Asteroid 27 Euterpe at opposition

2015 Dec 25

Dominic Ford – originally published on

Asteroid 27 Euterpe will be well placed for observation, lying in the constellation Gemini, well above the horizon for much of the night.

Regardless of your location on the Earth, Euterpe will reach its highest point in the sky at around midnight local time.

From London (click to change), it will be visible between 18:42 and 05:15. It will become accessible at around 18:42, when it rises 24° above your eastern horizon, and then reach its highest point in the sky at 23:57, 61° above your southern horizon. It will become inaccessible at around 05:15 when it sinks to 25° above your western 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 Euterpe 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 Euterpe lies opposite to the Sun in the night sky, the solar system is lined up so that Euterpe, the Earth and the Sun lie in a straight line with the Earth in the middle, on the same side of the Sun as Euterpe.

On this occasion, Euterpe will pass within 0.957 AU of us, reaching a peak brightness of magnitude 8.3. Nonetheless, even at its brightest, Euterpe 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.

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

Object Right Ascension Declination Constellation Magnitude
Asteroid 27 Euterpe 06h13m30s +23°18′ Gemini 8.3

The coordinates above are given in J2000.0.

The details of this observing event were provided courtesy of