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BAA Observing calendar

1 Ceres at opposition

Wednesday, 2019, May 29 - 02:27

Across much of the world 1 Ceres will be well placed for observation, in the constellation Ophiuchus. It will be visible for much of the night, reaching its highest point in the sky at around midnight local time.

From London however, it will not be readily observable since it will lie so far south that it will never rise more than 20° above the horizon.

1 Ceres opposite the Sun

This optimal positioning occurs when 1 Ceres is almost directly opposite the Sun in the sky. Since the Sun reaches its greatest distance below the horizon at midnight, the point opposite to it is highest in the sky at the same time.

At around the same time that 1 Ceres passes opposition, it also makes its closest approach to the Earth – termed its perigee – making it appear at its brightest and largest.

This happens because when 1 Ceres lies opposite the Sun in the sky, the solar system is lined up so that 1 Ceres, the Earth and the Sun form a straight line with the Earth in the middle, on the same side of the Sun as 1 Ceres.

In practice, however, 1 Ceres orbits much further out in the solar system than the Earth – at an average distance from the Sun of 2.77 times that of the Earth, and so its angular size does not vary much as it cycles between opposition and solar conjunction.

On this occasion, 1 Ceres will lie at a distance of 1.76 AU, and its disk will measure 0.0 arcsec in diameter, shining at magnitude 7.0. Even at its closest approach to the Earth, however, it is not possible to distinguish it as more than a star-like point of light without the aid of a telescope.

1 Ceres in coming weeks

Over the weeks following its opposition, 1 Ceres 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.

A chart of the path of 1 Ceres across the sky in 2019 can be found here, and a chart of its rising and setting times here.

The position of 1 Ceres at the moment it passes opposition will be:

Object Right Ascension Declination Constellation Magnitude Angular Size
1 Ceres 16h24m00s -17°41' Ophiuchus 7.0 0.0"

The coordinates above are given in J2000.0.

This entry in the observing calendar was provided by In-The-Sky.org

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