Sunday July 1st the 17-day old waning gibbous Moon will be within about 4o from Mars as the two rise in the east around midnight local time. Rising ahead of the Moon and Mars and further west are two of the four ringed planets, Saturn and Jupiter.
Our Moon reaches apogee, (greatest distance from Earth), on Friday June 29nd. At that time the Moon will more or less be at a distance of 31.83 Earth diameters (406,100 km or 252,338 miles) from the Earth.
Does our Moon actually go around the Earth as this graphic shows? From our perspective on the Earth the Moon appears to circle around the Earth. However, in reality, the Moon orbits the Sun together with the Earth*
Read this very informative article about the Earth-Moon system and their orbital motions, written by Joe Hanson. “Do We Orbit the Moon?”
Thursday June 28th the ‘Red Planet’ Mars begins its retrograde motion. 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. 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.
Mars ends its retrograde motion and resumes its regular direct or eastward motion on August 28th as it moves across the constellation of Capricornus the Sea Goat.
An Inner Planet Orbit
We typically think of retrograde motion as being done by an outer planet from the Earth. 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.
Coordinate Positions for Mars
Date Right Ascension h m June 25 20 51 July 5 20 50 July 15 20 45 July 25 20 35 August 4 20 23 August 14 20 14 August 24 20 08 September 3 20 09
Wednesday June 27th the outer planet Saturn reaches its orbital position known as opposition. This is a position which has the faster moving Earth passing Saturn and at opposition is centered between the outer planet and the Sun. Picture the arrangement with the Moon at full phase; Sun – Earth – Moon, and that is similar to the arrangement for Saturn at opposition.
When an outer planet, like Saturn, reaches opposition that planet rises around local time for sunset and is visible all night. Coincidentally the full Moon will rise with Saturn and be within about 1-2o from Saturn and should make for an interesting view with binoculars or picture.
For the next week or so the evening skies will be filled with planets and dwarf planets. With the right timing and a relatively flat horizon you might be able to see Venus just before it sets and Mars just after it rises. A caveat to this is that as each day passes Mars will rise earlier while Venus, each day, will be setting earlier. And with the exception of Ceres the dwarf planets are too dim to be seen with the naked eye.
As this graphic shows, the planets are closer to the ecliptic than the dwarf planets due to differences in the respective inclinations. Inclination: Every object orbiting the Sun has an orbital path that is tilted or inclined from the Earth’s orbit – the ecliptic.
The waxing gibbous Moon is roughly mid-way between the red star Antares in Scorpius the Scorpion and the planet Saturn.
Monday evening June 25th the planet Mercury will be about 5o from Pollux, one of the Gemini Twins stars. They will be low over the western horizon following sunset but with a clear horizon should be visible.
Also, after a couple of hours later turn toward the southeast to see the 12-day old waxing gibbous Moon rising within about 8-9o from the reddish star Antares in Scorpius the Scorpion. Further east is one of the ringed planets, Saturn, and the ‘Red Planet’ Mars.
Saturday June 23rd the 10-day old waxing gibbous Moon will come within about 4-5o from the giant ringed planet Jupiter. About 1-2o from Jupiter is the 3rd magnitude star Zubenelgenubi, one of the stars of Libra the Scales.
Asteroid 4 Vesta, the 2nd largest and brightest asteroid reached opposition this month (June 19th) and for a brief time following opposition, through July, the asteroid will be close to Earth and more visible. This graphic shows the view at about 10 pm CDT on June 21st. Vesta will essentially stay in this general area but over time will slowly move westward as the distance between Vesta and Earth increases. Keep in mind that over the next week or so the Moon will move past this part of the sky as it waxes through full phase. As the Moon gets closer to Vesta it will become increasingly difficult to see the much dimmer Vesta. The Moon light should no longer be an issue after the Moon has moved toward the east enough.
Vesta has an average diameter of 329 miles (530 km) and orbits the Sun in approximately 3.6 years in an elliptically shaped orbit that takes it to an aphelion distance of 2.57 AU (238,896,425 miles – 384,466,528 km) and a perihelion distance on 2.15 AU (199,854,986 miles – 321,635,422 km).
During the next month or so Vesta will be bright enough to be seen with binoculars and certainly with a telescope. It’s current apparent magnitude is 5.3 meaning it could be seen with the naked eye – under dark enough skies. Even if you cannot see the asteroid there are certainly other deep sky objects in the area near Vesta including one of the four the ringed planets, Saturn.
Over the next several days (evenings) both inner planets, Mercury and Venus, are moving along their respective orbits approaching each planet’s eastern elongation. From the animated graphic you can see that the stars in the background, like the two ‘Twin Stars’ Pollux and Castor, are also moving but toward the western horizon. This is a regular motion of the stars caused by the Earth’s own orbit, revolution, around the Sun. As the Earth revolves the stars appear to move westward – a real motion not to be confused with the apparent motion of stars toward the west as the Earth rotates.
On the evening of June 25th Mercury will pass within about 5-6o from the star Pollux.
On the evening of June 21st the the 8-day old waxing gibbous Moon will be within about 8o from the blue-white star Spica in Virgo the Harvest Maiden. In two days the Moon will have moved further east and be close to the planet Jupiter.