On Friday March 26th the inner planet Venus will have moved into superior conjunction – on the opposite side of the Sun from the Earth. Venus will reappear on the east side of the Sun later next month and start becoming visible in the evening skies over the western horizon.
Our Moon does not follow a path with the Earth around the Sun that is parallel with the Earth’s orbit, the ecliptic. The Moon is tilted or inclined by approximately 5.14o from the Earth’s orbital path meaning that there are places where the Moon’s orbital path intersects or crosses the Earth’s orbital path, the ecliptic. At up to 3 times each month the Moon will cross the ecliptic moving south or north in what is called a node crossing – one ascending and the other descending.
However with regard to the celestial equator, an extension of the Earth’s equator into space, the maximum declination for our Moon, as measured from the celestial equator, could be as much as about 28.64o either north or south based on the Earth’s axial tilt of 23.5o plus the Moon’s inclination angle 5.14o (23.5 + 5.14 = 28.64o).
This month our Moon reaches a maximum northernmost declination of 25.3o on Monday March 22nd.
Saturday March 20th is an equinox day. While typically called the Vernal or Spring Equinox it is more globally appropriate to call this day the March Equinox as it is the start of Fall in the Southern Hemisphere. The official time for the equinox is 09:40 UT on the 20th which for my time zone is 5:40 am CDT. So for those in the northern hemisphere winter is ending and spring has ‘sprung’ (starts). From a geographical perspective we would describe the Sun as being over the Earth’s equator, and as this graphic shows there would be an equal amount of daylight and night on our planet as a result.
At mid-day on the equator the sun is directly overhead and from that latitude you have no elongated shadow, just a ‘blob-like’ shadow at your feet as this picture of my feet taken at mid-day in Quito Ecuador shows.
Northern hemisphere spring, Astronomically speaking, is when the Sun reaches the celestial coordinates of 0 hours and 0 degrees as it moves northward along the ecliptic crossing the celestial equator. At this location the Sun is just within the constellation of Pisces the Fishes and not entering Aries the Ram as the pseudoscience of astrology would have you believe.
To learn more about the celestial coordinates click here to read a previous post about seasons and the equinox.
Click here to see the online world sunlight map used to make the day/night graphic at the top of the page.
Celebrate Solar Week March 22nd-26th. Click here to go to the Solar Week web site.
During a trip to Quito Ecuador to visit one of the exchange student we had hosted, and her family, we spent the day at a Museum on the equator, Mitad del Mundo. I brought along my over-sized protractor knowing in advance that we would be at the museum. So at mid-day I had my wife stand on the equator (yellow line) and hold a string to the top of her head while Cathy, a sister of our exchange student, held the protractor. This was done during the summer so the Sun was over the northern horizon at mid-day and the Sun’s angle above the northern horizon was around 75o.
Here is a short series of hourly pictures taken during the day on the September equinox on the equator in Quito Ecuador at Collegio Menor San Francisco de Quito, a private school that I visited and did the SunShIP project with (Sun Shadow Investigation Project).
Friday evening March 19th look for the 6.7-day old waxing crescent Moon to be about 3o from the ‘Red Planet’ Mars, and about 5-6o from the reddish star Aldebaran in Taurus the Bull. All three should just barely fit within the field of view of 7×50 binoculars.
Apogee – Descending Node – Conjunction with the Pleiades
Our Moon reaches apogee, (furthest from Earth), for this orbit, on Thursday March 18th. For this apogee the 6.6-day old waxing crescent Moon will be at a distance of 31.77 Earth diameters, 251,841 miles (405,300 km) from the Earth.
The 6.6-day old waxing crescent Moon crosses the plane of the ecliptic moving south. This is known as the descending node, one of two intersections the Moon’s orbital path (dark green line) has with the ecliptic.
Conjunction with the Pleiades
The apogee Moon, at nearly first quarter phase, will be above the western horizon and will be within a few degrees from the open star cluster the Pleiades. This should make for a good view with binoculars.
Does our Moon actually go around the Earth as this graphic shows? From our perspective on the Earth the Moon appears to circle around the Earth. However, in reality, the Moon orbits the Sun together with the Earth*
*Click here to read my Scope on the Sky column “The Real Shape of the Moon’s Orbit”. (PDF)
Click here to go to the Qué tal in the Current Skies web site for monthly observing information, or here to return to bobs-spaces.
Tuesday and Wednesday mornings, March 9th and 10th, the thin waning crescent Moon wil be passing by the planets Saturn. Jupiter, and the inner planet Mercury. On the 9th the 26-day old waning crescent Moon will be about 3-4o from Saturn and on the 10th the 28-day old Moon will be about 4-5o and about 6-7o from Mercury.
Several times each year a down-looking camera on the International Space Station (ISS) is made available by NASA for making picture requests for the surface of the Earth. The camera is the Sally Ride Earthkam and as the blog title says, this is Sally Ride EarthKam Week. As these pictures, show our planet has a remarkably diverse surface.
A popular thing to do is choose an orbital path and follow it across a part of the Earth you are interested in. Maybe where you live, a place you have visited or want to visit? Zoom in to see more detail, especially where the orbital path (the red one – for daylight), crosses. If satisfied click on the red line and make your request.
Participating in the program requires registering so you can receive e-mail notifications of the next Earthkam week. I am registered as a classroom Teacher however any educator may apply. This would be great for Scout groups, or any other group interested in learning more about our planet, not to mention learning about NASA and its missions to Earth as well as off world endeavors.
Pictures from March 3-5 2021 Earthkam Week
On Saturday March 6th Mercury, the innermost planet, will reach its orbital position known as greatest western elongation at 27.3o. At that moment Mercury, the Sun, and the Earth, would be arranged in something close to approximating a right angle as this graphic shows. Even though it sounds confusing, at western elongation for either Mercury or Venus the inner planet will be to the right of the Sun as we view them, meaning that at western elongation an inner planet rises in the east before the Sun rises. And at eastern elongation with the inner planet on the left side of the Sun the inner planet follows the Sun across the sky setting after the Sun sets.
From our perspective the orbits of Mercury and Venus appear to move from one side of the Sun to the other – out to the left (east) from the Sun to eastern elongation, then reverse and move westward (inferior conjunction) between the Earth and the Sun to western elongation. From there the inner planet moves eastward going behind the Sun (superior conjunction) and eventually reappearing on the eastern side of the Sun for an eastern elongation. Repeat over and over – do not stop!
Friday March 5th the 22-day old last quarter Moon crosses the plane of the ecliptic moving south. This is known as the descending node, one of two intersections the Moon’s orbital path (dark green line) has with the ecliptic.
On the date of the descending node the 22-day old last quarter Moon will be over the southern horizon at sunrise local time, and about 3-4o from the reddish star Antares in Scorpius the Scorpion.