First, we need to increase the timeout time to allow the download of data occur properly
In [1]:
from astropy.utils.data import conf
conf.dataurl
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In [2]:
conf.remote_timeout
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In [3]:
conf.remote_timeout = 10000
Then, we do the rest of the imports.
In [4]:
from astropy import units as u
from astropy.time import Time, TimeDelta
from astropy.coordinates import solar_system_ephemeris
solar_system_ephemeris.set("jpl")
from poliastro.bodies import Sun, Earth, Moon
from poliastro.ephem import Ephem
from poliastro.frames import Planes
from poliastro.twobody import Orbit
from poliastro.plotting import StaticOrbitPlotter
from poliastro.plotting.misc import plot_solar_system
from poliastro.util import time_range
EPOCH = Time("2017-09-01 12:05:50", scale="tdb")
C_FLORENCE = "#000"
C_MOON = "#999"
In [5]:
Earth.plot(EPOCH);
Our first option to retrieve the orbit of the Florence asteroid is to use Orbit.from_sbdb, which gives us the osculating elements at a certain epoch:
In [6]:
florence_osc = Orbit.from_sbdb("Florence")
florence_osc
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However, the epoch of the result is not close to the time of the close approach we are studying:
In [7]:
florence_osc.epoch.iso
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Therefore, if we propagate this orbit to EPOCH, the results will be a bit different from the reality. Therefore, we need to find some other means.
Let's use the Ephem.from_horizons method as an alternative, sampling over a period of 6 months:
In [8]:
from poliastro.ephem import Ephem
In [9]:
epochs = time_range(
EPOCH - TimeDelta(3 * 30 * u.day), end=EPOCH + TimeDelta(3 * 30 * u.day)
)
In [10]:
florence = Ephem.from_horizons("Florence", epochs, plane=Planes.EARTH_ECLIPTIC)
florence
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In [11]:
florence.plane
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And now, let's compute the distance between Florence and the Earth at that epoch:
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earth = Ephem.from_body(Earth, epochs, plane=Planes.EARTH_ECLIPTIC)
earth
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In [13]:
from poliastro.util import norm
In [14]:
min_distance = norm(florence.rv(EPOCH)[0] - earth.rv(EPOCH)[0]) - Earth.R
min_distance.to(u.km)
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In [15]:
abs((min_distance - 7060160 * u.km) / (7060160 * u.km)).decompose()
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In [16]:
from IPython.display import HTML
HTML(
"""<blockquote class="twitter-tweet" data-lang="en"><p lang="es" dir="ltr">La <a href="https://twitter.com/esa_es">@esa_es</a> ha preparado un resumen del asteroide <a href="https://twitter.com/hashtag/Florence?src=hash">#Florence</a> 😍 <a href="https://t.co/Sk1lb7Kz0j">pic.twitter.com/Sk1lb7Kz0j</a></p>— AeroPython (@AeroPython) <a href="https://twitter.com/AeroPython/status/903197147914543105">August 31, 2017</a></blockquote>
<script src="//platform.twitter.com/widgets.js" charset="utf-8"></script>"""
)
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And now we can plot!
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frame = plot_solar_system(outer=False, epoch=EPOCH)
frame.plot_ephem(florence, EPOCH, label="Florence", color=C_FLORENCE);
Finally, we are going to visualize the orbit of Florence with respect to the Earth. For that, we set a narrower time range, and specify that we want to retrieve the ephemerides with respect to our planet:
In [18]:
epochs = time_range(EPOCH - TimeDelta(5 * u.day), end=EPOCH + TimeDelta(5 * u.day))
In [19]:
florence_e = Ephem.from_horizons("Florence", epochs, attractor=Earth)
florence_e
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We now retrieve the ephemerides of the Moon, which are given directly in GCRS:
In [20]:
moon = Ephem.from_body(Moon, epochs, attractor=Earth)
moon
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In [21]:
from poliastro.plotting.static import StaticOrbitPlotter
plotter = StaticOrbitPlotter()
plotter.set_attractor(Earth)
plotter.set_body_frame(Moon)
plotter.plot_ephem(moon, EPOCH, label=Moon, color=C_MOON);
And now, the glorious final plot:
In [22]:
import matplotlib.pyplot as plt
frame = StaticOrbitPlotter()
frame.set_attractor(Earth)
frame.set_orbit_frame(Orbit.from_ephem(Earth, florence_e, EPOCH))
frame.plot_ephem(florence_e, EPOCH, label="Florence", color=C_FLORENCE)
frame.plot_ephem(moon, EPOCH, label=Moon, color=C_MOON);