Tomorrow before dawn – September 21, 2015 – Venus will display its greatest illuminated extent as the morning “star.” That means the planet’s daytime side is now covering more square area of sky than at any other time during this present apparition of Venus in our morning sky. So for the next several mornings, Venus will be shining at or near its greatest brilliancy before dawn!
You might think Venus appears most brilliant when we see its disk as most fully illuminated from Earth. Not so.
If you were to observe Venus with the telescope at its greatest illuminated extent, you’d see that Venus’s disk is only a touch more than one-quarter illuminated by sunshine. A full Venus is always on the far side of the sun from us, so its disk size at full phase is always small. It’s only when we see Venus as a crescent that this world comes close enough to us to exhibit its greatest illuminated extent, at which time its daytime side covers the greatest area of sky.
If you’re up at dawn around September 21, you’re likely to see only Venus and Jupiter. However, if you’re up a couple of hours before sunrise, you should also be able to make out Mars and Regulus, the brightest star in the constellation Leo. The green line depicts the ecliptic – approximate path of the sun, moon and planets on the great dome of sky.
Venus entered the morning sky on August 15, 2015 and will leave it on June 6, 2016.
Take a look at the chart below. Venus transitioned from the evening to morning sky when Venus swung more or less in front of the sun as viewed from Earth (inferior conjunction) on August 15.
Bird’s-eye view of Earth’s and Venus’ orbits
Earth and Venus orbit the sun counterclockwise as seen from the north of the solar system. Venus reaches its greatest eastern (evening) elongation about 72 days before inferior conjunction and its greatest western (morning) elongation about 72 days after inferior conjunction. Venus exhibits its greatest illuminated extent – greatest brilliancy as seen from Earth – midway between a greatest elongation and inferior conjunction.
Because Venus orbits the sun inside Earth’s orbit, we can never see Venus opposite (180o) the sun in our sky (like the full moon). We can’t even see Venus 90o from the sun (like the half-lit quarter moon). At most, Venus strays no farther than 47o from the sun in our sky. This is called Venus’ greatest eastern elongation when Venus appears in the evening sky and greatest western elongation when she predominates over the morning sky.
Venus reaches its greatest elongation in the evening sky about 72 days before inferior conjunction, and then reaches its greatest elongation in the morning sky some 72 days after inferior conjunction. If you look at Venus through a telescope at these times, you’ll see that its disk is about 50% illuminated by sunshine.
Venus exhibits its greatest illuminated extent about 36 days before – and after – inferior conjunction. Through the telescope, Venus appears about 25% illuminated in sunshine at these times. Thirty-six days before inferior conjunction, it’s Venus’ brightest appearance in the evening sky; thirty-six days after inferior conjunction, it’s Venus brightest appearance in the morning sky.
Let the golden triangle help you to remember these Venus’ milestones. The two base angles equal 72o and the apex angle equals 36o. Quite by coincidence, Venus’ greatest elongations happen 72 days before and after inferior conjunction, and Venus’ greatest illuminated extent happens 36 days before and after inferior conjunction. See the diagram above of Venus’ and Earth’s orbits.
Astronomy events, star parties, festivals, workshops for September-December, 2015
The Golden Triangle, with the apex angle = 36o and base angles = 72o
Bottom line: Even though this world is only about one-quarter illuminated in sunshine right around September 21, 2015, as seen from Earth, Venus is nonetheless shining at its brightest best in the morning sky!
The lunar calendars are almost here! View the moon phases throughout the year.
Super Blood Moon eclipse on night of September 27-28
Donate: Your support means the world to us
from EarthSky http://ift.tt/1FbOowe
Tomorrow before dawn – September 21, 2015 – Venus will display its greatest illuminated extent as the morning “star.” That means the planet’s daytime side is now covering more square area of sky than at any other time during this present apparition of Venus in our morning sky. So for the next several mornings, Venus will be shining at or near its greatest brilliancy before dawn!
You might think Venus appears most brilliant when we see its disk as most fully illuminated from Earth. Not so.
If you were to observe Venus with the telescope at its greatest illuminated extent, you’d see that Venus’s disk is only a touch more than one-quarter illuminated by sunshine. A full Venus is always on the far side of the sun from us, so its disk size at full phase is always small. It’s only when we see Venus as a crescent that this world comes close enough to us to exhibit its greatest illuminated extent, at which time its daytime side covers the greatest area of sky.
If you’re up at dawn around September 21, you’re likely to see only Venus and Jupiter. However, if you’re up a couple of hours before sunrise, you should also be able to make out Mars and Regulus, the brightest star in the constellation Leo. The green line depicts the ecliptic – approximate path of the sun, moon and planets on the great dome of sky.
Venus entered the morning sky on August 15, 2015 and will leave it on June 6, 2016.
Take a look at the chart below. Venus transitioned from the evening to morning sky when Venus swung more or less in front of the sun as viewed from Earth (inferior conjunction) on August 15.
Bird’s-eye view of Earth’s and Venus’ orbits
Earth and Venus orbit the sun counterclockwise as seen from the north of the solar system. Venus reaches its greatest eastern (evening) elongation about 72 days before inferior conjunction and its greatest western (morning) elongation about 72 days after inferior conjunction. Venus exhibits its greatest illuminated extent – greatest brilliancy as seen from Earth – midway between a greatest elongation and inferior conjunction.
Because Venus orbits the sun inside Earth’s orbit, we can never see Venus opposite (180o) the sun in our sky (like the full moon). We can’t even see Venus 90o from the sun (like the half-lit quarter moon). At most, Venus strays no farther than 47o from the sun in our sky. This is called Venus’ greatest eastern elongation when Venus appears in the evening sky and greatest western elongation when she predominates over the morning sky.
Venus reaches its greatest elongation in the evening sky about 72 days before inferior conjunction, and then reaches its greatest elongation in the morning sky some 72 days after inferior conjunction. If you look at Venus through a telescope at these times, you’ll see that its disk is about 50% illuminated by sunshine.
Venus exhibits its greatest illuminated extent about 36 days before – and after – inferior conjunction. Through the telescope, Venus appears about 25% illuminated in sunshine at these times. Thirty-six days before inferior conjunction, it’s Venus’ brightest appearance in the evening sky; thirty-six days after inferior conjunction, it’s Venus brightest appearance in the morning sky.
Let the golden triangle help you to remember these Venus’ milestones. The two base angles equal 72o and the apex angle equals 36o. Quite by coincidence, Venus’ greatest elongations happen 72 days before and after inferior conjunction, and Venus’ greatest illuminated extent happens 36 days before and after inferior conjunction. See the diagram above of Venus’ and Earth’s orbits.
Astronomy events, star parties, festivals, workshops for September-December, 2015
The Golden Triangle, with the apex angle = 36o and base angles = 72o
Bottom line: Even though this world is only about one-quarter illuminated in sunshine right around September 21, 2015, as seen from Earth, Venus is nonetheless shining at its brightest best in the morning sky!
The lunar calendars are almost here! View the moon phases throughout the year.
Super Blood Moon eclipse on night of September 27-28
Donate: Your support means the world to us
from EarthSky http://ift.tt/1FbOowe
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