Asteroid 42 Isis will be well placed, lying in the constellation Sagittarius, well above the horizon for much of the night.
Regardless of your location on the Earth, 42 Isis will reach its highest point in the sky around midnight local time.
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 42 Isis 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 42 Isis lies opposite to the Sun in the night sky, the solar system is lined up so that 42 Isis, the Earth and the Sun lie in a straight line with the Earth in the middle, on the same side of the Sun as 42 Isis.
On this occasion, 42 Isis will pass within 0.981 AU of us, reaching a peak brightness of magnitude 9.3. Nonetheless, even at its brightest, 42 Isis is a faint object beyond the reach of the naked eye; binoculars or a telescope of moderate aperture are needed.
Finding 42 Isis
The chart below indicates the path of 42 Isis across the sky around the time of opposition.
The position of 42 Isis at the moment of opposition will be as follows:
|Asteroid 42 Isis||18h35m50s||27°08'S||Sagittarius||9.3|
The coordinates above are given in J2000.0.
|The sky on 29 June 2024|
23 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 DE430 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.
© NASA/Galileo 1993. Pictured asteroid is 243 Ida.