Asteroid 89 Julia will be well placed, lying in the constellation Pegasus, well above the horizon for much of the night.
Regardless of your location on the Earth, 89 Julia will reach its highest point in the sky around midnight local time.
From Cambridge, it will be visible in the evening sky, becoming accessible around 20:19 (EDT) as the dusk sky fades, 28° above your eastern horizon. It will then reach its highest point in the sky at 00:27, 58° above your southern horizon. It will continue to be observable until around 05:07, when it sinks below 21° 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 89 Julia 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 89 Julia lies opposite to the Sun in the night sky, the solar system is lined up so that 89 Julia, the Earth and the Sun lie in a straight line with the Earth in the middle, on the same side of the Sun as 89 Julia.
On this occasion, 89 Julia will pass within 1.1 AU of us, reaching a peak brightness of magnitude 9.1. Nonetheless, even at its brightest, 89 Julia is a faint object beyond the reach of the naked eye; binoculars or a telescope of moderate aperture are needed.
Finding 89 Julia
The chart below indicates the path of 89 Julia across the sky around the time of opposition.
The position of 89 Julia at the moment of opposition will be as follows:
|Asteroid 89 Julia||22h43m20s||+10°51'||Pegasus||9.1|
The coordinates above are given in J2000.0.
|The sky on 06 September 2017|
16 days old
All times shown in EDT.
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.