Jan09-2021-at-5-pm-Mercury-below-Jupiter-and-Saturn
Mercury below Jupiter and Saturn (Chris Vaughan, Starry Night Education)
This Week’s Sky: January 4 to 10, 2021

Jupiter and Saturn provide a continuation of last month’s show, meeting with Mercury post sunset this week.

Wednesday, January 6 – Last quarter Moon (at 9:37 GMT)

Last quarter Moon (Chris Vaughan, Starry Night Education)

When the Moon reaches its third quarter phase at 9:37 GMT (or 2:37 a.m. EST) on Wednesday, January 6, it will rise at about midnight, and then remain visible in the southern sky all morning. At third, or last, quarter the Moon is illuminated on its western side, towards the pre-dawn Sun. Last 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 week of dark, moonless evening skies that follow this phase will be ideal for observing deep sky targets.

Saturday, January 9 – Mercury below Jupiter and Saturn (post-sunset)

Mercury below Jupiter and Saturn (Chris Vaughan, Starry Night Education)

From January 9 to 12, the planet Mercury will climb past the gas giants Jupiter and Saturn, which will be descending sunward. After sunset, look just above the southwestern horizon after sunset on Saturday, January 9 to see Mercury sitting just a thumb’s width to the lower left (or 1.7 degrees to the celestial south) of Saturn, with brighter Jupiter positioned above them. All three objects will fit within the field of view of binoculars (red circle). Mercury and Saturn will be a challenge to see within the evening twilight – except for skywatchers at southerly latitudes, where the sky will darken faster. The orbital motion (red arc) of Mercury will be carrying the speedy planet between Earth and the sun, while the gas giants will be on the far side of our star.

Sunday, January 10 – Jupiter, Saturn and Mercury in a 2.3-degree circle (post-sunset)

Jupiter, Saturn and Mercury in a 2.3-degree circle (Chris Vaughan, Starry Night Education)

Mercury will continue to move past Jupiter and Saturn on Sunday, January 10. After 24 hours, the speedy planet will be higher, forming a small triangle just above the southwestern horizon with Saturn two degrees to Mercury’s right and Jupiter positioned two degrees above them. Mercury and Saturn will be a challenge to see within the evening twilight. The trio will easily fit into the field of view of binoculars (red circle), but ensure that the Sun has completely vanished below the horizon before using them. The three planets will set at about 6 p.m. local time, an hour after sunset.

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.

Get a Free Digital Issue