Core Points - A rare astronomical event called "double star and crescent moon" will occur on October 23, featuring Mercury, Mars, and the crescent moon in close proximity in the southwestern sky [1][7] - Mercury will reach its eastern elongation on October 30, marking the last opportunity for observation this year, although conditions will be poor due to its low altitude [2] - Mars, known for its reddish appearance due to iron oxide, will also be visible in the southwestern sky shortly after sunset, but the observation window will be brief [5][7] Summary by Sections - **Astronomical Event**: The conjunction of Mercury, Mars, and the crescent moon will take place on October 23, creating a visually striking formation [1][7] - **Observation Conditions**: Mercury's eastern elongation on October 30 will provide a final chance for observation this year, but it will be challenging due to its low elevation of less than 10 degrees [2] - **Mars Visibility**: Mars will be positioned in the southwestern sky at sunset, but the viewing time will be limited [5][7] - **Viewing Recommendations**: Observers are encouraged to find a flat, unobstructed area for the best chance to view the event, although binoculars may be necessary due to the low altitude of the celestial bodies [7]

Group 1 - The article discusses a rare astronomical event where Mercury, Mars, and the crescent moon will closely "gather" in the southwestern sky at sunset on October 23, described as a "double star and crescent moon" phenomenon [1][6] - Mercury and Mars are well-known planets, with Mercury being the closest planet to the Sun, often hidden in its glare, making it difficult to observe except during its greatest elongation [1][2] - The event will occur shortly before Mercury's eastern elongation on October 30, which is noted to be the last opportunity for observing Mercury this year, although conditions will be poor due to its low altitude of less than 10 degrees above the horizon [2] Group 2 - Mars will be positioned highest in the sky during the event, followed by Mercury, with the crescent moon being the lowest [6] - Observers are encouraged to find a flat, unobstructed area for viewing, as the low altitude of the celestial bodies and their proximity to the horizon will make them challenging to see without binoculars [6] - The visibility of this event is limited due to the short observation window and the influence of sunlight, making successful observation a rewarding challenge [6]

Core Points - Mercury will have its best observation opportunity during the western elongation on August 19, 2023, with favorable conditions for the public to view the planet if the weather permits [1][4] - Mercury is the hardest planet to observe due to its proximity to the Sun, often being obscured by sunlight [2] - The best time to observe Mercury is during its greatest angular distance from the Sun, known as "greatest elongation," which occurs approximately every 116 days [2][4] Observation Conditions - This western elongation will allow Mercury to be seen in the eastern low sky during dawn, with a horizon height of about 18 degrees and a brightness of 0 magnitude [4] - Observers using telescopes may also see Mercury in a crescent shape, with approximately 40% of its surface illuminated by the Sun [4] - The observation opportunity is not limited to August 19; several days before and after also provide chances to view Mercury due to minimal height variation [7]

Core Viewpoint - The article discusses the upcoming western elongation of Mercury on August 19, which presents the best observation conditions for the planet this year, allowing the public to potentially view it in the early morning sky if weather permits [1][2]. Group 1: Observation Conditions - Mercury will be at a horizontal height of approximately 18 degrees at sunrise, with a brightness of 0 magnitude, making it visible to the public [2]. - The observation of Mercury is not limited to August 19; the days surrounding this date also provide good opportunities for viewing due to minimal changes in the planet's height [3]. Group 2: Characteristics of Mercury - Mercury is the most challenging planet to observe in the solar system due to its proximity to the Sun, often being obscured by sunlight [1]. - The planet completes its orbit around the Sun in just 88 days, resulting in 3 to 4 occurrences of both eastern and western elongations each year, with varying observation conditions based on its position relative to the Sun [1].

Core Points - Mercury will have its eastern elongation on July 4, 2023, providing good observation conditions for the public if the weather is clear [1][2] - Mercury is the closest planet to the Sun and is difficult to observe due to its proximity to the Sun's glare [1] - The best time to observe Mercury is during its eastern elongation when it appears in the western sky after sunset [1] Observation Conditions - This year, Mercury will have three eastern elongations, occurring on March 8, July 4, and October 30, with the first two having favorable observation conditions [2] - On July 4, Mercury's altitude will be approximately 18 degrees at sunset, with a brightness of about 0.4 magnitude [2] - Observers are encouraged to look for Mercury a few days before and after July 4, as the altitude will be higher in the days leading up to the event [2]

Group 1 - The event of Mercury accompanying the Moon on June 27 is highlighted as a noteworthy astronomical occurrence, with favorable observation conditions [1][2] - Mercury is the smallest planet in the solar system and is often difficult to observe due to its proximity to the Sun, only becoming visible during its greatest elongation, known as "greatest distance" [1][2] - This month, Mercury appears as an "evening star" after sunset, positioned in the northwest sky, while the crescent Moon will accompany it, creating a rare "star-moon dialogue" [2] Group 2 - The concept of "greatest distance" is explained, with distinctions made between eastern and western greatest distances, affecting visibility during dawn and dusk [2] - Observers are encouraged to use binoculars or small telescopes for better viewing of the Mercury-Moon conjunction, and astrophotographers are advised to capture this unique moment [2] - The nearby Beehive Cluster, a loose star cluster, can also be observed, although it may be challenging due to the remaining daylight [5]