Vesta at opposition

Vesta, the fourth asteroid, is at opposition, the middle of its nearest and brightest time.  Here is the evening scne as it rises into view.

See the end note about enlarging illustrations.

Vesta was only the 4th asteroid in order of discovery, yet is the only one that can rise to naked-eye visibility.  This opposition, though, is not one of the best.  Vesta is at magnitude 6.5, just a bit too dim for the naked eye even in perfect conditions.  And its is traveling a part of its orbit that is well south of the ecliptic; as you can see, it is nearer to the celestial equator than to the “anti-Sun” point.  This causes it to rise later (for north-hemisphere observers).  And the Moon is nearby, smearing the sky with light.

Nevertheless, Vesta is relatively easily findable with binoculars or telescope.

The chart shows the apparent retrograde loop that Vesta makes round the time of opposition because we are overtaking it on the inside in the journey around the Sun.  Vesta at opposition is near the stars Xi and Omicron Tauri, which are of about the same brightness/. They are not far east of the fairly familiar “head” of the whale Cetus, shown by the curving formline that goes off the picture.

The exact date of an asteroid’s opposition can be given differently, because it can mean opposition in ecliptic longitude (which I use) or in right ascension.  Also, it depends on the recentness of the orbital elements being used.  But Vesta’s positions in this map are not noticeably different from those in the map I gave back in July.

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ILLUSTRATIONS in these posts are made with precision but have to be inserted in another format.  You may be able to enlarge them on your monitor.  One way: right-click, and choose “View image”, then enlarge.  Or choose “Copy image”, then put it on your desktop, then open it.  On an iPad or phone, use the finger gesture that enlarges (spreading with two fingers, or tapping and dragging with three fingers).  Other methods have been suggested, such as dragging the image to the desktop and opening it in other ways.

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