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こと座流星群は、C/1861 G1 サッチャー彗星が残した破片の軌跡を地球が通過するときに発生する、毎年恒例の天体イベントです。 これらのちりや破片の小さな粒子が高速で地球の大気圏に突入すると、燃え尽きて、空に流星または「流れ星」として知られる明るい光の筋ができます。 通常、Lyrids は 4 月 22 日頃にピークに達し、最適な表示条件下では 1 時間あたり 10 ~ 20 個の流星が表示されます。 こと座流星群は、流星が発生したと思われる星座にちなんで名付けられ、2,600 年以上にわたって観測されており、知られている中で最も古い流星群の 1 つとなっています。 このアーティストの描写は、流星群を実際の写真よりも強烈に見せます。

2023 年 4 月のスカイウォッチングのハイライトは?

北半球の観測者にとって、水星はその年の夕方の空で最も高くなります。 月は、いくつかの惑星と美しく対をなすために、毎月のラウンドを行います。 また、月からの干渉がないため、毎年開催されること座流星群には理想的な観察条件かもしれません。


月の初めに日没後に水星を見つけ、月の惑星への訪問を追跡し、4 月 23 日に Lyrid 流星がピークに達したときに流れ星を捉えます。

2023 年 4 月のスカイウォッチングのハイライト

  • 4月 11 – 北半球の観測者にとって、水星はその年の夕方の空で最も高くなります。 日没直後の西の低空を見る [Best viewing is April 3-11, as it climbs a little higher each evening.]
  • 4月 11 –[{” attribute=””>Venus sits near the Pleiades star cluster this evening in the west.
  • April 15-16 – Find the Moon near Saturn in the east, in the couple of hours before sunrise.
  • April 23 – The crescent Moon hangs just five degrees above Venus in the west after sunset.
  • April 25 – The Moon and Mars pair up this evening, high in the west after dark.
  • April 6 – Full moon
  • April 20 – New moon
  • April 23 – The Lyrid meteor shower peaks this morning. Best viewing is between midnight and dawn.
  • April 26-27 – The Moon is at it’s first-quarter phase, which is a great time to observe with binoculars or a telescope if you have access to them. Around this time you can observe details in the lunar craters and mountains along the day-night line (the terminator) with ease.

Video Transcript

What’s Up for April? Mercury rising, this month’s Moon and planet pairings, and the Lyrid meteor shower.

First up, on April 11, the planet Mercury – smallest and fastest moving of the planets in our solar system – will reach its highest and most visible in the evening sky for the year.

Mercury is only visible in the sky for a few weeks every three to four months. The rest of the time, it’s too close to the Sun in the sky and is lost in its bright glare. And since the planet orbits so close to the Sun, it’s always near the Sun in the sky, appearing low near the horizon for no more than an hour or two, either following sunset, or preceding sunrise.

Some of Mercury’s fleeting appearances – known as “apparitions” – are better for observing than others, for a combination of reasons that have to do with how our view of the solar system changes with the seasons, what hemisphere you’re in, and what phase the planet happens to be showing us at the time. For this apparition, in the Northern Hemisphere, the best viewing is April 3rd through the 11th, as the planet appears higher in the sky each evening. It quickly fades in brightness after that, as the phase it shows us becomes an increasingly slimmer crescent.

Also on April 11, you’ll find planet Venus right next to the Pleiades star cluster. The two will be close enough to appear in the same field of view through binoculars. This pairing makes for a fun reminder that the night sky is kind of like a time machine – the farther out into space you look, the farther back in time you’re seeing. On that night you’re seeing light that left Venus about 9 minutes earlier, whereas the light of the Pleiades left those stars around 400 years ago.

The latter half of April includes some awesome close approaches of the Moon with three of the bright planets in the sky. On April 15th and 16th, you’ll find the crescent Moon rising with Saturn. Find them low in the southeastern sky in the couple of hours before sunrise. Then on the evening of the 23rd, find the slim crescent Moon hanging just five degrees above Venus in the west after sunset. And on April 25th the Moon finds its way over to Mars, high up in the west after dark.

At this time, around the 26th and 27th, the Moon will be at its first quarter phase, meaning it appears as a “half-moon,” high in the sky after dark. The first-quarter Moon is a great time to pull out your binoculars or telescope, if you have them, as it’s an ideal time to observe the Moon’s craters and mountains along the terminator  – the day/night boundary – with ease. Lots of astronomy clubs plan public observing nights around this time as well, and you can look for events in your area with NASA’s Night Sky Network.

April brings the annual Lyrid meteor shower. It’s a medium-strength shower that can produce up to 20 meteors per hour at its peak, under ideal conditions. The Lyrids peak this year in the pre-dawn hours of April 23rd, though you should see a few shooting stars on the morning before and after the peak as well. Fortunately, the peak falls just a couple of days after the new moon. That means the Moon won’t interfere with this year’s Lyrids, overwhelming fainter meteors in the glow of moonlight.

The Lyrids are named for the constellation Lyra, which is near the point in the sky where their meteors appear to come from, called the radiant. They’re one of the oldest known meteor showers, with the first recorded sighting in China some 2,700 years ago. They originate as dust particles from a comet during its 400-year orbit around the Sun.

The Lyrids tend to produce fast-moving meteors that lack persistent trails, but they can also produce the occasional bright meteor called a fireball. To observe them, find a comfortable spot away from bright city lights, get horizontal, and look straight up. You’ll see the most meteors by looking slightly away from the origin point, which is near the bright star Vega.

So here’s wishing you clear skies to catch a few shooting stars one April morning, when the forecast calls for light showers of comet dust, with a chance of fireballs.

Here are the phases of the Moon for April.

Moon Phases April 2023

The four main phases of the Moon are illustrated in a horizontal row, with the full moon on April 6, third quarter on April 13, new moon on April 20, and first quarter on April 27. Credit: NASA/JPL-Caltech

Stay up to date with all of NASA’s missions to explore the solar system and beyond at I’m Preston Dyches from NASA’s Jet Propulsion Laboratory, and that’s What’s Up for this month.

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