Vesta Gets Close and Bright

Vesta, the brightest asteroid, puts on one of its best shows ever in June, when it shines brightly enough to see without optical aid.

Vesta hangs with Saturn

Vesta appears in a moonless sky starting about June 5th. It's well-placed for viewing around midnight in early June and by 10:30 p.m. at month's end. Face southeast and look for the bright planet Saturn and the "Teapot" of Sagittarius to get oriented. Then use the maps below.
SkyMap with additions by the author

Imagine if you could look up in the sky and see an asteroid with nothing but your eyeballs. Guess what — you can! In the coming month, 4 Vesta will shine its brightest in years, affording skywatchers a rare opportunity.

The second largest main belt asteroid and a bona fide protoplanet, Vesta reaches opposition on June 19th, when it will come within 170.6 million kilometers of Earth, the closest it's been in at least two decades.

Currently at magnitude 5.7, Vesta will climb to magnitude 5.3 at opposition on June 19th, bright enough to pick out in less than perfect skies. By a stroke of good luck, Saturn will be nearby (only 7.5° southeast) to help point the way. For observers at mid-northern altitudes, extinction — the dimming of a celestial object due to absorption of light by the atmosphere at low altitudes — will rob the asteroid of ~0.4 magnitude.

The window for naked-eye Vesta viewing begins June 5th, when the asteroid is well-placed in the southeastern sky shortly before moonrise, and ends about July 16th, when it fades back to magnitude 6.0, the traditional naked-eye limit. Peak viewing, when the asteroid is brightest in a moonless sky, occurs from June 8–22.

Brightest asteroid at its brightest

Vesta plies the summer Milky Way during its brightest apparition in decades. To find it, begin at Saturn then star-hop with the naked eye or binoculars to 3.8-magnitude Mu (μ) Sagittarii. The asteroid is located 2.5°–4° northwest of that star through mid-June. Despite its location in star-rich Sagittarius, Vesta has little competition from similarly bright stars, making it easy to spot. Dates shown are for 0 hours Universal Time. For U.S. time zones, subtract 4 hours for Eastern Time; 5 for Central; 6 for Mountain; and 7 for Pacific. For example, May 15th, 0h UT = May 14th at 8 p.m. EDT. Click HERE or on the map for a sweet, black-and-white pdf chart you can print for use outdoors.

The last time Vesta came this close, but not quite, was at the May 30, 2007, opposition. Then, it glimmered at magnitude 5.4 from 171.2 million kilometers away. I made a special effort to see it at the time but wished now I'd taken better notes. Here's what I wrote: "Seen with the scope and naked eye. Dimly visible about 6 mag. along the Oph-Sco border."

Vesta starts out the month of June moving west in retrograde motion in Sagittarius near the eye-catching M24 Star Cloud. On the nights of the June 14–15, it will pass less than ½° southeast of the bright open cluster M23. Late in the month, Vesta segues into Ophiuchus before doing an about-face and resuming direct motion in early August before looping back to Sagittarius in early September. On the last nights of summer, it slides 1° south of the Lagoon Nebula.

Partway to planethood

NASA's Dawn space mission studied Vesta (diameter 530 km) up close from July 2011 to September 2012. It confirmed that many achrondrite meteorites in the HED group (Howardites, eucrites, and diogenites) originated here. Dawn also discovered that the asteroid had made tentative steps toward becoming a planet.
NASA / JPL-Caltech / UCAL / MPS / DLR / IDA

Vesta's shine has baffled astronomers for decades. The Moon reflects 12% of the light it receives from the Sun; Vesta returns 43%. What makes it so bright? There are at least two possibilities. Unlike the Moon and most small solar-system bodies that lack an atmosphere or magnetic field, Vesta shows little space weathering. Space weathering occurs when high-speed charged particles in the solar wind and micrometeorites bombard exposed rock, vaporizing tiny particles of iron in the minerals. Over time, the vaporized metal coats the rocks in a dark patina.

Vesta lava

A slice of the eucrite meteorite NWA 3147 found in the Sahara Desert  likely originated in a lava flow on the surface of Vesta. The rock is composed of feldspar and pyroxene crystals.
Bob King

The Dawn spacecraft found no sign of this classic weathering on Vesta's crust, so either the rocks there possess little iron or the asteroid is protected by a magnetic field, which would fend off much of the damaging effects of solar gusts. Recent studies of residual magnetic fields in meteorites derived from the minor planet provide indirect evidence of its existence.

Pity there wasn't enough money approved to provide a magnetometer for Dawn or we might have a definitive answer to this conundrum. We do know that Vesta was hot enough in the distant past to partially melt and differentiate into crust, mantle, and core, the first steps on a journey to a planethood abruptly scotched by Jupiter. Perhaps the core once seethed with molten iron, enough to generate a magnetic field for a time.

Even if Vesta eludes the naked eye from your location, take a look through binoculars or a telescope. Any optical aid will show it as a "star" creeping across the Sagittarius Milky Way night by night and week by week. Amateurs looking for a challenge will want to maximize their Vestan experience by attempted to discern the asteroid's shape. As seen in the wonderful sequence by astrophotographer Damian Peach, it's clearly oval.

Tough nut to crack, but ...

Can amateur scopes make out the ovoid shape of Vesta? These photos — and comparison images — were taken during the last favorable opposition in 2007.
Damian Peach

Vesta varies in apparent diameter from 0.20″ to 0.69″. The low end is impossible to see visually, but the protoplanet will swell to its maximum size this apparition. If you've seen Jupiter's moons as disks — not a terribly difficult feat in a 6-inch telescope at high magnification — you might, I say might just see Vesta. Let's look at the specs.

In June, Jupiter's four Galilean moons have the following apparent diameters: Ganymede (1.62″); Callisto (1.5″); Io (1.1″); and Europa (1.0″). While Europa looks very small indeed at 250×, I've seen all of them as disks in my 11-inch and 15-inch scopes. Vesta will be slightly larger than half-a-Europa. Given top notch seeing conditions I suspect that the asteroid's oval shape might be glimpsed at 500× in a 10-inch telescope.

Wait for a good night when Vesta's on the meridian and keep upping the magnification until the atmosphere won't allow. Pay attention to the color. Some amateurs, including myself, have noted a yellow hue. We'd love to hear about your attempts, successful or not.

Bonus 'roids

Use these scene-setter maps along with the more detailed individual asteroid maps to get a peek at 16 Psyche (magnitude ~10.5) and 13 Egeria (magnitude ~10.5) while you're waiting for Vesta to rise. You'll need a 4-inch or larger scope to see them.
SkyMap with additions by the author

Several other relatively bright asteroids are currently prowling the June skies. As warm-ups to Vesta viewing and to expand your list of minor planets, I've included finder maps for 16 Psyche and 13 Egeria, visible in the evening hours, and 9 Metis and 29 Amphitrite, visible after midnight. Just click on the links for charts. Stars are plotted to magnitude 11.0 except in the chart for 13 Egeria, which shows stars down to 11.5.

Vesta buds

This map features two additional main belt asteroids located not far from Vesta in the pre-dawn sky. Asteroid 9 Metis shines at magnitude 10.2 at opposition on June 16th, while 29 Amphitrite peaks at 9.9 on June 15the. Both are visible in a 3-inch scope under dark skies. Click on the links above for detailed charts.
SkyMap with additions by the author

Vesta won't get this close again until sometime after 2040. I'm as excited as you are at the opportunities. Hopefully, I'll do better on my observing notes this time around!

22 thoughts on “Vesta Gets Close and Bright

  1. Joe StieberJoe Stieber

    I too have been looking forward to spotting (4) Vesta with unaided eyes around opposition on June 19, 2018. I have seen Vesta with unaided eyes once before, at 2 am EDT on April 6, 2014 (a week before opposition on April 13). It was magnitude 5.8 in Virgo (so it was at a favorable 52 deg altitude for me vs. just 30 deg this June) and was in the same binocular field as magnitude 7.0 (1) Ceres. Bright Mars, magnitude -1.4, was just 11.5 deg away and I vividly remember having to hold my hand up to block the glare from Mars. At the time, I was under relatively dark skies in the New Jersey Pinelands.

    1. Bob KingBob King Post author

      Good luck, Joe. I’m sure you’ll spot it again even with a bit of extinction. This time though you’ll have to block Saturn!

  2. Graham-Wolf

    Hi Bob!

    A timely and much appreciated reminder for Vesta hunters out there.

    Did get a glimpse of it mid May with the 12cm f9 at high power, lurking in the M24 Star cloud. At 180x, it did look slightly oval, but not as impressive as Damien’s mind-blowing photos! Grabbed the 10x25s a few minutes later and star hooped across the same M24 Star cloud to find it again. Not quite visible naked eye, as my local Dunedin City Council “fun police” have upgraded my retiremnent village security lights with far more powerful light polluting versions…. arrrrg!

    I’ve seen Vesta naked eye about half a dozen times naked eye in my lifetime. You really need a Bortle 1 or 2 sky if possible! Best ever time time for me, was in the mid 1990’s atop the famous Mt John Observatory at -23 deg C, and with a Zenith sky peaking at +7.6, and better than 1.5 arcsec seeing. Later went inside the dome, and cranked up the 24 inch OC Ritchey Chretien with Observatory Technician:- (now retired) Graeme Kershaw. At ~ 750x, Vesta was DEFINITELY oval!!

    Was -5 deg C, just 2 days ago… just before dawn. Icy local roads three days in a row, this week. Brrrrrrr!!

    Regards from Graham W. Wolf:- 46 South, Dunedin, NZ.

    1. Bob KingBob King Post author

      Hi Graham,
      Dang lights! Sorry to hear it. I suppose they’re LEDs like the ones that are spreading across my city. Your observation of Vesta’s shape got me very excited. I’m hoping to see it for the first time ever though I’ll need a VERY steady night, since it’s less than 30° high from here.

  3. VestaameVestaame

    Hi Bob, I have only recently (in this last year) gained an interest in Vesta and coincidentally this newfound interest just keeps getting better being I just read the information on seeing Vesta with the naked eye this month! Thanks

    1. Bob KingBob King Post author

      Vestaame,
      It’s a great time to get interested in Vesta for sure. I hope you’ll be able to see it with the naked eye. Just head out on a moonless night to the country and the asteroid is as high in the southern sky as possible.

  4. JRJR

    Hi, Bob–Just stopping by to say that our skies this weekend weren’t great — too cloudy to go through the effort of setting up a scope — but we did manage to pick up Vesta on Saturday with 8×42 binos. I don’t think it’s going to be a naked-eye object for Metrowest Boston even at 5.3.

    1. Anthony BarreiroAnthony Barreiro

      Likewise, I don’t expect to see Vesta naked eye here in San Francisco, but I’ve started following her through 10×42 binoculars. Dead easy to find just north of mu Sag, and moving noticeably from one morning to the next. The hardest part is observing when Vesta is above the horizon, the sky is clear, and I’m not sleeping! I’ve been catching Vesta and Saturn in the southwest during dawn.

  5. Tom-Reiland

    Bob,
    Finally got a decent night without interference from the Moon. The southern sky at Wagman Observatory is not very good because of light pollution, so I could not see Vesta with my nude-eyes, but it was easy to spot through my 10 X 50 binoculars thanks to the S & T chart. About 45 to 50 minutes later I spotted Comet PANSTARRS C/2016 M1at 127X and 282X. I estimated it at 9 magnitude as small, compact, fuzzy blob. LP hinder this observation, also. Thanks again for the info on both objects.

    1. Bob KingBob King Post author

      Tom,
      You’re welcome. I’m happy to hear you found the comet, too. I’ve got to head over for another look at that one — still our brightest comet currently. I tried for 21P/Giacobini-Zinner two nights ago in Cygnus and saw nothing. That should be a good one come August.

  6. Fabrice MoratFabrice Morat

    Hello Bob,

    I’ve already seen Vesta naked eye at an earlier opposition in mountain location but your informative text concerns me because i didn’t know we can resolve the disk of this big asteroid. Two nights ago, with a seeing quite good, i tried first to see it without instrument but it was not so easy that i thought perhaps due to its albedo a little hot or the relative proximity of Saturn. Transparency was excellent with naked eye limit magv of 7.3 in Draco (not the zenith for me). Then, i used my 600mm around 500x and was surprised to see easily not a classical star but an oval yellow disk (shaped like a rugby ball). This is so unusual for me that i’ve thought first my scope suffered from astigmatism !
    Then, i looked the trajectory on you map to see if Vesta would meet a deep sky object. It seems the case with the interesting PN NGC 6445 after the 22th (i didn’t look precisely if this conjunction would be close or not) and the gibbous moon wouldn’t be a problem.
    Bob, do you think there is another asteroid accessible visually which presents a strange form ?. If you answer yes, it would be a second surprise for me ! Regards from +29° lat. La Palma island.

    1. Bob KingBob King Post author

      Congratulations, Fabrice! What a thrill it must have been to see Vesta’s shape. Pallas is slightly flattened similar to Vesta and only a little smaller, so it might be possible to see its shape during an exceptionally close opposition like the one Vesta is experiencing now.

  7. Tom-Reiland

    Yesterday evening we had clear skies and I could see Venus, Pollux and Castor in a straight line. It clouded up a couple of hours later and cleared off by 12:45 AM. I was able to locate Vesta as it is getting closer to M23. Saturn, Mu Sagittarii and Vesta almost formed another straight line with Saturn and Vesta about equal distances from Mu Sag. They should be in a straight line tonight. I tried to spot Vesta without using my 10 X 50 binocs, but I was not totally convinced that I saw it. I tried with and without my glasses and, at times, I thought I saw very brief blip. I was able to spot many M objects from my place, which is less than 10 miles North of Pittsburgh, using my 10 X 50s. M8, M20 through M25. Transparency was very good, but the light pollution prevented a confirmed sighting of Vesta. I’ll give it another try later this week after the storms move through.

    1. Bob KingBob King Post author

      Thanks for reporting your report on Vesta, Tom. I was fortunate in getting a very clear night earlier this week. From a dark sky, Vesta was difficult to see when it came into view around 11 (faintly seen on occasion with averted vision) but by 12:30 when nearing the meridian it was still faint but considerably easier. I also spotted M23 and a number of other Messier objects without optical aid in the vicinity of the asteroid.

      1. Tom-Reiland

        Bob, I final got a chance to try to observe Vesta without optical aid. First I located with 10 X 50 binoculars. Then I sat down on the floor of the room for the 21″ Scope at Wagman Observatory to cut off any lights. Next I repeatedly viewed it to confirm my observation. I was able to spot it at least 6 times. I then observed Vesta at 462X on the 21″ and I could definitely see an angular diameter that was very slightly oval. Right after that I went onto to Pluto, which is becoming more difficult to see every year. I’m certainly glad that I was able to view Pluto during the prime viewing period from 1979 to 1999.

        1. Tom-Reiland

          I forget to say thanks to S & T Magazine for the excellent chart for locating Pluto. Very nicely done. Far better than other charts I have seen.

  8. Sunflower

    When Vesta was mentioned during the news broadcast, I immediately jumped up and stepped out on my back balcony and WHOA! it was shining bright yellow between the leaves. I waited a while for it to become completely visible from behind the trees and called the hubs to come out to look also! It was an awesome view

    1. Sunflower

      I forgot to mention this was back in June. I just came across this site tonight looking for information on if Vesta was presently visible because I looked up tonight and saw a bright yellow star…

    2. Bob KingBob King Post author

      Hi Sunflower,

      Vesta is faint to the eye. You can see it, but you have to look carefully to find it. Based on when you saw the object, I think what you saw instead was Jupiter. Still a nice catch!

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