Saturday March 24th the position of the planet Mars, with respect to the Earth and the Sun, places this planet at what is called western quadrature. At that orbital position Mars, and actually any outer planet at their respective quadrature, is at a 90 degree angle from the Earth as this graphic shows, and the banner graphic at the top of the page shows. Think last quarter Moon as that is a fair comparison of the relative positions of Earth, Sun, and Mars. At this position Mars leads the Sun across the sky from east to west as the Earth is rotating, meaning that Mars rises before the Sun.
Wednesday and Thursday evenings March 21st and 22nd the waxing crescent Moon will pass across the constellation of Taurus the Bull. It will first be several degrees from the open star cluster the Pleiades and then the next day the Moon will be within 1-2o from the reddish star Aldebaran and the open star cluster the Hyades. The latter should prove to be a striking sight through binoculars.
Tuesday March 20th is an equinox day. This means that for those in the northern hemisphere winter is ending and spring has ‘sprung’ (starts). For our counterparts south of the equator summer is ending and fall is beginning. 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 officially (well at least astronomically) begins at 16:15 UT on the 20th (11:29 am CDT) 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 within the constellation of Pisces the Fishes and not just 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 19th-23rd. 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).
Over the next week or so the two inner planets will pass by each other coming the closest on the 19th when the two will be less then 4o from each other. With only casual observation one should notice that both planets are moving with respect to each other, but in opposite directions. Mercury is recently past its eastern elongation and is now moving westward, in retrograde, toward the Sun and inferior conjunction. On the other hand, or orbit, Venus is moving eastward out from a recent superior conjunction, opposite side of the Sun, toward its own respective eastern elongation.
This animated graphic shows Venus and Mercury over a period of several days from March 16th to the 29th of March. The time is set for 7:15 pm CDT and in the first several frames the planets are first shown as they would appear at 7:15 pm, then I added labels, then their respective orbits. To make the animation easier to see I also turned off daylight, and then finally the labels were turned off then back on at the end.
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.
Sunday evening March 19th the thin 1.5-day young waxing crescent Moon, and the two inner planets, Venus and Mercury, will be over the western horizon about 1 hour after sunset local time. All three will fit within the width of a 7×50 binoculars field of view (about 7o).
On Thursday March 15th Mercury, the innermost planet, will reach its orbital position known as greatest eastern elongation. At that moment Mercury, the Sun, and the Earth, would be arranged in something close to approximating a right angle as this graphic shows.
From our perspective the orbits of Mercury and Venus appear to move from one side of the Sun to the other – from superior conjunction, behind the Sun, out to the left (east) from the Sun to eastern elongation, then reverse and move westward through (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!
Currently Mercury is visible over the south to western horizon at sunset shining with an apparent magnitude of -0.14. About 3o from Mercury is the planet Venus with a much noticeable apparent magnitude of -3.91.
Wednesday March 14th the thin waning crescent Moon will be crossing 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.