{"id":47776,"date":"2023-07-30T08:12:19","date_gmt":"2023-07-30T08:12:19","guid":{"rendered":"https:\/\/www.skyatnightmagazine.com\/?p=120691"},"modified":"2023-07-30T09:32:32","modified_gmt":"2023-07-30T09:32:32","slug":"see-and-photograph-thin-crescent-venus-as-it-reaches-inferior-conjunction","status":"publish","type":"rss_feed","link":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/rss_feed\/see-and-photograph-thin-crescent-venus-as-it-reaches-inferior-conjunction\/","title":{"rendered":"See and photograph thin crescent Venus as it reaches inferior conjunction"},"content":{"rendered":"

Inferior conjunction on 13 August brings Venus to 7.7\u00b0 from the Sun\u2019s centre at 12:15 BST (11:15 UT). <\/p>

By Pete Lawrence\n \t\t<\/p>

Published: Sunday, 30 July 2023 at 08:10 AM<\/p>

\n\n

Venus reaches inferior conjunction on 13 August, when at 12:15 BST (11:15 UT) it will pass 7.7\u00b0 from the centre of the Sun.<\/p>\n

This is an inferior conjunction, the moment when Venus<\/a> lines up with the Sun on the Earth side of its orbit.<\/p>\n

The alignment isn\u2019t precise and in 2023 Venus ends up passing south of the Sun.<\/p>\n

Some inferior conjunctions are closer than others.<\/p>\n

\"Venus\u2019s<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>
Venus\u2019s changing appearance as it orbits; it\u2019s now approaching 50% lit (dichotomy). Credit: Pete Lawrence<\/span><\/figcaption><\/div>\n

The inferior conjunction on 13 August brings Venus to 7.7\u00b0 from the Sun\u2019s centre at 12:15 BST (11:15 UT) and with great care and pre-existing knowledge of how to observe such an event, Venus can still be picked up using a camera.<\/p>\n

The dangers of observing this close to the Sun are obvious and it\u2019s important not to push your limits if you\u2019re not sure what you\u2019re doing.<\/p>\n

Pointing a telescope this close to the Sun runs the risk of light passing down the optical tube.<\/p>\n

If this happens, the scope may be damaged. You should certainly not attempt to view this close to the Sun visually, only via a camera with a live feed.<\/p>\n

Observing Venus in August<\/strong><\/h2>\n
\"Images<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>
Images from 2007 showing an ultra-thin crescent Venus passing south of the Sun. Credit: Pete Lawrence<\/span><\/figcaption><\/div>\n

On 1 August<\/strong>, Venus sits 18.6\u00b0 from the Sun but isn\u2019t visible in the evening sky after sunset.<\/p>\n

Therefore it\u2019s necessary to hone your skills for locating the planet during the day (see below <\/span>for more on how to go about this).<\/p>\n

On this date, Venus shows as a slender 5%-lit crescent, 53 arcseconds across.<\/p>\n

One week later on 8 August<\/strong> the separation from the Sun will have decreased to 10.4\u00b0, Venus showing as a very delicate 1%-lit crescent with an apparent diameter of 57 arcseconds.<\/p>\n

At inferior conjunction on 13 August<\/strong>, Venus will be showing a phase of 0.9%, now appearing 58 arcseconds across.<\/p>\n

An interesting phenomenon occurs when Venus\u2019s separation from the Sun decreases below 12\u00b0, the horns of the planet\u2019s delicate crescent appearing to extend further than they should to form what are known as cusp extensions.<\/p>\n

Record Venus at inferior conjunction<\/strong><\/h2>\n
\"telescope<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>\n

With care you can make a record of Venus as it approaches inferior conjunction.<\/p>\n

First and foremost, pointing a telescope close to the Sun is dangerous and extreme care needs to be exercised.<\/p>\n

If you\u2019re not sure what you\u2019re doing, we strongly recommend that you don\u2019t attempt this.<\/p>\n

The safest setup to use would be a small to mid-sized refractor along with a high-frame-rate camera fitted with a red or infrared pass filter.<\/p>\n

Don\u2019t attempt to see this visually.<\/p>\n

Any finderscopes<\/a> will also need to be capped or removed.<\/p>\n

You\u2019ll need a full-aperture white-light solar filter and for the purposes of this challenge we assume that you\u2019ll use a driven, polar-aligned equatorial mount which has setting circles<\/a>.<\/p>\n

\u00a0<\/p>\n

\"setting<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>
Setting circles aren\u2019t complicated to use, but you need to pay attention to the values to make sure you\u2019re using the correct scale<\/span><\/figcaption><\/div>\n

Set the telescope up and turn on the mount drive.<\/p>\n

A wide camera field is recommended, ideally one that sees the entire Sun in one go.<\/p>\n

Remove or cap finders.<\/p>\n

Check that the solar safety filter isn\u2019t ripped or lets light through \u2013 discard it and use a new one if so.<\/p>\n

Once checked, fit it and point the telescope at the Sun.<\/p>\n

Focus as accurately as possible on the Sun\u2019s disc.<\/p>\n

Once focused, centre the Sun in your field of view using a crosshair overlay, if your camera\u2019s control program has this option.<\/p>\n

Otherwise, use your best judgment. Set the mount\u2019s slew speed slow enough that it takes several seconds for the Sun to cross the field of view.<\/p>\n

Use a planetarium app (for example Cartes du Ciel<\/a>) and work out the Sun\u2019s right ascension (RA) and declination (dec.) for the time you\u2019re observing.<\/p>\n

\"setting<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>\n

Unlock the dec. setting circle scale and rotate it so it reads the Sun\u2019s dec., then lock it again.<\/p>\n

Make sure you\u2019re using the part of the scale that increases in value if you move the telescope north.<\/p>\n

Similarly, set the setting circles to the Sun\u2019s current RA value.<\/p>\n

Use the scale that increases if you move the scope east.<\/p>\n

Once set, look up the RA and dec. coordinates of Venus.<\/p>\n

Carefully move the scope so the setting circle pointers indicate the values for Venus.<\/p>\n

As a safety check, ensure you\u2019re not pointing at the Sun, then carefully remove the solar filter.<\/p>\n

Double-check that sunlight isn\u2019t passing too far down the tube \u2013 if it is, re-cover the scope and abort the attempt.<\/p>\n

Adjust the camera settings to boost the sky brightness and look for the fine, 0.9%-lit Venusian crescent.<\/p>\n

If it\u2019s not visible, you can apply short slew bursts to emulate a spiral pattern in the sky.<\/p>\n

Be careful though \u2013 you don\u2019t want to slew too far so that the Sun appears!<\/p>\n

If you simply can\u2019t find the planet, replace the solar filter and start over.<\/p>\n

This guide originally appeared in the August 2023 issue of BBC Sky at Night Magazine.<\/strong><\/em><\/p> <\/body><\/html>\n

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