In The Sky This Month – May 2011

This feature highlights a number of meteor showers, comets and asteroids which are visible during the month of May 2011.

May 2011 Highlights
* Venus, Jupiter, Mercury and Mars gather low in the dawn sky
* Saturn is easy to spot in the evening
* Eta Aquariids put on a night display for southern observers

Note: If anyone has pictures or observations of these objects/events and want to share them with my readers, send them to the Transient Sky at <transientsky1@yahoo.com>.

Planets

Moon – The table below lists important lunar dates for the month, including the phases of the Moon and nights of lunar-planetary and lunar-stellar conjunctions.

May 1 - Moon 7° from Mercury, 6° from Jupiter and 5° from Mars
May 3 - New Moon
May 5 - Moon 7° from bright star Aldebaran
May 8 - Moon 9° from bright star Pollux
May 9 - Moon 5° from Beehive Cluster
May 10 - First Quarter Moon
May 11 - Moon 5° from bright star Regulus
May 14 - Moon 8° from Saturn
May 15 - Moon 3° from bright star Spica
May 17 - Full Moon
May 18 - Moon 3° from bright star Antares
May 24 - Third Quarter Moon
May 29 - Moon 5° from Jupiter
May 30 - Moon 4° from Mars
May 31 - Moon 4° from Venus

Saturn – Saturn is now a month past opposition. As a result, the ringed planet is still near its brightest for the year (currently magnitude +0.5 to +0.7) and is also visible throughout the evening and most of the morning hours. Saturn is a slow moving planet and takes 29 years to circle the Sun as well as 29 years to do one circuit around the ecliptic constellations. As has been the case all year long, Saturn is still located in Virgo about 13-14° from 1st magnitude Spica.

May 14 - Saturn and Moon 8° apart

Venus, Mercury, Mars and Jupiter –  The planetary show of the year is a series of compact groupings involving Venus, Mercury, Mars and Jupiter. Unfortunately, all the action will take place very close to the eastern horizon in a bright dawn sky for northern observers. South of the equator the view will be much easier to see.

From May 7 to 15, Venus, Mercury and Jupiter will be within 5° of each other. On May 11, the trio will be within ~2° of each other. A similar trio of Venus, Mercury and Mars will be within 5° of each other from May 15-25 with their tightest grouping of ~2° on May 21.

May 1 - Moon 7° from Mercury, 6° from Jupiter and 5° from Mars
May 1 - Jupiter and Mars within 0.4° of each other
May 6 - Mercury at greatest elongation west
May 7 - Mercury and Venus within 1.4° of each other
May 11 - Venus, Mercury and Jupiter within 2.1° of each other
May 18 - Mercury and Venus, again, within 1.4° of each other
May 21 - Venus, Mars and Mercury within 2.1° of each other
May 23 - Venus and Mars within 1° of each other
May 29 - Moon 5° from Jupiter
May 30 - Moon 4° from Mars
May 31 - Moon 4° from Venus

Meteors

Meteor activity is near a seasonal minimum in May. The year is usually split in 2 with January through June having low rates with few major showers while July through December have high rates with many major showers.

Sporadic Meteors

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 May mornings, 10-12 or so Sporadic meteors can be observed per hour from a dark moonless sky.

Major Meteor Showers

Eta Aquariids (ETA)

The Eta Aquariids are a major shower, especially for southern hemisphere observers, when they peak on May 6. For northern observers, the shower will only be observable for an hour or two before dawn. Since the radiant doesn’t get very high for NH observers, rates can be low. The radiant is located near the “jar” of Aquarius.

The ETA were produced by Comet Halley which also gives us the Orionids in October. Models suggest that the ETA were released by Comet Halley no later than 837 AD. The Orionids are easy to see because the particles are hitting the Earth from the anti-solar direction. This means the meteor shower can be seen in the middle of the night. The ETA are produced by meteoroids moving outbound from the Sun, as a result the radiant is located relatively close to the Sun. As a result the ETA radiant is only visible for an hour or so before twilight. This year the Moon is near New so the sky will be dark.

The shower spans from April 19 to May 28 with a peak around May 5 with a maximum ZHR of ~60. The poor placement of the radiant for northern observers will greatly limit the number of observed meteors.

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 2011 Meteor Shower Calendar.

Comets

Naked Eye Comets (V < 6.0)

None this month…

Binocular Comets (V = 6.0 – 8.0)

None this month…

Small Telescope Comets (V = 8.0 – 10.0)

C/2011 C1 (McNaught)

It seems like every year sees a bright Comet McNaught and this year is no different. The 58th comet discovery by Rob McNaught and 74th from Siding Spring Observatory, C/2011 C1 was first seen on February 10th of this year. Though intrinsically faint, the comet is currently being reported as bright as magnitude 9.0. CCD images taken by the author on Apr 1 UT confirm that the comet was between magnitude 9.0 and 9.5 at that time (see image below). Unfortunately the comet should fade this month as it passed perihelion on April 17 at a distance of 0.88 AU from the Sun. The comet starts May 0.92 AU from the Sun and 1.23 AU from Earth. These distances will have increased to 1.02 AU from the Sun and 1.39 AU from Earth by mid-month and 1.17 AU from the Sun and 1.52 AU from Earth at the end of the May.  Comet C/2011 C1 is a morning object low in the east and travels from Pegasus to Pisces this month.

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Asteroids

Binocular and Small Telescope Asteroids (V < 8.0)

(4) Vesta

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 this summer 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 spends the month around magnitude 7.3 to 6.9 as it moves eastwards through western Capricornus. Opposition is on August 4 at magnitude 5.6.

A finder chart (needs to be flipped upside down for Northern Hemisphere observers) can be found at the Royal Astronomical Society of New Zealand. Finder chart for Vesta from Heavens Above.