Minimum Elongation for sighting planets

A question on observing: What would be the minimum elongation
(angle betwixt a planet and the Sun) that would allow it to be
spotted by naked eye? We can assume the use of filters to save
our eyes.

Does it vary for different naked-eye planets?

"Paul Schlyter" wrote in message
...
In article ,
Greg Neill wrote:
A question on observing: What would be the minimum elongation
(angle betwixt a planet and the Sun) that would allow it to be
spotted by naked eye? We can assume the use of filters to save
our eyes.

Does it vary for different naked-eye planets?

It varies with the brightness of the planet and with what instruments
you use. And the Sun should preferably be blocked, because if you use
a solar filter safe for solar viewing, the planet won't be visible...

Hi Paul, yes that makes sense. But what are typical values
of elongation for, say, Mars or Venus? Assume ideal viewing
conditions.

Would it be possible to detect Mars a half degree from
the Sun's limb? A full degree? More? How about Venus?

In message , Greg Neill
writes
"Paul Schlyter" wrote in message
...
In article ,
Greg Neill wrote:
A question on observing: What would be the minimum elongation
(angle betwixt a planet and the Sun) that would allow it to be
spotted by naked eye? We can assume the use of filters to save
our eyes.

Does it vary for different naked-eye planets?

It varies with the brightness of the planet and with what instruments
you use. And the Sun should preferably be blocked, because if you use
a solar filter safe for solar viewing, the planet won't be visible...

Hi Paul, yes that makes sense. But what are typical values
of elongation for, say, Mars or Venus? Assume ideal viewing
conditions.

Would it be possible to detect Mars a half degree from
the Sun's limb? A full degree? More? How about Venus?


IIRC, Venus has been seen at conjunction (i.e. when it's between Earth
and sun and either north or south) but I'm not sure how close it was.
We'll have a nice chance to see it close to the sun next year, before
and after the transit :-)
On August 7 1921 an object "brighter than Venus" was seen 3 degrees east
of the sun; it's thought this was a sun-grazer comet or a nova.
--
"Roads in space for rockets to travel....four-dimensional roads, curving with
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Mail to jsilverlight AT merseia.fsnet.co.uk is welcome.
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In article ,
Greg Neill wrote:

"Paul Schlyter" wrote in message
...
In article ,
Greg Neill wrote:
A question on observing: What would be the minimum elongation
(angle betwixt a planet and the Sun) that would allow it to be
spotted by naked eye? We can assume the use of filters to save
our eyes.

Does it vary for different naked-eye planets?

It varies with the brightness of the planet and with what instruments
you use. And the Sun should preferably be blocked, because if you use
a solar filter safe for solar viewing, the planet won't be visible...

Hi Paul, yes that makes sense. But what are typical values
of elongation for, say, Mars or Venus? Assume ideal viewing
conditions.

Would it be possible to detect Mars a half degree from
the Sun's limb? A full degree? More? How about Venus?

Personally I've observed Venus near superior conjunction somewhat
less than one degree from the Sun -- it was surprisingly easy to see!
I did this with a 4" refractor with the Sun just outside my field of
view (this observation is NOT recommended for anyone but an
experienced observer!). I've also attempted a similar observation of
Venus at inferior conjunction, but then I failed to detect Venus.
However, at the upcoming Venus transit in June 2004, Venus will
probably be detectable some time immediately before first contact and
after 4th contact, due to forward scattering of sunlight in Venus'
atmospere -- and then Venus will be VERY near the Sun's limb.

Naked-eye detections are more tricky, but I have seen Venus naked-eye
right at inferior conjunction, during one of those April conjunctions
when Venus is some 7 to 8 degrees north of the Sun. The Sun was a
few degrees below the horizon of course, and thus Venus was a few
degrees above the horizon. It was difficult to see Venus naked-eye,
but in ordinary binoculars Venus was very easy to see, and its
crescent shape was obvious in the binoculars. I also went up the
next morning to see Venus before sunrise, but then I saw it only with
the binoculars, not naked-eye. My high northern latitude (about 60
deg N) surely helped -- this is more difficult to observe at lower
latitudes.

Venus is very easy though because it's so bright: it's both near the
Sun and has a high albedo. Mars is much more difficult: it receives
only about 1/4 of the solar illumination that Venus does, and in
addition its albedo is much lower. Thus the surface brightness of
Mars' disk is only about 1/10 - 1/15 the surface brightness of Venus
disk. And I don't think ordinary telescopes can show Mars very near
the Sun in the sky. But you could of course try tricks like
observing from a high mountaintop using deep red filters..... To see
MArs with the naked eye I would guess it will have to be at least
some 15 to 20 degrees away from the Sun: when Mars is near the Sun in
the sky it's also most distant from the Earth, and its typical
magnitude at those times is around +1.5. This makes Mars harder to
spot than even Mercury, since Mercury frequently gets as bright as -1
when near maximum elongation.

--
----------------------------------------------------------------
Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
e-mail: pausch at stockholm dot bostream dot se
WWW: http://www.stjarnhimlen.se/
http://home.tiscali.se/pausch/

In article ,
Jonathan Silverlight wrote:

IIRC, Venus has been seen at conjunction (i.e. when it's between Earth
and sun and either north or south) but I'm not sure how close it was.
We'll have a nice chance to see it close to the sun next year, before
and after the transit :-)

When Venus is in inferior conjunction in April, it's some 7-8 degrees
north of the Sun. The next time this will happen is in 2009. During
such an inferior conjunction, Venus is easy to see right at the
moment of conjunction, at least from high northern latitudes.
Observers at high southern latitudes (in e.g. Terra del Fuego in
southernmost Argentina and Chile, and of course also in Antarctica)
can make a similar observation when Venus is in inferior conjunction
in October.

However, when Venus is at superior conjunction, the surface
brightness of its disk is so much brighter, and Venus will then be
much easier to see against the bright sky near the Sun. Of course a
telescope must be used and the Sun must be kept out of the field of
view; this is a somewhat risky observation which should not be
attempted by anyone but an experienced skywatcher.

On August 7 1921 an object "brighter than Venus" was seen 3 degrees east
of the sun; it's thought this was a sun-grazer comet or a nova.

--
----------------------------------------------------------------
Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
e-mail: pausch at stockholm dot bostream dot se
WWW: http://www.stjarnhimlen.se/
http://home.tiscali.se/pausch/

"Mark Gingrich" wrote in message
...
Greg Neill asked:

A question on observing: What would be the minimum elongation
(angle betwixt a planet and the Sun) that would allow it to be
spotted by naked eye? We can assume the use of filters to save
our eyes.

Does it vary for different naked-eye planets?


From page 480 of _Explanatory Supplement to the Astronomical Almanac_,
P. Kenneth Seidelmann (Editor), 1992:

Visibility Criteria for Geocentric Phenomena

Body Minimum Elongation

Moon, Mars, Saturn 15 degrees
Minor planets 15 degrees
Venus, Jupiter 10 degrees
Mercury 10 degrees + visual magnitude of Mercury


[These numbers strike me as being suspiciously uniform and crudely
rounded. But then, they come from the same people who persist in
playing up a fictitious event for Venus called "greatest brilliancy."]

Interesting.
I have to agree with your observation on the numbers seeming to
be a tad contrived.

Paul Schlyter indicated that he's successfully spotted Venus
near superior conjunction within a degree of the Sun while
employing a 4" refractor.

Thanks for the reference.