2019 May 19 A Circumhorizontal Arc Over Ohio Image Credit &…

2019 May 19

A Circumhorizontal Arc Over Ohio
Image Credit & Copyright: Todd Sladoje

Explanation: Why would clouds appear to be different colors? The reason here is that ice crystals in distant cirrus clouds are acting like little floating prisms. Sometimes known as a fire rainbow for its flame-like appearance, a circumhorizon arc lies parallel to the horizon. For a circumhorizontal arc to be visible, the Sun must be at least 58 degrees high in a sky where cirrus clouds are present. Furthermore, the numerous, flat, hexagonal ice-crystals that compose the cirrus cloud must be aligned horizontally to properly refract sunlight in a collectively similar manner. Therefore, circumhorizontal arcs are quite unusual to see. This circumhorizon display was photographed through a polarized lens above Dublin, Ohio in 2009.

∞ Source: apod.nasa.gov/apod/ap190519.html

2019 May 18 Atlas, Daphnis, and Pan Image Credit: Cassini…

2019 May 18

Atlas, Daphnis, and Pan
Image Credit: Cassini Imaging Team, SSI, JPL, ESA, NASA

Explanation: Atlas, Daphnis, and Pan are small, inner, ring moons of Saturn. They are shown at the same scale in this montage of images by the Cassini spacecraft that made its grand final orbit of the ringed planet in September 2017. In fact, Daphnis was discovered in Cassini images from 2005. Atlas and Pan were first sighted in images from the Voyager 1 and 2 spacecraft. Flying saucer-shaped Atlas orbits near the outer edge of Saturn’s bright A Ring while Daphnis orbits inside the A Ring’s narrow Keeler Gap and Pan within the A Ring’s larger Encke Gap. The curious equatorial ridges of the small ring moons could be built up by the accumulation of ring material over time. Even diminutive Daphnis makes waves in the ring material as it glides along the edge of the Keeler Gap.

∞ Source: apod.nasa.gov/apod/ap190518.html

Meteor Activity Outlook for May 18-24, 2019

Timothy Pierce captured this brilliant green fireball at 7:13 Universal Time on February 25, 2019 from Key West, Florida USA. © Timothy Pierce

During this period the moon reaches its full phase on Saturday May 18th. At this time the moon lies above the horizon all night long, making meteor observations difficult at best. As the week progresses the moon’s phase will wane and it will rise later each night. This will provide some dark skies between dusk and moon rise but unfortunately this is a very slow time for meteor activity. The estimated total hourly meteor rates for evening observers this week is near 2 for those viewing from the northern hemisphere and 3 for those located south of the equator. For morning observers the estimated total hourly rates should be near 4 as seen from mid-northern latitudes (45N) and 9 as seen from tropical southern locations (25S). The actual rates will also depend on factors such as personal light and motion perception, local weather conditions, alertness and experience in watching meteor activity. Rates are reduced by moonlight during this period. Note that the hourly rates listed below are estimates as viewed from dark sky sites away from urban light sources. Observers viewing from urban areas will see less activity as only the brightest meteors will be visible from such locations.

The radiant (the area of the sky where meteors appear to shoot from) positions and rates listed below are exact for Saturday night/Sunday morning May 18/19. These positions do not change greatly day to day so the listed coordinates may be used during this entire period. Most star atlases (available at science stores and planetariums) will provide maps with grid lines of the celestial coordinates so that you may find out exactly where these positions are located in the sky. A planisphere or computer planetarium program is also useful in showing the sky at any time of night on any date of the year. Activity from each radiant is best seen when it is positioned highest in the sky, either due north or south along the meridian, depending on your latitude. It must be remembered that meteor activity is rarely seen at the radiant position. Rather they shoot outwards from the radiant so it is best to center your field of view so that the radiant lies at the edge and not the center. Viewing there will allow you to easily trace the path of each meteor back to the radiant (if it is a shower member) or in another direction if it is a sporadic. Meteor activity is not seen from radiants that are located far below the horizon. The positions below are listed in a west to east manner in order of right ascension (celestial longitude). The positions listed first are located further west therefore are accessible earlier in the night while those listed further down the list rise later in the night.

Radiant Positions at 22:00 LDST

Radiant Positions at 22:00 Local Daylight Saving Time

Radiant Positions at 01:00 LDST

Radiant Positions at 1:00 Local Daylight Saving Time

Radiant Positions at 04:00 LDST

Radiant Positions at 4:00 Local Daylight Saving Time

These sources of meteoric activity are expected to be active this week..

Details on each source will continue next week when viewing conditions are more favorable.

SHOWER DATE OF MAXIMUM ACTIVITY CELESTIAL POSITION ENTRY VELOCITY CULMINATION HOURLY RATE CLASS
RA (RA in Deg.) DEC Km/Sec Local Daylight Saving Time North-South
tau Herculids (TAH) Jun 03 14:36 (219) +37 15 01:00 <1 – <1 III
Anthelions (ANT) 16:44 (251) -23 30 02:00 1 – 2 II
eta Aquariids (ETA) May 07 23:16 (349) +04 66 09:00 <1 – 3 I
June mu Cassiopeiids (JMC) Jun 08 23:40 (355) +48 42 09:00 <1 – <1 IV
Arietids (ARI) Jun 08 01:48 (027) +21 41 11:00 <1 – <1 II

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