(SHOW & TELL) generate a 180 degree skymap for a specific location

[bathoorn]

I continued work on creating some functional skymaps for myself

I can generate a 180 degree map of all the stars as can be seen for a specific datetime and location

for now i added

• the horizon as a dashed line
• messier objects
• star names for some of the bigger stars
• constellation lines
• as an example i highlighted the summer triangle (just to see if i could do it)

todo

• add NGC objects
• add constellation boundaries

an example picture

[brandon-rhodes]

Thanks for sharing! It's fun to see where the M objects cluster together in the sky like this. Have you tried turning off the objects that are below the horizon, to make the overall shape circular?

Which system of constellation lines are you using? I usually see Andromeda simply as two lines stretching from the corner of the Great Square, but in this case a whole little figure is shown. I'll have to test whether I can see it the next night it's clear!

[bathoorn]

Below is my code i think i took the constellation lines from the comet example (data from stellarium)

I will check indeed how to turn off everything below the horizon.

import numpy as np
from matplotlib import pyplot as plt
from matplotlib.collections import LineCollection, PolyCollection

from skyfield.api import Star, load, wgs84, N, S, W, E
from skyfield.data import hipparcos, mpc, stellarium
import dsos
from skyfield.projections import build_stereographic_projection
from datetime import datetime
from pytz import timezone

# time `t` we use for everything else.

AMS = timezone('Europe/Amsterdam')
ts = load.timescale()
t = ts.from_datetime(AMS.localize(datetime(2021, 9, 12, 23, 0, 0)))
# 180 = South 0 = North
degrees = 0.0


amsterdam = wgs84.latlon(52.377956*N, 4.897070*E, elevation_m=28).at(t)
position = amsterdam.from_altaz(alt_degrees=90, az_degrees=degrees)

# An ephemeris from the JPL provides Sun and Earth positions.

eph = load('de421.bsp')
sun = eph['sun']
earth = eph['earth']

# Center on Albireo middle of Summer Triangle

albireo = Star(ra_hours=(19, 30, 45.40),
               dec_degrees=(27, 57, 55.0))

# The Hipparcos mission provides our star catalog.

with load.open(hipparcos.URL) as f:
    stardata = hipparcos.load_dataframe(f)

# DSO's from stellarium

with open('catalog.txt') as f:
    dsodata = dsos.load_dataframe(f)

# starnames

with open('starnamesHIP.tsv') as f:
    starnames = dsos.load_names(f)

# And the constellation outlines come from Stellarium.  We make a list
# of the stars at which each edge stars, and the star at which each edge
# ends.

url = ('https://raw.githubusercontent.com/Stellarium/stellarium/master'
       '/skycultures/western_SnT/constellationship.fab')

with load.open(url) as f:
    consdata = stellarium.parse_constellations(f)

url2 = ('https://raw.githubusercontent.com/Stellarium/stellarium/master'
       '/skycultures/western_SnT/star_names.fab')

with load.open(url2) as f2:
    star_names = stellarium.parse_star_names(f2)

summer_triangle = [
    [   "Summer Triangle",
        [
            [102098, 91262],
            [91262, 97649],
            [97649, 102098]
        ]
    ]
]


def generate_constellation_lines(data, polygon=False):
    edges = [edge for name, edges in data for edge in edges]
    edges_star1 = [star1 for star1, star2 in edges]
    edges_star2 = [star2 for star1, star2 in edges]
    xy1 = stardata[['x', 'y']].loc[edges_star1].values
    xy2 = stardata[['x', 'y']].loc[edges_star2].values

    if polygon:
        return [xy1]
    else:

        # The constellation lines will each begin at the x,y of one star and end
        # at the x,y of another.  We have to "rollaxis" the resulting coordinate
        # array into the shape that matplotlib expects.

        return np.rollaxis(np.array([xy1, xy2]), 1)


# We will center the chart on the comet's middle position.

center = earth.at(t).observe(albireo)
#projection = build_stereographic_projection(center)
projection = build_stereographic_projection(position)
field_of_view_degrees = 180.0
limiting_magnitude = 6.0
dso_limit_magnitude = 8.0

# Now that we have constructed our projection, compute the x and y
# coordinates that each star will have on the plot.

star_positions = earth.at(t).observe(Star.from_dataframe(stardata))
stardata['x'], stardata['y'] = projection(star_positions)

dso_positions = earth.at(t).observe(Star.from_dataframe(dsodata))
dsodata['x'], dsodata['y'] = projection(dso_positions)


# Create a True/False mask marking the stars bright enough to be
# included in our plot.  And go ahead and compute how large their
# markers will be on the plot.

bright_stars = (stardata.magnitude <= limiting_magnitude)
magnitude = stardata['magnitude'][bright_stars]
marker_size = (0.7 + limiting_magnitude - magnitude) ** 2.0

bright_dsos = (dsodata.magnitude <= dso_limit_magnitude)
dso_magnitude = dsodata['magnitude'][bright_dsos]
dso_size = (0.9 + dso_limit_magnitude - dso_magnitude) ** 2.0

# Time to build the figure!

fig, ax = plt.subplots(figsize=[12, 12])

# Draw Horizon as dashed line
# 24 points horizon

horizon = []
h0 = projection(amsterdam.from_altaz(alt_degrees=0, az_degrees=0.0))
for i in range(1, 73):
    delta = 5.0
    current = i * delta
    h1 = projection(amsterdam.from_altaz(alt_degrees=0, az_degrees=current))
    horizon.append([h0, h1])
    h0 = h1

ax.add_collection(LineCollection(horizon,
                         colors='#00f2', linewidths=1, linestyle='dashed', zorder=-1, alpha=0.5))

# Draw the constellation lines.

constellations = LineCollection(generate_constellation_lines(consdata),
                                colors='#00f2', linewidths=1, zorder=-1, alpha=0.5)
ax.add_collection(constellations)

# Draw the Summer Triangle lines.

print(f"triangle poly = {generate_constellation_lines(summer_triangle, polygon=True)}")
triangle = PolyCollection(generate_constellation_lines(summer_triangle, polygon=True), facecolors='orange',
                          edgecolors='orange', alpha=0.5, linewidths=0, zorder=-2)
ax.add_collection(triangle)


# Draw the stars.

ax.scatter(stardata['x'][bright_stars], stardata['y'][bright_stars],
           s=marker_size, color='k')

ax.scatter(dsodata['x'][bright_dsos], dsodata['y'][bright_dsos],
           s=dso_size, color='red')

# Finally, title the plot and set some final parameters.

angle = np.pi - field_of_view_degrees / 360.0 * np.pi
limit = np.sin(angle) / (1.0 - np.cos(angle))

print(f"starnames = {starnames}")
for i, s in stardata[bright_stars].iterrows():
    if -limit < s['x'] < limit and -limit < s['y'] < limit:
        if i in starnames:
            print(f"star {starnames[i]} mag {s['magnitude']}")
            ax.text(s['x'] + 0.004, s['y'] - 0.004, starnames[i], color='k',
                    ha='left', va='top', fontsize=9, weight='bold', zorder=1).set_alpha(0.5)

for i, d in dsodata[bright_dsos].iterrows():
    if -limit < d['x'] < limit and -limit < d['y'] < limit:
        print(f"dso {d['label']} mag {d['magnitude']}")
        ax.text(d['x'] + 0.004, d['y'] - 0.004, d['label'], color='red',
                ha='left', va='top', fontsize=9, weight='bold', zorder=1).set_alpha(0.5)


ax.set_xlim(-limit, limit)
ax.set_ylim(-limit, limit)
ax.xaxis.set_visible(True)
ax.yaxis.set_visible(True)
ax.set_aspect(1.0)
ax.set_title(f"To the South in Amsterdam on {t.utc_strftime('%Y %B %d %H:%M')}")

# Save.

fig.savefig('summer-triangle.png', bbox_inches='tight')

[kamekaioken]

@bathoorn Thank you so much for sharing your code example. This helped me a lot.
@CTugTEZ you can find an earlier version of the dsos script in another discussion thread of the @bathoorn

[ramonefoster]

Very nice!
Im building something to plot on top of a allsky image, how can I rotate the projection, lets say, 40 degrees on azimuth?

[NorthBaandee]

This fails at line 7, in import dsos
ModuleNotFoundError: No module named 'dsos'
I can find no trace of any such module in any thread here or anywhere else for that matter

[kamekaioken]

@NorthBaandee #634

[NorthBaandee]

Thanks for that. I'm very much a nooby at this. I have been using PyEphem to produce spreadsheets that are published in the local newspaper as a fortnightly almanac of sun moon and planet rise set constellation and phase. It seems quite fit for that purpose, but the documentation suggests skyfield should be used for new projects.
Expect some pretty dumb questions as I start fooling around more. I'm a cook not a chef, and I burn myself a lot on the stove...

[JPZEBRA]

How about this ?
The sample code for removing under-ground lines.

[bathoorn]

The dsos module was added to show deep sky objects like for example messier objects. You can find the code here #634

…

On Sun, 8 Jan 2023, 07:50 markusd112, ***@***.***> wrote: Hi! I am a pythin and skyfield newbe and tried to run your code example above: python is throwing an exception because "dsos" is unknown. Could you give me some hint, where I can find this dsos module? Thanks a lot! — Reply to this email directly, view it on GitHub <#636 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAFZWJ346JPTYITCLI3QPVDWRJPUFANCNFSM5EABHRMQ> . You are receiving this because you were mentioned.Message ID: ***@***.*** com>

[gmiller123456]

Nice. Some star charts show a little of what's below the horizon so that it can be used at slightly different times and locations than what it was generated for. So you might consider leaving it.