October 21, 2017

AstroEvent: A Solstice, an Occultation and More!

Summer Noctilucents over Astroguyz HQ… (Photo by Author).

Astronomy lovers of the northern hemisphere take heart; the summer solstice occurs this Tuesday June 21st at 1:16 PM EDT/5:16 PM UT as the Sun reaches its most northerly point in its journey as viewed from Earth.  Of course, this motion is apparent (at least, to all but geo-centrists and flat-Earthers!) as our northern rotational pole is now tipped towards the Sun. From here on out until the December solstice, we slowly take back the night. This solstice, being pre-leap year, is about the latest it can fall, as 2012 will see a once every four year reset back to a June 20th solstice, which will again start the yearly creep ahead by 6 hours.

One interesting phenomena to keep an eye out for from mid-northern latitudes are noctilucent clouds. These formations high in the mesosphere may linger into the dawn or dusk hours and glow with a strange neon hue. We’re no stranger to these high flying clouds on the Space Coast of Florida, as they frequently follow sunrise or sunset rocket launches. As twilight lingers over high latitudes, be on the lookout for noctilucents… there is also some controversy as to why they’ve been more apparent over the last half century, and what they may have to do with climate change or even the global dimming effects of contrails. It’s even been postulated that the space shuttle program has added to the surge in noctilucent cloud activity over its past 30+ years; will activity decrease in the coming years after launches cease this summer?

Speaking of manned space travel, the International Space Station has been making splendid series of worldwide passes and continues to do so this week, passing some high latitude locations up to five times in one night. (Its been proposed on Twitter by @OzoneVibe that this phenomena should be termed as a FISION: Five ISS Sightings In One Night) This is occurring because the ISS has reached a phase in its orbit where its continuously illuminated, which occurs right around the solstice. Even this week, nighttime aboard the ISS is measured in mere minutes… also the ISS has just completed a series of boosts raising it to a high orbit of 380 kilometers. This was done using the remaining fuel from ESA’s ATV module prior to its jettison this Monday, June 20th.

Finally, a fine asteroid occultation of a +6 magnitude star occurs early this Sunday on the morning of the 19th for viewers across the US Northwest and central Canada. The asteroid is 90 Antiope, and it will cover the multiple star HIP 112420 in the constellation Aquarius for up to 40 seconds around 10:39 UT… a unique event, and one of best asteroid occultations of the year!

The Astronomy Word of the Week is; Analemma. Ever wonder what that funky figure eight thing was on the class room globe? The Analemma represents a projection of our path about the Sun from a given vantage point; some pretty neat images demonstrating the Analemma have been constructed by photographing a filtered Sun on the same time once every week or so for a year. The figure eight is a result of two factors; one the 23.439° degree tilt of our axis (the vertical displacement), and the variation in speed due to the obliquity and eccentricity of our orbit about the Sun. During the northern hemisphere summer solstice, the Sun would be approaching the northern most apex of the figure eight. The Analemma varies in shape depending where on Earth it is viewed from, looking squashed at the poles and wide at the equator… and yes, and Analemma from another planetary vantage point such as mercury or Mars would look completely different!

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