A diagram of Earth at aphelion on July 5, 2021. | SkyNews
Earth at aphelion on July 5, 2021 (Chris Vaughan, Starry Night Education)

This Week’s Sky: July 5 to 11, 2021

The Earth will be at its farthest point from the Sun this week, while the Moon reaches its new phase.

Monday, July 5 – Earth at aphelion (at 22:00 GMT)

A diagram of Earth at aphelion on July 5, 2021. | SkyNews
Earth at aphelion on July 5, 2021 (Chris Vaughan, Starry Night Education)

On Monday, July 5 at 6 p.m. EDT, or 22:00 GMT, Earth will reach aphelion, its farthest position from the Sun for this year. The aphelion distance of 152,100,533 million kilometres is 1.67 per cent farther from the Sun than the mean Earth-Sun separation of 149,597,871 kilometres, which is also defined to be 1 Astronomical Unit (1 AU). Earth’s minimum distance from the sun, or perihelion, will occur on January 4.

Thursday, July 8 – Crescent Moon with Mercury (pre-dawn)

A diagram of the Crescent Moon with Mercury, pre-dawn on July 8, 2021. | SkyNews
Crescent Moon with Mercury, pre-dawn on July 8, 2021 (Chris Vaughan, Starry Night Education)

For a brief period before sunrise on Thursday, July 8, the slim crescent of the old, waning Moon will be positioned several finger widths to the left (or 4 degrees to the celestial northeast) of the bright dot of Mercury. Look for the pair sitting very low over the east-northeastern horizon from the time they rise at about 4:20 a.m. local time until about 5 a.m. The Moon and Mercury will be close enough to see them together through binoculars (red circle) — but turn your optics away before the Sun rises.

Friday, July 9 – New Moon (at 9:16 p.m. EDT)

A diagram of the New Moon on July 9, 2021. | SkyNews
New Moon on July 9, 2021 (Chris Vaughan, Starry Night Education)

The Moon will officially reach its new phase on Friday, July 9 at 9:16 p.m. EDT (or 01:16 GMT on Saturday, July 10). While new, the Moon is travelling between Earth and the Sun. Since sunlight can only reach the far side of the Moon, and the Moon is in the same region of the sky as the Sun, the Moon becomes unobservable from anywhere on Earth for about a day (except during a solar eclipse). After the new Moon phase Earth’s celestial night-light will return to shine in the western evening sky.

Sunday, July 11 – Crescent Moon passes Venus and Mars (after sunset)

A diagram of the Crescent Moon passing Venus and Mars on July 11, 2021. | SkyNews
Crescent Moon passes Venus and Mars on July 11, 2021 (Chris Vaughan, Starry Night Education)

Low in the west-northwestern sky after sunset on Sunday, July 11, the young crescent Moon will shine a generous palm’s width to the right (or 6.5 degrees to the celestial northwest) of two planets — bright Venus and much fainter Mars. Before they set at about 10 p.m. local time, the trio will make a nice wide-field photo when composed with some interesting scenery. On the following evening, the Moon’s orbital motion will lift it to sit a similar distance above those two planets.

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.

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