Ceres was the first asteroid discovered, in 1801, and then was reclassified as a dwarf planet in 2006. As the largest object in the asteroid belt, it was the only one with enough gravity to have a round shape. Therefore, Ceres is now the only dwarf planet in the asteroid belt, or even inside the orbit of Neptune, for that matter. With Ceres at opposition on November 27, or opposite the sun in our sky, it will rise at sunset and set at sunrise. The dates around opposition are the best times to view the dwarf planet, because it’s closest to Earth and at its brightest. But a close encounter with one of the brightest stars in the sky provides additional viewing opportunities for Ceres in early November.
Ceres is about 600 miles (1,000 km) across, or about 1/4 the size of our moon. With its size wedged somewhere between an asteroid and a planet, Ceres has been a target of study for the Dawn mission.
How to view Ceres at opposition
Ceres is too dim to view without optical aid, so dust off your binoculars or telescope and head to a dark-sky site. The brightness of astronomical objects is measured in something called magnitude, with lower numbers equating to brighter objects. From a location free of light pollution, you can see objects down to about magnitude 6. Ceres at opposition will be magnitude 7; therefore, you’ll need optical aid to bag this unique object.
On November 27, you can head outside late in the evening when the sky has grown nice and dark, but before the nearly half-lit moon rises after midnight. Use the chart here to find Ceres residing next to the Hyades cluster, or the V-shaped group of stars in Taurus the Bull. In fact, Ceres spends all of fall meandering through Taurus, cutting across the Hyades star cluster.
November 6/7 may not be opposition or when Ceres is brightest, but it will be the date that Ceres is easiest to find. Magnitude-7.5 Ceres will be just 10 arcminutes from the bright, reddish-orange star Aldebaran in Taurus. 10 arcminutes is about 1/3 the size of the full moon, or 1/6 the width of your pinky held at arm’s length. Either way, if you focus binoculars or a telescope on Aldebaran, the point of light just to the northeast of the star will be Ceres.
Observing Ceres
Ceres is not easy to observe. Being far away and dim, it requires at least binoculars to spot and even then it only appears as a point of light like a distant star. Ceres does us no favors in how reflective it is. Objects have a measurement called albedo, which is a number between 0 and 1 for how black or white it is. Fresh snow or ice can have an albedo of 0.8 or 0.9. Venus, with its thick cloud cover, has an albedo of 0.65. Venus is bright because it reflects so much sunlight. On the other hand, low-albedo objects absorb most sunlight and are quite dark. Charcoal and fresh asphalt both score a 0.04 for their albedo. Ceres’ albedo is 0.07. It’s practically hiding in the dark against the blackness of space.
Ceres may be the brightest dwarf planet, but only because it lies within the asteroid belt, the zone of solar system debris between Mars and Jupiter. Pluto’s albedo is 0.30 and Eris’ is 0.86, one of the highest albedos in the solar system. Ceres is only about 3 times farther from the sun than Earth. Compare that to Pluto, which is 40 times farther from the sun than Earth. And Eris is a whopping 68 times farther from the sun.
Ceres does have a couple of bright patches on its surface, which the spacecraft Dawn inspected in 2015.
Dawn’s discoveries at Ceres
Dawn arrived at Ceres in 2015. Some of the discoveries Dawn has made while orbiting Ceres are finding icy deposits in the dwarf planet’s crust, a 2.5-mile (4,000-meter) high mountain named Ahuna Mons, and bright spots made by salty water in Ceres’ interior.
Bottom line: With Ceres at opposition November 27, the dwarf planet is closest to Earth and therefore brightest, making it a great time to observe. Ceres will be by Aldebaran around November 6 and 7.
The post Ceres at Opposition on November 27 first appeared on EarthSky.
from EarthSky https://ift.tt/3nNzxZ2
Ceres was the first asteroid discovered, in 1801, and then was reclassified as a dwarf planet in 2006. As the largest object in the asteroid belt, it was the only one with enough gravity to have a round shape. Therefore, Ceres is now the only dwarf planet in the asteroid belt, or even inside the orbit of Neptune, for that matter. With Ceres at opposition on November 27, or opposite the sun in our sky, it will rise at sunset and set at sunrise. The dates around opposition are the best times to view the dwarf planet, because it’s closest to Earth and at its brightest. But a close encounter with one of the brightest stars in the sky provides additional viewing opportunities for Ceres in early November.
Ceres is about 600 miles (1,000 km) across, or about 1/4 the size of our moon. With its size wedged somewhere between an asteroid and a planet, Ceres has been a target of study for the Dawn mission.
How to view Ceres at opposition
Ceres is too dim to view without optical aid, so dust off your binoculars or telescope and head to a dark-sky site. The brightness of astronomical objects is measured in something called magnitude, with lower numbers equating to brighter objects. From a location free of light pollution, you can see objects down to about magnitude 6. Ceres at opposition will be magnitude 7; therefore, you’ll need optical aid to bag this unique object.
On November 27, you can head outside late in the evening when the sky has grown nice and dark, but before the nearly half-lit moon rises after midnight. Use the chart here to find Ceres residing next to the Hyades cluster, or the V-shaped group of stars in Taurus the Bull. In fact, Ceres spends all of fall meandering through Taurus, cutting across the Hyades star cluster.
November 6/7 may not be opposition or when Ceres is brightest, but it will be the date that Ceres is easiest to find. Magnitude-7.5 Ceres will be just 10 arcminutes from the bright, reddish-orange star Aldebaran in Taurus. 10 arcminutes is about 1/3 the size of the full moon, or 1/6 the width of your pinky held at arm’s length. Either way, if you focus binoculars or a telescope on Aldebaran, the point of light just to the northeast of the star will be Ceres.
Observing Ceres
Ceres is not easy to observe. Being far away and dim, it requires at least binoculars to spot and even then it only appears as a point of light like a distant star. Ceres does us no favors in how reflective it is. Objects have a measurement called albedo, which is a number between 0 and 1 for how black or white it is. Fresh snow or ice can have an albedo of 0.8 or 0.9. Venus, with its thick cloud cover, has an albedo of 0.65. Venus is bright because it reflects so much sunlight. On the other hand, low-albedo objects absorb most sunlight and are quite dark. Charcoal and fresh asphalt both score a 0.04 for their albedo. Ceres’ albedo is 0.07. It’s practically hiding in the dark against the blackness of space.
Ceres may be the brightest dwarf planet, but only because it lies within the asteroid belt, the zone of solar system debris between Mars and Jupiter. Pluto’s albedo is 0.30 and Eris’ is 0.86, one of the highest albedos in the solar system. Ceres is only about 3 times farther from the sun than Earth. Compare that to Pluto, which is 40 times farther from the sun than Earth. And Eris is a whopping 68 times farther from the sun.
Ceres does have a couple of bright patches on its surface, which the spacecraft Dawn inspected in 2015.
Dawn’s discoveries at Ceres
Dawn arrived at Ceres in 2015. Some of the discoveries Dawn has made while orbiting Ceres are finding icy deposits in the dwarf planet’s crust, a 2.5-mile (4,000-meter) high mountain named Ahuna Mons, and bright spots made by salty water in Ceres’ interior.
Bottom line: With Ceres at opposition November 27, the dwarf planet is closest to Earth and therefore brightest, making it a great time to observe. Ceres will be by Aldebaran around November 6 and 7.
The post Ceres at Opposition on November 27 first appeared on EarthSky.
from EarthSky https://ift.tt/3nNzxZ2
Aucun commentaire:
Enregistrer un commentaire