October 18, 2017

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!!!” [Read more...]

AstroEvent: The Autumnal Equinox.

An African Sunset. (Credit: Art Explosion).
An African Sunset. (Credit: Art Explosion).

 

   The Balance between the forces of darkness and light are restored on Thursday in the form of the autumnal equinox. This is the point that the position of the Sun along the ecliptic intersects the equator, causing the length of daylight and darkness to be approximately equal from pole to pole. This can vary slightly in reality, owing to respective positions across time zones, the sun fast, and the equation of time. Keep in mind; like the Full or New Moon, the equinox is also a precise moment in time. From here on in until the December solstice, nights will get shorter in the northern hemisphere and days will get longer in the southern. Catch that sunrise or sunset today, and you are looking exactly at the point which is due east or due west of your locale, respectively. [Read more...]

14.04.10: Milankovitch Cycles…On Titan?

 

(Credit: NASA/JPL/University of Arizona).

(Credit: NASA/JPL/University of Arizona).

An amazing sight; sunlight reflected off the Kraken Mare caught by Cassini! 

   NASA’s Cassini spacecraft has revealed an elusive mystery on the surface of Titan; namely, why does the northern hemisphere of the large moon contain numerous lake basins, while in the south they’re relatively scarce? Now, scientists at Caltech working with JPL think they may have an answer. These lakes show up as bright (empty) and dark (filled) patches as the Cassini spacecraft pings them with its Synthetic Aperture Radar (SAR). Of course, on Titan, the hydrologic chemical of choice is liquid ethane and methane, and it is thought that some transport mechanism results in a net flow imbalance between the two hemispheres. Seasons on Titan last roughly 15 years as it dances around Saturn in its 29.5 year orbit about the Sun. But simple seasonal drainage of about a meter per year couldn’t empty the 100 meter-plus deep basins in a single season. This also doesn’t account for the overall disparity in number of basins seen, both filled and unfilled. Instead, scientists point towards the eccentricity of Saturn’s orbit as the possible cause. Saturn’s eccentricity is 0.055, or a little over 5% deviation from a perfect circle. This would make for periodic inequalities in the seasons, much like what occurs on Earth. For example, the perihelion of Earth actually occurs in northern hemisphere winter, somewhat ameliorating the severity of the seasons. But the variation of eccentricity coupled with the obliquity of the planetary spin axis and the precession of the equinoxes can vary over geologic time scales, causing variations in the climate. This is known as the Milankovitch cycle, and is thought to be a major contributing factor to the onset of Ice Ages. On Titan, a similar process is thought to occur, resulting in a net imbalance over thousands of years in the methane flow cycles between the two hemispheres. We may now simply be observing Titan during an epoch when seasonal methane pooling favors the northern hemisphere. Whatever the case, Titan is proving to be a fascinating and changing world deserving of further scrutiny.

24.10.09: Enceladan Seas?

Move over Europa ; yet another moon may harbor a subsurface sea. Saturn’s moon Enceladus has been inching its way up the charts as of late as a candidate world for extraterrestrial life. Barely 300 miles in diameter, the tiny world is repeatedly flexed by Saturn’s gravity and an increased orbital eccentricity pumped up by the nearby moon Dione. This has caused the tiger-striped surface seen by the Cassini space probe, a surface that shows evidence of repeated fissuring and freezing that almost certainly covers a liquid interior. In fact, Cassini has caught several of the geysers in the act during four recent flybys of the moon. One flyby was close enough that Cassini actually flew through a geyser plume! Activity on Enceladus is now known to almost exclusively contribute to Saturn’s E ring…and recently, a much broader ring system has been revealed by the Spitzer space telescope. Sodium chloride has also been detected in the E ring, presumably from the interior of Enceladus…clearly, the Saturnian system is a dynamic place warranting more scrutiny. Let’s hope that NASA approves Cassini’s seven year mission extension!

21.9.9: The Autumnal Equinox.

Can you feel it? The brunt of northern hemisphere summer is about over, giving  way to our favorite season here at Astroguyz; Fall. It’s not just our collective imagination; this Tuesday marks the Autumnal Equinox, or the spring (vernal) Equinox for those down under. This marks the mid way point for the Sun’s apparent journey form north to south, and the beginning of spring and fall, respectively. Of course, we’re the ones in motion!To be technical, this is the point that the Sun rests at 180 degrees along the ecliptic, and at a right ascension of 12 hours and a declination of exactly 0. This occurs this year at precisely 21:18 hours Universal Time on Tuesday, September 22nd. The Sun will rise exactly due east from your locale and set due west, our personal favorite observation to make on this day (weather willing) to site any potential local “Stonehenge” alignments. [Read more...]

Astro-event of the Week: July 15-21st 2008

Comets are the great surprise packages of the solar system. Often appearing out of nowhere, they can brighten up with surprising rapidity, or unexpectedly fizzle, like Kahoutek did in the 1970s. Hence, astronomers are very reluctant to cry “comet of the century” unless they are very certain.

[Read more...]