Nighttime occult asterism refers to a phenomenon occurring in astronomy where a celestial body passes in front of another, blocking its view from the Earth's perspective. Asterisms are patterns formed by stars in the night sky. They are not official constellations but rather groupings of stars that form recognizable shapes or figures. During nighttime occultations, one of these asterisms may be hidden from view by a passing object such as the Moon or a planet. The occultation can occur when the object passes between the observer on Earth and the asterism in question. This can result in a temporary disappearance of the asterism from the night sky.
It’s why, in the evenings following April 23, you’ll see the moon on the other side of Regulus on the sky’s dome, as shown on the chart below:
But from anywhere worldwide, tonight s moon will be near Regulus on the sky s dome unless you re in that part of the world where the moon occults passes in front of Regulus. The star has an atmosphere enriched with barium, indicating that it may have an unseen companion, a more evolved star from which mass is transferred to Gacrux.
This can result in a temporary disappearance of the asterism from the night sky. Nighttime occult asterisms can be captivating events for skywatchers and astronomers. They provide an opportunity to witness the alignment of celestial bodies and appreciate the dynamic nature of space.
Moon sweeps through Leo the Lion April 23 to 25
On the nights of April 23 to 25, 2018, the moon is moving through the constellation Leo the Lion. An important occultation of Leo’s brightest star – the concluding occultation in a series of 19 in a row – will happen on the night of April 24. Read more about the occultation below.
The Lion is one of the easiest constellations to pick out in the sky, although – as the moon passes through it – the lunar glare will somewhat obscure the view. Still, watch for Leo’s brightest star, Regulus, sometimes called the little king. And notice the backwards question mark pattern extending above Regulus. This pattern is an asterism, not a constellation but just a noticeable pattern of stars, called the Sickle. It represents the Lion’s head and shoulders.
Also notice the triangle of stars at the rear of Leo. The brightest star in this triangle is called Denebola, which means tail of the lion.
Chart of the constellation Leo via the IAU.
If you see the moon on April 23, you’ll see it as it’s heading toward Regulus. Just as the sun does during the day, the moon and Regulus go westward across the sky during the night. But the moon – as always – moves eastward relative to the backdrop stars of the zodiac. The eastward motion of the moon – on April 23 to 24, toward Regulus – is a reflection of its orbit around Earth.
It’s why, in the evenings following April 23, you’ll see the moon on the other side of Regulus on the sky’s dome, as shown on the chart below:
The chart above shows the moon to the east of Regulus, as seen from middle North American latitudes, on April 24. If you live in the Eastern Hemisphere, you’ll see the moon offset in the direction of Regulus, or to the west of this star. But from anywhere worldwide, tonight’s moon will be near Regulus on the sky’s dome – unless you’re in that part of the world where the moon occults (passes in front of) Regulus.
Occultation of Leo’s bright star Regulus. From precise areas on Earth, you could watch the moon occult (cover over) Regulus on the night of April 24. Regulus will disappear behind the moon’s dark side and then reappear on its illuminated side.
This is, in fact, the concluding occultation in what has been a long series of 19 monthly occultations of Regulus by the moon. The series began on December 18, 2016, and finally concludes on the night of April 24, 2018.
Regulus undergoes these occultation series because it lies along the ecliptic, which marks the path of the sun, moon and planets across our sky. Regulus is the only 1st-magnitude star – the only one of our sky’s brightest stars – to sit almost squarely on the ecliptic.
The lunar occultation of Regulus happens in the nighttime sky in north-central Russia (above the white line) on the night of April 24 (morning of April 25). Click here for more information. Worldwide map via IOTA.
Three other 1st-magnitude stars – that is, bright stars – reside close enough to the ecliptic to be occulted by the moon: Aldebaran, Antares and Spica. As it happens, Aldebaran, too, is in the midst of a series of 49 monthly occultations that started on January 29, 2015, and will conclude on September 3, 2018.
Antares and Spica have no occultaion series going on at present. Spica will have a series of 20 monthly occultations from June 16, 2024, to November 17, 2025. Antares will have a series of 68 monthly occultations from August 25, 2023, to August 27, 2028.
The green line on the sky charts above represents the ecliptic – Earth’s orbital plane projected onto the constellations of the zodiac. We often see the moon near the ecliptic on the sky’s dome, but not necessarily right on the ecliptic. That’s because the moon’s orbit around Earth is tilted about 5 degrees relative to Earth’s orbit around the sun.
However, the moon in its orbit crosses the ecliptic – Earth’s orbital plane – twice a month. When the moon is traveling from south to north, the moon crosses Earth’s orbital plane at its ascending node; when the moon crosses the ecliptic from north to south, it’s called the moon’s descending node.
The moon reaches its ascending node – going from south to north – on April 23. By April 24, the moon is a bit north of the ecliptic in our sky, residing a scant 1/2 degree north (1/2 degree = moon’s apparent diameter). Click here to know the moon’s present ecliptic latitude.
The moon will remain north of the ecliptic until it next crosses the ecliptic at its descending node (north to south) on May 7, 2018.
Bottom line: On the nights of April 23 to 25, 2018, enjoy the moon sweeping through the constellation Leo the Lion.
The star has a mass of 1.52 solar masses and a radius 28.41 times that of the Sun. With a surface temperature of 4,294 K, it is 302 times more luminous than the Sun. It is a relatively slow spinner, with a projected rotational velocity of 3.14 km/s. the star’s estimated age is 2.17 billion years.
The occultation of a well-known asterism can be a rare and exciting occurrence. A popular example of a nighttime occult asterism is the Pleiades, also known as the Seven Sisters. The Pleiades is an open star cluster in the constellation of Taurus. It consists of several bright stars that form a distinct pattern in the night sky. The Moon, as it travels along its orbit, can sometimes pass in front of the Pleiades, causing an occultation and temporarily blocking the view of this beautiful asterism. Observing nighttime occult asterisms can be done with the naked eye or with the help of telescopes or binoculars. Skywatchers can keep track of upcoming occultations through astronomical calendars and online resources. The precise timing and duration of an occultation can vary depending on the location of the observer and the objects involved. Overall, nighttime occult asterisms provide an opportunity to witness celestial events that add to the wonder and fascination of the night sky. They remind us of the vastness and intricacies of the universe and the constant movement of celestial bodies in our cosmos..
Reviews for "Unraveling Nighttime Occult Asterisms: A Journey Through the Night Sky"
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