December 2007 - Utah-Astronomy - mailman.xmission.com

Cutting the cord
by Patrick Wiggins 28 Dec '07

28 Dec '07

FYI: Sometime in the next 2 weeks or so my current home phone number, 435 882 1209 is going to become my cell phone number. At that time my current cell number, 801 918 9092 will stop working. Email addresses will remain unchanged. Please update your records. patrick

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Electronic SLAS roster
by Jerry Foote 27 Dec '07

27 Dec '07

Hi Patrick, Would it be possible to get the SLAS roster in electronic format? Some of us use PDA's to store our contact information. Thanks Jerry Foote ScopeCraft, Inc. 4175 E. Red Cliffs Dr. Kanab, UT 84741 435-644-3167 jfoote(a)scopecraft.com

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Mars impact odds upped
by Patrick Wiggins 27 Dec '07

27 Dec '07

I see on MPML today that some prediscovery images of 2007 WD5 have been found. Adding those to the orbit solution appears to have increased the chances of impact to 1 in 25. Still a long way from certain but it is the first time I can recall that prediscovery images have increased the chances of an impact. patrick

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Tis' the season to remember Utah Astro Gallery and Cynthia Blue
by Kurt Fisher 26 Dec '07

26 Dec '07

It's the day after Christmas and all is quiet in the house; not a telescope is slewing, not a photon is watched. Your wallet is empty and your credit cards are just about maxed out. The wife or SO is out shoppping the post-Christmas sales; so I slumber in my cap catching a quick winter nap. When deep in my rest, my conscience started to give such a clatter. Who did I forget to thank in all this holiday banter? In the season of holiday giving, you might want to consider adding a donation to the Utah Astro Gallery and Cynthia Blue, who has selflessly kept the gallery going for some years in part apparently using her own gear. There is a PayPal donation button at the top left hand corner of the main gallery page: http://gallery.utahastronomy.com/main.php which links to another donation volunteer activity of Cynthia "Utah Collies". If you do not have a PayPal account, PayPal will also process any major credit card without setting up a PayPal account. If the 27 gallery members each donate $20 at a 75 percent participation rate, that should gross Cynthia about $400. I've thrown in $25. Merry X-Mass, Happy: Boxing Day - Hanukkah - Eid ul Adha - Kwanzaa - HumanLight Day - Festivus-for-the-rest-of-us, etc., etc. etc. - Kurt _______________________________________________ Sent via CSolutions - http://www.csolutions.net

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Top Utah Astro Observed Events for 2007
by Kurt Fisher 26 Dec '07

26 Dec '07

What would you rate as the top Utah asto events for 2007? To qualify, the event must have been actually observed, or unsuccessfully attempted to have been observered, either in Utah or Hawaii. - Kurt _______________________________________________ Sent via CSolutions - http://www.csolutions.net

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Re: [Utah-astronomy] Top Utah Astro Observed Events for 2007
by Kurt Fisher 26 Dec '07

26 Dec '07

Joe B wrote: > Definitely the mysterious exploding comet. -- Joe With respect to your earlier question sometime ago, about why comets have round heads, I made a pit stop at the Marriott library and have also bought a couple of books on comet physics. Haven't had the time to type up any notes. The short answer on 17P is that the venting side of the comet faces the Sun. Gitto image of venting Halley's Comet nucleus in 1986 http://seds.lpl.arizona.edu/nineplanets/nineplanets/halley.html The ultra-low density magnetically neutral comet gas moves sunward from the vent at between 500 meters/sec to 1000 meters/sec. The intuitive model of the comet - because venting is on the Sun side - would be that the tail should point towards the Sun. But the counter-intutitive reality is that this comet gas runs into the solar wind - another ultra-low density gas moving between 400 meters/sec to 800 meters/sec but going in the opposite direction. The head-on or slightly oblique collision of these two gas molecules make a bow shock wave on the leading edge of the expanding comet gas and the rebounding molecules travel into orbits that make the characteristic spherical-cone shaped coma. The leading bow shock wave of a comet coma can be seen in some images of 17P, depending on how the images were processed. Sebastian Voltmer 11-12 Animated color 11-2 to 11-12 http://spaceweather.com/comets/holmes/13nov07/Sebastian-Voltmer1.gif This leading bow shock and the denser gas around the psuedo-nucleus also gets ionized by these collisions. Comets also traverse the spiral magnetic fields emanating from the Sun - the Parker spiral - and the magnetic field lines wrap around the comet's magnetic field and trail almost straight-out behind the comet. This is analogous to the Earth's magnetosphere-sheath that also passes through the Sun's spiral magnetic field. The ionized gas around the pseudo-nucleus and at the bow shock travels follow those magnetic lines trailing straight behind the comet and become concentrated in the magnetic current sheet trailing the comet. In 17P, the small trailing sheet or coma psuedo-short-tail is very easily seen. Patrick's 11-14 image http://gallery.utahastronomy.com/v/patrickw/HOLMES14NOV2007-030.JPG.html It is the bow-shock and trailing current-sheet short-tail that gives 17P its defining trilobite or "space bug" look. The diameter of the coma is a function of the intensity of the solar wind - which decreases by the d^2 exponential distance from the Sun. Compare McNaught in Jan. 2007 going inbound (tiny coma, huge tail) with Holmes going outbound in Oct.-Dec. 2007 (huge coma, no tail). Inbound comets have larger comas the further they are from the Sun. The size of the coma decreases as the comet moves closer to the Sun (within the orbit of Earth) due to the increased density and pressure of the solar wind. Conversely, the tail gets bigger because the increased pressure of the solar wind strips more molecules off the venting coma. 17P is outbound between 2 and 3 a.u. Somewhere near 3 a.u. the heat of the Sun will become insufficient to vaporize any water molecules on 17P. At 2.1 to 2.7 a.u., the solar wind is still moving around 400-800 meters second, but is much less dense. As the comet moves further from the Sun, the pressure decreases, there are less solar wind molecules to collide with venting comet gas, and the coma gets bigger before the molecules get turned around in their tajectory into a spherical coma - well alot bigger coma in the case of 17P. Not all vents on a comet point directly at the Sun all the time. Some comet nucleui rotate. This rotation has been seen indirectly in the subtle changes in the magnitude (<0.1 mags) of the psuedo-nucleus. Meech page of rotating comet nucleus light curves http://www.ifa.hawaii.edu/faculty/meech/rot.html A consequence of this rotation are so-called "non-gravitational" changes in a comet's orbit. It is one reason why periodic comets have to be re-acquired on each new orbit. These subtle non-gravitational parameters change the comet's orbit chaotically and result in a slightly different inbound tajectory on the next pass. In closing, 17P's coma is not so mysterious. A big coma on a far away-outbound comet is consistent with dynamics between the relative intensities of inbound venting comet gas and the outboud solar wind. Because of Utah's extended December cloud-out, I have not seen 17P for weeks. Current (12-23) internet list traffic says that 17P is still faintly visible in binoculars before the Moon rises. - Kurt _______________________________________________ Sent via CSolutions - http://www.csolutions.net

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Re: 2007 WD5
by Kurt Fisher 24 Dec '07

24 Dec '07

In my wildest imaging of the event, if the long odds play out, the impactor hits Phobos and we end up with two ringed planets! Face slap!! Okay, now I'm back to reality. -:) Kurt _______________________________________________ Sent via CSolutions - http://www.csolutions.net

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Re: 2007 WD5
by Kurt Fisher 24 Dec '07

24 Dec '07

2008/01/30.45932 = 2008/01/30 11:01:25 UT = 2008/01/30 04:01:25 MST Mars from SLC Azimuth :+296°17' Altitude :+10°38' May have to buy a ticket to Rob R's place for this one. -:) I suspect the whole thing is another media attention getting exercise, but hope that one of the Rovers gets a picture of the fireball flying directly overhead through the upper atmosphere followed by the impact live on CNN through the cameras of the USA MRO and ESA Mars Express - while I'm looking at the impact flash through e.p.! Here's the NASA-JPL 3D orbital diagram: http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2007+WD5&orb=1 Merry X-mas, Boxing Day and Kwanzaa to all! - Kurt _______________________________________________ Sent via CSolutions - http://www.csolutions.net

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Moon in the Beehive Wednesday A.M.
by Patrick Wiggins 24 Dec '07

24 Dec '07

Not that the weather is going to allow us in northern Utah to see it but the Moon will be passing through M-44 Wednesday morning between ~5:00 and dawn. Weather for southern Utah looks like it might be a bit better so Jerry and Debbie will have to post pictures. patrick

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Re: 2007 WD5
by Kurt Fisher 24 Dec '07

24 Dec '07

P.S. - Patrick, any indication in the specialty mailing lists how big of a rock this is? Is a pebble, a boulder, a house, a mountain? What's the mass? - Kurt _______________________________________________ Sent via CSolutions - http://www.csolutions.net

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