Light ray in Archimedes

I've seen the effect your describing in Clavius...
Orion

"kandr" wrote in message
...
I got up around 2:30 EDT on Wed 8/20 to have a look at Mars. Seeing
was unremarkable and when Mars finally set around 3:30 (behind my
neighbor's rooftop) I turned the 10" lx200gps toward the Moon.

I guess I haven't been observing very long because I still always find
it fascinating to scan the lunar surface. I consider it a natural
wonder. With a telescope it's like having the Grand Canyon in your
backyard to look at whenever you want.

Anyway, while travelling down the terminator I noticed a thin
triangular wedge along the floor of Archimedes, extending from near
center and broadening toward the eastern side of the crater: a beam of
sunlight poking through a pass in the western wall had painted a slice
of light on the floor of the crater and splashed up against the
opposite inside wall.

It even appeared to me that the slice was slightly hooked toward the
north, but now I am doubting this. Would one be able to see the
curvature of the lunar surface over the short distance of Archimedes'
radius? If you have observing experience with this (or can do the
math) I'd like to hear.

--
kandr



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kandr wrote in message . ..

EDIT

Anyway, while travelling down the terminator I noticed a thin
triangular wedge along the floor of Archimedes, extending from near
center and broadening toward the eastern side of the crater: a beam of
sunlight poking through a pass in the western wall had painted a slice
of light on the floor of the crater and splashed up against the
opposite inside wall.

It even appeared to me that the slice was slightly hooked toward the
north, but now I am doubting this. Would one be able to see the
curvature of the lunar surface over the short distance of Archimedes'
radius? If you have observing experience with this (or can do the
math) I'd like to hear.

What you saw was the Arcimedes Sunset Lunar Ray, which was discovered
by Bill Arnett a number of years ago (see
http://www.lunar-occultations.com/rl...archimedes.htm). I'm quite
active when it comes to observing lunar light rays, having discovered
a number of them including the first sunset ray in the crater Walter.
I observed Archimedes that morning too. When I first saw the crater
there were 4 distinct rays of varying sizes. By ~8:00 UT only the
longest ray was still visible.

My friend Tony Donnangelo, who has discovered more rays than anyone
else to date, noticed a faint sunset ray in a mountain range to the
north of Archimedes that morning.

Observations were made with Tony's 14.5" Starmaster Sky Tracker Dob
and my 101mm Tele Vue Genesis sdf.

Dave Mitsky

kandr wrote in message . ..

EDIT

Anyway, while travelling down the terminator I noticed a thin
triangular wedge along the floor of Archimedes, extending from near
center and broadening toward the eastern side of the crater: a beam of
sunlight poking through a pass in the western wall had painted a slice
of light on the floor of the crater and splashed up against the
opposite inside wall.

It even appeared to me that the slice was slightly hooked toward the
north, but now I am doubting this. Would one be able to see the
curvature of the lunar surface over the short distance of Archimedes'
radius? If you have observing experience with this (or can do the
math) I'd like to hear.

What you saw was the Arcimedes Sunset Lunar Ray, which was discovered
by Bill Arnett a number of years ago (see
http://www.lunar-occultations.com/rl...archimedes.htm). I'm quite
active when it comes to observing lunar light rays, having discovered
a number of them including the first sunset ray in the crater Walter.
I observed Archimedes that morning too. When I first saw the crater
there were 4 distinct rays of varying sizes. By ~8:00 UT only the
longest ray was still visible.

My friend Tony Donnangelo, who has discovered more rays than anyone
else to date, noticed a faint sunset ray in a mountain range to the
north of Archimedes that morning.

Observations were made with Tony's 14.5" Starmaster Sky Tracker Dob
and my 101mm Tele Vue Genesis sdf.

Dave Mitsky

"Brian A" wrote in message news:Ea32b.244819$uu5.50767@sccrnsc04...

EDIT

Hi Dave,
That's fascinating stuff. This is the first I've ever heard of lunar sunset
rays. Do you know of any links that give good examples of what they actually
look like? Or perhaps the times and locations of when and where they can be
seen?

Thanks
Brian A

Brian,

Some of the ray reports on Rob Robinson's site (the URL I mentioned)
include sketches and images. I've posted a photo of the Maginus Ray
there as a matter of fact. It also appears at http://www.dvaa.org
under the members astrophotgraphy section.

Correction: the ray that Tony discovered was south of Archimedes.

"Brian A" wrote in message news:Ea32b.244819$uu5.50767@sccrnsc04...

EDIT

Hi Dave,
That's fascinating stuff. This is the first I've ever heard of lunar sunset
rays. Do you know of any links that give good examples of what they actually
look like? Or perhaps the times and locations of when and where they can be
seen?

Thanks
Brian A

Brian,

Some of the ray reports on Rob Robinson's site (the URL I mentioned)
include sketches and images. I've posted a photo of the Maginus Ray
there as a matter of fact. It also appears at http://www.dvaa.org
under the members astrophotgraphy section.

Correction: the ray that Tony discovered was south of Archimedes.