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Neptune will reach
opposition, when it lies opposite to the Sun in the sky.
Lying in the constellation
Pisces, it will be visible for much of the night, reaching its
highest point in the sky around midnight local time.
From Los Angeles, it will be visible between 20:43 and 04:56. It will become accessible at around 20:43, when it rises to an altitude of 21° above your eastern horizon. It will reach its highest point in the sky at 00:49, 54° above your southern horizon. It will become inaccessible at around 04:56 when it sinks below 21° above your western horizon.
2024 apparition of Neptune
A close approach to the Earth
At around the same time that Neptune passes opposition, it also makes
its closest approach to the Earth – termed its perigee –
making it appear at its
brightest.
This happens because when Neptune lies opposite to the Sun in the sky, the
Earth passes between Neptune and the Sun. The
solar system is lined up with Neptune and the Earth on the same side of the Sun,
as shown by the configuration labelled perigee in the diagram below:
When a planet is at opposition, the solar system is aligned such that the planet
lies on the same side of the Sun as the Earth. At this time, the planet makes its
perigee, or closest approach to the Earth.
Not drawn to scale.
In practice, however, Neptune orbits much further out in the solar system
than the Earth – at an average distance from the Sun of
30.07 times that of the Earth,
and so its
angular size does not vary much as it cycles between
opposition and
solar conjunction.
Observing Neptune
At opposition, Neptune is visible for much of the night. When it lies opposite
to the Sun in the sky, this means that it rises at around the time the Sun sets, and it sets at
around the time the Sun rises. It reaches its
highest point in the sky at
around midnight local time.
But even when it is at its closest point to the Earth,
it is not possible to distinguish it as more than a
star-like point of light
without the aid of a telescope.
A chart of the path of Neptune across the sky in 2024 can be found here, and a chart of its rising and setting times here.
At the moment of opposition, Neptune will lie at a distance of
28.89 AU,
and its disk will measure
2.4 arcsec
in diameter, shining at magnitude 7.8.
Its celestial coordinates at the moment it passes opposition will be:
| Object | Right Ascension | Declination | Constellation | Magnitude | Angular Size |
| Neptune | 23h55m20s | 1°56’S | Pisces | 7.8 | 2.4″ |
The coordinates above are given in J2000.0.
Over the weeks following its opposition, Neptune will reach
its highest point in the sky four minutes earlier each night, gradually
receding from the pre-dawn morning sky while remaining visible in the evening
sky for a few months.
The sky
on 20 Sep 2024
Source
The circumstances of this event were computed using the DE430 planetary ephemeris published by the Jet Propulsion Laboratory (JPL).
This event was automatically generated by searching the ephemeris for planetary alignments which are of interest to amateur astronomers, and the text above was generated based on an estimate of your location.
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Image credit
© NASA/Voyager 2
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