February’s long, dry nights are usually favourable for sky viewing, if you know how to protect yourself from the cold. This month, you’ll have the chance to observe two planets in the evening and two others in the morning... with the added bonus of a 29th night in this leap year.
Saturn bows out
February kicks off with one last opportunity to observe the ringed planet Saturn before it becomes undetectable in the final rays of sunlight as of the middle third of the month. Watch for it 30 to 45 minutes after sunset when it appears as a rather modest dot of light above the west-southwestern horizon. Fortunately, Saturn reigns supreme in the constellation Aquarius, where no other bright objects compete for attention. If conditions are right, see if you can spot it in conjunction with a very thin lunar crescent hanging 3½ degrees just below it on February 10 at twilight. Be forewarned that it will be a difficult view, 30 minutes after sunset above a perfectly clear west-southwestern horizon.
Jupiter, a beacon in the night
Jupiter will be much easier to observe throughout the month, given that it’s the most luminous object in the evening sky (except for the Moon, of course). At the start of the month, the giant planet appears more than 50 degrees high in the south at twilight and doesn’t set until midnight. Note how it sinks lower and lower in the west from one evening to the next, but it can still be seen more than 40 degrees above the horizon by late February, setting at around 11 p.m. On February 14 at sunset, the waxing Moon lies 5 degrees to the right of Jupiter; the Moon will continue on its orbit throughout the evening, narrowing the gap to less than 3½ degrees as the two celestial bodies set.
Venus passes the reins to Mars
Early bird observers will have become accustomed to seeing brilliant Venus shine majestically above the southeastern horizon for several weeks now. This month, however, Venus is heading towards superior conjunction, effectively closing its gap with the Sun: It appears lower above the horizon and increasingly struggles to escape the glow of dawn. Mars, on the other hand, pulls away from our daytime star, marking the start of the long period leading up to its January 2025 opposition. Mars rises ever higher each morning, making it easier for us to recognize its characteristic orange hue by month’s end. You’ll have two opportunities to spot the planet: The first is on February 7 at dawn, when the very thin waning Moon lies 7½ degrees to the lower right of Venus, with Mars hanging 7 degrees to the lower left and completing the triangle formed by the three celestial bodies. The second opportunity is on the mornings of February 21, 22 and 23, when Venus and Mars are in conjunction, separated by less than 1 degree. In both cases, make sure you have a perfectly clear view of the southeastern horizon and look for them 30 minutes before sunrise.
Occultation of Beta Virginis
On the morning of February 26, the Moon, just past full, will eclipse the dim naked eye star Beta Virginis (mag. +3.6), a phenomenon known as an occultation. Although the event unfolds at a reasonable height in the sky, approximately 30 degrees above the southwestern horizon, a small telescope will be needed to cut through the Moon’s much brighter glow. As seen from Montreal, Beta Virginis disappears at 4:28:11 a.m. (EST) behind the Moon’s illuminated edge; less than one hour later, at 5:22:37 a.m., the star reappears at our satellite’s dark limb.
An extra day in 2024
This is a leap year, so February will have a 29th day. In school we learn that Earth completes one revolution around the Sun not in 365 days, but in 365 and ¼ days. This adjustment to compensate for the extra quarter of a day each year that it takes Earth to complete its orbit has been understood since ancient Roman times, when Emperor Julius Caesar decreed that a 366th day should be added to the calendar every 4 years...
... well, almost every 4 years. It’s important to understand that the 365.25-day year is just a rough approximation. We also want the calendar to stay in sync with the seasons, to make sure summer doesn’t end up running from December to March! To achieve this, the calendar needs to line up with the so-called tropical year, which is exactly 365.242189 days long.
Strict adherence to the Julian reform, which systematically adds one day every 4 years, would quickly create a misalignment of the calendar with the seasons: 1 full day every 128 years, or 15 days in 2,000 years. There are simply too many “February 29ths” in the Julian calendar! Our Gregorian calendar was adopted in 1582 to correct this surplus by removing some of those extra February 29ths according to fairly simple rules.
In the Gregorian calendar system, like the Julian calendar before it, a leap year occurs every 4 years, except for years that end in “00” and are not multiples of 400 (1700, 1800, 1900, 2100, etc.). This is enough to re-establish an almost-perfect correspondence between the Gregorian year and the tropical year: A shift of only one day occurs after 3,200 years. We could further improve very long-term correspondence by eliminating February 29 in years that are multiples of 4,000 (the year 4000, 8000, 12000, etc.).
Some of you are sure to experience the next “exception to the 4-year rule” in just 76 years’ time, in the year 2100.
Clear skies!
