Images and illustrations credit & copyright: NASA & Naked Eye Planets.
It’s not every day that you can observe a main belt asteroid with nothing more than your eyes and right now is one of those times. Asteroid 4 Vesta is the second largest main belt asteroid after dwarf planet 1 Ceres and it reaches opposition (its closest point to Earth in its orbit) on Tuesday, June 19. Its apparent magnitude is around 5.7 now and is scheduled to reach about 5.2 or 5.3 at opposition and remember, the lower the number the brighter the object is, and in very dark skies anything under 6 or 6.5 is naked eye visible.
Understanding Magnitudes: https://danspace77.com/magnitudes/
There are a couple things to mention here to help your hunt be slightly less miserable.
First: Even though Vesta will be brightest during opposition, the moon will have returned and be nearly first quarter (half full) and in the sky until roughly midnight. That means this week (new moon week) is likely to be your best opportunity to catch a glimpse.
Second: This isn’t something you will be able to just look up at and notice unless you know exactly what you’re looking for. It’s too far away to notice real time movement so knowing your way around is crucial to finding it. Below I have listed many links to help you pinpoint where it can be found. If you have the ability, take a photo of that region of sky (near Saturn in Sagittarius) then take another every couple days and it’s pretty fun to track the movement through the weeks.
4 Vesta Basic Data:
Name: 4 Vesta, Vesta, Roman Goddess of Home and Hearth
What is it?: Main belt asteroid
Size (diameter): Second largest main belt object after Ceres at 572.6 km (355.79 mi.) diameter at its widest point and a mean (average) diameter of 525 km (326 mi)
Size (mass): Second most massive main belt object after Ceres though only 28% as massive as Ceres.
Orbital Period (a Vesta year): 3.63 Earth years or 1,325.7 Earth days
Rotational Period (Vesta day): 0.22 Earth days or 5.34 Earth hours
Satellites (moons): None
Discovery: March 29, 1807 by Heinrich Wilhelm Olbers
4 Vesta Opposition 2018 Data:
Date of Opposition: Tuesday, June 19, 2018
Time of Opposition: 20:00 EDT (00:00 UTC) but not entirely important
Where is it? (constellation): Sagittarius
Where is it? (exact RA/Dec J2000): RA 17h 52m 20s Dec -19° 49′ 12”
Apparent Magnitude: A naked eye visible 5.4
Apparent Size (Angular Size): 0.6” arcseconds and 100% illuminated. For perspective Jupiter is nearly 44” arcseconds at opposition.
Altitude: It will reach about 30 degrees in altitude.
Distance from Earth: 1.14 AU (170.8 million km or 106.1 million mi.)
Opposition Frequency: About 512 days.
Moon Phase: Nearly 1st quarter (half full)
Current Visiting Spacecraft: None
Former Visiting Spacecraft: NASA Dawn
Sky & Telescope Sky Map w’ Plotted Course: http://wwwcdn.skyandtelescope.com/wp-content/uploads/June18_Vesta_Findr_BW.pdf
Naked Eye Planets Vesta Finder Chart: http://www.nakedeyeplanets.com/vesta-2018.htm
Naked Eye Planets B&W Vesta Finder Chart: http://www.nakedeyeplanets.com/vesta-path-may-aug-2018-b&w.png
Dominic Ford’s “In-The-Sky” page for this event: https://in-the-sky.org/news.php?id=20180620_14_100
In-The-Sky’s, Solar System Body Finder Chart: https://in-the-sky.org/findercharts.php?startday=1&startmonth=6&startyear=2018&duration=3&objtype=0&objtxt=&objs=26027
The Sky Live page for Vesta: https://theskylive.com/vesta-info
The Sky Live, Vesta Tracker: https://theskylive.com/vesta-tracker
The Sky Live, Vesta Planetarium: https://theskylive.com/planetarium?obj=vesta
The Sky Live, Vesta Rise & Set Times: https://theskylive.com/riseset?obj=vesta
Chris Peat’s “Heavens-Above” Planet Summary: https://heavens-above.com/MinorPlanet.aspx?desig=4&lat=0&lng=0&loc=Unspecified&alt=0&tz=UCT
U.S. Naval Observatory Planet Rise and Set Times: http://aa.usno.navy.mil/data/docs/mrst.php
Time and Date Sunrise and Sunset calculator: http://www.timeanddate.com/sun/
Time and Date Moonrise and Moonset calculator: http://www.timeanddate.com/moon/
Time and Date Lunar Calendar: https://www.timeanddate.com/moon/phases/
Moon Calendar: https://www.calendar-12.com/moon_calendar/2018/june
Moon Giant Moon Phase: https://www.moongiant.com/phase/06/19/2018
Heavens-Above Moon Data: http://www.heavens-above.com/moon.aspx?alt=0&lat=0&lng=0&loc=Unspecified&tz=CET
The Planets Today (current solar system configuration): http://www.theplanetstoday.com/
NASA JPL Small Body Database: https://ssd.jpl.nasa.gov/sbdb.cgi#top
Asteroid 4 Vesta Wiki: https://en.wikipedia.org/wiki/4_Vesta