In The Sky This Month – April 2010
April 5, 2010
This feature highlights a number of meteor showers, comets and asteroids which are visible during the month of April 2010. This first half of the month is a great time to see Mercury, the innermost planet. It can be easily located low in the west during evening twilight right next to Venus.
Note: If anyone has pictures or observations of these objects/events and want to share them, send me a comment and I’ll post them on the blog.
Mercury and Venus – Venus is the brilliant star low in the west right during evening twilight. It sets an hour and a half after the Sun at the start of the month. By the end of the month, it is up for 2 hours and 15 minutes after sunset. Venus will continue to climb higher and brighten for the next few months.
Mercury is usually difficult to observe. This month, on the other hand, is a perfect time to see this elusive planet. Not only is Mercury as high above the western horizon as it can get for observers in the Northern Hemisphere, but Venus can be used to easily find it. Mercury and Venus are located within 5° of each other until April 12. Mercury is the bright, though still much fainter than Venus, “star” to the lower right of Venus. By the 2nd half of the month, Mercury will be too faint and too close to the Sun to be seen.
Apr 3 - Mercury and Venus within 3° of each other Apr 8 - Mercury at Greatest Elongation East Apr 15/16 - Moon passes 4° from Venus and 1.5° from Mercury
Mars – This month the Earth and Mars continue to move further apart. As a result, Mars will continue to fade from magnitude +0.2 to +0.7. Still it will be a brilliant red beacon nearly overhead right after sundown. It’s brightness is comparable to that of the other bright stars. Note that unlike the stars which twinkle, Mars shines with an unwavering red glow.
Apr 17 - Mars within 1.1° of center of Beehive Cluster Apr 22 - Moon passes close (4°) to Mars
Saturn – Saturn was at opposition in Virgo on March 21. This month Saturn is visible low in the east-southeast during the early evening hours. It will slowly fade from magnitude +0.6 to +0.8 throughout the month. Telescope users should note that Saturn’s rings are still within a few degrees of edge-on.
Apr 25 - Moon and Saturn within 7° of each other
Jupiter – Jupiter once again returns to sight as a brilliant star low in the east-southeast right before dawn. The magnitude -2 planet will get brighter and better place for observing over the next few months.
Apr 11 - Moon and Jupiter within 6° of each other
April is still a time of low meteor activity though it will experience a slight uptick in activity due to the Lyrids. The year is usually split in 2 with January through June having low rates with few major showers while July through December (really through the 1st week of January) have high rates with many major showers.
Sporadic meteors are not part of any known meteor shower. They represent the background flux of meteors. Except for the few days per year when a major shower is active, most meteors that are observed are Sporadics. This is especially true for meteors observed during the evening. During April, 9-11 or so Sporadic meteors can be observed per hour from a dark moonless sky.
Major Meteor Showers
April brings the first major meteor shower since the Quadrantids in early January. The Lyrids are produced by Comet Thatcher, a comet on a ~400 years orbit that has only been observed in 1861. The Lyrids, on the other hand, can be seen every year.
The radiant is located between the constellations of Lyra and Hercules. Though the radiant rises during the evening, the best time to see Lyrids is after 11 pm when the radiant is high in the sky.
The shower is active from April 16 to 25 with a peak on the morning of April 22. The shower only shows good levels of activity on the night of the peak. Even then, this is the most minor of the major showers with a peak rate of ~15-25 meteors per hour.
Though there are no predictions on enhanced activity, the Lyrids have been known to put on grand displays. The 1st great display goes back almost 25oo years while the last happened in 1982. So you never know, this year could be the next good display.
Minor Meteor Showers
Minor showers produce so few meteors that they are hard to notice above the background of regular meteors. Starting this month, info on most of the minor showers will be provided on a weekly basis by Robert Lunsford’s Meteor Activity Outlook.
Additional information on these showers and other minor showers not included here can be found at the following sites: Wayne Hally’s and Mark Davis’s NAMN Notes, and the International Meteor Organization’s 2008 Meteor Shower Calendar.
Naked Eye Comets (V < 6.0)
Binocular Comets (V = 6.0 – 8.0)
Small Telescope Comets (V = 8.0 – 10.0)
Comet 81P/Wild 2
Comet Wild 2 is a short-period Jupiter-family comet on a 6.4 year orbit. In 1974 a close approach to Jupiter placed the comet on its current orbit which allows (relatively) close approaches to the Sun and Earth. Swiss professional astronomer Paul Wild found the comet photographically on its first close perihelion in 1978. During its last perihelion passage it was the target of the NASA Stardust spacecraft which flew through its coma, collected cometary dust, and returned the dust to Earth. Though Wild 2 has become bright enough to be seen in small backyard telescopes before, this year’s apparition will be its best since discovery. Not till 2042 will it come closer, and even then only marginally so.
This year Wild 2 reached perihelion on February 22 at 1.60 AU while closest approach to Earth will occur on April 5 at 0.67 AU. The comet should fade this month but still be as bright as magnitude ~9.0 to 10.0 in April, it should remain brighter than magnitude 10.0 through May. At mid-month the comet a morning object located in Virgo at a distance of 1.68 AU from the Sun and 0.68 AU from Earth.
A finder chart for Comet Wild 2 can be found at Comet Chasing.
Comet C/2009 K5 (McNaught)
Comet McNaught is the brightest comet in the sky this month. It was discovered by Rob McNaught on the night of May 27, 2009 deep in the southern sky. The discovery was made with the 0.5-m Uppsala Schmidt telescope from Australia as part of the Siding Spring Survey (one of the three Catalina Sky Survey components) for unknown asteroids and comets. At the time, the comet was a faint 17th magnitude.
With perihelion on April 30 of this year at a distance of 1.42 AU from the Sun, C/2009 K5 is now bright enough to be seen in small backyard telescopes from dark sites. During the month it should be as bright as 8.0 to 8.5 magnitude as it moves north while paralleling the Milky Way in Aquila. The comet will be a morning object all month long. At mid-month it will be located 1.44 AU from the Sun and 1.27 AU from Earth.
A finder chart for Comet McNaught can be found at Comet Chasing.
Comet C/2009 O2 (Catalina)
This long-period comet was supposed to be as bright as magnitude 8 this month but fell short. In fact, images taken since the middle of March suggest the comet may be slowly “fizzling out”. I plan to write a liitle more on this comet and other “disintegrating” comets in a future post.
Binocular and Small Telescope Asteroids (V < 9.0)
Vesta is the brightest asteroid in the Main Belt. This is due to its high albedo (or reflectivity) which causes it to reflect ~42% of the light that strikes it. Vesta is also peculiar in that it appears to have evidence of volcanism on its surface. Similar to the Moon, Vesta may be covered with large expanses of frozen lava flows. It is classified as a V-type asteroid and is the only large asteroid with this classification. Many of the smaller V-type asteroids are chips of Vesta blasted off it by past asteroid and comet impacts. Vesta has dimensions of 347x336x275 miles or 578×560×458 km.
The maps below were created from images taken with the Hubble Space Telescope. The geography is dominated by a large impact crater located near the south pole (the blue ‘donut’ in the elevation map). Perhaps this crater is the result of the impact that blasted off the smaller V-type asteroids. We’ll know more next year when NASA’s Dawn spacecraft enters orbit around Vesta for a full year. Currently the encounter is scheduled for July 2011 to July 2012.
Vesta starts the month at magnitude 6.8 and steadily fades to mag 7.3. A small pair of binoculars will allow you to see Vesta among the stars in the “Sickle” of Leo.
Pallas is a dark carbonaceous asteroid though with a slightly bluish B-type spectrum. Due to its high inclination (tilt of its orbit with respect to Earth’s orbit) of 34 degrees it is a difficult target for future spacecraft missions. Pallas is similar in size to Vesta with dimensions of 350x334x301 miles or 582x556x501 km. The reason it is fainter than Vesta is its darker albedo of 16%. Though no spacecraft are scheduled to visit Pallas, Hubble was able to get some good images that clearly show its nearly spherical shape.
This month it brightens from magnitude 8.7 to a peak of 8.6 at opposition on April 20. By month’s end, Pallas is back down to magnitude 8.7. Over the course of the month as it travels north through the constellation of Serpens.