Friday evening June 15th the 3.75-day young waxing crescent Moon will be to the left from the ‘Twin’ stars of Pollux and Castor. A little further east or higher above the Moon is the ‘hard-to-miss’ planet Venus.
Our Moon reaches perigee, (closest distance from Earth), for this orbit on Thursday June 14th. At that time the Moon will be at a distance of 28.18 Earth diameters (359,500 km or 223,383 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*
Thursday evening May 14th, shortly after sunset local time (8:26 CDT), look toward the western horizon for a conjunction between a thin 1.25-day young waxing crescent Moon and the innermost planet Mercury. The two will be about 2-3o apart but very low over the western horizon.
Read this very informative article about the Earth-Moon system and their orbital motions, written by Joe Hanson. “Do We Orbit the Moon?”
Thursday evening June 14th the thin 1.25-day young waxing crescent Moon will be about 2-3o from the innermost planet Mercury as the two are setting about an hour after sunset local time.
As the graphic shows both will be low over the horizon before the sky is dark so this may be an interesting challenge to see either one or both. On the other hand further east, higher above the horizon, and very bright appearing is the other inner planet, Venus.
Saturday June 9th two of the outer planets, Mars and Saturn, will be at the same heliocentric longitude of about 278o, and would be in what is called a heliocentric conjunction. Heliocentric (Sun-centered) coordinates uses an overhead view of the solar system with planet location given as degrees of heliocentric longitude. The heliocentric longitude is based on a view from the Sun and is given as the angle between a planet and the vernal equinox. The vernal equinox, 0o, is located within the constellation of Pisces the Fishes, and is the intersection between the ecliptic and the celestial equator.
As the Earth revolves around the Sun it ‘gives’ the Sun its apparent motion eastward along the ecliptic. When the Sun crosses the celestial equator at this intersection it is moving north. At the crossing northern hemisphere winter becomes spring – the opposite seasonal change for the southern hemisphere.
Despite having the same heliocentric longitude, when viewed from the surface of the Earth, the two show an east to west difference of about 2 hours of right ascension.
Over the next few evenings, June 7th to 10th, the inner planet Venus will pass the star Pollux, marking the head of one of the Gemini Twins. Pollux is on the left side as we view the ‘Twins’ face-on. This animated graphic is set for 10 pm CDT and shows the daily movement of Venus toward the east, combined with the daily motion of the stars toward the west as the Earth revolves around the Sun.
The separation between Venus and Pollux will vary from about 4.5o to about 5.5o allowing at least these two to fit within a binocular field of view.
Yesterday I posted about the planet Mercury being at inferior conjunction. My mistake!! Mercury is actually 180o away from inferior conjunction on the opposite side of the Sun at superior conjunction.
I’ve edited the posting to show the correct position of Mercury.
Tuesday June 5th the innermost planet Mercury reaches superior conjunction. At superior conjunction Mercury will be on the opposite side of the Sun. The graphic to the right shows the planet positions relative to the Earth and Sun for both inner planets and outer planets.
While at this superior conjunction Mercury will not be directly in line with the Earth and the Sun – on the ecliptic. Mercury has an orbital inclination of 7o with respect to the ecliptic. So like our Moon, Mercury during each complete orbit, will cross the plane of the ecliptic moving north (ascending node) and also moving south (descending node). For this superior conjunction Mercury will be a few degrees north of the ecliptic having crossed the ecliptic on June 1st with its ascending node..