perhaps with time I may change my opinion.

On a final note one may ask why there should be such a vote and if scientists can actually vote on scientific aspects. The answer to the first question is that there had not been an official definition of what a planet is, only the historical notion that planets are “wanderers” among the stars on the celestial sphere. The answer to the second question is that scientists are prohibited from voting on scientific issues because it’s nature and the evidence it reveals that determines scientific conclusions. However, voting on a definition is not about science: a definition of what a planet is is merely meant to categorize objects; hence the vote at the IAU conference is completely legitimate (as is the nonacceptance of individualized star names).

A few years ago astronomers voted that, based on the data, the universe is not only expanding but that its expansion is even accelerating. Now that is a scientific conclusion (based on the data) for which a vote — even among respected astronomers — is meaningless.

Andy Veh is the physics and astronomy instructor at Kenai Peninsula College. He can be reached at aveh@uaa.alaska.edu.



CONTACT US

  • Switchboard: 907-283-7551
  • Circulation and Delivery: 907-283-3584
  • Newsroom Fax: 907-283-3299
  • Business Fax: 907-283-3299
  • Accounts Receivable: 907-335-1257
  • View the Staff Directory
  • or Send feedback

ADVERTISING

SUBSCRIBER SERVICES

SOCIAL NETWORKING

MORRIS ALASKA NEWS