November 23, 2011

AstroEvent: The Moon Makes a Pass at Mars.

Mars + Moon as seen from North America 5PM EDT on the 27th. (Created by Author in Starry night).

As July 2011 comes to an end, has the great August “Mars Hoax” viral email finally died a deserved death? Spawned during the close 2003 opposition of the Red Planet, this email has been a favorite of chain-mailing coworkers & the bane of science skeptics as friends and family members worldwide perpetuate the Woo every summer… usually, we’ve fielded multiple inquires as to how to see Mars as “Big as a Full Moon!!!” by this time of year. Perhaps the urban legend didn’t make the transition to social media… nevertheless, a study on how and where the Hoax email went to survive the winter months could prove to be an entertaining exercise.

The good news is, an event involving Mars does occur this week for observers along a path crossing the South Pacific to the western coast of South America on July 27th, as the waning crescent Moon occults the planet Mars. The action centers on about 17:00 UT, and the rest of the world will see a close pass. Look for tiny Mars next to the crescent Moon at dawn, and be sure to physically block out the nearby blinding Sun for any potential daytime sighting attempts. A telescope with a good GOTO mount should be able to allow you to track Mars into daylight from locations where it’s near the limb of the Moon.

Meanwhile, in dusk skies, the planet Mercury passes the bright star Regulus from July 25-27. The pair will make a good binocular target about 3° degrees apart. Mercury just passed evening elongation on the 20th and will now be sinking into the dusk.

A deserved shout-out also goes out to this years’ Stellafane convention in Vermont, which starts the 28th of July. This is not just a standard old Star Party; every year, telescope makers the world over converge on Stellafane to share their wizardry. It’s the sort of event that folks are already booking to attend next year… someday, Astroguyz will make the pilgrimage…

Finally, the Southern Delta Aquarids peak with a ZHR of about 20 on 29th, a day before New Moon on the 30th. This is one of the better meteor showers with a southern radiant, and they may actually best the Perseid meteors this year, which peak on the same date as the Full Moon. The Southern Delta Aquarids are believed to have originated from an ancient breakup of a Kracht or Marsden sungrazing comet.

The Astro-word for the week is eccentricity. No, we’re not referring to those chain-mailing family members we all have hidden away again here. In astronomy, this is the deviation that an orbit departs from circular; an eccentricity of value of 0 is a perfect circle, and a maximum value of 1 is an open parabola. Eccentricity is sometimes expressed in percentage, such as a current value for the Earth’s orbit of 0.017 or1.7%. Eccentricity is also one of the six Keplerian elements, and is usually expressed as a lower case “e”. The planet Mars has a relatively high eccentricity of 0.093, and thus varies in distance from the Sun from 1.7 AU at aphelion to 1.4 AU at perihelion. Likewise, the apparent angular diameter of Mars during oppositions can vary from a maximum of 25” as happened in 2003 when opposition coincided with perihelion, to a tiny 13”, which we’ll get for opposition near the upcoming Martian aphelion next spring. An average Full Moon is 30’ across, or 1800”; Even at its best, Mars falls short of the promised “Hoax” size by 1/72nd in angular size!

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