can someone please supply details of a planetary positioning involving the moon & another planet this month?

Answer 1

That big noisy flap about Mars being bigger and brighter than the moon is a LIE. Somebody's going around spreading this falsehood, probably through ignorance.

The close approach to Mars to Earth happened on 27 August 2003. Three years ago! If you missed it then, you'll have to wait for the next of Mars' closest passes.

Mars' orbit and Earth's orbit approach each other by a minimum distance of 0.372669 astronomical units. One astronomical unit is equal by definition to exactly 149,597,870,691 meters, which is about equal to 92,955,807 miles. So the orbits of Mars and Earth have a minimum separation of about 34,642,000 miles. In order for this minimum separation to be achieved, both Earth and Mars must be in exactly the right spot in their respective orbits, which is at 330.145 degrees heliocentric longitude for Earth and 330.337 degrees heliocentric longitude for Mars.

The technical way to refer to these passes of Earth by Mars is "Earth and Mars in conjunction with respect to the sun." Another way to say it is "Mars and the sun are in opposition with respect to Earth." It means the same thing, namely, Earth reaching the point in its orbital lap where it passes the slower Mars.

Mars and Earth have a conjunction about every 780 days (on the average). But typically the distance of closest approach is something like 54.8 million miles, which is what it will be on the NEXT conjunction on 18 December 2007. There will be no conjunction in 2006.

But the really close conjunctions occur at intervals of 15 or 17 years - usually. The special thing about the pass in 2003 was the fact that it was marginally closer than any other pass in recorded history. Not spectacularly closer. Only marginally so. It set a record that won't be broken until the year 2208 (and then not by much).

Here are the closest passes between Mars and Earth between 2003 and 2287.

27 August 2003, 0.3729 AU
30 July 2018, 0.3846 AU
9 September 2035, 0.3805 AU
13 August 2050, 0.3742 AU
17 July 2065, 0.3991 AU
23 September 2067, 0.3970 AU
28 August 2082, 0.3736 AU
31 July 2097, 0.3818 AU
12 September 2114, 0.3831 AU
15 August 2129, 0.3733 AU
19 July 2144, 0.3950 AU
25 September 2146, 0.4012 AU
29 August 2161, 0.3748 AU
2 August 2176, 0.3793 AU
13 September 2193, 0.3861 AU
18 August 2208, 0.3727 AU
22 July 2223, 0.3913 AU
1 September 2240, 0.3763 AU
6 August 2255, 0.3772 AU
15 September 2272, 0.3895 AU
20 August 2287, 0.3726 AU

Mars will be visible at other times, of course. But those are the days when it will be the brightest. But even when Mars is at one of these closest conjunctions, it is still much dimmer than the moon is.

Mars has an apparent magnitude at such times of -2.8. The moon's apparent magnitude, when full, is -12.6. The way the scale is set up, the more largely negative the number is, the brighter it is. Not only that, the scale is logarithmic, with a base equal to the fifth root of 100, or about 2.51186. So the full moon is 8318 times brighter than Mars ever gets.

Nor does Mars' size in our sky ever get anywhere close to the Moon's size. Mars' physical diameter is 6794 kilometers, so at it's nearest possible approach to Earth, it's angular diameter would be 25.14 arcseconds. The moon's angular diameter is about half a degree (it varies slightly), which is 1800 arcseconds. So Mars never gets bigger than about one seventy-first (1/71) of the moon's size.

Here are Mars' orbital elements.

Mars
a = 1.523688 AU
e = 0.093405
i = 1.8497 degrees
L = 49.5574 degrees
w = 286.5016 degrees
T = JD 2447385.9

And here are Earth's orbital elements.

Earth
a = 1.00000011 AU
e = 0.016761
i = defined zero
L = defined zero
w = 102.846 degrees
T = JD 2446799.26

There's a mathematical procedure to solve for the heliocentric positions of a planet for any time you choose, once you know the planet's orbital elements. You'll find that procedure given in great detail here:

http://www.jabpage.org/posts/trans2.html

After you've solved for the positions of Earth and Mars, each with respect to the sun, you can apply the distance formula (sometimes called the three-dimensional Pythagorean Theorem) to get the distance between Earth and Mars. If you program all that into a computer, you can just flip forward or backward in time until you locate the minimum distances and the associated calendar date.

The "T" number in the orbital element tables is the "time of perihelion passage," the moment when the planet is nearest to the sun. It is customarily given in Julian Date format, which is a rolling count of days since that day in 4004 BC, on which, Bishop Ussher's scholarly Bible research informed him, God created the world.

There are formulas that can convert Julian Date to Calendar Date, or vice versa. But it's probably easier to use somebody else's program, which you can find at

http://wwwmacho.mcmaster.ca/JAVA/JD.html
http://wwwmacho.mcmaster.ca/JAVA/CD.html

Don't believe everything you hear about celestial events. There's always some ignorant yahoo out to impress others with some sort of "special knowledge" that he supposedly has.

Answer 2

Hi. The freeware program "Stellarium" works really well. www.stellarium.org .