46P, can't see

I live in the city, major light pollution, could not see 46P with my 80mm APO, mounted on NexStar GT goto.
I know my GOTO points to the right location. I slew the scope in auto between Aldebaran and other 2 stars, like Mira back and forth, all came in to the center of my eyepiece.
Alt/Az kind of suck, coordinates all ways changing.
Day before tried it with my 50 mm bino, no luck to see it either.
Is it still hard to see this comet?

On Sun, 9 Dec 2018 02:18:24 -0800 (PST), StarDust
wrote:

I live in the city, major light pollution, could not see 46P with my 80mm APO, mounted on NexStar GT goto.
I know my GOTO points to the right location. I slew the scope in auto between Aldebaran and other 2 stars, like Mira back and forth, all came in to the center of my eyepiece.
Alt/Az kind of suck, coordinates all ways changing.
Day before tried it with my 50 mm bino, no luck to see it either.
Is it still hard to see this comet?

I saw it again last night, with a very thin haze in the sky. No
problem with 8x50 binoculars, but the haze prevented me from seeing it
with averted vision. Not obviously brighter than a few nights ago, but
less contrast because of the poorer sky. But still a dark sky. It's
very big, so I think it will be easily lost in any light pollution.
I'd guess your best chance is with the lowest possible magnification,
or with high enough magnification that you just get the core part of
the coma (which requires accurate pointing, of course).

On Sunday, December 9, 2018 at 6:36:56 AM UTC-8, Chris L Peterson wrote:
On Sun, 9 Dec 2018 02:18:24 -0800 (PST),
wrote:

I live in the city, major light pollution, could not see 46P with my 80mm APO, mounted on NexStar GT goto.
I know my GOTO points to the right location. I slew the scope in auto between Aldebaran and other 2 stars, like Mira back and forth, all came in to the center of my eyepiece.
Alt/Az kind of suck, coordinates all ways changing.
Day before tried it with my 50 mm bino, no luck to see it either.
Is it still hard to see this comet?

I saw it again last night, with a very thin haze in the sky. No
problem with 8x50 binoculars, but the haze prevented me from seeing it
with averted vision. Not obviously brighter than a few nights ago, but
less contrast because of the poorer sky. But still a dark sky. It's
very big, so I think it will be easily lost in any light pollution.
I'd guess your best chance is with the lowest possible magnification,
or with high enough magnification that you just get the core part of
the coma (which requires accurate pointing, of course).

How big is the comet in arc minutes?
I used my Celestron Onyx ED f6.2 and Pentax XL40 mm eyepiece, I know this combination gives me a very wide field at low power.

On Sun, 9 Dec 2018 12:13:29 -0800 (PST), StarDust
wrote:

On Sunday, December 9, 2018 at 6:36:56 AM UTC-8, Chris L Peterson wrote:
On Sun, 9 Dec 2018 02:18:24 -0800 (PST),
wrote:

I live in the city, major light pollution, could not see 46P with my 80mm APO, mounted on NexStar GT goto.
I know my GOTO points to the right location. I slew the scope in auto between Aldebaran and other 2 stars, like Mira back and forth, all came in to the center of my eyepiece.
Alt/Az kind of suck, coordinates all ways changing.
Day before tried it with my 50 mm bino, no luck to see it either.
Is it still hard to see this comet?

I saw it again last night, with a very thin haze in the sky. No
problem with 8x50 binoculars, but the haze prevented me from seeing it
with averted vision. Not obviously brighter than a few nights ago, but
less contrast because of the poorer sky. But still a dark sky. It's
very big, so I think it will be easily lost in any light pollution.
I'd guess your best chance is with the lowest possible magnification,
or with high enough magnification that you just get the core part of
the coma (which requires accurate pointing, of course).

How big is the comet in arc minutes?
I used my Celestron Onyx ED f6.2 and Pentax XL40 mm eyepiece, I know this combination gives me a very wide field at low power.

In my binoculars it looks about a quarter the size of the Moon. So
maybe 5-10 arcmin. Photographically I think it is now larger than the
Moon. But again, this is with no light pollution at all. Obviously, a
comet's coma has a pretty steep radial intensity gradient, so its
apparent size will be strongly influenced by the sky background.

StarDust wrote:
^^^^^^^^
Please post using your real name(, too).

How big is the comet in arc minutes?

Good (and free) astronomy software like Stellarium[1][2] can give you
the numbers (be sure to use the latest version, currently 0.18.2).

For now:

Distance (D) (from Terra) ≈ 0.087 AU ≈ 1.3 × 10� km
(and closing; perigee on 2018-12-16)
Radius of coma (estimated) ≈ 36'000 km (0°09'30")
Tail length (estimated) ≈ 0.00812 × 10� km (0°02'08")
Core diameter (d) = 10.0 km

If you know the diameter d and the distance D in SI units (or any other
non-angular measure), you can calculate the diameter of a celestial object
in degrees (of arc) using the equation

φ = d/D/(2π) × 360°

because sin(φ) ≈ φ for small angles φ (otherwise calculate
φ = arcsin(r/D)/π × 360°):

φ/2 _______ __
\ _.-': |PE
_.-\ .: r
-:'--------:--- d = φ
`-._ :
`-._:______
:-- D ---:

This gives you the diameter in degrees (of arc), so for minutes of arc you
must multiply by 60.

For example, you can get Celestia’s 0°09'30" for the estimated radius of
the coma with

φ ≈ (36'000 km)/(1.3 × 10� km)/(2π) × 360(°) × 60 ≈ 9.09'

[arcsin(18'000 km/(1.3e7 km))/π × 360° × 60 ≈ 9.5' is the exact value
as displayed by Stellarium].

So ignoring the uncertainty of the coma, the comet’s core diameter in
minutes of arc is approximately only

φ ≈ (10 km)/(1.3 × 10� km)/(2π) × 360(°) × 60 ≈ 0.0026'.

See also:
https://www.wolframalpha.com/input/?i=(10+km%2F1.3e7+km)%2F(2pi)*360*60

Thus, in combination with a visual brightness of only 9.05 mag (9.25 mag
with extinction; both according to Stellarium), and light pollution, it
might be very hard to see with an amateur telescope. OTOH, as it should
become brighter when it approaches Sol, observing it might be possible.

However, the simulation with Stellarium indicates to me that even if it is
observable, it might not be easily distinguishable from the fixed stars,
because it is not moving sufficiently fast at this point. And ISTM that an
equatorial mount is highly recommended, otherwise, once found, the comet is
already out of the field of view after ca. 30 s (due to Terra’s rotation).

I used my Celestron Onyx ED f6.2 and Pentax XL40 mm eyepiece, I know this combination gives me a very wide field at low power.

Good luck. (It has been raining here all week, so no luck for me yet.)

[1] https://stellarium.org/
[2] http://dslr-astrophotography.com/add-comets-stellarium/

--
PointedEars

Twitter: @PointedEars2
Please do not cc me. / Bitte keine Kopien per E-Mail.

Thomas 'PointedEars' Lahn wrote:
For example, you can get Celestia’s 0°09'30" for the estimated radius of

_Stellarium’s_. Celestia https://celestia.space is the other free
astronomy software that I use and can recommend

the coma with […]
--
PointedEars

Twitter: @PointedEars2
Please do not cc me. / Bitte keine Kopien per E-Mail.

On Sunday, December 9, 2018 at 2:26:42 PM UTC-8, Thomas 'PointedEars' Lahn wrote:
StarDust wrote:
^^^^^^^^
Please post using your real name(, too).

How big is the comet in arc minutes?

Good (and free) astronomy software like Stellarium[1][2] can give you
the numbers (be sure to use the latest version, currently 0.18.2).

For now:

Distance (D) (from Terra) ≈ 0.087 AU ≈ 1.3 × 10� km
(and closing; perigee on 2018-12-16)
Radius of coma (estimated) ≈ 36'000 km (0°09'30")
Tail length (estimated) ≈ 0.00812 × 10� km (0°02'08")
Core diameter (d) = 10.0 km

If you know the diameter d and the distance D in SI units (or any other
non-angular measure), you can calculate the diameter of a celestial object
in degrees (of arc) using the equation

φ = d/D/(2π) × 360°

because sin(φ) ≈ φ for small angles φ (otherwise calculate
φ = arcsin(r/D)/π × 360°):

φ/2 _______ __
\ _.-': |PE
_.-\ .: r
-:'--------:--- d = φ
`-._ :
`-._:______
:-- D ---:

This gives you the diameter in degrees (of arc), so for minutes of arc you
must multiply by 60.

For example, you can get Celestia’s 0°09'30" for the estimated radius of
the coma with

φ ≈ (36'000 km)/(1.3 × 10� km)/(2π) × 360(°) × 60 ≈ 9.09'

[arcsin(18'000 km/(1.3e7 km))/π × 360° × 60 ≈ 9.5' is the exact value
as displayed by Stellarium].

So ignoring the uncertainty of the coma, the comet’s core diameter in
minutes of arc is approximately only

φ ≈ (10 km)/(1.3 × 10� km)/(2π) × 360(°) × 60 ≈ 0.0026'.

See also:
https://www.wolframalpha.com/input/?i=(10+km%2F1.3e7+km)%2F(2pi)*360*60

Thus, in combination with a visual brightness of only 9.05 mag (9.25 mag
with extinction; both according to Stellarium), and light pollution, it
might be very hard to see with an amateur telescope. OTOH, as it should
become brighter when it approaches Sol, observing it might be possible.

However, the simulation with Stellarium indicates to me that even if it is
observable, it might not be easily distinguishable from the fixed stars,
because it is not moving sufficiently fast at this point. And ISTM that an
equatorial mount is highly recommended, otherwise, once found, the comet is
already out of the field of view after ca. 30 s (due to Terra’s rotation).

I used my Celestron Onyx ED f6.2 and Pentax XL40 mm eyepiece, I know this combination gives me a very wide field at low power.

Good luck. (It has been raining here all week, so no luck for me yet.)

[1] https://stellarium.org/
[2] http://dslr-astrophotography.com/add-comets-stellarium/

--
PointedEars

Twitter: @PointedEars2
Please do not cc me. / Bitte keine Kopien per E-Mail.

I use C2A!
http://www.astrosurf.com/c2a/english/

But to remind you, not every one is professor in math!

StarDust wrote:
I use C2A!
http://www.astrosurf.com/c2a/english/

ACK.

But to remind you, not every one is professor in math!

This is a stupid reaction. I am not a professor in math either. I happen
to study astrophysics (where this is repeated), but this is basic geometry
(how to calculate the arc length on the circumference of a circle) that you
learn in (high)school already.

I took some of my *precious* *free time* to explain it to you *for free*,
so that you can answer your question for an arbitrary celestial object for
yourself next time, and you are *complaining* about that?

And you still do not have the decency to introduce yourself to strangers
with your real name?

Tell me: Why should I read any of your postings again?

--
PointedEars

Twitter: @PointedEars2
Please do not cc me. / Bitte keine Kopien per E-Mail.

StarDust wrote:
On Sunday, December 9, 2018 at 6:36:56 AM UTC-8, Chris L Peterson wrote:
On Sun, 9 Dec 2018 02:18:24 -0800 (PST),
wrote:

I live in the city, major light pollution, could not see 46P with my
80mm APO, mounted on NexStar GT goto.
I know my GOTO points to the right location. I slew the scope in auto
between Aldebaran and other 2 stars, like Mira back and forth, all came
in to the center of my eyepiece.
Alt/Az kind of suck, coordinates all ways changing.
Day before tried it with my 50 mm bino, no luck to see it either.
Is it still hard to see this comet?

I saw it again last night, with a very thin haze in the sky. No
problem with 8x50 binoculars, but the haze prevented me from seeing it
with averted vision. Not obviously brighter than a few nights ago, but
less contrast because of the poorer sky. But still a dark sky. It's
very big, so I think it will be easily lost in any light pollution.
I'd guess your best chance is with the lowest possible magnification,
or with high enough magnification that you just get the core part of
the coma (which requires accurate pointing, of course).

How big is the comet in arc minutes?
I used my Celestron Onyx ED f6.2 and Pentax XL40 mm eyepiece, I know
this combination gives me a very wide field at low power.



I just found it again from my back yard. Not perfect seeing. I can just
make out the Milky Way but only one star in the bowl of USA minor is
visible. I make it out to about 8 seconds of arc. It took me a while to
find it. Eventually I used a combined high/low tech method and held my iPad
mini running Luminos against the objectives of my 8x50 binoculars (on a
tripod) and moving the pan/tilt until the comet was in the centre of the
screen.
At least in the back yard there are no Christmas lights. This is the
British not US use of back yard, A small paved area not a big area of
grass.
It was not that dark so you should be able to find it from a city
sky. But you have to stare at it for a long time to convince yourself that
it’s there. I kept moving the binoculars away and then back again to
convince myself that it really was the comet.
But it definitely matched the position shown in Luminos in the straight
line part of an asterism like an inverted question mark (or a tiny version
of Leo’s head).

Mike Collins wrote:
StarDust wrote:
On Sunday, December 9, 2018 at 6:36:56 AM UTC-8, Chris L Peterson wrote:
On Sun, 9 Dec 2018 02:18:24 -0800 (PST),
wrote:

I live in the city, major light pollution, could not see 46P with my
80mm APO, mounted on NexStar GT goto.
I know my GOTO points to the right location. I slew the scope in auto
between Aldebaran and other 2 stars, like Mira back and forth, all came
in to the center of my eyepiece.
Alt/Az kind of suck, coordinates all ways changing.
Day before tried it with my 50 mm bino, no luck to see it either.
Is it still hard to see this comet?

I saw it again last night, with a very thin haze in the sky. No
problem with 8x50 binoculars, but the haze prevented me from seeing it
with averted vision. Not obviously brighter than a few nights ago, but
less contrast because of the poorer sky. But still a dark sky. It's
very big, so I think it will be easily lost in any light pollution.
I'd guess your best chance is with the lowest possible magnification,
or with high enough magnification that you just get the core part of
the coma (which requires accurate pointing, of course).

How big is the comet in arc minutes?
I used my Celestron Onyx ED f6.2 and Pentax XL40 mm eyepiece, I know
this combination gives me a very wide field at low power.



I just found it again from my back yard. Not perfect seeing. I can just
make out the Milky Way but only one star in the bowl of USA minor is
visible. I make it out to about 8 seconds of arc. It took me a while to
find it. Eventually I used a combined high/low tech method and held my iPad
mini running Luminos against the objectives of my 8x50 binoculars (on a
tripod) and moving the pan/tilt until the comet was in the centre of the
screen.
At least in the back yard there are no Christmas lights. This is the
British not US use of back yard, A small paved area not a big area of
grass.
It was not that dark so you should be able to find it from a city
sky. But you have to stare at it for a long time to convince yourself that
it’s there. I kept moving the binoculars away and then back again to
convince myself that it really was the comet.
But it definitely matched the position shown in Luminos in the straight
line part of an asterism like an inverted question mark (or a tiny version
of Leo’s head).




Apple’s spell check decided I wanted USA instead of Ursa. I cant see any of
the USA from longitude 1 degree East.