Last month it seemed that Jupiter and Saturn were the stars of the sky, if you will, but this month is being dominated by Mars. There are a few conjunctions this month and even one occultation! Read below for everything happening this month.
October 1: International Observe the Moon Night
Starting off the month is a full moon! Since this full moon is the closest to the autumnal equinox in 2020, it is known as the Harvest Moon. Its name is unlike the other monthly full moon names, as the Harvest Moon can sometimes fall in September, replacing the Corn Moon, or in October, replacing the Hunter’s Moon. It is called the Harvest Moon because it rises soon after sunset, providing an abundance of light in the early evening for farmers to continue harvesting their summer crops.
The first full moon in October is also usually International Observe the Moon Night. Some local libraries or astronomy organizations will host events for people to come and look at the Moon in their telescopes and learn about the Moon. If you missed it this year, don’t worry! You can observe the Moon any night!
October 2: Aphrodite and a King, Luna at War
Venus, named after the Roman goddess of beauty, who’s Greek version is Aphrodite, will continue to be an early morning planet this month. On Friday, October 2 it will rise at about 3:45 AM local time, positioned less than a finger-width from the bright star Regulus, the brightest star in Leo. Regulus is not actually a single star, but four stars arranged into two pairs. The bright star labeled Regulus in the image above is a spectroscopic binary: the pair can only be separated by looking at their spectrum. They take only 40 days to orbit their common center of mass. If you don’t want to wake up early to see this pairing, they’ll still be close together at midnight on October 3.
If you missed the Venus and Regulus pairing in the morning, then all night the Moon and Mars will appear close together in Pisces. Both will be close enough to be viewed through a pair of binoculars all night long. This close pairing is called a conjunction, but for observers in southern and southeastern South America, western Antarctica, the Ascension Islands, and southwestern Africa they will witness an occultation of Mars by the Moon. An occultation is when one object appears to pass in front of another. Don’t worry if you’re in the northern hemisphere; another occultation will come later this month.
October 5-6: Mars at Closest Approach
Mars will reach its closest approach to Earth in the early hours of October 6. At that point, Mars will be 38.57 million miles or 0.515 astronomical units from Earth. Observers with backyard telescopes can expect to see the surface of Mars with more detail than it will exhibit for 15 years!
In the image above, several geographical features can be seen. The bright circular region in the southern hemisphere is Hellas Planitia, the “Greek plains.” It measures 2,300 km (1,400 mi) across and over 9,000 m (30,000 ft) deep. Hellas Planitia was thought to have formed when a large asteroid hit Mars about 4 billion years ago. The two dark spots near the right terminator are Syrtis Major Planum (top) and Tyrrhena Terra (bottom), named for the Gulf of Sidra off of Libya and Tyrrhenian Sea off of Italy. Both are dark because there is very little red dust here, so what you’re looking at is dark volcanic rock.
October 9: The Last Quarter Moon
The Moon will reach its last quarter phase at 8:39 PM Eastern, but won’t rise until almost midnight on October 9. Here, the Moon is illuminated on its western side, towards the pre-dawn Sun. The Moon will begin waning, becoming a thin sliver over the coming nights. These nights will be perfect for observing deep sky objects.
October 11: The Moon Visits the Beehive
Early in the pre-dawn sky, just like last month, the Moon will visit the Beehive Cluster (M44). Although it will be nearly four degrees above the cluster, both objects should still be visible in a pair of binoculars. To see the bees of the hive more easily, hide the Moon just below your binocular’s or telescope’s field of view. I’ll refer you to the September 14 entry for more info on the Beehive.
October 13: Mars at Opposition
Mars will officially reach opposition on Tuesday evening, October 13. It will rise at sunset among the stars of Pisces and set at sunrise, characteristic of opposition. Opposition here does not refer to a political party, but rather Mars’ placement in the sky with respect to the Sun. On October 13, Mars will be exactly opposite in the sky to the Sun. Although it will be slightly further away than it was a week earlier, Mars will still be an impressive sight in the night sky.
Apparent in the image above, but hard to see in a telescope, are Mars’ two moons, Phobos and Deimos. Named after the gods of fear and terror, respectively, both are tiny compared to Earth’s moon. They are likely captured asteroids. Three spacecraft have been sent to Phobos, all by the Russians, and all have failed either while still in Earth orbit or before they reached Mars.
October 14: The Moon and Venus
Early in the morning before sunrise on October 14, the Moon and Venus will appear close together in the sky. The Moon will be old, only a thin sliver of a crescent at this point while Venus shines brightly. The pair will make a lovely photo opportunity if you can pair them with some foreground scenery on Earth.
October 16: The New Moon
At this point in its orbit, at 2:31 PM Eastern, the Moon is between the Sun and Earth. Since sunlight can only reach the far side of the Moon, Earth-bound observers will not be able to see the Moon; the near side will be in darkness. This particular new moon occurs only 4.5 hours after its closest approach, triggering high tides around the world.
October 17: Double Transit on Jupiter with the Great Red Spot
Every now and then, the Great Red Spot and shadows caused by eclipses from its moons appear at the same time on Jupiter. Telescopic observers in the Eastern time zone will be treated to a double eclipse caused by two Galilean moons, Io and Callisto, at the same time as the Great Red Spot is visible! In the above image, Callisto (not pictured) is causing the diffuse shadow furthest up the disk of Jupiter while Io is causing the crisper shadow below that. The entire event will begin at 5:25 PM Eastern and end two hours later at 7:25 PM.
October 21: The Orionid Meteor Shower and the Moon near Jupiter and Saturn
The Orionids are an annual meteor shower that happens between October 2 and November 7, but peaks around October 21. Meteor showers are produced when the Earth passes through the debris trail left behind by long-gone comets. In this case, this debris trail is left by Comet Halley. The meteors will appear anywhere in the sky, but will seem to be traveling away from the constellation of Orion, thus the name. Typical rates for this shower are 10-20 meteors per hour, but rates have been as high as 70 meteors per hour in 2007.
Just like last month, the Moon will complete another visit with the gas giants Jupiter and Saturn in the southwestern skies. The three objects will form a nice triangle: Jupiter to the upper right and Saturn to the upper left. This is another excellent chance for some astrophotography, especially paired with foreground scenery here on Earth.
October 23: Ceres Pauses and the First Quarter Moon
On Friday, October 23, the dwarf planet Ceres will complete a retrograde loop that began in July, causing it to temporarily pause its motion as seen with respect to the background stars. Ceres is a dwarf planet located in the Asteroid Belt between Mars and Jupiter. It is the largest object in the Asteroid Belt and also the only dwarf planet further in than Neptune. Despite all that, it is still about 3.7 times smaller than Earth’s moon. In 2015, NASA’s Dawn spacecraft entered into orbit around Ceres and later it detected evidence of a subsurface saltwater brine! Every now and then that brine escapes to the surface and freezes, creating bright reflective spots in some of Ceres’ craters.
The Moon will enter its first quarter phase at 9:23 AM Eastern, although it won’t rise in the sky until about noon. As always, the appearance of the Moon is caused by its relative position in its orbit to the Earth and the Sun. Here, Earth-bound observers are looking at the Moon side-on, with its eastern side illuminated. For those observers with an interest in the lunar geography, during the first quarter is the best time to see lunar features dramatically lit by low-angle sunlight.
October 29: The Moon near Mars Again!
As if the Moon didn’t have enough of Mars earlier in the month, once again you can spot the two close together in the sky. They will be a bit further apart, this time the Moon is a few finger-widths below Mars, but still close enough to appear together in binoculars.
October 31: Occultations, Full Moons, and Uranus
Overnight on Friday, October 30 and in the early morning of October 31, those observers with binoculars or a telescope will finally be treated to an occultation! The Moon will occult (or pass in front of) the star ξ1 Ceti, pronounced “ksi one see-tye.” The star system is a binary, one yellow giant star and one blue main sequence star orbiting their common center of mass. The system is a spectroscopic binary, the two stars unresolvable optically as they orbit each other closer than Jupiter orbits the Sun. The times for ingress and egress of the occultation vary based on your latitude, so I would suggest using a program like Stellarium or another planetarium app to look up the exact times for your town.
October 2020 is lucky enough to have a second full moon at the end of the month. The second full moon is commonly called a Blue Moon, and the full moon in October is also called the Hunter’s Moon, so this would make this particular moon the Blue Hunter’s Moon! It was likely named the Hunter’s Moon because it signaled the time to go hunting in preparation for winter. With the field’s harvest reaped under the Harvest Moon, hunters could easily see the deer and other animals that had come out of the forests.
What’s even more amazing is that this Blue Hunter’s Moon falls on Halloween! This is not at all a common occurrence and only happens every 18-19 years. Enjoy a night full of frights!
At the same time of the Blue Hunter’s Moon, Uranus will reach opposition. At that point, Uranus will be closest to the Earth for this year at a distance of 1.75 billion miles or 18.83 astronomical units. Observed through telescopes, it will appear slightly larger and a little bit brighter for a few weeks.
All Month Long: Deep Sky Objects
For those of you who want to view some spectacular deep sky objects, here are four that are visible all month. The Andromeda and Triangulum Galaxies are the two other spiral galaxies in our Local Group, with Andromeda being the nearest and most massive. The Double Cluster are two interacting open clusters within the Milky Way. To view all of those objects, you’ll need at least some binoculars to see them.
The Sculptor Galaxy is a spiral galaxy much further away than Andromeda or Triangulum. However, it is still one of the brighter galaxies in the night sky and relatively easy for amateur astronomers with a small telescope to see.
I highly suggest you check the website In-The-Sky to see when these objects will be best visible for you.