18 replies to this topic

[RMay]

I’m curious if anyone else is tracking Vesta… First time asteroid hunting for me; I’m trying to just get a handle on its location and movement over the next week or so, and will keep following it.

 

Ron

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[Redbetter]

Yes. I track it at times.  Mostly I do this naked eye from dark sites, but I follow that up by observing in the 20".  I didn't try for it last night as the session length was limited by the Moon, although I did in the prior two months.  

 

Vesta is brighter than 6th magnitude at this time, so not hard to find in any sort of dark sky if you know the coordinates and can apply them to a naked eye chart. (I have tracked it down into the 7+ range.)  Looking at a chart you can identify the interloper.  With a sufficiently large scope in good seeing the ~0.6" size disk appears distinctly non-stellar at high enough power.  It has a size larger than the spurious disk of stars of the same magnitude and lacks the diffraction pattern of a star.

 

The same approach works for Ceres and Uranus naked eye.  With Uranus I mostly don't even look up approximate position and instead search for it among stars along the portion of the ecliptic where I expect for it to be.

[RMay]

Yes. I track it at times.  Mostly I do this naked eye from dark sites, but I follow that up by observing in the 20".  I didn't try for it last night as the session length was limited by the Moon, although I did in the prior two months.  

 

Vesta is brighter than 6th magnitude at this time, so not hard to find in any sort of dark sky if you know the coordinates and can apply them to a naked eye chart. (I have tracked it down into the 7+ range.)  Looking at a chart you can identify the interloper.  With a sufficiently large scope in good seeing the ~0.6" size disk appears distinctly non-stellar at high enough power.  It has a size larger than the spurious disk of stars of the same magnitude and lacks the diffraction pattern of a star.

 

The same approach works for Ceres and Uranus naked eye.  With Uranus I mostly don't even look up approximate position and instead search for it among stars along the portion of the ecliptic where I expect for it to be.

Thank you for the info; it’s most helpful. I’ve caught Uranus with my Questar Seven (snap below); I’ll drag it out tonight to try for a closer look at Vesta if the weather holds.

 

Thanks again,

 

Ron

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[Dave Mitsky]

Here's a screen shot of a finder chart at In-The-Sky.org

 

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[Dave Mitsky]

This is a screen shot of a 15-day ephemeris from The Sky Live.

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[Dave Mitsky]

Nightly finder charts for currently bright asteroids can be generated at https://www.heavens-...lt=170.0&tz=EST

[Dave Mitsky]

There's more on 4 Vesta at https://astro.vanbui...norplanet/Vesta

[RMay]

Dave, thanks for the info… I did spot Vesta two nights ago; snapped a pic, but it’s not to my liking so I won’t post it; I’ll try again tonight.

Again, many thanks. I’ll be looking through the information in your posts very shortly.

Ron

[Special Ed]

Hi Ron,

 

4 Vesta can be fun to follow through the sky--I've done it from time to time over the years.  All it takes to track its motion against the starfield is some clear weather over a couple of days or more--not always the easiest thing to pull off.   

 

As Redbetter said, if you know the general location, it is not hard to pick out.  I use a star chart and binoculars--it's the star that shouldn't be there.  Here is an example where I tracked it over a period of about a week.

 

Now that I have a Seestar, I will try to track its motion with images--if the weather cooperates (it has been terrible here this spring).

 

[RMay]

Hi all, thanks for the encouragement and info. The weather has been (dare I say) absolutely splendid recently.

I’ve been noodling on other things, including prepping for this coming Monday’s 0.68% full thin crescent moon rising (which will probably be impossible, but would be a personal best for me), and I’ll take another look at Vesta tonight and in the coming days as long as the weather cooperates.

Ron

[azure1961p]

There's more on 4 Vesta at https://astro.vanbui...norplanet/Vesta

Dave,

 

Sky Safari claims a max diameter of 0.5" for Vesta this season.   Some claim 0.7" - I don't see 0.7" anywhere for this particular apparition.

 

Have you any info on that?

 

Pete

[ButterFly]

Dave,

 

Sky Safari claims a max diameter of 0.5" for Vesta this season.   Some claim 0.7" - I don't see 0.7" anywhere for this particular apparition.

 

Have you any info on that?

 

Pete

JPL Horizons can return the apparent size.  See the details for "13. Target angular diameter".  Remember that it also has a phase, so adjust accordingly.  If you are having trouble, I can send a link that includes that info for an exemplary location and times.

[Dave Mitsky]

Dave,

 

Sky Safari claims a max diameter of 0.5" for Vesta this season.   Some claim 0.7" - I don't see 0.7" anywhere for this particular apparition.

 

Have you any info on that?

 

Pete

Stellarium lists an apparent diameter of 0.61" at opposition.

[azure1961p]

Had it been 0.7 I would've regretted missing it.  Thanks ever Dave.

 

Pete

[Redbetter]

Dave,

 

Sky Safari claims a max diameter of 0.5" for Vesta this season.   Some claim 0.7" - I don't see 0.7" anywhere for this particular apparition.

 

Have you any info on that?

 

Pete

 

Sky Safari is unsurprisingly mistaken, assuming  that it is rounding to 0.5".  It might also be a truncated value which would produce a particularly large error in this case (see below.)

 

The simplest calc uses the mean diameter and distance form Earth at the time.  Vesta is moderately flattened with dimensions listed as 572.6 km × 557.2 km × 446.4 km with the mean being given as ~525 km.  Back on the evening of 5/19/25 (local) when I observed it naked eye, then as a disk in the 20", the distance was about 1.211 AU.  That works out to 0.598" by my calculations.  Stellarium gave it as 0.60" at this time.  There would be some phase angle reduction although that would be fairly small at the given angle (similar to Jupiter at max phase angle IIRC.)  

 

[Stellarium added the hundredths digit to apparent diameters at my request several years ago.  I also notified them of an error which they corrected in the calculation of diameter of many lesser asteroids that estimated their diameters based on magnitude (since they only have tabulated diameters for a portion of them in a file.)]

 

Looks like it reached a minimum distance of 1.186 AU around 5/2/25.  That would put it at 0.610" by my calcs and Stellarium reported 0.60".  In June of 2018 it made a relatively close approach of 1.143 AU and would reach 0.633".   

 

The above use the mean diameter, if one uses the longest dimension, then the 2018 opposition would be 0.690"...obviously rounding to 0.70".

 

There are some variations in the reported values for mean diameter and the minimum distance (MOID).  JPL lists the Earth MOID as 1.13652 AU.  

[ButterFly]

Or ... you can just ask NASA and get the correct answer of around 0.6748" near May 6, 2025, at a distance around 1.180887 AU.  Get it down to the minute if you so choose.

[RMay]

Third in my series. What are the odds… Vesta gets photobombed by a passing satellite… 

 

Ron

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[Special Ed]

Actually, the odds of getting photobombed by a satellite are pretty good these days.  

 

I captured Vesta last night with the Seestar.  I wasn't sure it would show enough movement in just two hours to be perceptible, but it did.

 

Here are the two captures.  Both are 60 second exposures.  I will have to post the gif in a separate post.

 

Edited by Special Ed, 25 May 2025 - 04:17 PM.

[Special Ed]

Here is the gif: