The Sky This Week, 2020 September 15 – 22 — Naval Oceanography Portal
The astronomical season of autumn begins on the 22nd at 9:31 am EDT. This is the moment when the Sun’s disc reaches an ecliptic longitude of 180 degrees and crosses from the northern hemisphere of the sky into the southern hemisphere. While the term “equinox” means “equal night”, a glance at a sunrise/sunset table reveals that the difference between sunrise and sunset on this date isn’t exactly 12 hours as one might expect. Since the Sun subtends a tangible disc and we measure sunrise and sunset by the first and last appearances of the solar limbs, the duration of daylight is 12 hours and 8 minutes on the 22nd here in Washington. The actual date when day and night are equal falls on the 26th. From then until March 16th next year our nights will be longer than our days.
[“Hello, darkness, my old friend.”]
The Sky This Week, 2020 June 23 – 30 — Naval Oceanography Portal
The year’s latest sunset occurs on the 27th for folks living in northern temperate latitudes. Here in Washington Old Sol slips below the horizon at 8:38 pm EDT that evening. Most of us probably won’t notice the Sun’s gradual return to earlier set times for a couple of weeks; he won’t set before 8:30 pm until July 20th. On the other end of the day, though, sunrise is now four minutes later than it was on June 13th, so the days are indeed beginning to gradually get shorter.
The Sky This Week, 2020 June 16 – 23 — Naval Oceanography Portal
Astronomical summer officially arrives on the 20th at 5:44 pm EDT. This is the moment when Old Sol reaches an ecliptic longitude of 90 degrees, and it also happens to be the time when he reaches his highest northern declination, with the center of his disc perched over the Tropic of Cancer. This is the longest day for residents of the Northern Hemisphere, but the length of day varies widely with latitude. Here in Washington we will have 14 hours 54 minutes between sunrise and sunset. Residents of Hawai’i will only see 13 hours 20 minutes of daylight, while residents of Fairbanks will have 21 hours and 50 minutes to enjoy the Sun along with twilight to fill the remaining hours.
The Sky This Week, 2020 May 5 – 12 — Naval Oceanography Portal
Full Moon occurs on the 7th at 6:45 am Eastern Daylight Time. May’s Full Moon is popularly known as the Grass Moon, Flower Moon, Milk Moon, Corn Planting Moon, or (in honor of an important day) Mother’s Moon.
The Sky This Week, 2020 March 17 – 24 — Naval Oceanography Portal
The vernal equinox occurs on the 19th at 11:50 pm EDT. This moment marks the instant when the ecliptic longitude of the Sun reaches zero degrees and begins another circuit around the sky. This is the earliest occurrence of the equinox since the year 1896, and we will continue to see equinoxes on the 19th (in EDT) every four years through the year 2096.
[T]he actual day of “equilux” occurred on March 16th. From now until the next “equilux” day on September 25th we will have more daylight than darkness.
The Sky This Week, 2020 January 7-14 — Naval Oceanography Portal
Full Moon occurs on the 10th at 2:21 pm Eastern Standard Time. January’s Full Moon is popularly known as the Wolf Moon …
The Sky This Week, 2019 December 3 – 10 — Naval Oceanography Portal
This week we begin to see the phenomena associated with the winter solstice. The solstice “season” begins with the year’s earliest sunsets, which occur all of this week. Here in Washington the Sun disappears below the horizon at 4:46 pm EST. He will gradually start to set later starting on December 13th. Although this gives the illusion of the days getting longer, we won’t see our latest sunrise until early January. In between the solstice occurs on the 21st, which will be the year’s shortest day. This seemingly odd behavior is due to the way we now keep time.
December’s Full Moon is variously known as the Long Night Moon, Old Moon, or the Moon Before Yule. Since this Full Moon occurs closest to the winter solstice is will be the most northerly one of the year, beaming down on the frosty landscape below.
The Moon brightens the evening sky this week, waxing toward the Full phase as she courses through the late autumn and early winter constellations. Full Moon occurs on the 13th at 7:06 pm Eastern Standard Time. December’s Full Moon is known as the Moon Before Yule in the skylore of European Christianity. Other names, such as the Cold Moon, Big Moon, and Long Night Moon, reflect the influence of Celtic and Native American lore. December’s Full Moon occurs near Luna’s most northerly declination for the year, flooding the winter landscape with her pale light. This year she appears a bit brighter than usual thanks to the Full phase occurring near the Moon’s close perigee, which falls on the 12th. On the evening of the 12th you’ll find the nearly-full Moon pass through the heart of the Hyades star cluster which forms the “face” of Tauris, the Bull. Watch Luna creep closer to the bright star Aldebaran as the evening passes. At 11:07 pm EST the star will wink out as the Moon’s limb covers it. You can see it re-appear at 12:21 am.
The Full Moon washes out the annual Geminid meteor shower, which peaks on the night of the 13th. This is normally one of the year’s most reliable showers, and under dark skies it usually produces one or two “shooting stars” per minute. The meteors are generally slower than the August Perseids, and the radiant, in the constellation of Gemini, is well-placed after around 10:00 pm. Bright moonlight will hamper the number of meteors that the average observer will see this year, but a patient observer may be able to spot 20 or so per hour, even from urban locations.
2016 Ends with Three Supermoons
Since the moon’s orbit is elliptical, one side (perigee) is about 30,000 miles closer to Earth than the other (apogee). The word syzygy, in addition to being useful in word games, is the scientific name for when the Earth, sun, and moon line up as the moon orbits Earth. When perigee-syzygy of the Earth-moon-sun system occurs and the moon is on the opposite side of the Earth from the sun, we get a perigee moon or more commonly, a supermoon!
This coincidence happens three times in 2016. On October 16 and December 14, the moon becomes full on the same day as perigee. On November 14, it becomes full within about two hours of perigee—arguably making it an extra-super moon.
The full moon of November 14 is not only the closest full moon of 2016 but also the closest full moon to date in the 21st century. The full moon won’t come this close to Earth again until November 25, 2034.
Full Moon occurs on the 16th at 12:23 am Eastern Daylight Time. October’s Full Moon is popularly known as the Hunter’s Moon. The geometry of the Moon’s path in the sky is similar to last month’s Harvest Moon, so the interval between successive moonrises around the time of Full Moon causes Luna to appear to rise at nearly the same time for a few nights. In September this phenomena was used by farmers to use the light of the rising Moon to help them bring in more crops. This month hunters have a bit of extra light to pursue game across the stubble of the harvested fields.
The Sky This Week, 2016 August 9 – 30
Full Moon occurs on the 18th at 5:27 am Eastern Daylight Time…. August’s Full Moon is popularly known as the Corn Moon, Grain Moon, or Sturgeon Moon, indicating the time of year when crops mature for the harvest and fish return to their spawning grounds.
Full Moon occurs on the 19th at 6:57 pm Eastern Daylight Time. July’s Full Moon is popularly known as the Hay Moon, Buck Moon, or Thunder Moon, with the latter being particularly appropriate for this time of the year.
from The Sky This Week
Great stuff, as usual, from The Sky This Week.
This is a good week to try to make sense of the sheer scale of the cosmos as we have a variety of bright objects that we can look at and think of in terms of distance as well as brightness. The first thing we need to do is find a convenient “measuring stick”, and fortunately the laws of physics provide us one that’s good for measuring vast distances. Light, the essential “messenger” of all celestial objects, travels at a finite speed that amounts to about 300,000 kilometers (186,000 miles) per second, so if we can measure the time it takes light to reach us from an object we can gauge its distance.
When we look at the Moon, we see it as it appeared a just over a second ago. Light from the Sun takes eight minutes to get from there to here. The ruddy glow of Mars is five minutes old by the time it arrives here at earth. Giant Jupiter’s bright glow has taken 50 minutes to cross the gulf of space that separates us. … Our last bright planet is Saturn, and the view you’ll get of his wonderful rings tonight will take 77 minutes to get here. Far-flung Pluto, which marked the edge of the solar system when I was in school, is still relatively close-by, just under 4.5 hours at light speed.
Now let’s jump to the rising stars of the summer Triangle in the eastern part of the sky. Bright Vega, highest and brightest star of the trio, is located at a distance that takes light 27 years to cross! Altair, southernmost of the three stars, is even closer, a mere 16 “light years” away. Looking at the last, northernmost member of the triangle one would naturally assume that Deneb would be a similar distance from Earth, but here is where assumptions break down. Vega and Altair are relatively bright “normal” stars, but Deneb is a “blue supergiant” star that shines with the equivalent light of 100,000 suns! Its distance is some 100 times farther away than Altair, so the light you see from it tonight started its journey toward us when Constantine was Emperor of Rome. And we’ve barely ventured into the vast starfields of the Milky Way.
from The Sky This Week