October marks the withdrawal of the monsoon, thus making it one of the best months for skywatchers to witness some phenomenal celestial events, without the constant interference of clouds. The month also displays some unique, spectacular sky events from full moon to planets taking a sneak-peek of Earthlings. And the best thing is that almost all of these events are visible to the unaided eye.
For all the night sky lovers and stargazers out there, here are some dates to mark on your October calendar:
It’s the new Moon night! At about 4.35 pm exactly, the new moon occurs. Mars will be very close to Moon; however, thanks to the bright Sun—the visibility would dampen.
The planet’s natural satellite, Moon would be at the perigee position i.e., the closest approach to the Earth in this round. Today, it is positioned approximately at a distance of 3,63,386 km from the Earth.
Planet Mercury is likely to attend the position of greatest eastern elongation. From September 14, onwards it started approaching the Sun and tonight the planet will exactly be in between the Sun and the Earth. This position is known as the inferior conjunction. The planet will not be visible from Earth.
Venus will be seen just 3-degree south of the Moon and sky lovers can enjoy the crescent phase of the Moon along with bright Venus.
Saturn will come to an end to its retrograde movement on this night.
This is the first quarter night of the Moon. Two days after this will mark the ‘Vijayadashami’ or ‘Dussehara’ festival.
Planet Saturn is positioned at just 4-degree near the Moon. The next day, Jupiter can be seen at a very close distance to the Moon.
This month is great to watch Sagittarius and Scorpius. Tonight, individuals can see Venus just at 1-degree off Antares, the bright red star in Scorpius. If the sky is dark, sky lovers can easily see the famous scorpion in the sky.
Now is the time for Jupiter to stop its retrograde and get moving in direct motion.
Mercury is now coming out of the Sun’s glow and it can be seen in the morning sky just before the Sunrise. Tonight, it is closest to the Sun in this round just like a tiny bright spot. It is not easy to find it! Try this game in the morning sky. Moreover, tonight is the fourteenth day of Gibbous Moon and it is the day of the Id-e-Milad festival.
The full moon marks the Kojagiri Pournima, a tradition to stay awake late at night to bask in the pleasant Moonlight. It also marks the countdown to the Diwali festival which will be just a fortnight ahead.
The not so famous Orionid Meteor Shower marks the peak on this day. Sadly, not more than 20 meteors per hour can be spotted in the night sky.
The Moon will be at apogee or the farthest distance from the Earth tonight i.e., 405,615 km from us.
Mercury is at the greatest elongation in the morning sky. This means the planet is expected to rise well before the Sun and will be seen the maximum time before the day begins. So if you wish to spot it, get up early!
By this date, Venus attends the greatest eastern elongation in the setting sky. It also means it will set a maximum late after the sunset. It is expected to reach high up in the sky and can be seen until 9.30 pm.
Nicolai Copernicus used this property of Mercury and Venus to measure the distance of these planets from the Sun. Both these planets are closer to the Sun than Earth and are called Interior Planets. The angle between Sun-Earth-Venus (or Mercury) is called the angle of elongation. When the planet is in between Sun and Earth or exactly beyond the Sun, the angle is zero degrees. When the line joining Sun-Planet makes a right angle with Planet-Earth, then this Sun-Earth-Planet angle is maximum. See the following figure.
By calculating the sine function of the angle, it will give the distance of the planet from the Sun. The angle is called the angle of maximum elongation. For Venus, it is nearly 48 degrees and for Mercury, it is nearly 25 degrees. Hence, the distance of Venus will be sine (48) which is 0.72 astronomical units—one astronomical unit (au) is the average distance between Sun and Earth. Copernicus concluded that Mercury is at 0.39 times Sun-Earth distance while Venus is at 0.72 times Sun-Earth distance.
Modern measurements put these distances very close to the distances predicted by Copernicus. It is seen as the triumph of Copernicus’ theory that removed Earth from the centre of the universe and brought in the Sun at the centre.
Mercury: Mercury is not seen at the beginning of the month and it is at inferior conjunction on October 9. It will steadily climb high in the morning sky and is expected to attain maximum elongation on October 25.
Venus: Venus can be seen bright in the evening sky just after sunset throughout the month. On October 30, it attends maximum elongation and will be seen setting very late after the Sunset.
Mars: Mars is behind the Sun, therefore, the planet would not be on display this month.
Jupiter and Saturn: Both these giant planets will display a bright show all night in the sky. The retrograde ends for both this month and they will continue direct motion for next year or so.
This article was produced in collaboration with Khagol Mandal, a non-profit collective of astronomy enthusiasts who organise various sky observation programmes, lectures and study tours. Dr Abhay Deshpande is a Senior Scientist (Physicist) working for SAMEER, R&D Lab of MeitY, Government of India. He is also the Honorary Secretary of Khagol Mandal.
This article is a guest column reflecting the author’s opinions and do not necessarily represent the official views of The Weather Channel.
For weather, space science and COVID-19 updates on the go, download The Weather Channel App (on Android and iOS store). It’s free!