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I live in Los Angeles and have a camera adapter for my telescope -- nothing fancy just an Astromaster 114. What is the optimal time, in terms of dark sky and bright comet, to take a photo of Comet NEOWISE? I.e., when will it be brightest relative to the surround sky? When will it be largest?

And, lastly, what is the best time tonight to view it?

EDIT: I've spent the last two nights at sunset trying to locate it, but it doesn't really get dark until about an hour after sunset around 8pm. I also spent over an hour on the roof this morning from about 4am til 5:15am. I couldn't see it despite clear skies (or what passes for clear in LA).

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I don't know if this is helpful but using the Python package Skyfield one can calculate the positions of things including comet C/2020 F3 (NEOWISE) and the times that they rise and set for the month of July:

position of comet C/2020 F3 (NEOWISE) in July 2020

Here are the rise and set times of the Sun and the comet for reference for the next week

sunset:  2020-07-12T03:06:17Z
sunrise:  2020-07-12T12:51:20Z
sunset:  2020-07-13T03:05:55Z
sunrise:  2020-07-13T12:51:56Z
sunset:  2020-07-14T03:05:32Z
sunrise:  2020-07-14T12:52:33Z
sunset:  2020-07-15T03:05:07Z
sunrise:  2020-07-15T12:53:10Z
sunset:  2020-07-16T03:04:41Z
sunrise:  2020-07-16T12:53:48Z
sunset:  2020-07-17T03:04:13Z
sunrise:  2020-07-17T12:54:27Z
sunset:  2020-07-18T03:03:43Z
sunrise:  2020-07-18T12:55:06Z

cometset:  2020-07-12T04:15:12Z
cometrise:  2020-07-12T10:46:43Z
cometset:  2020-07-13T04:34:10Z
cometrise:  2020-07-13T10:48:01Z
cometset:  2020-07-14T04:54:27Z
cometrise:  2020-07-14T10:51:29Z
cometset:  2020-07-15T05:15:33Z
cometrise:  2020-07-15T10:57:33Z
cometset:  2020-07-16T05:36:48Z
cometrise:  2020-07-16T11:06:45Z
cometset:  2020-07-17T05:57:17Z
cometrise:  2020-07-17T11:19:29Z
cometset:  2020-07-18T06:16:07Z
cometrise:  2020-07-18T11:36:02Z

Here's the python script:

from skyfield.api import Topos
from skyfield.api import Loader
from skyfield.data import mpc
from skyfield import almanac
import numpy as np
import matplotlib.pyplot as plt
from skyfield.constants import GM_SUN_Pitjeva_2005_km3_s2 as GM_SUN

from skyfield.api import load
loaddata = Loader('~/Documents/fishing/SkyData')  # avoids multiple copies of large files

ts = loaddata.timescale() # include builtin=True if you want to use older files (you may miss some leap-seconds)

with load.open(mpc.COMET_URL) as f:
    comets = mpc.load_comets_dataframe(f)

comets = comets.set_index('designation', drop=False)

print(len(comets), 'comets loaded')

row = comets.loc['C/2020 F3 (NEOWISE)']
print(row)

eph = loaddata('de421.bsp')

earth, sun, moon = [eph[x] for x in ('earth', 'sun', 'moon')]

comet = sun + mpc.comet_orbit(row, ts, GM_SUN)

times = ts.utc(2020, 7, range(1, 32))
ra, dec, distance = earth.at(times).observe(comet).radec()

RA, Dec = [thing._degrees for thing in (ra, dec)]

plt.plot(RA, Dec, 'ok')
plt.gca().set_aspect('equal')
plt.show()

t0 = ts.utc(2020, 7, 12)
t1 = ts.utc(2020, 7, 19)
LA = Topos('34.05 N', '118.25 W') # 34.05, -118.25

times, is_sunrises = almanac.find_discrete(t0, t1, almanac.sunrise_sunset(eph, LA))
for time, is_sunrise in zip(times, is_sunrises):
    if is_sunrise:
        print('sunrise: ', time.utc_iso())
    else:
        print('sunset: ', time.utc_iso())

times, is_rises = almanac.find_discrete(t0, t1, almanac.risings_and_settings(eph, comet, LA))
for time, is_sunrise in zip(times, is_rises):
    if is_sunrise:
        print('cometrise: ', time.utc_iso())
    else:
        print('cometset: ', time.utc_iso())
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  • 1
    $\begingroup$ I love this answer so much, but my understanding of RA and Dec is woefully insufficient to translate that chart into any me-centric coordinates. Those times are UTC time, yes? So I'd need to subtract 7 hours to convert those to LA local time, yes? $\endgroup$
    – S. Imp
    Commented Jul 12, 2020 at 23:15
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    $\begingroup$ @S.Imp yes subtract 7 hours to convert to Pacific Daylight time i.sstatic.net/lx4aE.png Okay this is new feature to me too and I need to double check it but I can see if I can give you altitude and azimuth instead. I'll ping you again when I've updated it. $\endgroup$
    – uhoh
    Commented Jul 13, 2020 at 1:08
  • $\begingroup$ I'm guessing that the me-centric coordinates will be a lot more elaborate because of the earth rotating, etc. I.e, the coordinates will change greatly throughout the day -- or even while the comet is visible at morning/night. $\endgroup$
    – S. Imp
    Commented Jul 13, 2020 at 1:31
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You may try few hours before the sun rise tomorrow (12). Something to get started is here. https://theskylive.com/c2020f3-info

The bright start Capella, which is relatively easy to spot, could guide you to the comet.

Now that it has passed the perihelion of its orbit, it is receding from the Sun. So the brightness will gradually drop. Some details that might interest you are here.

http://astro.vanbuitenen.nl/comet/2020F3

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  • $\begingroup$ That first link is very helpful once I enter my own location, especially the section Comet C/2020 F3 (NEOWISE) rise and set times which tells me when it rises and sets and provides alt-az coordinates. $\endgroup$
    – S. Imp
    Commented Jul 12, 2020 at 23:05
  • $\begingroup$ I have marked this as the answer because the skylive link allows you to enter your geographic location and get information specific to your location on the globe. Additionally, it provides easy-to-use azimuth and altitude details which are easy to comprehend and interpret with just a compass. I am delighted to report that I saw the comet last night. I was unable to photograph it, but really enjoyed having a look. $\endgroup$
    – S. Imp
    Commented Jul 18, 2020 at 19:51
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    $\begingroup$ great, so glad that you did see it in the end. $\endgroup$
    – mysterium
    Commented Jul 19, 2020 at 20:56
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Nothing is more helpful to an aspiring astronomer than a good planetarium program.

Download and install Stellarium

https://stellarium.org/

It will show you the sky from your doorstep at any time of the day. No need to speculate the comets position. It will be displayed exactly where it is in relation to the rest of the sky.

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  • $\begingroup$ The first thing I did was go to stellarium. I'm guessing its object database must be out of date or something because it has NEOWISE in the wrong place entirely. $\endgroup$
    – S. Imp
    Commented Jul 12, 2020 at 23:09
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    $\begingroup$ @S.Imp NEOWISE has discovered other comets. You might have to use the solar system editor plugin to import elements for C/2020 F3. $\endgroup$
    – Mike G
    Commented Jul 13, 2020 at 2:58
  • $\begingroup$ @MikeG could you elaborate? I'd love for Stellarium to stay up to date with new objects, but I'm probably not competent enough to enter elaborate trajectories or anything if editing is required. $\endgroup$
    – S. Imp
    Commented Jul 13, 2020 at 12:14
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    $\begingroup$ @S.Imp Try Configuration > Plugins > Solar System Editor; configure > Solar System; Import orbital elements... > Lists; Comets; MPC's list of observable comets; Get orbital elements > check C/2020 F3; Add objects. $\endgroup$
    – Mike G
    Commented Jul 13, 2020 at 12:50

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