Sky-Watching

by tte-77

Mercury profile from Mariner - Credit: NASA

In his book “The Solar System and Back” (Doubleday, 1970), famed science writer Isaac Asimov (1920-1992) argued that the planet Mercury:

“… is hardly ever visible when it is truly dark. Mercury … will be seen only near the horizon in dawn or twilight, amid haze and sun glare. I suspect, in fact, that many people today (when the horizon is dirtier and the sky much hazier with the glare of artificial light than it was in centuries past) have never seen Mercury.”

Weather permitting 8-15 September amateur astronomers will be presented with an excellent opportunity to view Mercury in the early morning dawn sky. An “inferior planet” because its orbit is nearer to the sun than the Earth’s, Mercury, as Asimov indicated, always appears from our vantage point to be in the same general direction as the sun.

Mercury will be surprisingly easy to see from now through 15 September and will be rising before the sun in the northern hemisphere. Just look low above the eastern horizon during the morning twilight and be sure that it’s about 30 to 45 minutes before sunrise – search for a bright yellowish-orange “star.”

As mentioned in our monthly events guide Mercury was at its greatest elongation just west of the sun, on 3 September. The planet, like Venus, appears to go through phases like the moon.

At its greatest elongation Mercury appeared roughly half-illuminated and the amount of its surface illuminated by the sun has steadily increased as each day passes helping keep it in relatively easy view over the next 7 days.

Position of Mercury and Regulus early September (click to enlarge) - Credit: Stellarium/Sky-Watching

As a bonus, early on Friday morning, Mercury will have a close conjunction with the bright bluish 1st-magnitude star, Regulus, in the constellation of Leo. Look for them, they will appear to be almost side by side, low near the east-northeast horizon and around 45 minutes before sunrise.

If you intend to view, Mercury will be to the left of Regulus and will shine about 8x brighter than the star. Binoculars may make it easier to sight Regulus – Mercury will then pull rapidly away to the east on successive mornings.

By 15 September it will have substantially brightened, more than any star in the sky with the exception of Sirius. Days later, despite its brightness it will be swallowed up by the dawn glow.

Let’s hope for clear skys over the week ahead!

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