Sunday, February 19, 2017

Two Dim Comets May Be Visible in a Telescope

Radar image of the "Green" Comet 45P / Honda-Mrkos-Pajdušáková on
2017 February 12, by the huge Arecibo Radio Telescope in Puerto Rico. This
display combines 13 images of the comet received over two hours. This is only
the seventh comet to come close enough to be imaged by radar. On 2011 August
19 and 20, it became only the fifteenth comet to be detected by a ground radar
(Image Sources: Arecibo Observatory, NASA, National Science Foundation, Sky and Telescope
Magazine )

By Glenn A. Walsh
Reporting for SpaceWatchtower

At the present time, two dim comets may be visible in a telescope (and, possibly binoculars), if you know where to look. While the “Green” Comet was in the early morning sky earlier this month, now both the Green Comet and Encke's Comet are in the evening sky.

American astronomer Fred Whipple described a comet as a “dirty snowball.” Comets are a combination of rocks, dust, water ice, and other frozen gases, from the early days of our Solar System.

The solid core of a comet is known as the nucleus. Streams of dust and gas released from the comet, as it nears the Sun, form a thin atmosphere around the comet nucleus called the coma. The coma is composed mostly (90 per-cent) of water, with dust making-up the rest of the coma.

Most, but not all, comets have one or more visible tails. The tail(s), which are usually not visible in the Outer Solar System, are caused by solar radiation as the comet comes closer to the Sun; this radiation usually is too weak to create tails in the Outer Solar System. Normally, a comet's tail(s) points away from the Sun, no matter the direction of movement of the comet; hence, a comet leaving the Inner Solar System often has a tail pointing in the direction of the comet's motion.

Comets usually have a highly-eccentric, elliptical orbit around the Sun, which brings a comet into the Inner Solar System for a short time, while it spends most of its time in the Outer Solar System. Short-period comets originate in the Kuiper Belt, just beyond the orbit of the Planet Neptune, while long-period comets are thought to originate in the Oort Cloud, a spherical cloud of icy bodies beyond the Kuiper Belt.

                                                    The “Green” Comet

The first one, nick-named the “Green” Comet due to its coloration, is actually Comet 45P / Honda-Mrkos-Pajdušáková. This comet passed closest to the Earth on February 11. At that time it was 7.4 million miles / 12 million kilometers from Earth. This distance can also be expressed as 0.08 Astronomical Units (1 A.U. or Astronomical Unit is the mean distance between the Sun and the Earth) and 30 times the mean distance between the Earth and the Moon.

At this distance, the Green Comet cannot be seen with the naked-eye; the astronomical Visual Magnitude at its closest point to Earth was expected to be around +6.5 to +7, but in reality it never was brighter than +8. It might be seen with strong binoculars, but a telescope is best for trying to find this comet. Unlike stars which shine their own light and appear as pin-points of light in the sky, comets only reflect sunlight. Hence, they appear as diffuse, fuzzy objects, which make them even more difficult to find.

The Green Comet may still be visible until the end of February. However, it will be a challenge to find. You will need a dark sky, away from city lights. Until a few days ago, this was even more complicated as the Moon was in the early morning sky. But, now the comet is rising in the late evening sky as the Moon rises even later. However, as the end of February gets closer, the comet will be fading in brightness.

The best time to view this comet is around 10:00 to 11:00 p.m. local time. As the comet fades, it will be moving through the constellations Corona Borealis, Boötes, Canes Venatici, Ursa Major and into Leo the Lion. Internet links to additional news articles, which include star charts to help find the comet, are located at the end of this blog-post.

The Green Comet was discovered on 1948 December 3 by Japanese astronomer Minoru Honda. It is named for Minoru Honda, Czech astronomer Antonin Mrkos, and Slovak astronomer Ludmila Pajdusakova. The comet appears green because it emits diatomic carbon, which glows green in the near-vacuum of Outer Space.

This apparition of the Green Comet is the second-closest to Earth between the years 1900 and 2043. The comet's closest approach to Earth came in August of 2011, when it came as close as 0.06 A.U or 5.6 million miles / 9.01233 million kilometers. While this comet comes toward the Sun fairly often (it is a short-period comet with an elliptical orbit of 5.25 years), the next time it is bright from Earth's vantage-point will be in October of 2032 when it is expected to reach a Visual Magnitude of +7.

                                                         Encke's Comet

Comet Encke or Encke's Comet is now visible in the evening sky, but will only be visible through early March. Like the Green Comet, Encke's Comet is not bright enough to be seen with the naked-eye (it has a very low albedo, reflecting only 4.6 per-cent of the light it receives), but it may be visible in binoculars or a telescope.

Enke's Comet is currently visible in the western sky about 90 minutes after local sunset. It is to the left of the Great Square of Pegasus, near the planets Mars and Venus. At the end of this blog-post is an Internet link to pages that show a map of how to find Comet Encke.

Encke's Comet was discovered in 1786 by French astronomer and surveyor Pierre Mechain. However, it was not immediately recognized to be a comet. It was not understood to be a periodic comet until 1819, when its orbit was calculated by German astronomer Johann Franz Encke.

Hence, as with the more famous Halley's Comet, Encke's Comet is one of the few comets named after the person who computed the comet's orbit, instead of the comet's discoverer. In fact, Encke's Comet was the first periodic comet discovered after Halley's Comet.

Encke's Comet has the shortest orbital period, 3.3 years, of any reasonably bright comet. A fainter comet, 311P / PANSTARRS, has an orbital period of 3.2 years.

In 1978, Slovak astronomer Lubor Kresak proposed that a fragment of Comet Encke may be the cometary body that caused the 1908 Tunguska Event. On the morning of 1908 June 30, a huge explosion occurred over a sparsely-settled area of Siberia in Russia known as the Stony Tunguska River Valley, which flattened 1,200 square-miles / 2,000 square-kilometers of forest, but caused no human casualties. The cause of the Tunguska Event, which was not observed by any living person, is thought to be an air-burst explosion of the atmospheric entry of a meteoroid, asteroid, or comet.

Internet Links to Additional Information ---

Information & Maps On How to View the 2 Comets -

"Green" Comet:
Link 1 >>>
Link 2 >>>
Link 3 >>>

Encke's Comet:
Link 1 >>>
Link 2 >>>

The "Green" Comet - Comet 45P / Honda-Mrkos-Pajdušákov:

Encke's Comet - Comet Encke: Link >>>

Tunguska Event: Link >>>

Related Blog Posts ---

"Comet of 1491: Self-Correction of Science." 2016 Feb. 20.

Link >>>


"Comet Lovejoy: Best View Next 2 Weeks." 2015 Jan. 7.

Link >>>


"Comet ISON vs. the Solar Storm." 2013 Nov. 26.

Link >>>


"Comet: Source of Mysterious Water on Jupiter." 2013 May 4.

 Link >>>


"Comet of the Century?" 2013 Jan. 19.

Link >>>

Source: Glenn A. Walsh Reporting for SpaceWatchtower, a project of Friends of the Zeiss.
             2017 February 19.

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