Entries tagged as dwarf planet

Testing sensitivity with Pluto imaging

Pluto's movement from Sept. 9 to Sept. 10, 2015 (50% size)

One of the main reasons I decided to buy a new camera was that it would yield a lower-noise photo at high ISO settings, making it better for long-exposure astrophotography. To confirm this, one of the first objects I chose to take photos of was the dwarf planet Pluto.

It moved a little to the east since the last time, already past the ξ2(Xi 2) Sagittarii and not near a particularly bright star. The brightest stars in the animated frames above are only about magnitude 11. Nevertheless, Pluto was discernible when comparing the two frames taken a day apart under a bright monitor. Dimmest stars visible reached magnitude 15, and Pluto itself moved clearly enough to see that it's not a background star.

If you feel particularly bored, you can try picking it out of the full version of the September 10 photo.

Pluto is in here somewhere
Telescope: Celestron NexStar 6SE
Device: Sony A5000 (prime focus)
Settings: (1500mm) - (f/10)
Filters: None
Location: Naju, Korea

#1: ISO 800 - 20s - 2015-09-09 22:09 KST
#2: ISO 1000 - 30s - 2015-09-10 21:44 KST

Staring at Pluto out the window

My telescope told me Pluto was in this view

For the past few weeks, clouds and rain due to the monsoon prevented me from seeing a clear sky at night. But that period is nearing its end, and last night I had a near-perfect opportunity - no clouds and no haze. Brightness of the first-quarter Moon was about the only fly in the ointment.

As I was only able to observe the southern sky out the window of my room, I consulted a star chart to see if anything interesting was there to see. Pluto immediately caught my eyes. As you might know, this dwarf planet is making headlines at the time of this writing because the New Horizons probe made a flyby two weeks ago. The unprecedented details of the images from the probe is capturing public interest, and mine. So I wondered if I could see a glimpse of it with my own telescope.

Problem is, Pluto is very faint - 14.1-magnitude right now. Based on my past observations, it would be at or just outside my limits even with astrophotography. Sure enough, when I pointed my telescope to the right position, I couldn't make it out visually. So I attached my DSLR camera and took several long-exposure photos in hoping that they'd be more revealing. One of such result is the photo you see above. The brightest star is ξ1(Xi 1) Sagittarii, a 5.1-magnitude star. Most of the rest are fainter than 10-magnitude.

Pluto found - it was 2/3 from the top and 1/3 from the left

After carefully comparing the photo with a detailed star chart, I finally found a dot that didn't belong to a star. This seemed to be Pluto that I was looking for. But to make sure, I compared all the photos I took over the span of about an hour and looked to see if there was any movement - a telltale sign that it's not a star, but an object moving around the solar system.

Movement of Pluto animated

Indeed there was. This was the dwarf planet I was looking for. This process of comparison was basically how Pluto was identified and discovered in the first place back in 1930, so it was pretty satisfying to retrace the steps. I'm also glad to know that the southern sky at Naju is still dark enough to see this faraway world.

Telescope: Celestron NexStar 6SE
Device: Canon EOS 450D (prime focus)
Settings: (1500mm) - ISO 1600 - 30s - (f/10)
Filters: None
Time: 2015-07-26 00:06 - 01:13 KST
Location: Naju, Korea

Asteroid Vesta & dwarf planet Ceres

3 days of observing Vesta and Ceres (42% size)

I've recently bought a motorized equatorial mount called iOptron SkyTracker, which enables the camera to track the stars at the same speed as they move in the sky. This is useful for photographing faint objects through long exposures. But since the light pollution in the city sky hinders long exposure photography in the first place, I was unsure whether this would be of much use.

To see that the mount works as intended and is still useful under an uncooperative sky, I decided to try photographing two kinds things - asteroids and galaxies. For asteroids, the two brightest, Vesta and Ceres, were chosen. They were close to each other while moving in the constellation Virgo, between Arcturus and Mars, in the southern sky around midnight. Ceres is also a dwarf planet, so I would be photographing two types of celestial body at once.

For three nights (April 21-22, 23-24, and 24-25), I photographed the area just above Zeta Virginis (a.k.a. Heze) to catch the movement of two objects. The SkyTracker mount was used on the first and third night because the sky was clear, but the second night was riddled with fog in the lower sky, hindering the view of Polaris which is needed to calibrate the mount. So I had to take the photo using only the camera on high-ISO, (relatively) short exposure settings.

Two things became evident in this round of photographing. One, Vesta (magnitude 5.7) and Ceres (magnitude 7.0) could be clearly seen moving towards west each day. Two, the SkyTracker mount did an excellent job tracking the stars and the asteroids, producing images far better than using camera only. The second night's photo had small streaks, despite having only 10 seconds of exposure. Here are the full resolution photos used for the animation.

Full resolution crops of Vesta and Ceres

Device: Canon SX50 HS
Filters: None
Location: Suwon, Korea

#1: 121mm - ISO 80 - 300s - f/5.0 - 2014-04-22 00:05 KST
#2: 121mm - ISO 1600 - 10s - f/5.0 - 2014-04-24 00:07 KST
#3: 119mm - ISO 80 - 300s - f/5.0 - 2014-04-24 23:19 KST

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