Speaking of Jupiter, our closest encounter this orbit will be at the end of January. Jupiter will be 4.33 A.U. distant, shine at -2.6 magnitude, and will have an angular size of 46". On the other hand, at the end of August it will be on the other side of the Sun (appearing to be very near the Sun) at 6.38 A.U. and very hard to pick out of the glare though still at -1.7 magnitude and 31" angular size.
Note that Jupiter's "year" is about 12 Earth years.
Earth's orbital motion is responsible for most of the change in distance to Jupiter.
Why is the the object with the bigger angular size (Jupiter) not as bright as the object with a smaller angular size (Mars) at close Earth encounter? Answer: Both are reflecting sunlight, but Jupiter is over 3 times as far from the Sun as is Mars. Thus it doesn't get as much light to reflect. So although Jupiter is twice as reflective as Mars, it only gets a tenth the sunlight Mars gets. So even though Jupiter appears bigger in angular size, it still doesn't QUITE shine as bright as Mars at its best does.
