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2021, September 28:  Morning Moon, Evening Planets

The Beehive or Praesepe star cluster (National Science Foundation Photo)

The Beehive or Praesepe star cluster (National Science Foundation Photo).

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September 28, 2021:  This morning the moon, as it approaches its Last Quarter phase, is high in the south at the Gemini – Taurus border.  The evening planet pack – Venus, Jupiter, and Saturn – brightly shine after sunset.

Chart Caption – 2021, September 28: The moon is high in the south-southeast before sunrise, at the Gemini – Taurus border.

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by Jeffrey L. Hunt

Chicago, Illinois:  Sunrise, 6:45 a.m. CDT; Sunset, 6:37 p.m. CDT.  Check local sources for sunrise and sunset times for your location.

Morning Sky

An hour before sunrise, the bright moon, 56% illuminated, is high in the south-southeast near the Gemini – Taurus border.  The horns of the Bull, Elnath and Zeta Tauri – are to the right of the moon. Propus – the forward foot – is to the lower left of the lunar orb.

Chart Caption – 2021, September 28: Through a binocular, the moon, Messier 35, and Propus fit into the same starfield.

Use a binocular to note that the moon is 4.0° to the upper right of the star cluster Messier 35.  As shown on the chart above, note that the moon, star cluster, and Propus can fit into a binocular field at the same time.

Once you see the view that includes the moon, move the binocular slightly so the moon is no longer in the view.  This reduces the lunar glare to see the star cluster easier.

Star clusters can be used to determine distances in our galaxy and to relatively nearby galaxies as well as to determine the ages of the clusters.

Astronomical theory predicts that the stars in a cluster form at about the same time.  The stars are not equal in mass.  When their nuclear fires ignite, the blue stars consume their fuels at tremendous rates, to keep the stars shining.  When the hydrogen is converted to helium, the nuclear fusion turns up the core’s temperature.  The outer layers respond by expanding and cooling to become red giants.  Comparing the numbers of red giant stars between clusters allow astronomers to determine the relative ages of the clusters as well as predict their actual ages from theories of stellar cycles.

Evening Sky

Chart Caption – 2021, September 28: Forty-five minutes after sunset Venus is 5.7° to the left of Zubenelgenubi.

Evening Star Venus, bright Jupiter, and Saturn – the evening planet pack – shine brightly.  Begin about 45 minutes after sunset with Venus.  The brilliant planet is low in the southwest, about 9° up in the sky. It is quickly stepping eastward in Libra, 5.7° to the left of Zubenelgenubi.

Venus is moving toward a conjunction next month with Dscubba – the Scorpion’s forehead – and then with Antares – “the rival of Mars” – that represents the heart.

Farther eastward at this hour, bright Jupiter and Saturn are in the southeastern sky.  Saturn is 15.9° to the upper right of the brighter planet.  After Venus sets, the brightest “stars” are Jupiter, Arcturus, Vega, and Saturn.

Venus sets 100 minutes after sunset.

Chart Caption – 2021, September 28: Jupiter and Saturn are retrograding in Capricornus.

By two hours after sunset, after the end of evening twilight, Jupiter is about one-third of the way up in the sky in the south-southeast.  Jupiter and Saturn are retrograding in Capricornus.

Their apparent westward motion compared to the stars ends next month and they resume their usual eastward direction.

This evening Jupiter is to the upper right of Deneb Algedi – “the kid’s tail” – and to the upper left of Nashira.  Saturn is to the lower right of dim Upsilon Capricorni (υ Cap on the chart).  Use a binocular to spot the sidereal backdrop.

Detailed Daily Note: One hour before sunup, the moon (21.4d, 56%) is over 70° up in the south-southeast.  It is to the left of the Bull’s horns, at the Gemini – Taurus border.  The lunar orb is 6.7° to the lower left of Elnath and 5.4° to the upper left of Zeta Tauri (ζ Tau, m = 3.0).  Forty-five minutes after sunset, three bright planets are along an arc across the southern sky.  Brilliant Venus is nearly 9° up in the southwest, 5.7° to the left of Zubenelgenubi and 0.7° to the lower right of ι Lib.  The planet is 19.5° to the lower right of Antares.  Bright Jupiter and Saturn (m = 0.5) are in the southeastern sky.  By two hours after sunset, Jupiter is nearly one-third of the way up in the south-southeast.  In the starfield it is 3.2° to the lower right of μ Cap, 1.6° to the upper right of Deneb Algedi, and 1.6° to the upper left of Nashira.  Saturn, nearly 29° up in the south and east of meridian, is 15.9° to the lower right of Jupiter.  In the starfield, the Ringed Wonder is 1.4° to the lower right of υ Cap.  As the calendar day closes, the moon (22.2d, 48%) is less than 5° above the east-northeast horizon.

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