Mercury at Greatest Eastern Elongation
Mercury at Greatest Eastern Elongation

This Week’s Sky: February 10 to 16

Among this week’s highlights, Mercury reaches its greatest eastern elongation and Neptune passes Phi Aquarii.

Monday, February 10 evening – Mercury at Greatest Eastern Elongation

Mercury at Greatest Eastern Elongation

On the evening of Monday, February 10, Mercury (orbit shown as red curve) will reach its widest separation, 18 degrees east of the Sun. With Mercury sitting above a nearly vertical evening ecliptic, this will be the best appearance of the planet in 2020 for Northern Hemisphere observers. The optimal viewing times fall between 6 and 7 p.m. local time. Viewed in a telescope (inset) the planet will exhibit a waning half-illuminated phase.

Monday, February 10 after dusk – Neptune close to Star Phi Aquarii

Neptune close to Star Phi Aquarii

On the evenings surrounding Monday, February 10, distant, dim Neptune (annotated red path) will pass very close to a golden, naked-eye star designated Phi (φ) Aquarii — allowing Neptune to be easily located and viewed in backyard telescopes after dusk. Closest approach will occur on February 10, when the planet and the star will be separated by only 2 arc-minutes and will easily appear together in the eyepiece of a telescope at high magnification (red circle). Your telescope is likely to flip and/or invert the view shown here.

Tuesday, February 11 to Sunday, February 23, after evening twilight – Evening Zodiacal light

Evening Zodiacal light

For about half an hour after dusk during the two-week period preceding the New Moon on February 23, look west-southwest for a broad wedge of faint light rising from the horizon and centered on the ecliptic (green line). This is the zodiacal light — reflected sunlight from interplanetary particles of matter concentrated in the plane of the solar system. Try to observe from a location without light pollution, and don’t confuse the zodiacal light with the brighter Milky Way to the northwest.

Thursday, February 13 pre-dawn – Moon Occults Stationary Asteroid Juno

Moon Occults Stationary Asteroid Juno

On Thursday, February 13, the main belt asteroid designated (3) Juno will cease its regular eastward motion across the distant stars of Virgo and begin a westward retrograde loop that will last until early June. Between 5:15 and 6 a.m. EST that morning, the bright, waning gibbous Moon will occult the dim, magnitude 10.2 asteroid (exact times vary by location). Observers in North America (except northeastern Canada), Central America, the Caribbean, and northern South America can see this event.

Saturday, February 15 at 22:17 GMT – Last Quarter Moon

Last Quarter Moon

At its last quarter phase, the Moon rises around midnight and remains visible in the southern sky during morning daylight. At this time, the Moon is illuminated on the eastern side, towards the pre-dawn sun. Last quarter moons are positioned ahead of the Earth in our trip around the sun. About three-and-a-half hours later, Earth will occupy that same location in space. After this phase, the waning Moon will traverse the last quarter of its orbit around the Earth, on the way to New Moon.

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 to tour the universe together.