(4) Vesta at Opposition, June 19, 2018
It will reach magnitude 5.3
On Tuesday, June 19, 2018, the asteroid, or minor planet if you prefer, (4) Vesta will reach opposition at 4:16 pm EDT. What's special about this opposition is that Vesta will be relatively close to earth and become as bright as magnitude 5.3 for a few days, well within the range of visibility with unaided eyes from a dark site. However, its position in Sagittarius means that it will only be about 30° altitude when it transits the meridian for an observer at 40°N latitude.
I have seen Vesta with unaided eyes once before, at 2 am EDT on April 6, 2014, from Batsto in the New Jersey Pinelands. It was a week before opposition, already at its magnitude 5.8 peak and 52° altitude. It was in the same binocular field as (1) Ceres (magnitude 7.0) 2.5° away. Bright Mars (magnitude -1.4) was 11.5° away, so I had to block its glare with my outstretched hand.
I have prepared an ephemeris (using the U.S. Naval Observatory's MICA software) showing among other things, Vesta's magnitude from May 20 through July 18, 2018 (Vesta will be at magnitude 6 or brighter during that period). I also prepared a listing of Vesta's oppositions from 1988 to 2018 showing the peak magnitude for each opposition. The average span between those oppositions is about 16.6 months, and the peak magnitude is less than 5.5 every fifth or eighth opposition during that time period, roughly every 7 to 11 years.
Bob King has a nice online article at Sky & Telescope discussing this upcoming opposition of Vesta, along with finder charts.
I decided to copy any of my Vesta observations and pictures on the home page to this page, and post observation updates here...
(4) Vesta Nears Opposition
June 5, 2018
This picture of the Milky Way region above Sagittarius
was captured on June 5, 2018,
at 12:44 am from Carranza Field in Wharton State Forest, NJ. However,
the Milky Way was not the prime target, rather it was the asteroid (or
minor planet), (4) Vesta.
This is a single frame taken with a Canon 6D digital SLR camera on a
fixed tripod and a Tamron 45 mm f/1.8 lens, which provides a field about
43.5° wide x 30° high. Exposed 4 seconds at f/2, ISO 3,200 and 3,600K
white balance. Other than size reduction for this web page, no
processing was applied. Mouseover for labels.
I went to Carranza in hope of seeing Vesta with unaided eyes since it was at magnitude 5.7 (it will reach magnitude 5.3 at opposition on June 19. I arrived just before midnight and stayed until about 1 am EDT. Vesta would transit at 2:13 am, but the almost-third-quarter Moon rose at 12:53 am. The Milky Way through the Summer Triangle and continuing down into Sagittarius was prominent, but not billowing. The air seemed moist after heavy rain over the weekend and dew was forming on my camera and tripod. However, it was quite pleasant to be under a starry sky for a change, and sweeping the sky with 15x56 binoculars revealed numerous deep-sky objects, especially in the pictured Milky Way. And for a sonic background, the chorus frogs were going strong at nearby Skit Branch.
Vesta was easily visible in the binoculars, but I was not able to make a definite sighting of it with unaided eyes. I think I might have glimpsed Vesta with averted vision a couple of times when I was able position M24, the Sagittarius Star Cloud, in the averted sweet spot (nice view) and I thought I was seeing a ghostly outline of the dark Prancing Horse Nebulae (which includes the dark Pipe Nebula), but Vesta was much too fleeting to be claimed as a sighting. One has to guard against the brain filling-in things that are expected, but not really visible. I was also unable to see M13 with unaided eyes, something I've done many times in the past, even though it was virtually at the zenith. Perhaps the transparency wasn't that good, or perhaps advancing age is catching up with my eyes. However, looking at SkyTools, Vesta was 28° altitude at 12:44 am, so the airmass for it was 2.1, which yielded a mean extincted magnitude of 6.6, which would indeed be dimmer than the nominal magnitude 6 limit for unaided eyes (and the dimmest I've confirmed seeing in the past from New Jersey is magnitude 6.1). I also failed to see M51 (about 60° altitude) in the 15x56s, which I was able to do without difficulty last month at Atsion in Wharton State Forest.
Note that Atlantic City, with its attendant light pollution, is only about 30 miles away in nearly the same direction as Vesta in the picture (≈160° azimuth), hence the light cone rising from the tree tops in the middle of the frame. Last, but not least, I need a better way to block Saturn besides a hand at the end of my outstretched arm, which quickly becomes tiresome; perhaps a piece of cardboard at the end of a stick? Saturn may not seem particularly bright in a suburban sky, but under a dark sky looking for a nearby faint object (Vesta was less than 7° away), it looks bright and becomes disruptive. In any case, a couple more weeks remain before Vesta's opposition and maximum brightness — and before the moon interferes. Let's hope for some more clear nights!
The image below was taken at 12:19 am EDT with the 6D and a Canon 100 mm f/2.8L macro lens on a fixed tripod, providing a field about 20° wide x 14° high to better show Vesta. Exposed 4 seconds at f/2.8, ISO 12,800, 3,600K white balance. No processing was applied besides size reduction. Mouseover for labels.
The image below is a 41% crop of the previous image taken with the 100 mm lens, providing a field about 8.4° wide x 5.6° high. Again, no processing was applied besides the cropping and size reduction. Vesta was located in front of a small asterism of several stars in the magnitude 8 to 10 range that was shaped a bit like an arrowhead. The stars of the "arrowhead" were visible in the 15x56 binoculars, but Vesta is currently moving about 0.22°/day west (retrograde motion, to the right in this view), so it was only there temporarily. Mouseover for labels.
Update, June 12, 2018: We had another clear and moonless sky last night, June 11-12, 2018. Such nights have been all too infrequent recently. Anyway, since the moon wouldn’t rise until 4:40 am EDT, I took another run out to the Pines, this time to the old railroad crossing on Carranza Rd, about half a mile due south of where I was on Carranza Field last week. The tracks at the crossing were pulled out years ago and an open space remains at the former crossing, just past of where the road transitions from paved to dirt (next to the patch of endangered Pickering's Morning Glory). Elsewhere along Carranza Rd, you’re boxed-in with trees and can only see the sky overhead.
The tree line at the crossing was far enough away that Sagittarius was visible, but close enough that I was able to position myself so that bright Mars on the left and bright Jupiter on the right were blocked by taller trees. I taped a black plastic take-out food tray to the end of an old walking stick (a 6 x 9 inch tray at the end of a 4 ft stick) and used it to block moderately-bright Saturn near Vesta.
I arrived about 1:30 am on June 12, shortly before Vesta would transit at 1:38 am. Again, the Milky Way was prominent, but not billowing, and to the unaided eyes, the sky extending above Sagittarius was splendid. In my 15x56 binoculars, numerous deep-sky objects were visible. These views in themselves were almost worth the trip. In any case, Vesta was easy to see in the binoculars, and of course, it had moved about 1.5° from its position at the little “arrowhead” asterism where I saw it last week.
With unaided eyes and using Mu Sgr, M20 and M24 as guides, while blocking Saturn with my improvised tray-on-a-stick, I was still unable to spot magnitude 5.5 Vesta. Perhaps the transparency wasn’t ideal, or maybe my eyes aren’t as good as they used to be. I also stopped, before 2 am, on Brace Lane off Carranza Rd, a mile south of the four-way stop in Tabernacle, and took a last look over the farm fields there, but I was still unable to see Vesta unaided. In any case, it’s still a week before Vesta reaches opposition at magnitude 5.3, so I’ll be on standby for another clear night when I can make another attempt to see Vesta with unaided eyes.
Update, June 17, 2018: We had a WAS Member's Star Watch at Atsion on Saturday night, June 16-17. It started out cloudy, but cleared after midnight, and by 1 am, the Milky Way was easily visible from the Summer Triangle down into Sagittarius. I looked for Vesta at least half an hour, blocking Saturn with a tree. Vesta was at magnitude 5.4 and located just southwest of M23, so it formed a nearly equilateral triangle with Mu Sgr and M20, both of which were visible with unaided eyes (as was M24). Again, I saw fleeting glimpses a few times in the expected position, but I think those momentary blips of light were just "noise" of some sort. I was not able to reliably repeat my sightings, so it's another negative. Vesta transited at 1:15 am, but since the sky was so nice when I left Atsion, I went to the Carranza railroad crossing for another attempt (a bit darker at Carranza and no annoying light from Atsion's ranger station or vehicles on Rt 206). The sky was beautiful, and I looked from about 2:15 to 2:30 am, again blocking Saturn with a tree, but alas, no sighting (not even momentary blips). At both location I was able to see the elongated trapezoid of nominal fifth-magnitude stars in Draco that surround the Cat's Eye Nebula (they range from magnitude 4.8 to 5.1 and were about 61° to 65° altitude at the time). However, it's still a couple of days before opposition, maximum brightness and interference from the moon, which sets about 1:15 am on June 20, so a chance of spotting it remains.
Update, June 20, 2018: Vesta was at opposition on June 19 at 4:16 pm EDT, so the night of June 19-20 was opposition night. Due to a patchwork of thin clouds in the sky, I decided it wasn't worth a trip to the Pines for another attempt with unaided eyes. However, since it was opposition night, I did want to take a look, so at 12:30 am on June 20, I stepped out to my front porch in Maple Shade, NJ, with my 15x56 binoculars. Magnitude 5.3 Vesta was easy to find about 8.5° WNW of Saturn and 1.5° SW of M23. It was in a distinctive asterism of five magnitude 7 & 8 stars in Sagittarius. Almost surprisingly, M23 was faintly visible in the suburban sky with the 15x56s, while M8 and M24 were fairly easy to locate. Vesta will become difficult to spot with unaided eyes in the coming days, as its magnitude will soon begin to dim and the moon will encroach. As of June 20, the moon sets after Vesta transits, then sets later on succeeding nights. Full moon is June 28. New moon is July 12, and by then, Vesta will be at magnitude 5.8.
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Last Update: Wednesday, June 20, 2018 at 05:33 PM Eastern Time