Understanding the Importance of Tracking for Astrophotography: Can Your Orion XT8 Handle It?

Many amateur astronomers wonder if a telescope that tracks is a must-have for astrophotography or if their Orion XT8 can be used for astrophotography without it. Here, we'll explore the concept of tracking and its significance in astrophotography.

Understanding Earth's Movement and Its Impact

Stars, while appearing to be in fixed positions, do move across the sky due to the Earth's rotation and orbital motion. The Earth completes one rotation on its axis every 24 hours, which means that in one hour, it rotates approximately 15 degrees. This rotation translates to a speed of 15 arcminutes per minute and 15 arcseconds per second. This may seem like a small amount, but for a narrow field of view, it can make a significant difference.

Let's consider a concrete example: if you use your Orion XT8 and point it at a star near the celestial equator, with a 25mm or 10mm eyepiece, the field of view is around 1.1° in diameter. A star in the center of this field will drift towards the edge in about 2 minutes and be completely out of view in a few seconds. This is due to the Earth's rapid rotation, specifically 15 arcminutes per minute.

Impact on Camera Usage

When using a camera for astrophotography, the effect of the Earth's rotation becomes even more pronounced. For a camera with a 1921080 pixel resolution and a 6μ pixel sensor, 1 pixel is roughly equal to 1 arcsecond. A 10-second exposure with this setup means that a star, moving at 15 arcseconds per second, will cover 150 pixels, forming a streak rather than a round dot. This effect becomes even more noticeable with a broader field of view, such as 0.71 arcseconds per pixel on a Canon 60D (an APS-C sensor).

The Solution: Tracking

The only effective way to counteract this rotational movement is to use a tracking system, specifically, an equatorial mount. These mounts are designed to mimic the Earth's movement, making it possible to keep your target in the field of view without it drifting out of the frame. An equatorial mount has two axes: the right ascension (RA) and declination (Dec) axes. When properly aligned with the Earth's poles, the RA axis allows for smooth, tracking motion, while the Dec axis allows for fine adjustments.

Monte Carlo's Orbital Motion

It's not just the rotation that matters. The mount must track the stars accurately, which means moving in both the altitude and azimuth axes depending on the star’s position. This can cause the object to appear to rotate as it moves across the sky, a phenomenon known as frame rotation. Proper equatorial mounts, when used correctly, can avoid this and provide a smooth, accurate tracking experience.

Conclusion

In summary, while your Orion XT8 can be a valuable tool for astrophotography, the lack of a tracking mount means that long exposures will result in blurred, streaked images. To achieve the best results, an equatorial mount is essential. Equipped with the right hardware, you can capture stunning, clear images of the stars and galaxies you observe in the night sky.

Key Takeaways:

The Earth's rotation causes stars to move, impacting astrophotography. A tracking mount, such as an equatorial mount, is necessary to counteract this movement. An equatorial mount aligns with the Earth's poles for accurate tracking.

Keywords: astrophotography, tracking, equatorial mount