2021, July 19: Helical Rising of Betelgeuse

Astronomy, Sky Watching
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July 19, 2021:  Betelgeuse is making its first morning appearance or heliacal rising in the eastern sky.

2021, July 19: Betelgeuse is making its first morning appearance in the eastern sky. Mercury is over 20° to the left of the star.
Chart Caption – 2021, July 19: Betelgeuse is making its first morning appearance in the eastern sky. Mercury is over 20° to the left of the star.

by Jeffrey L. Hunt

Chicago, Illinois:  Sunrise, 5:33 a.m. CDT; Sunset, 8:21 p.m. CDT.  Check local sources for sunrise and sunset times for your location.

The star Betelgeuse is making its first morning appearance this week, known as the heliacal rising.  The star’s name means “the armpit of the white-belted sheep.”

Betelgeuse is part of the constellation Orion, the Hunter, that is prominent in the evening sky during the winter season.  It is one of the largest stars in our stellar neighborhood.  The solar system, from the sun extending nearly out to Jupiter’s orbit, could fit within this enormous star.

The star’s brightness varies.  During the past few years, the star’s visual intensity has changed considerably, causing some to speculate that Betelgeuse was reaching near the end of its lifetime.  Recent studies seem to indicate dust ejected from the star has been blocking the star’s light.

A Twitter account (@betelbot) tracks the star’s brightness from estimates that are posted on an astronomy website that tracks the varying brightness of variable stars. Because the star is in the sky during the daytime during summer, accurate measurements will not be made until Betelgeuse appears in a dark sky again.

The bright stars have their first morning appearances at various times of the year. Likely the most popular first appearance is for Sirius that occurs near mid-August each year. The heliacal rising of Sirius garners considerable attention because of its historical connection to the seasonal changes in the Nile River valley in Egypt.

The first appearance of a star can be predicted, but it is affected by the clarity of the sky, weather, and the sky watcher’s visual acuity.  While a star might be in the sky, making its theoretical first appearance, seeing the star without a binocular’s optical assist is what is important.

All the bright stars go through seasonal changes in their places in the sky from Earth’s revolution around the sun.  The stars overhead make a calendar that can be used to determine time of year.

Each year during late July, Betelgeuse, and the stars of Orion, appear in the eastern sky before sunrise.  By October they are high in the south as sunup approaches.  By November they are shining in the eastern sky after sunset, followed by their grand appearance in the south during February.  By May they are disappearing into the bright western twilight to begin the cycle again in July.

This year, the bright planet Mercury is at about the same altitude above the horizon.  Find a clear horizon toward the east-northeast about 45 minutes before sunrise.  A binocular initially helps you find Mercury and Betelgeuse. 

What is the first date you can see Betelgeuse without a binocular?  That’s the heliacal rising for you!

Mercury is heading toward a conjunction with the sun on August 1. It is quickly leaving the sky. 

Detailed Daily Note: One hour before sunrise, Saturn – 20° up in the southwest – is retrograding in Capricornus, 2.9° to the lower right of θ Cap.  Bright Jupiter – over 33° above the south-southwest horizon – is 19.7° to the upper left of Saturn.  Retrograding in Aquarius, the Jovian Giant is 2.1° to the upper left of ι Aqr, 4.6° below θ Aqr, and 4.8° to the lower right of σ Aqr.  Thirty minutes before sunrise, Mercury is nearly 6° up in the east-northeast.  With a binocular note that Betelgeuse (α Ori, m = 0.4) is nearly 21° to the right of the speedy planet. The star is making its first morning appearance (heliacal rising). Forty-five minutes after sunset, Venus is over 8° above the west-northwest horizon.  Use a binocular to see Mars 3.8° to the lower right of Venus and Regulus to the left.  The trio fits into the field of a binocular this evening.  An hour after sunset, use a binocular to note that Graffias (β Sco, m = 2.5) and Dschubba (δ Sco, m = 2.3) bracket the moon (10.0d, 79%), nearly one-third of the way up in the south, from above and below. Saturn rises 42 minutes after sunset, followed by Venus setting 51 minutes later.  Have you seen them in nearly opposite directions in the evening sky?  Jupiter rises three minutes after Venus sets.  The Venus – Jupiter opposition (celestial longitude 180° apart) occurs in two evenings.  As midnight approaches, the moon is over 17° above the southwest horizon.  Farther eastward, Saturn is 23.0° up in the south-southeast, while bright Jupiter, 18.0° up in the southeast, is to the Ringed Wonder’s lower left.

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