C∕2020 F3 (NEOWISE) Comet
| Polish version is here |
Even though I’ve been interested in astronomy since childhood, I never had the chance to observe a comet with the naked eye. This is only possible for bright comets. That remained true until this year, when a beautiful comet with the designation C/2020 F3 (NEOWISE) unexpectedly graced our skies.
This comet belongs to the class of long-period comets, as its orbital period is 6,912 ± 9 years—meaning we can expect its return in about that many years. It was discovered on March 27, 2020, just a short time before we could observe it with the naked eye, by the NEOWISE space telescope [2].
To grasp how far within the outer reaches of our Solar System this comet traveled to meet us, it is helpful to look at the diagram below:
Like all comets, this object follows a highly elongated elliptical orbit with a steep inclination relative to the ecliptic and the orbital planes of all our Solar System’s planets. Its orbital semi-major axis measures about 363 astronomical units, whereas Neptune’s, by comparison, is just over 30 astronomical units.
Observation
July 14, 2020, around 11:00 PM – Jaworzno (Poland)
urban environment, high level of light pollution
In July, the comet was relatively low above the northern horizon. In the photograph, you can see its beautiful coma surrounding the comet’s nucleus, as well as the splendid gas-and-dust tail. Naturally, the tail always points away from the Sun.
This photograph was taken as a single-exposure photo, meaning no additional imaging techniques—like stacking—were used. As a result, it closely resembles the view one might see through a pair of powerful binoculars.
Sometimes it is easier to visualize the positions of celestial bodies by using an animation:
July 16, 2020, 10:39 PM – Jaworzno (Poland)
urban environment, high level of light pollution
Only two days later, I again had the chance to observe this magnificent comet. This time, I traveled a bit farther from city lights and was able to capture the comet shining relatively low above the northern horizon (Photo 2).
In the photograph, you can also see stars that primarily belong to two constellations: Ursa Major (Ursa Major) and Lynx (Lynx). Below is a brief overview of a few of these stars.
Alpha Ursae Majoris (α UMa), also known as Dubhe, is one of the brightest stars in Ursa Major. Located about 123 light-years from Earth, Dubhe is part of a quadruple system composed of two spectroscopic binaries. The primary component, α UMa A (the true Dubhe), is a yellow giant of spectral type G9 with an apparent magnitude of 2.00m. Its surface temperature is around 4,500 K, and its intrinsic luminosity is 300 times that of the Sun. Its mass is over four times the mass of our daytime star, and it has already left the main sequence. Helium is currently being fused into carbon in its core.
Beta Ursae Majoris (β UMa), or Merak, is a star located about 79 light-years away. Merak is a white dwarf of spectral type A1, with a luminosity around 58–69 times that of the Sun. It is also surrounded by a gaseous disk, similar to those found around Fomalhaut (α PsA) and Vega (α Lyr). Although no planets have been observed within that disk so far, it is possible that they either already exist or are in the process of forming.
Omicron Ursae Majoris (ο UMa), or Muscida, is a binary star system composed of two stars: ο UMa A (the primary Muscida), a yellow giant of spectral type G, and ο UMa B, an M1 red dwarf with an apparent magnitude of only 15.2m. The primary component is about 360 million years old, having ceased hydrogen fusion in its core and progressing toward becoming a far brighter red giant. It is a variable star—its apparent magnitude shifts from 3.3m to 3.8m over roughly a year. Components A and B are separated by at least 400 astronomical units, so their orbital period is over 4,100 years. Orbiting the giant star is a gas giant designated ο UMa b, confirmed in 2012.
Iota Ursae Majoris (ι UMa), or Talitha, is another quadruple star system. The primary component, ι UMa A, is of spectral type A7 or F0, classified either as a main-sequence star or a subgiant. Its temperature is around 7,260 K, its mass is about 1.7 M☉, and it shines 8–9 times brighter than the Sun. Orbiting it at a distance of 5–6 astronomical units is a smaller star, most likely a white dwarf with a mass close to that of the Sun. This pair has an orbital period of about 12.2 years and an eccentricity of 0.6. Much farther out—around 132 astronomical units away—is a pair of M3 V and M4 V red dwarfs (ι UMa B and ι UMa C), each with a mass of about 0.35 M☉ and 0.30 M☉, respectively, and apparent magnitudes of 10.8m and 11.1m. They orbit their common center of mass at a separation of 10 AU, with an orbital period of 40 years. When considering the entire quadruple system, this red dwarf pair takes about 2,084 years to orbit the mutual center of mass, following a highly eccentric path (e ~ 0.9).
Kappa Ursae Majoris (κ UMa), or Alkaphrah, is a binary star system located about 357 light-years from the Sun. Both components are main-sequence stars of spectral type A. κ UMa A has an apparent magnitude of 4.16m, and κ UMa B 4.54m, while the entire system’s brightness is 3.60m. Their orbital period is just over 35 years. Interestingly, orbital parameters suggest a combined mass of 11 M☉, but other estimations (based on temperature and luminosity) yield a figure closer to 7 M☉.
10 Ursae Majoris (10 UMa, belonging to the constellation Lynx) is a white dwarf of spectral type A, situated about 52 light-years from Earth, with a luminosity about seven times greater than that of the Sun. It is less well-known than other stars in this constellation but is noteworthy for its relatively short distance from Earth and significant brightness.
31 Lynx (31 Lyn) is a K-type star in Lynx, about 390 light-years away, shining at around 52 times the Sun’s luminosity. It is an orange giant and one of the brighter stars in this faint constellation.
21 Lynx (21 Lyn) is a white star of spectral type A7, at a distance of roughly 180 light-years. Its luminosity is about 10 times that of the Sun.
15 Lynx (15 Lyn) is a binary star whose primary component is a white dwarf of spectral type A. Located about 130 light-years from Earth, it has a luminosity about five times that of the Sun.
The spectacle this comet provided in the night sky is something I’ll remember for a long time.
Photo 1 Parameters:
- Total exposure time: 5 seconds (single shot)
- Canon EOS 60D
- ISO: 1500
- Maksutov-Cassegrain telescope (100/1400), prime focus exposure
- A filter was used to reduce the effects of artificial light pollution and atmospheric glow
- Mount: photographic tripod
Photo 2 Parameters:
- Total exposure time: 1.5 minute
- Xiaomi Redmi Note 8 Pro + DeepSkyCamera (beta)
- ISO: 800
- Mount: photographic tripod
Further readings:
- Falk D., One of the brightest comets in decades is passing Earth. Here's how to see it, National Geographic, 2020, online: https://www.nationalgeographic.com/science/article/one-of-brightest-comets-in-decades-passing-earth-how-to-see [14.05.2021]
- Anderson E., Francis C, HIP 54061, Extended Hipparcos Compilation (XHIP), online: http://vizier.cds.unistra.fr/ [14.07.2022]
- Boyajian T. S., von Braun K., van Belle G., Farrington C., Schaefer G., Jones J., White R., McAlister H. A., ten Brummelaar T. A., Ridgway S., Gies D., Sturmann L., Sturmann J., Turner N. H., Goldfinger P. J., Vargas N., Stellar diameters and temperatures III. Main-sequence A, F, G, and K stars: additional high-precision measurements and empirical relations, The Astrophysical Journal, 771(1), 2013, pp. 40
- Sato B., Omiya M., Harakawa H., Izumiura H., Kambe E., Takeda Y., Yoshida M., Itoh Y., Ando H., Kokubo E., Ida S., Substellar Companions to Seven Evolved Intermediate-Mass Stars, Publications of the Astronomical Society of Japan, 64(6), 2012, pp. 135
- Zhuchkov R. Ya., Malogolovets E. V., Kiyaeva O. V., Orlov V. V., Bikmaev I. F., Balega Yu. Yu., Physical parameters and dynamical properties of the multiple system ιUMa (ADS 7114), Astronomy Reports, 56(7), 2012, pp. 512-523.
Marek Ples