Wednesday, April 12, 2017

4 Comets May Be Visible w/ Small Telescopes
Image of Comet Johnson (C/2015 V2) at visual magnitude +8, with an obvious tail, photographed in the Constellation Hercules the Hero on the night of April 1-2 by Ade Ashford.
(Image Source: AstronomyNow Magazine from the United Kingdom)

By Glenn A. Walsh
Reporting for SpaceWatchtower

This month, four comets may be visible to stargazers with small telescopes, and possibly binoculars. Although it is unlikely any of these comets will be bright enough to see with the naked-eye (at least, not this month), those with a small telescope, or possibly good binoculars, may have a chance to see one or more of these cosmic “dirty snowballs.”

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 is usually not visible in the Outer Solar System, is composed of dust and gases emanating from the comet, 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.

Short-period comets may have an orbit of only a few years, while long-period comets, potentially, could have an orbit of several million years. Some comets have very short lives, and they disappear into the Sun before they can resume traveling to the Outer Solar System. Other comets, known as hyperbolic comets, go around the Sun once and never come back, continuing into Interstellar Space forever.

To more easily see comets, it is better to be away from city lights, as artificial lighting can drown-out the dimmer comets. Bright moonlight can also drown-out some of the dimmer comets, so monitor the Moon Phase on the monthly SpaceWatchtower Astronomical Calendar.

When looking for a comet, it is best to be in an area that gets a good view of the entire sky (with few obstructions such as buildings, trees, or hills). Of course, you definitely want an unobstructed view for the area of the sky where you expect to find the comet. And, if the comet is expected to be low on the horizon where you expect to view it, you want your observation site to be as high in elevation as possible.

Of course, viewing comets, like all celestial observations, are weather-permitting. If there are more than a very few clouds in the sky, a comet will be much more difficult to find.

And, you want to go out ahead of time, before you actually start looking for comets, to get your eyes accustomed to the dark sky. Dark-adapting your eyes for comet-watching could take up to a half-hour.

                                    Comet 41P/Tuttle-Giacombini-Kresák

Comet 41P/Tuttle-Giacombini-Kresák has been called by some the “April Fool's Comet,” because it approached Earth, on the first day of this month, at a closer point than any other fly-by since the comet's discovery in 1858: 13.2 million miles / 21.2 million kilometers. Today (April 12), this comet reaches the point in its orbit called perihelion (closest approach to the Sun for this apparition): 97.1 million miles / 156.3 million kilometers.

This is a short-period comet, which comes around once every 5.5 years. Astronomer Horace Tuttle of the Harvard College Observatory first discovered this comet on 1858 May 3. It was next observed by Professor M. Giacombini of France's Nice Observatory on 1907 June 1, and after that by Slovak astronomer Lubor Kresak on 1951 April 24.

It was only after this third observation that it was realized that the comets of 1858, 1907, and 1951 were all the same comet. Hence, all three astronomers' names were given to this comet as the comet's discoverers.

On April 18 and 19, this comet will be in the Constellation Draco the Dragon, passing the bright Star Rastaban, in the dragon's head on the 18th. After that, the comet heads into the Constellation Hercules the Hero, where it will start to fade in brightness as it travels further from the Earth.

                                          Comet Lovejoy (C/2017 E4)

A new Comet Lovejoy should not be confused with the Comet Lovejoy (C/2014 Q2) SpaceWatchtower reported on back on 2015 January 7. Discovered just last month by a prolific amateur astronomer, Terry Lovejoy in Australia, this Comet Lovejoy has continued brightening to about +7.0 visual magnitude.

This Comet Lovejoy rises in the early morning just above the east-northeast horizon, having just passed the Constellation Pegasus the Winged Horse a few days ago.

                                         Comet Johnson (C/2015 V2)

Discovered in 2015, it is unsure whether Comet Johnson is a long-period comet (that might not come back to the Inner Solar System for another 14 million years) or a hyperbolic comet (which is destined to leave our Solar System after this one pass around our Sun).

Later this month, Comet 41P/Tuttle-Giacombini-Kresák will join Comet Johnson in the Constellation Hercules. Comet Johnson will be easier to spot when it passes three bright stars in Hercules on April 22 [when it will lie between Stars Tau (τ) Herculis and (υ) Upsilon Herculis], and again on April 25 [when it will lie between Stars Phi (φ) Herculis and (υ) Upsilon Herculis].

Comet Johnson is expected to reach visual magnitude +7.4 by the end of the month. However, since it will not fly-by the Sun until mid-June, there is a chance it could get even brighter—perhaps, reaching naked-eye brightness. So, this is a comet to keep watching!

                                    Comet Pan-STARRS (C/2015 ER61)

This month, we may get to see another Comet Pan-STARRS, this time C/2015 ER61. On 2013 March 5, SpaceWatchtower reported on a Comet Pan-STARRS (C/2011 L4), that was then brightening in the sky.

Pan-STARRS (Panoramic Survey Telescope and Rapid Response System) is a robotic system of astronomical cameras, telescopes, and computers continually watching the sky for asteroids (particularly near-Earth asteroids which could one day threaten Earth), comets, variable stars, and other celestial objects. It is expected to eventually create a data-base of space objects, down to 24th visual magnitude, over 75 percent of the sky—the part of the sky visible from its base in Hawaii.

Although this Comet Pan-STARRS was very dim (visual magnitude +21) when it was discovered two years ago, it has brightened considerably as it approaches our Sun. This month, it has brightened to visual magnitude +6.5.

It passes the Earth on April 19 at a distance of 109 million miles / 175 million kilometers, before it swings around the Sun on May 10. So, it could brighten even more over the next few weeks.

Currently, this Comet Pan-STARRS appears as a tiny fuzz-ball in Constellation Aquarius the Water Bearer, very low in the pre-dawn sky. It may become a little easier to spot as it rises just before dawn, but it will become more difficult to see as the sky brightens.

Internet Links to Additional Information ---

SpaceWatchtower Monthly Astronomical Calendar ---
Current Month (2017 April):
Link >>>
Calendar Archives: Link >>>

Comet: Link >>>

Comets ---
Comet 41P/Tuttle-Giacombini-Kresák:
Link >>>
Comet Lovejoy (C/2017 E4): Link >>>
Comet Johnson (C/2015 V2): Link >>>
Comet Pan-STARRS (C/2015 ER61):
Link >>>

Pan-STARRS: Link >>>

Related Blog Posts ---

"Two Dim Comets May Be Visible in a Telescope." 2017 Feb. 19.

 Link >>>


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

Link >>>


"European Space Probe Aims for 1 Comet, Finds 2." 2014 July 22.

Link >>>


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

Link >>>


"Comet LINEAR Suddenly Brightens." 2013 Oct. 22.

Link >>>


"Comet ISON to Fly by Mars." 2013 Aug. 24.

Link >>>

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

"Possible Naked-eye Comet in March." 2013 Feb. 7.

Link >>>

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

Link >>>

     Safe Public Viewing of the Great American Solar Eclipse
                         Monday, August 21, 2017
     Mt. Lebanon Public Library, South Suburban Pittsburgh
More Info: Link >>>

Source: Glenn A. Walsh Reporting for SpaceWatchtower, a project of Friends of the Zeiss.
             2017 April 12.

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