=============================
Mercury Greatest Elongations:
=============================

 Date__(UT)__HR:MN       Illu% Ang-diam    delta (AU)         deldot    S-O-T /r Cnst
*************************************************************************************
 1954-Mar-28 00:00      50.425    7.586 .886846316859036  25.3333999  27.8121 /L  Aqr
 1980-Apr-03 00:00      50.559    7.563 .889596007300126  25.3211661  27.8188 /L  Aqr
 2013-Apr-01 00:00      50.810    7.549 .891243346892766  25.3066236  27.8284 /L  Aqr
 2026-Apr-04 00:00      50.103    7.599 .885351880487698  25.3211288  27.8194 /L  Aqr
 2059-Apr-02 00:00      50.347    7.586 .886868536796618  25.3080831  27.8300 /L  Aqr
 2092-Mar-30 00:00      50.583    7.572 .888494289354257  25.3186064  27.8257 /L  Aqr

 1957-Sep-26 00:00      50.762    7.016 .958904074550907  49.1516063  17.8605 /L  Leo
 1964-Sep-19 00:00      50.449    7.017 .958801595445232  49.0243057  17.8574 /L  Leo
 2023-Sep-23 00:00      50.866    7.003 .960740213064695  49.0916537  17.8486 /L  Leo
 2030-Sep-16 00:00      50.583    7.003 .960634794958359  48.8919185  17.8719 /L  Leo
 2062-Sep-30 00:00      50.288    7.043 .955191520489120  49.1868519  17.8763 /L  Leo
 2089-Sep-19 00:00      50.989    6.990 .962499029771588  48.9956009  17.8520 /L  Leo

Number generated using the Solar System Dynamics Group, Horizons On-Line Ephemeris System at:
http://ssd.jpl.nasa.gov/horizons.cgi?find_body=1&body_group=mb&sstr=1
Ephemeris Type: OBSERVER
Target Body: Mercury
Observer Location: Geocentric [500]
Time Span: 1950-01-01 to 2100-01-01
QUANTITIES=10,13,20,23,29

Key:
Illu% = Phase
Ang-diam = equatorial angular width
delta  deldot =  A positive "deldot" means the target center is moving away from the observer.
A negative "deldot" means the target center is moving toward the observer.
Units: AU and KM/S
S-O-T /r = Sun-Observer-Target angle; If negative, the target center is behind the Sun
/T indicates target trails Sun (evening sky)
/L indicates target leads Sun  (morning sky)
Cnst = Constellation ID
AU = 149,597,870km


====================================================
Mercury Closest Approach to Earth from 1950 to 2160:
====================================================

 Date__(UT)__HR:MN       Illu% Ang-diam    delta (AU)         deldot    S-O-T /r Cnst
*************************************************************************************
 1969-May-30 00:00       0.202   12.253 .549075130721575   0.2194351   2.3648 /L  Tau
 1982-Jun-02 00:00       0.205   12.253 .549054065295807  -0.0654885   2.3827 /T  Tau
 2015-May-31 00:00       0.176   12.254 .549035959479560  -0.2875441   2.2105 /L  Tau
 2061-May-31 00:00       0.166   12.253 .549079339116339  -0.7903549   2.1419 /T  Tau
 2107-Jun-03 00:00       0.247   12.254 .549032924114352   0.6652478   2.6150 /L  Tau
 2153-Jun-03 00:00       0.216   12.256 .548947071016823   0.1574896   2.4444 /L  Tau

A single AU = 149,597,870km.  In the year 2153, Mercury will come within 0.548947 AU (82,121,301 km) of the Earth.

Mercury always comes closest to the Earth when it is near the new phase (Illu%)<1 since it is located inside of Earth's orbit.
It is also interesting to note that during this time peroid Mercury is always in the constellation of Taurus when it comes to its closest point
to the Earth.  These numbers were only plotted once a day, thus the exact time of closest approach could be several hours earlier or later than 00 hour UT.


To reproduce these JPL-Horizons (Mercury-Earth) distances you need the following details:

Number generated using the Solar System Dynamics Group, Horizons On-Line Ephemeris System at:
http://ssd.jpl.nasa.gov/horizons.cgi?find_body=1&body_group=mb&sstr=1
Ephemeris Type: OBSERVER
Target Body: Mercury
Observer Location: Geocentric [500]
Time Span: 1950-01-01 to 2160-01-01
QUANTITIES=10,13,20,23,29

1. Go to http://ssd.jpl.nasa.gov/horizons.cgi?find_body=1&body_group=mb&sstr=1
2. Click change on "Time Span", change to 1950-01-01 and 2160-01-01 and click "Use Specified Times".
3. Click change on "Table Settings", make sure only "10,13,20,23,29" are selected. (#20 "Obsrv range" is the important one.) Click "Use Selected Settings".
4. Click "Generate Ephemeris" to generate JPL RESULTS. (You will need to wait 2 minutes for it to generate)
5. Use "Ctrl-F" (text search) to find the values for " .5490".  This will reproduce 1969, 1982, 2015, 2061, and 2107.
6. Use "Ctrl-F" to find the value " .5489".  This will reproduce the result for 2153.
7. Use "Ctrl-F" to *try and find* the value " .5488".  Since it is not listed, 0.5489AU is the closest Mercury will come to the Earth between 1950 and 2160.

Also see the key from the top table for more information/details.

Kevin Heider (Wikipedia user kheider)
updated 2009-03-30