[AZ-Observing] FW: [hac] Antares Occultation Thursday Morning
- From: "Keller, Jennifer T." <kellerjt@xxxxxxxxxxxxxx>
- To: "AZ-Observing (E-mail)" <AZ-Observing@xxxxxxxxxxxxx>, "Sac-Announce (E-mail)" <sac-announce@xxxxxxxxxxxxx>
- Date: Wed, 2 Mar 2005 12:05:36 -0800
Here is some information from Doug Snyder at Huachuaca Astronomy Club about
tomorrow morning's Antares occultation by the Moon. So set those coffee
makers to 3am and hope for clear skies.
Jenn.
-----Original Message-----
From: Doug Snyder [mailto:starhaven@xxxxxxxxxxxxx]
Sent: Wednesday, March 02, 2005 11:56 AM
To: HACList
Subject: [hac] Antares Occultation Thursday Morning
There is going to be a bright star occultation Thursday morning. The double
star Antares (the Alpha star of Scorpius) will pass behind the bright limb
of the Moon shortly after 3:15 am and reappear from the dark limb around
4:12 am. Both events will be visible here in SE AZ. Antares, a cool Red
Giant, is a magnitude 1 star with a magnitude 5.4 Dwarf companion. This
companion star is only 2.4 seconds of arc away from Antares, and is at a
position angle of 275 degrees.
This occultation will provide you with the opportunity to view the dimmer
companion of Antares (more likely during the reappearance from the dark
limb).
http://skyandtelescope.com/aboutsky/pressreleases/article_1469_1.asp
http://skyandtelescope.com/observing/objects/occultations/article_1401_1.asp
If you have nothing to do between 3 am and 4:30 am, give it a try!
Here's a 'copied' discussion about position angles:
Position angles are most commonly used to express the orientation of two
objects in the sky as they relate to each another and the compass points.
For
instance, take a double star like Albireo. Using the 3rd magnitude primary
as
a starting point, in which direction is the 5th magnitude companion? The
answer is to the primary's northeast, in position angle 54 degrees. Position
angles are expressed starting with due north (0 degrees) running through
east
(90 degrees), south (180 degrees), and west (270 degrees). This may seem
peculiar, since this is counterclockwise as you look up at the sky. It's
something of a concession, actually, to old cartographers who couldn't get
the idea of east being anything but 90 degrees.
It's important to remember, when talking about position angles, that they
always reference celestial north. And the relative direction of that in your
eyepiece shifts constantly as you move your scope around. Then there is the
matter of flipped and inverted images - you always have to be aware of these
factors when either using PA as a guide to identifying something (like a
double star's companion) or when describing the relative position of
something you are observing - say a planetary's position in relation to a
nearby star.
Position angles are also used commonly to express the orientation of the
axes
of galaxies and other celestial objects. For instance, M81 is in position
angle 157 degrees - one "end" pointing in that compass direction, with the
other pointing 180 degrees in the other direction, 337 degrees. So we can
visualize it being lined up in the sky from the SSE to the NNW, without ever
having looked at it directly.
Doug Stewart
Doug
Huachuca Astronomy Club
http://c3po.cochise.edu/astro
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