Mercury Update - Details for 2017 through September

Mercury has six elongations in 2017. The initial sighting for each of these is tabulated below:


Initial Sighting Date (2017)

Observing Location

Greatest Elongation (2017)


January 5, 6:15 am EST Old Mart Site, Pennsauken, NJ

January 19, western (morning)


March 16, 7:16 pm EDT Baseball Fields, Maple Shade, NJ

April 1, eastern (evening)


May 14, 5:05 pm EDT Old Mart Site, Pennsauken, NJ

May 17, western (morning)


June 26, 8:33 pm EDT New Albany Rd, Moorestown, NJ

July 29, eastern (evening)


September 4, 5:50 am EDT Swede Run, Moorestown, NJ

September 12, western (morning)



November 23, eastern (evening)


Elongation #5

The first sighting of the fifth elongation of the year was on September 4, 2017 at 5:50 am EDT from Swede Run Fields in Moorestown, NJ, with 10x50 binoculars (magnitude +1.7, altitude 4.0). It was actually seen a couple of minutes earlier, but its identity could not be confirmed until nearby Regulus and Mars were also seen to establish the relative positions. Magnitude +1.8 Mars was 1.0 from magnitude +1.4 Regulus at the 11 o'clock position, Mercury was 2.9 from Regulus at the 2 o'clock position, as shown in the clip from a SkyTools chart below. None of them were seen with unaided eyes in the brightening twilight (sunrise at 6:31 am), compounded by some low fog.

September 4, 2017, at 5:50 am EDT. The nearly-vertical blue line represents the ecliptic.
The horizontal line near the bottom is the horizon.

The second sighting of the fifth elongation of the year was on September 9, 2017 at 5:50 am EDT from Carranza Field in Wharton State Forest, NJ, with a nearly-full moon in the sky. Nevertheless, Mercury had brightened greatly since September 4, from magnitude +1.7 to +0.1, so it was easily visible with unaided eyes. An image was also captured, including nearby Mars and Regulus (Mars showed distinct movement since Sept 4). The third sighting of Mercury for Elongation #5 was on September 16, 2017 from the field next to Seneca High School in Tabernacle, NJ. I encountered considerable fog at Carranza Field between 5:30 and 6:00 am, such that the trees on the eastern side of the field were not visible as viewed from the western side where I parked. When I left about 6 am, trees were just beginning to peek through the fog in brightening twilight (sunrise would be at 6:41 am). After driving 7 miles back (northwest) on Carranza Road, there was much less fog around Seneca High School, so I pulled in and parked on the side of the entrance road looking east across a field into fairly bright twilight. The crescent moon and Venus were still easily visible, so starting at Venus and dropping down about 11.5 (and slightly left), I spotted Mercury with 10x50 binoculars at 6:12 am EDT. It was just above dimmer Mars (17 arc minutes separation at the time). Having found it with the 10x50s, I could now see Mercury relatively easily with unaided eyes. It was about 10 altitude, magnitude -0.8 (Mars was not visible without the binoculars).


Elongation #4

The first sighting of the fourth elongation of the year was on June 26, 2017 at 8:33 pm EDT (same time as sunset) from New Albany Rd, near the intersection of Church St, in Moorestown, NJ, 5.4 days after superior conjunction on June 21 at 10:14 am. Mercury was initially spotted with 16x70 binoculars (at 5.1 altitude, magnitude -1.6 and 6.8 solar elongation), then followed until 8:50 pm (at 2.4 altitude). It was not seen with unaided eyes. With the 16x70s, I was unable to spot magnitude +1.7 Mars, 2.7 east of Mercury. On July 9, 2017, Mercury was spotted at Carranza Field, initially at 8:55 pm with 10x50 binoculars (7.6 altitude), then with unaided eyes at 9:10 pm (5.0 altitude). It was at magnitude -0.4 and 19.2 solar elongation. On July 30, 2017, Mercury was spotted at Swede Run Fields in Moorestown, NJ, initially at 8:47 pm (32 minutes after sunset) with 10x50 binoculars (5.9 altitude), then with unaided eyes at 9:00 pm (3.5 altitude). It was at magnitude +0.4 and 27.2 solar elongation, a little more than 20 hours after Greatest Eastern Elongation at 12:39 am EDT on July 30. However, since the ecliptic was only tilted 29 to the horizon at the time, the elongation did not produce that much elevation above the horizon after sunset. Mercury was observed with an 85 mm spotting scope (27 to 60x) between 8:55 and 9:00 pm, but the woozy image from poor seeing at the low altitude did not reveal any non-circular shape of the partially illuminated disc (45%). With the 85 mm scope, I was also able to find the magnitude +1.4 star Regulus (Alpha Leonis) about 5.5 to the right of Mercury, and slightly lower than it. I then saw it with the 10x50s. On August 21, 2017, the totally-eclipsed sun will be close to Regulus.


Elongation #3

The first sighting of the third elongation of the year was on May 14, 2017 at 5:05 am EDT from the old Mart site in Pennsauken, NJ. It was initially spotted with 16x70 binoculars (at 2.3 altitude, magnitude +0.8), then subsequently seen with 10x50 binoculars, but not with unaided eyes. 5:05 am was 13 minutes after Mercury rose and 41 minutes before sunrise. I spotted Mercury again on May 17, 2017 (the day of Greatest Western Elongation) at 4:58 am EDT with 16x70 binoculars from the old Mart site in Pennsauken, NJ. It was at 1.9 altitude, magnitude +0.6. I subsequently looked at it with an 85 mm spotting scope at 60x and could see that it was elongated from the upper left to the lower right (such that a line perpendicular to the middle was pointed toward the sun), but the 39% illuminated crescent was blurred by poor seeing at the low altitude. It was not seen with unaided eyes. This is probably the most unfavorable elongation of the year. The ecliptic is at a shallow angle to the horizon before sunrise and Mercury has been below (south) of the ecliptic, so much of its solar elongation has been sideways rather than vertical. On May 17, nearby Venus, which was higher in the sky and greater in diameter Mercury, but similarly 40% illuminated, showed a thick, but nice crescent in the 85 mm scope.


Elongation #2

The first sighting of the second elongation of the year was on March 16, 2017 at 7:16 pm EDT from the baseball field complex in Maple Shade, NJ. Initially, my objective was to see the crescent Venus little more than a week from inferior conjunction on the morning of March 25. Looking at SkyTools earlier in the day, I noticed that Mercury was just 9.5 from Venus at the 7:30 o'clock position, and it was fairly bright at magnitude -1.4. Sunset was at 7:08 pm EDT and I arrived about 7:10 pm. I set up my mounted 16x70 binoculars, and after a quick scan with unaided eyes, saw Venus at 7:13 pm. The crescent showed well in the 16x70s (and later in the 10x50s, but not with unaided eyes; Venus was 57.4" diameter). However, the crescent looked thicker than the 3.6% illumination at the time would suggest, probably due to the glare of its great brightness compounded by the low altitude (about 13 when first spotted). I then looked for Mercury with the 16x70s and found it at 7:16 pm. It was also seen with 10x50 binoculars, and perhaps glimpsed with unaided eyes. However, the visibility did not improve as I watched until 7:30 pm when Mercury disappeared behind a fence. Twilight was too bright and decreasing altitude negated any benefit from increasing darkness. In contrast, similar magnitude Sirius was easily visible to unaided eyes higher in a darker blue sky to the south. On March  21, 2017, there were still some streaky clouds along the western horizon at 7:30 pm, but I went to the Maple Shade baseball field complex anyway to look for Venus and Mercury. Venus was spotted in the tree tops at 7:40 pm with 10x50 binoculars. Looking 11.5 degrees from Venus at the 10:30 o'clock position, I picked up Mercury with the 10x50s then saw it with unaided eyes fairly easily when it was between passing clouds. On March  22, 2017, I was at Belleplain State Forest for a college student field trip (so they could see the night sky from a dark location). Mercury was easily spotted with unaided eyes at 7:45 pm (half an hour after sunset). On March  29, 2017, while taking pictures of Mercury near the crescent moon after sunset at the old Collins Farm site in Maple Shade, NJ (around 8 pm EDT), Mercury was about 9 from the moon and easily visible with unaided eyes.


Elongation #1

The sighting on January 5, 2017 was the first of the 2017 elongation cycle. It was accomplished with 16x70 binoculars from the old Mart site in Pennsauken, NJ. Luckily, it was relatively clear along the eastern horizon (the rest of the sky was partly to fully cloudy) and Saturn was visible naked eye, which served as a guide to Mercury about 8 below-left of the ringed planet. Mercury was at magnitude +1.1 and 1.5 altitude when first spotted (and bloated/twinkling), but even by 6:30 am when I left, it was not visible naked eye. After several inches of snow during the day on January 7, it  cleared after nightfall and on the morning of January 8, guided by naked-eye Saturn, Mercury was spotted at 6:11 am EST with 16x70 binoculars from inside the car at the old Mart site (the temperature was about 15F). I stepped out of the car and was able to see Mercury with unaided eyes at 6:15 am. I had hoped to see comet C/2016 U1 (NEOWISE) nearby in Serpens Cauda, but transparency wasn't that good and it was already half an hour into twilight. When I arrived home, I was able to spot Mercury and Saturn in brightening twilight with unaided eyes at 6:35 am. Mercury was up to magnitude +0.5. On February 5, I went to the old Mart site and picked up magnitude -0.2 Mercury at 6:30 am EST with an 85 mm spotting scope at 27x. It was not seen with unaided eyes.




The current sighting streak is now 43 elongations in a row, starting in January 2011, which includes five complete calendar years of six or seven elongations each (click here for previous sightings). The purpose of this ongoing effort is not to set some sort of record, especially since I have no idea what sort of record might exist, but to demonstrate that locating and seeing Mercury is not nearly as difficult as many suppose. It just takes some planning and a little effort.


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Last Update: Tuesday, October 03, 2017 at 09:19 PM Eastern Time