© NASA/Galileo 1993. Pictured asteroid is 243 Ida.

Asteroid 40 Harmonia at opposition

Fri, 23 Jun 2017 at04:32 EDT(208 days ago)
08:32 UTC

Dominic Ford, Editor
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The sky at

Asteroid 40 Harmonia will be well placed for observation, lying in the constellation Sagittarius, well above the horizon for much of the night.

Regardless of your location on the Earth, 40 Harmonia will reach its highest point in the sky at around midnight local time.

From Ashburn (click to change), it will be visible between 23:46 and 02:32. It will become accessible at around 23:46, when it rises 24° above your southern horizon, and then reach its highest point in the sky at 01:11, 27° above your southern horizon. It will become inaccessible at around 02:32 when it sinks to 25° above your southern 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 40 Harmonia 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 40 Harmonia lies opposite to the Sun in the night sky, the solar system is lined up so that 40 Harmonia, the Earth and the Sun lie in a straight line with the Earth in the middle, on the same side of the Sun as 40 Harmonia.

On this occasion, 40 Harmonia will pass within 1.255 AU of us, reaching a peak brightness of magnitude 9.3. Nonetheless, even at its brightest, 40 Harmonia 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 40 Harmonia

The star charts below mark the path of 40 Harmonia 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 40 Harmonia at the moment of opposition will be as follows:

Object Right Ascension Declination Constellation Magnitude
Asteroid 40 Harmonia 18h07m50s -23°06' Sagittarius 9.3

The coordinates above are given in J2000.0.

The sky on 23 June 2017
Sunrise 05:43
Sunset 20:38
Twilight ends
Twilight begins

29-day old moon
Age of Moon
29 days

All times shown in EDT.
Rise Culm. Set
Mercury 05:51 13:22 20:53
Venus 03:14 10:05 16:56
Moon 05:38 12:46 19:53
Mars 06:28 13:55 21:23
Jupiter 14:01 19:51 01:45
Saturn 19:45 00:36 05:23


The circumstances of this event were computed from orbital elements made available by Ted Bowell of the Lowell Observatory. The conversion to geocentric coordinates was performed using the position of the Earth recorded in the DE405 ephemeris published by the Jet Propulsion Laboratory (JPL).

The star chart above shows the positions and magnitudes of stars as they appear in the Tycho catalogue. The data was reduced by the author and plotted using PyXPlot. A gnomonic projection of the sky has been used; celestial coordinates are indicated in the J2000.0 coordinate system.

Image credit

© NASA/Galileo 1993. Pictured asteroid is 243 Ida.




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