A diagram of the radiant of the Eta Aquariids Meteor Shower on May 6, 2021. | SkyNews
Eta Aquariids Meteor Shower peak (Chris Vaughan, Starry Night Education)

This Week’s Sky: May 3 to 9, 2021

Mercury starts to show itself after sunset this week — and don’t forget to look for Eta Aquariid meteors before dawn on Thursday.

Monday, May 3 – Third quarter Moon (at 19:50 GMT)

A diagram of the Third quarter Moon May 3, 2021. | SkyNews
Third quarter Moon (Chris Vaughan, Starry Night Education)

The Moon will officially reach its third quarter phase at 3:50 p.m. EDT (or 19:50 GMT) on Monday, May 3. At third quarter, our natural satellite always rises in the middle of the night and remains visible in the southern sky all morning. The Moon will appear half-illuminated, on its western side towards the pre-dawn Sun. Third quarter moons are positioned ahead of the Earth in our trip around the Sun. About 3.5 hours later, Earth will occupy that same location in space. The ensuing week of moonless evening skies will be ideal for observing deep sky targets.

Tuesday, May 4 – Moon between Jupiter and Saturn (pre-dawn)

A diagram of the Moon between Jupiter and Saturn on May 4, 2021. | SkyNews
Moon between Jupiter and Saturn (Chris Vaughan, Starry Night Education)

When the third quarter Moon rises over the southeastern horizon at about 3 a.m. local time on Tuesday, May 4, it will be positioned below and between bright Jupiter on the Moon’s left (or celestial northeast), and dimmer Saturn to the Moon’s upper right (or celestial northwest). The trio will make a lovely wide-field photograph when composed with some interesting landscape scenery.

Wednesday, May 5 – May is Mercury month (after sunset)

A diagram of Mercury in May. | SkyNews
Mercury in May (Chris Vaughan, Starry Night Education)

After sunset throughout the month of May, Mercury will be easily visible by Northern Hemisphere observers while it travels on the high side of a nearly vertical evening ecliptic plane. The speedy planet will climb away from the Sun until mid-month, when it will be at peak visibility. In the second half of the month Mercury will descend sunward, passing much brighter and slower Venus near month-end. As the sky grows darker each night, look for Mercury low in the west-northwest as a white point of light shining some distance above Venus. Since the planet will be traversing the space between us and the Sun, telescope views of Mercury in May will show that its disk is growing larger while waning in illuminated phase (inset).

Thursday, May 6 – Eta Aquariids Meteor Shower peak (pre-dawn)

A diagram of the radiant of the Eta Aquariids Meteor Shower on May 6, 2021. | SkyNews
Eta Aquariids Meteor Shower peak (Chris Vaughan, Starry Night Education)

The annual Eta Aquariids Meteor Shower is produced by particles of material left behind by repeated passages of Halley’s Comet. The shower, which runs from April 19 to May 28, will peak in intensity before dawn (according to the 2021 Observer’s Handbook, at 2 a.m. UTC) on Thursday, May 6. Aquariids meteors will appear to be travelling away from a radiant point in Aquarius. That spot will lie near the southeastern horizon, not far from Jupiter. The southerly radiant makes this shower better for observers at low latitudes. On the peak night, watch for up to a few dozen meteors per hour, including some fireballs. A 25-per-cent-illuminated, waning crescent Moon in the sky on the peak morning will reduce the number of meteors seen.

Friday, May 7 – The Virgo cluster of galaxies (all night)

A diagram of the Virgo cluster of galaxies on May 7, 2021. | SkyNews
The Virgo cluster of galaxies (Chris Vaughan, Starry Night Education)

The Virgo Cluster contains as many as 2,000 galaxies, dozens of which are visible with amateur telescopes under dark sky conditions during spring evenings. The cluster spans nearly a fist’s diameter (eight degrees) of sky on the border between Virgo and Coma Berenices. The brightest member is the elliptical galaxy Messier 49, which is located a generous palm’s width to the lower right (or 8.5 degrees to the celestial southwest) of the bright star Vindemiatrix (Epsilon Virginis). Using low magnification, aim your telescope mid-way between Vindemiatrix and the bright star Denebola (Beta Leonis). That region contains a large number of bright galaxies, including the Messier objects M84 and M86 through M91. Markarian’s Chain is a spectacular, curved line of galaxies spanning 1.5 degrees. It arcs to the upper left (celestial north) from M84.

Saturday, May 8 – Whirlpool and Pinwheel Galaxies (all night)

A diagram of the Whirlpool and Pinwheel Galaxies on May 8, 2021. | SkyNews
Whirlpool and Pinwheel Galaxies (Chris Vaughan, Starry Night Education)

On evenings during May, the Big Dipper is positioned nearly overhead in the northeastern sky. Under dark sky conditions, two impressive galaxies can be seen in binoculars (red circle) and backyard telescopes. You can use the bright star Alkaid at the tip of the Big Dipper’s handle to locate them. The Pinwheel Galaxy, or Messier 101, is a spectacular face-on spiral galaxy positioned a palm’s width to the lower left (or 5.5 degrees to celestial north) of Alkaid, forming an equilateral triangle with Mizar, the double star at the bend of the handle. This relatively close galaxy (21 million light-years away) is nearly as large as the full Moon in the sky (inset). Since the galaxy’s light is spread over such a large area, its overall brightness is low. Aim your binoculars several finger’s widths above Alkaid to discover the iconic Whirlpool Galaxy, also known as Messier 51. This spiral galaxy’s angular size is smaller, but it will look somewhat brighter in your binoculars and telescope (inset). A secondary galaxy core designated NGC 5195 is linked to Messier 51 by a stream of stars.

Chris Vaughan is a science writer, geophysicist, astronomer, planetary scientist and an “outreach RASCal.” He writes Astronomy Skylights, and you can follow him on Twitter at @astrogeoguy. He can also bring his Digital Starlab portable inflatable planetarium to your school or other daytime or evening event. Contact him through AstroGeo.ca to tour the universe together.