April 16, 2023: The waning crescent moon is under Saturn before daybreak. During the evening Mercury fades from easy viewing. Venus moves through rich Taurus’ starfield. Mars marches eastward in front of Gemini.
by Jeffrey L. Hunt
Chicago, Illinois: Sunrise, 6:09 a.m. CDT; Sunset, 7:33 p.m. CDT. Check local sources for sunrise and sunset times for your location. Times are calculated by the U.S. Naval Observatory’s MICA computer program.
Summaries of Current Sky Events
Here is today’s planet forecast:
Morning Sky
Before sunrise, the crescent moon is passing Saturn low in the east-southeast. Find a clear view toward the east-southeast horizon to see the waning crescent moon, 17% illuminated, over 5° above the horizon and 5.0° to the lower left of Saturn.
The lunar orb is displaying earthshine, from sunlight reflected from Earth’s features that gently illuminates nighttime on the moon. It is visible to the unassisted human eyes, but easily visible through a binocular or spotting scope. Capture the scene with a tripod-mounted camera and exposures up to one second.
Saturn is emerging from bright sunlight after its solar conjunction. The planet rises two minutes earlier each morning compared to sunrise. By month’s end, it rises nearly 150 minutes before daybreak, and stands over 15° above the horizon during morning twilight.
Evening Sky
Mercury is setting earlier compared to sunset and fading in brightness after is greatest elongation from the sun. To locate the speedy planet, first locate easy-to-find Venus.
The Evening Star is nearly 30° up in the west at 45 minutes after nightfall. It is 8.0° to the upper right of Aldebaran and 6.8° to the upper left of the Pleiades star cluster.
Through a binocular Venus appears in front of a rich starfield that includes members of the Hyades star cluster. The main part of the cluster, is to the left of Venus through the binocular. The planet is over 2° to the lower right of Kappa Tauri (κ Tau on the chart) and Upsilon Tauri (υ Tau). The planet passes to the upper right of this pair in two nights.
Aldebaran, not part of the Hyades, is part of the “V” of Taurus, that makes the Bull’s head. The shape easily fits into the same binocular field. The starry letter extends from Aldebaran to Gamma Tauri (γ Tau) and back to Epsilon Tauri (ε Tau). Through the binocular notice the subtle color differences of the stars. Aldebaran is brightest of the view and distinctly yellow-orange. Without formal names, the star names have somewhat clumsy-sounding catalog designations. Compare the colors of Theta one Tauri (θ1 Tau) and Theta two Tauri (θ2 Tau), and Delta one Tauri (δ1 Tau) and Delta two Tauri (δ2 Tau). Notice the yellow-white and the blue-white hues.
While not visible together in the binocular simultaneously, notice that Venus, Epsilon Tauri, and Aldebaran are along an imaginary line tonight.
Aldebaran, nearly 70 light years away, is considerably closer than the Hyades stellar bundle at a distance of 150 light years. The Hyades bundle is closer than the famous Pleiades cluster.
The Hyades cluster is one of the most-studied star clusters in the sky. Its stars are traveling together to the left of Aldebaran generally in the direction of Orion’s Betelgeuse. This cluster is thought to be nearly 700 million years old compared to the Pleiades at 150 million years. The Hyades has more yellow stars than the Pleiades.
The core of the age concept is that if a group of stars forms at about the same time, the blue stars consume their nuclear fuel at a much higher rate than the yellow stars – like the sun. To maintain a very high temperature the blue stars need a higher core temperature and a faster rate of the conversion of hydrogen to helium at their centers. When the hydrogen is consumed, the star must convert helium to heavier elements at higher temperatures. As a consequence, the star expands and turns red-orange, a red giant – like Aldebaran, remember it is not part of the Hyades – or red super giant, like Betelgeuse and Antares. The Hyades has some yellow stars, indicating that these stars are older than the Pleiades’ blue stars. The Hyades do not appear to have the bright, hot stars that are in the neighboring cluster that indicate a younger star cluster.
Back to the innermost planet, Mercury is less than 10° above the west-northwest horizon and over 20° to the lower right of Venus. Use a binocular to find it as the planet is dimmer than Aldebaran and in the bright blush of evening twilight. It continues to dim and set earlier each evening.
Mercury is headed toward inferior conjunction between Earth and the sun. This evening the planet is over 70 million miles from Earth and quickly overtaking our world on its inner orbital path. When it passes inferior conjunction, the separation is less than 53 million miles.
The third evening planet, Mars, is high in the west-southwest and 34.0° to the upper left of Venus. It is below Castor and Pollux, the Gemini Twins. As the sky darkens further, dimmer stars appear, showing two stick-like figures and outlining the Twins. The Red Planet is 1.2° to the upper left of Mebsuta and 12.2° below Castor.
Mars is marching eastward, generally toward Pollux, passing by in a wide conjunction on May 8th.
Mercury continues to dim and set earlier, while Venus closes the gap to Mars each night.
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