This is the Skywatch Line for Monday and Tuesday, February 25th and 26th.
The Sun sets at 5:39 PM; night falls at 7:13. Dawn breaks at 5:02 AM and ends with the Sun rising at 6:36.
Mars remains the easiest planet to spot in the evening sky. The Red Planet, in Aries, is moderately high in the southwestern sky at Civil Dusk. In our telescopes, it appears about 91% illuminated, shines at first magnitude and is a small 5 arc-seconds. This past week marked the demise of the Mars Rover Opportunity; it was officially declared dead due to last year’s planet-wide dust storms. Curiosity, nuclear powered, is still very much in operation. Other Martian spacecraft are in various stages of planning or construction. Mars sets at 10:53 PM.
Uranus, 8º below Mars, shares Aries with the Red Planet. Uranus displays a blue-green dot, about 3 arc-seconds in size and shines with 5th magnitude. It sets at 10:08 PM.
Mercury, in Pisces, is moderately low in the western sky. It appears about 53% lit, shines with minus zero magnitude, and shows a 7 arc-second dot in our binoculars. This is an ideal time to observe Mercury, which is notoriously difficult to locate. Monday, Mercury is at perihelion, which means that it is closest to the Sun and brightest. Tuesday, it reaches greatest elongation, which means that it is highest in our sky for this year. These two factors make Mercury ideally situated for people to see this planet under the best possible conditions, weather permitting. However, it is still quite close to the western horizon and should be observed well before it sets at 7:13 PM.
Neptune, in Aquarius, may be difficult to spot, since it is about 2º above the horizon, glows with 8th magnitude, is a tiny 2 arc-seconds in size and sets at 6:21 PM.
Tuesday’s Last Quarter Moon rises in Scorpius at 12:52 AM. It appears about 50% lit and blazes with minus 9th magnitude; it is best observed at 5:56 AM. Wednesday, the 23-day-old Moon occupies Ophiuchus, appears about 40% lit and is slightly dimmer. It rises at 1:54 AM.
The Moon’s absence from evening and early night sky, present an opportunity for comet hunters. Comet 46P/Wirtanen still occupies Ursa Major (The Great Bear). Since it is receding from Earth, it becomes dimmer daily. It is currently near the star Theta and is about 8th magnitude. It is best observed around 11:10 PM. Comet C/2018Y1 (Iwamoto) is not that far away, in Auriga. It is reported to be at 6th magnitude and high in the southwest. The comet will be easy to find since it lies above the Messier objects M37, M38 and M39, all binocular visible. This is why Messier made his famous list. He was a comet hunter, and was constantly seeing objects that looked like comets but never moved. Compare Iwamoto and the three objects to see for yourself. Finder charts for these comets are available from various online astronomy sites.
Thursday is February 28th. When most months have 30 or 31 days, why does February have 28 or 29? The old Roman calendar was a lunar calendar of ten months containing 304 days. There was no standard system for inserting “leap months.” The result was chaos. While Julius Caesar was in Egypt, he met Sosigenes, a prominent mathematician, who suggested reforms to the Roman calendar.
Julius Caesar adopted those reforms that resulted in the current system of twelve months containing 365 days and leap years. Months contained 30 or 31 days. What is less well known is that he shifted a day from February to the newly named month of July (after himself). Augustus, his successor, also borrowed a day from February, so that August (his month) would be equally as long as July’s.