British Astronomical Association
Supporting amateur astronomers since 1890

Secondary menu

Main menu

BAA Observing calendar

Asteroid 20 Massalia at opposition

Monday, 2019, May 20 - 17:48

Asteroid 20 Massalia will be well placed for observation, lying in the constellation Libra, well above the horizon for much of the night.

Regardless of your location on the Earth, 20 Massalia will reach 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 19° above the horizon.

The geometry of the alignment

This optimal positioning occurs when it makes its closest approach to the point in the sky directly opposite to the Sun – an event termed opposition. 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 20 Massalia passes opposition, it also makes its closest approach to the Earth – termed its perigee – making it appear at its brightest in the night sky. This happens because when 20 Massalia lies opposite to the Sun in the night sky, the solar system is lined up so that 20 Massalia, the Earth and the Sun lie in a straight line with the Earth in the middle, on the same side of the Sun as 20 Massalia.

On this occasion, 20 Massalia will pass within 1.624 AU of us, reaching a peak brightness of magnitude 9.7. Nonetheless, even at its brightest, 20 Massalia is a faint object beyond the reach of the naked eye or binoculars; a telescope of moderate aperture and a good star chart are needed.

Finding 20 Massalia

The star charts below mark the path of 20 Massalia across the sky around the time of its opposition.

This star chart is also available to download:

Light-on-dark PNG image PDF document
Dark-on-light PNG image PDF document

The exact position of 20 Massalia at the moment of opposition will be as follows:

Object Right Ascension Declination Constellation Magnitude
Asteroid 20 Massalia 15h48m10s -19°21' Libra 9.7

The coordinates above are given in J2000.0.

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

.