Everything you need to know about celestial conjunctions
We will skip any discussion of grammar and, instead, discuss celestial conjunctions this week.
A celestial conjunction is when two objects in the solar system — such as two planets, or the moon and a planet — or one object in the solar system and a more distant object (for example, a planet and a star) have the same right ascension (the angular distance of a particular point measured eastward along the celestial equator from the sun at the March equinox to the reference point) or the same ecliptic longitude (a positive measurement, from zero to 360 degrees, eastward along the ecliptic plane).
As mentioned in last week's column, the planet Mercury will reach inferior solar conjunction on Oct. 25. This means Mercury will pass close to the sun, and between Earth and the sun (as viewed from Earth) on that date.
If Mercury were to pass directly across the disk of the sun (as seen from Earth), it would be referred to as a transit. Mercury and Venus are the only two planets in our solar system that can have inferior solar conjunctions and transits, as they are the only two planets with orbits between Earth and the sun.
A superior conjunction occurs when a celestial object
(such as a planet), whose orbit lies outside another object's orbit, passes behind a much larger object (such as the sun) as viewed from the observer's point of reference (Earth).
The superior planets in our solar system are Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto (with reference to Earth), and are all capable of having a superior solar conjunction. Earth would be considered a superior planet if you were standing on Mercury or Venus.
THIS WEEK'S SKY
Once Mercury reaches inferior solar conjunction on Oct. 25, it will transition from an evening object to a morning object (around Oct. 29).
Venus (magnitude -4.04) is still a pre-dawn object, rising around 4:20 a.m., and reaching an altitude of 29 degrees above the eastern horizon before fading from view as dawn breaks around 7:20 a.m.
Mars (magnitude -2.5), having passed opposition on Oct. 13, is visible seven degrees above the eastern horizon by about 7 p.m., reaching its highest altitude of 48 degrees above the southern horizon around 12:35 a.m., before disappearing in the western, pre-dawn sky around 6:10 a.m., when it drops below eight degrees above the horizon.
Jupiter (magnitude -2.3) and Saturn (magnitude +0.55) remain early evening objects, with Jupiter visible at 21 degrees above the southern horizon around 6:40 p.m., followed by Saturn at 22 degrees above the southern horizon around 6:55 p.m. Neither planet manages to get any higher in the sky before they both disappear from view in the southwest sky by 10 p.m. and 10:10 p.m., respectively.
Watch for the near half-full moon, Jupiter and Saturn to form a triangle in the southern sky on the evening of Oct. 22, with Jupiter to the right of the moon, and Saturn above. It will make a great photo op.
The Orion meteor shower (radiant in the constellation of Orion — the Hunter) peaks during the midnight to dawn hours of Oct. 21. Expect about 20-plus meteors per hour during the peak, under a dark sky away from city lights once your eyes have darkadapted (30-45 minutes).
Until next week, clear skies.
EVENTS
• Oct. 21 — Orion meteor shower peak (midnightdawn)
• Oct. 22 — Moon-JupiterSaturn triangle in southern evening sky
• Oct. 23 — First quarter moon