Dominic Ford, Editor
From the Asteroids feed
Asteroid 4 Vesta 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, 4 Vesta will reach its highest point in the sky around midnight local time.
From Fairfield, it will be visible between 22:26 and 03:16. It will become accessible around 22:26, when it rises to an altitude of 20° above your south-eastern horizon. It will reach its highest point in the sky at 00:53, 29° above your southern horizon. It will become inaccessible around 03:16 when it sinks below 20° above your south-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 4 Vesta 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 4 Vesta lies opposite to the Sun in the night sky, the solar system is lined up so that 4 Vesta, the Earth and the Sun lie in a straight line with the Earth in the middle, on the same side of the Sun as 4 Vesta.
On this occasion, 4 Vesta will pass within 1.149 AU of us, reaching a peak brightness of magnitude 5.3. Nonetheless, even at its brightest, 4 Vesta 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 4 Vesta
The chart below indicates the path of 4 Vesta across the sky around the time of opposition.
The position of 4 Vesta at the moment of opposition will be as follows:
|Asteroid 4 Vesta||17h53m50s||-19°50'||Sagittarius||5.3|
The coordinates above are given in J2000.0.
|The sky on 20 June 2018|
7 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.
© NASA/Galileo 1993. Pictured asteroid is 243 Ida.