Sunday May 22nd Mars will reach a point in its orbit around the Sun where it is at opposition relative to the Earth. at opposition The Earth is between the Sun and Mars, or any of the outer planets. At opposition both the Earth and the planet at opposition will have near identical heliocentric longitude. The opposition of Mars sometimes happens around the time that Mars is at its respective perihelion, closest to the Sun. If this happens during or near July when the Earth is at its respective aphelion, furthest from the Sun, then Mars will appear larger relative to when these dates are further apart. However Mars will never be as large as the full Moon, as explained in previous posts: “Mars Closest to Earth this Time”, or “Mars Madness” to read this one.
The ‘Red Planet’ Mars has been in retrograde Motion since this past April, and will continue to retrograde until the end of June.
Retrograde motion is the apparent backward, or westward motion that a planet will appear to make at a regular point in its revolution around the Sun.
We typically think of retrograde motion as being done by an outer planet from the Earth. This happens when the faster orbiting Earth catches up and passes by an outer planet. As this is happening the outer planet appears to slow down and then reverse its orbital direction toward the west. After a period of time (days to months) the outer planet again appears to slow down and then return to its regular eastward, or direct motion.
However the two inner planets Mercury and Venus also undergo retrograde motion. Approximately one-half of their respective orbits is eastward as is with all the other planets. This then brings the inner planets to what is know as eastern elongation in the evening skies. The other half of the orbit for Mercury and Venus is toward the west as they move from eastern elongation through inferior conjunction toward western elongation in the morning skies.
Click here to go to the Qué tal in the Current Skies web site for more observing information for this month.