August 12, 2022: Sirius is making its first morning appearance – the heliacal rising. Saturn, nearing its solar opposition, appears in the morning with Venus, Mars, and Jupiter. The Ringed Wonder is in the evening sky as well.
by Jeffrey L. Hunt
Chicago, Illinois: Sunrise, 5:56 a.m. CDT; Sunset, 7:55 p.m. CDT. Check local sources for sunrise and sunset times for your location.
Sirius is at its heliacal rising today. The star makes its first morning appearance in the east-southeast before sunrise for the latitude of Chicago, Illinois.
During a star’s annual westward trek, it appears in the eastern morning sky before sunrise. Each week it is higher in east and then in the south a few months later. Soon the star sets in the west at sunrise and rises into the eastern sky at sunset. The star is in the sky all night. Then it appears farther south each evening. The star then sets during bright twilight to reappear again in the morning sky to repeat the yearly pattern.
Sirius, the night’s brightest star, begins this annual trek during summer and the date of the first appearance depends on the observer’s latitude. Locations farther south, see the star earlier than more northerly latitudes. Local effects, such as weather and obstacles at the horizon, may delay the observation of the first sighting. See the mathematical note below for a detailed explanation.
|Heliacal Rising of Sirius|
|20° N||July 24, 2022|
|25° N||July 29|
|30° N||August 1|
|35° N||August 5|
|40° N||August 10|
|45° N||August 15|
|50° N||August 21|
To see the star near the morning of its first appearance, begin looking for it a few days before the predicted heliacal rising date. Venus is quite easy to locate. It is over 10° above the east-northeast horizon at about 30 minutes before sunrise. Sirius is over 40° to the lower right of the Morning Star.
A binocular may be necessary to first locate Procyon and Betelgeuse. They are two of the three points on the Winter Triangle. The shape is nearly equilateral. Gauge the distance between the two stars and then apply that gap toward the east-southeast horizon to complete the triangle shape.
Sirius is visible a day or two before the predicted date through a binocular, although the sky brightness is dim enough to see the star without an optical assist on the predicted date. As noted earlier, this is dependent on the clarity of the sky near the horizon. Each morning after the predicted first appearance, the star is easier to see in the southeastern sky during morning twilight.
As you look for the first appearance of Sirius, note the bright moon in the western sky. At forty-five minutes before sunrise, the lunar orb is nearly 10° up in the southwest. Locate Saturn 4.5° to the right of the moon.
This bright moon interferes with the peak Perseid meteor shower that is occurring earlier this morning when the sky is darker. The bright moonlight washes out the dimmer meteors.
Saturn is nearing its opposition with the sun in two evenings. It is opposite the sun, rising at sunset and setting at sunup.
Bright Jupiter is higher in the sky, over halfway up in the south-southwest, over 45° to the upper left of Saturn.
Farther eastward, Mars is approaching its conjunction with the Pleiades star cluster on August 20. This morning the Red Planet, nearly two-thirds of the way up in the southeast, is 7.5° to the lower right of the stellar bunch.
This morning farther eastward, brilliant Venus is about 8° above the east-northeast horizon and 9.6° below Pollux.
Bright Mercury is about 5° above the west horizon at 30 minutes after sunset. The planet’s evening appearance is not favorable, setting nearly an hour after sundown. Use a binocular to attempt to view it.
Fifteen minutes later, Saturn is about 7° up in the east-southeast. It is in the sky all night long, appearing in the south around midnight and low in the west before sunrise.
In his book Mathematical Astronomical Morsels, Jean Meeus generates a formula for predicting the first date of the appearance of any star. When the astronomical coordinates of the star and the observer’s latitude are entered, the formula calculates the sun’s longitude along the ecliptic when the star is about 2° above the horizon, Meeus’ estimate for Sirius’ first appearance.
Then it is necessary to generate a list of the sun’s celestial longitude for summer dates, using the computer program MICA from the US Naval Observatory. Applying some tiny, but important factors that account for the radius of our planet, the dates that follow were determined by aligning the Meuss equation output with the MICA computations.
The dates reflect the day following when the sun appeared at the Meeus coordinates. For example, for latitude 20° north, the formula generates a solar longitude of 121.1479°. MICA calculates that July 24 at 10 hours UT (5 a.m. CDT), the sun’s longitude is 121.50759°. A day earlier and the sun’s longitude is still west of Meeus’ predicted location for the heliacal rising date. This was carried forward for the other latitudes.
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