AstroCal – October 2025
We begin this month’s observations with a term that was unfamiliar to me. Maybe it has just slipped my mind as it only takes place every 18.6 years, but the event is known as ‘lunistice’ (also called a ‘lunar standstill’). Lunistice is kind of like a ‘solstice’ only it involves the Moon and not the Sun: “A lunar standstill occurs when the Moon reaches its furthest north or south point during a tropical month (a ‘tropical month’ is the period of time it takes the Moon to travel from one specific celestial longitude to the next – about 27.3 days),” according to our friends at Wikipedia. The October 6, 2025 Full Moon will be what is known as a ‘major lunar standstill’ and it has ‘observable effects’ that last at least 3 years. If one begins marking the spot on the horizon where the Moon rises in the ESE on Oct 3, each successive night will see it rise slightly further north until Oct 11 when it will rise in the NE*. It will also be the Harvest Moon.
A Harvest Moon is defined as, ‘the Full Moon closest to the Autumnal Equinox’. The split between the September and October Full Moons is nearly an equal split so this pushes the Harvest Moon into October this year. Combined with the lunar standstill, the October Harvest Moon will display the Harvest Moon Effect described in the paragraph above (meaning for several days the Full Moon will rise at roughly the same time each night and provide light for an extended period*). If you note that the rising Full Moon looks especially large, it is an optical illusion called ‘the Moon effect’. To prove it is in the eye of the beholder, hold out a piece of paper with a hole punched in it so the Moon fills the circle as it rises. In a few hours, repeat this after the Moon is higher in the sky – you will notice the Moon fills the hole with the paper held at the same distance from your eye. The October Harvest Moon is sometimes called a Blood Moon not so much in reference to the color one sees (like during a Lunar Eclipse), but because of the blood shed during the fall hunts.
Other dates in this month’s Lunar Cycle include the Last Quarter Moon on Oct 13 and the New Moon on Oct 21. The New Moon will be timed perfectly so there will be dark skies for the annual Orionid Meteor Shower peak in the predawn skis of Oct 21. The Orionids can typically show increased numbers for a few days before and after the peak date of Oct 21. Look for the Young Crescent Moon for the new Lunar cycle low in the western sky beginning on Oct 24. The Moon will be at Perigee on October 8 (223,581 miles from Earth) and Apogee on October 23 (252,552 miles from Earth). The month ends with the Moon’s First Quarter on Oct 29. If you are still waiting for that perfect convergence of a Full Moon taking place on Halloween night, do not hold your breath – it won’t align like this again for your spooky Halloween fun until 2039.
As for the evening planets, look for Mars very low in the WSW (binoculars may be helpful in the twilight hours just after sunset) shining at magnitude +1.6. Mars is 2.2 AU (Astronomical Units) or 222 million miles from the Earth and will reach conjunction with the Sun on January 9, 2026. Mercury will join the party at mid-month in the WSW shining slightly brighter than the Red Planet at mag -0.1. Mercury reaches its greatest elongation from the Sun on October 29.
Saturn rises in the ESE 22 minutes to an hour and 42 minutes after sunset from beginning to the end of the month. It is well positioned for viewing throughout the night but its rings will only be tilted 1 degree from edge on this month making them hard to see. At mag +7.8, Neptune will be difficult to see without a telescope, look for it 3 to 4 degrees NE of Saturn. Venus and Jupiter can be seen low in the eastern sky two hours before sunrise and higher in the sky near the twin stars of Castor and Pollux in Gemini – the Twins, respectively. Venus will be very close to the Old Crescent Moon on Oct 19.
Our historical note this month goes back to the 11th century and Arab mathematician and physicist Ibn al-Haytham. He is credited with the first written explanation of this thing we call ‘the Moon illusion’(the phenomenon that makes the Moon appear larger when it rises near the horizon and smaller when it is high overhead). al-Haytham proposed, “[that] our perception of an object’s size depends on its perceived distance. Because objects on the horizon appear farther away due to intervening terrain, our brain scales them to appear larger. The Moon high in the empty sky, lacking these reference points, appears closer and therefore smaller.” This effect would later be called the ‘size-distance invariance hypothesis’ (historical reference – Wikipedia – I do not usually promote any particular reference source, but I often use Wikipedia. By making an occasional donation, I am one of the 2 percent of Wiki users who donate to keep them in operation. If you Wiki, you should consider donating).
Compiled by Ken Raisanen of WOAS-FM 91.5 – information provided by Abrams Planetarium Sky Calendar, Michigan State University. More information and subscription information can be found on their website at http://abramsplanetarium.org/skycalendar/. Yearly subscriptions cost $12 and can be started anytime. Comments and questions can be emailed to kraisanen@oasd.k12.mi.us
Top Piece Video: Will Orion the Hunter be a suitable stand in for the Orionid Meteor showers? Why not?